2014/2015
FINAL YEAR PROJECT Submitted in fulfillment of the requirements for the ENGINEERING DEGREE FROM THE LEBANESE UNIVERSITY FACULTY OF ENGINEERING – BRANCH II Major: Mechanical Engineering Prepared By: Majd MAKHLOUF Firas HADDAD __________________________________________________________________
LINEAR FREE PISTON ENGINE : STUDY AND DESIGN Supervised by: Dr Marwan AZZI Defended on the 23rd of July 2015 in front of the jury:
Dr Fady HANNA Dr Marlène CORDAHI Dr Ghazi TAWTAH Dr Rany RIZK
President Member Member Member
Dedicated to our families for their continuous support, and to the founders of Wikipedia, including Jimmy Wales.
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Acknowledgment First of all, we would like to thank our advisor Dr Marwan AZZI for all his efforts throughout the duration of this project. In addition, we would like to thank Dr Fady HANNA, Dr Rany RIZK, Mr Atef HACHEM and Mr Tanios GEMAYEL for all their support throughout this project. Moreover, we would like to thank the head of Phoenix Machinery's research and development department Mr Dany KADDOUM for all his contributions to this work. We would like to give our most warmful thanks to Mr Hady EL BOUSTANY, Mr Rony SEIF and Mr Ibrahim SFEIR for the great help they kindly offered us, and for spending a great amount of their precious time dealing with some of the difficulties that we encountered and consulted them about. We would also like to thank Mr Charles BERBERI for providing us with many tools that proved to be very helpful in the design process of this project, in addition to Mr Fady EL SAIFI, Dr Elie ABOU CHAKRA, Mr Rony SFEIR, Mr Wissam NASR, and all of Phoenix Machinery's staff and employees. We would like to thank Mr Charbel AKIKI, Mr Kamil DAGHFAL, and Mr Mario El HADDAD for generously providing us with many of the essential parts that were used in this project. Finally, we would like to thank Dr Ghazi TAWTAH for generously sharing with us a great deal of his vast knowledge and experience with internal combustion engines, and for helping us move forward at many occasions during the design process of this project. MAKHLOUF-HADDAD
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Abstract Being a fully linear crank-less engine, a free piston engine requires in itself a thorough detailed study and a careful design approach to take into account its unconventional aspects. After a thorough investigation of many of the free piston engines that have been manufactured throughout history, it was found that the most efficient and most practical one was the Pescara opposed piston engine, which uses a pneumatic rebound system. The aforementioned engine was the one used as a basis for the design of this engine. A detailed numerical simulation has been conducted based on the Pescara opposed piston engine, which showed the higher thermal efficiency of these engines, and provided many of the parameters that were used later in the design. Moreover, and due to the fact that this engine is a linear one, and that it operates at a relatively high frequency, many challenges have been overcome throughout the design of this engine, most of which are related to the linear guides required in such an engine, and to the unconventional reciprocating starting system. The unconventional aspects of this engine also require the conception of an ignition system that is adapted to this type of engines, which led to the design of an electronic engine control unit in order to overcome the aforementioned requirements, although such a feat is beyond the scope of mechanical engineering. All the aforementioned details will be thoroughly discussed throughout this document.
Keywords : free piston engine, linear, crank-less, Pescara, opposed piston, rebound system, numerical simulation, starting system, electronic engine control unit.
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Contents
I- Introduction...........................................................................................1 II- Literature Review................................................................................3 II-1 Historic Overview.........................................................................3 II-2 Free Piston Engine Layouts........................................................10 II-3 Rebound Systems.......................................................................16 II-4 Advantages Of Free Piston Engines...........................................21 II-5 Starting Systems.........................................................................23 III- Kinetic And Thermodynamic Simulation.........................................25 III-1 Kinetic Characteristics Of The Sliders......................................28 III-2 Thermodynamic Characteristics Of The Free Piston Engine....31 III-3 Simulation Models....................................................................37 III-4 Simulation Results.....................................................................45
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IV- Main Design.....................................................................................53 V- Starting System..................................................................................59 VI- Engine Electronic Control Unit........................................................63 VI-1 Ignition Sensors.........................................................................64 VI-2 Microcontroller Selection And Ignition Algorithm...................66 VI-3 Power Transistor........................................................................70 VI-4 Ignition Circuit..........................................................................71 VII- Conclusion......................................................................................74 Appendix A : Numeric Simulation Of The Free Piston Engine................80 Appendix B : Simulation Of A Free Piston Linear Alternator..................95 Appendix C : SKF Bearing Life Calculator Report...............................106 Appendix D : Free Piston Engine Execution Drawings.........................114 Appendix E : Autodesk Inventor Stress Analysis Reports.....................148 Appendix F : Arduino Source Code Of The Engine Control Unit…....184
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List Of Tables
Table 1 : Forces Acting On The Sliders....................................................29 Table 2 : Additional Results Calculated By The Simulation....................50 Table 3: Characteristics Of The OMRON E2A-S08KN04.......................64
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List Of Figures
Figure II.1 : Otto And Langen's Free Piston Engine..................................3 Figure II.2 : Pescara Synchronization Mechanism.....................................4 Figure II.3 : Junckers' Synchronization Mechanisms.................................5 Figure II.4 : Vertical Section Of The SIGMA GS-34.................................6 Figure II.5 : Stirling Colgate's Free Piston Linear Alternator.....................7 Figure II.6 : Faraday Torch.........................................................................7 Figure II.7 : Toyota's Free Piston Linear Alternator...................................9 Figure II.8 : Beetron Free Piston Engine....................................................9 Figure II.9 : Single Piston Layout.............................................................11 Figure II.10 : Pescara Single Piston Free Piston Engine..........................12 Figure II.11 : Dual Piston Layout.............................................................13 Figure II.12 : Phoenix Machinery's Free Piston Alternator......................14 Figure II.13 : Opposed Piston Engine Layout..........................................15 Figure II.14 : SIGMA GS-34 Slider Assembly.........................................15 Figure II.15 : INNAS Chiron Hydraulic Circuit.......................................18 Figure II.16 : INNAS Chiron External Layout.........................................18 Figure II.17 : Pescara Free Piston Compressor.........................................20 Figure II.18 : SIGMA GS-34 Power Plant...............................................24 Figure III.1 : Diagrammatic Sketch Of A Free Piston Gas Generator......26 MAKHLOUF-HADDAD
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Figure III.2 : Reed Valve..........................................................................27 Figure III.3 : Slider Free Body Diagram..................................................29 Figure III.4 : Standard Spark-ignition Pressure-Volume Diagram...........31 Figure III.5 : Schematic Diagram Of The Compression Chamber Cycle...................................................................................34 Figure III.6 : Schematic Diagram Of The Bounce Chamber Cycle........36 Figure III.7 : First Expansion Phase SIMULINK Model.........................38 Figure III.8 : Second Expansion Phase SIMULINK Model.....................39 Figure III.9 : Exhaust SIMULINK Model................................................40 Figure III.10 : First Admission Phase SIMULINK Model.......................41 Figure III.11 : First Admission Phase SIMULINK Model.......................42 Figure III.12 : First Compression Phase SIMULINK Model...................43 Figure III.13 : Second Compression Phase SIMULINK Model..............44 Figure III.14 : Piston Position With Respect To Time..............................46 Figure III.15 : Piston Velocity With Respect To Time..............................47 Figure III.16 : Combustion Chamber Pressure With Respect To x..........48 Figure III.17 : Bounce Chamber Pressure With Respect To x..................49 Figure III.18 : Compression Chamber Pressure With Respect To x.........50 Figure III.19 : Colgate Alternator Layout.................................................52 Figure IV.1 : Bounce Chamber Volume Control System..........................54
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Figure IV.2 : Early Draft Of The Synchronization Mechanism................55 Figure IV.3 : Free Piston Engine Final Design.........................................58 Figure V.I : Scotch-yoke Mechanism.......................................................60 Figure V.2 : Early Draft Of The Crank-rocker Starting System...............61 Figure V.3 : Rack And Pinion Starting System.........................................62 Figure VI.1 : Ignition Algorithm Implemented On The Microcontroller...................................................................68 Figure VI.2 : Schematic Diagram Of The Ignition Circuit.......................72 Figure VI.3 : Power Transistor Circuit PCB Layout................................72 Figure VI.4 : Main Ignition Electronic Circuit PCB Layout....................73
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Notation
FPEG
Free Piston Electric Generator
FPE
Free Piston Engine
NOx
Nitrogen Oxides
P-V Diagram
Pressure-Volume Diagram
ECU
Electronic Control Unit
DC
Direct Current
CDI
Capacitive Discharge Ignition
LED
Light-Emitting Diode
ΣF
Sum Of Forces
Ms
Mass Of The Sliders
d2(x)/dt
Slider Acceleration
Fc
Force Due To The Pressure Of The Gases Present In The Combustion Chamber
Fb
Force Due To The Pressure Of The Air Inside The Bounce Chamber
Fcomp
Reaction Force Of The Scavenge Pump
Ffric
Friction Force On The Slider
Falt
Laplace Force On The Slider In Case The Engine Is Also A Linear Alternator
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Τs
Shear Stress Occurring In The Lubricant Between The Rings And The Cylinder Walls
Ar
Side Area Of The Piston Rings
B
Piston Bore
h
Piston Ring Height
μ
Dynamic Viscosity Of The Lubricant
v
Instantaneous Velocity Of The Slider
c
Piston Ring-Cylinder Wall Clearance
x
Position Of The Slider
V
Volume
vf
Fluid Flow Speed At A Point On A Streamline
g
Value Of Acceleration Due To Gravity
z
Elevation Above A Reference Plane
p
Pressure At The Chosen Point
ρ
Density Of A Fluid
Pc
Pressure Of The Gases Present In The Combustion Chamber
Pb
Pressure Of The Air Inside The Bounce Chamber
A1
Area Of The Small Piston
A2
Area Of The Large Piston
m
Meter
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mm
Millimeter
ms
Millisecond
m/s
Meters Per Second
Hz
Hertz
J
Joule
Kw
Kilowatt
i
Induced Current
l
Equivalent Length Of Each Of The Coils
B
Magnetic Field Of The Magnets
min
Minute
N
Newton
Pa
Pascal
bar
Unit Of Pressure ( 1 bar = 100,000 Pa)
ϴ
Angle
ω
Angular Velocity
V
Volt (not to be confused with the volume notation)
cc
Cubic Centimeter
rpm
Revolutions Per Minute
A
Ampere
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I–
Introduction
A linear free piston engine is an unconventional type of internal combustion engines that is relieved out of many of the common features that can be found in other common types of engines. In fact, conventional elements such as flywheels, crankshafts, camshafts, or any other rotating element, cannot be found in these engines, which leads to many advantages that include but are not limited to weight reduction, construction simplification, efficiency improvement, emission reduction... Unlike other conventional engines, and due to the fact that this type of engines lacks any rotating element, its output is not a rotating motion. Therefore, other types of outputs are extracted from that engine. These include fluid compression, gas generation, and linear electric generation. The latter constitutes one of the most researched topics nowadays in the automotive industry. In fact, a linear free piston alternator can be used as the main range extender of a battery powered car, thus preventing power shortage in case the stored electric power in the batteries runs down. However, the design of a free piston engine is met with a multitude of challenges, which are mainly due to the fact that many of the conventional engine components that are essential in order to maintain a proper engine operation are missing, and that no full rotational motion occurs during the operation of this engine, which requires exceptional energy storage systems and exceptional design
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characteristics. Therefore, the design of such an unconventional piece of machinery requires a lot of research and a detailed numerical study, which in itself constitutes a research project. And in addition to the aforementioned academic work, a careful attention to details is needed to overcome the practical challenges of such an engine, which are many due to the unconventional features present in this project. Moreover, much of the work necessary throughout the study of this project involves features that fall beyond mechanical engineering's scope, which includes features that are usually classified as electrical and electronics engineering subjects. It is however necessary for these features to be included in this work, for they are essential since they replace the conventional features that such an engine lacks. Throughout this document will be shown in detail all the work accomplished throughout the study and the design of a compact free piston engine. A literature survey that details all the features that free piston engines include will be presented in this work, followed by the detailed numerical studies that have been conducted to verify the operational parameters of this engine, and the whole design methodology and the resulting design will be finally presented in detail.
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II-
Literature Review
II-1 Historic Overview Free piston engines date back to the invention of the internal combustion engine. In fact, Otto, who is credited with the invention of the spark-ignition combustion engine, built his first engine as a linear engine which used a rack and pinion mechanism to transfer the motion of its piston into a rotational motion. It was known as the Otto-Langen Free Piston Engine, and it was built in 1860[1][2].
Figure II.1 : Otto And Langen's Free Piston Engine [1]
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However, the main person that has been credited with the invention and the development of the free piston engine was Raul Petaras Pescara : having invented one of the first helicopters back in 1922, Pescara noticed that his helicopter was heavily struggling while trying to take off[3]. It was due to its heavy weight, which was mostly due to the weight of its engine and its heavy flywheel, a part that forms the main energy accumulation system that internal combustion engines use. Therefore, he decided to build a lighter engine for his helicopter, and thus, the free piston engine was conceived. He built a single piston free piston engine at first, which was found to be unbalanced[4]. He later proceeded into building an opposed piston engine with uniflow scavenging, which was found to be perfectly balanced and extremely efficient[5]. Being the first to build that type of engines, he was able to secure a patent for the synchronization mechanism of his two piston engine[6].
Figure II.2 : Pescara Synchronization Mechanism[3]
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In the late 1920s, interest increased widely in free piston engines. Junkers, a German inventor, built a free piston compressor with the same aforementioned layout[7]. However,
and due to the fact that Pescara held the patent for the
synchronization mechanism, Junkers' engine was unable to achieve the same level of efficiency that the Pescara Engine used to reach. Junkers had many attempts to conceive a different synchronization system that was as reliable as Pescara's with no success[3]. He then ended up with a rack and pinion synchronization system, which couldn't withstand jerking properly. That same engine was used by the NAZI military as an air compressor that was used to launch torpedos and power submarines, which was due to its low weight[8].
Figure II.3 : Junckers' Synchronization Mechanisms[3] MAKHLOUF-HADDAD
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After World War II, Pescara resumed manufacturing his free piston engines in partnership with a french company known as SIGMA GS-34, a diesel engine which is the most efficient free piston engine of all time, with a thermal efficiency of 50% and a mechanical efficiency of 80%[9]. They were gasifiers which generated hot exhaust gases that where expanded through turbines coupled to alternators.
Figure II.4 : Vertical Section Of The SIGMA GS-34[9] Later on, many free piston engines were based on the Pescara layout. In fact, Stirling A. Colgate patented a free piston linear alternator that used the same layout that the Pescara engine used[10]. However, this time the power was directly extracted from the motion of the pistons, which were equipped with permanent magnets that induced power into a multi-turn coil that surrounded them on the outside[10], which was based on the Faraday Torch, a flashlight that is charged by a shaking motion that causes a free permanent magnet to oscillate in and out of a coil. MAKHLOUF-HADDAD
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That engine had the advantage of providing the piston with a magnetic coupling synchronization which was due to the Laplace force that the magnets were subjected to and which was equal on both pistons since this force depends on the current flowing through the coils, and both coils were mounted in series. Thus, the need for a mechanical synchronization was eliminated, which simplified the engine further more[10]. However, it is unclear whether this engine has been actually built or not.
Figure II.5 : Stirling Colgate's Free Piston Linear Alternator[10]
Figure II.6 : Faraday Torch[11]
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Many notable other free piston engines have been built throughout history. These include but are not limited to: • General Motors GMR 4-4 'Hyprex' : the first and one of the only free piston engines that have been used to power a car. It is basically a SIGMA GS-34 replica. The motion of the exhaust turbine is however directly transmitted through a transmission shaft to the rear wheels of the car. It wasn't proven to be very successful, apart from the fact that it was extemely quiet and vibration free[8][17].
•
INNAS Chiron : it is a diesel hydraulic single piston free piston pump which uses some of the energy that it provides to the oil circuit it compresses for the storage of the energy necessary for the bounce back operation. It is one of the few free piston engines that are fully controlled and it can achieve a variable stroke length operation, which is a feature that highly increases efficiency and allows the use of different kinds of fuel. It has been used to power a forklift[8].
•
SANDIA Labs Free Piston Engine: it is a free piston linear alternator that is based on the Pescara layout[13].
•
TOYOTA FPEG : built and tested in 2014, this gasoline engine has the same layout as the first Pescara free piston engine, which also happens to be a twostroke gasoline engine with uniflow scavenging. It has been equipped with some of the advanced features of common engines (electronic fuel injection, electronically controlled exhaust valves, ceramic cylinder sleeves...). It is also a linear alternator[14]. However, it suffers from a design flaw since single free piston engines are unbalanced, which Toyota must have realized by now.
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Figure II.7 : Toyota's Free Piston Linear Alternator[14]
•
Beetron FPE: a free piston engine that is based on the Pescara engine. Being used as a linear alternator, it is thought to be based on the Colgate free piston alternator. It is a very promising engine, especially that its inventor Daniel Hagen did a very thorough research on every free piston engine ever made, which he shared a great part of on his website [3]. Moreover, he claims that he combined all the successful free piston engines and alternators ever made in his own[15]. However, it is a privately funded project, which limits its chances of commercial success.
Figure II.8 : Beetron Free Piston Engine[15] MAKHLOUF-HADDAD
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•
Libertine FPE : built in 2015 by a British company named Libertine, this engine is the most recent free piston engine as of this date. It was revealed in April 2015. The company has been granted nearly a million pounds to carry on with its development of free piston engines. It is also based on the Pescara engine[16]. In Lebanon, SIGMA GS-34 free piston engines have been used back in 1967 as
the main power sources of the Zouk Power Station (also known as the Camille Chamoun Power Station), and have been used in a power plant in Chekka[9]. In addition, Phoenix Machinery, one of the leading industrial companies in Lebanon, have been experimenting with free piston linear engines for a while, which lead to the execution of many free piston engines in the past. Most of them are, however, of the dual piston type.
II-2 Free Piston Engines Layouts
Throughout the history of free piston engines, three main layouts have governed the designs of these engines : the single piston , dual piston, and opposed piston configurations[8]. Although they may be different, all these layouts share some features in common, which include the fact that all of them are linear engines, and that all of them are two-stroke engines. Single piston free piston engines are, as their name suggests, monocylindrical MAKHLOUF-HADDAD
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free piston engines that include only one piston. That piston is driven forwards by the combustion process of the gases of the combustion chamber, and later bounced back by its respective rebound system, which is essentially an energy accumulation system that replaces the conventional flywheel that is usually found on other types of engines, and that is the main component that stores the required energy that keeps the engine running (the conventional rebound systems that are usually found in free piston engines will be discussed in detail in the next section). These engines have the advantage of simplicity over other free piston engines, since the piston of such an engine is the exclusive part that is in motion. They are also easier to control, as it can be seen on the INNAS Chiron [12] and the Toyota FPEG that were discussed early on. However, these engines have a critical flaw, since it is impossible for them to be balanced, which has proven to be a great inconvenience because it would make its supporting structure vibrate critically at very high frequencies, and thus they would eventually be subjected to fatigue failure, which is what lead Pescara to abandon his initial single piston design[3]. This layout can be mainly found nowadays in hydraulic pumps, such as the Chiron[12].
Figure II.9 : Single Piston Layout[8] MAKHLOUF-HADDAD
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Figure II.10 : Pescara Single Piston Free Piston Engine[4]
Another configuration of free piston engines is the dual piston free piston engine, which is found on engines that include two opposed combustion cylinders. Their pistons are thus rigidly connected by a non-rotating connecting rod. These engines do not require a rebound system for their operation, because the combustion that drives one of the pistons forwards serves as a rebound process for the other. They MAKHLOUF-HADDAD
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are mainly used in linear alternators[8]. These engines can be however very challenging to control, especially that any small variation in its ignition timing can cause such an engine to malfunction, even if its of the order of 100 microseconds. Another main disadvantage is the fact that these engines are subjected to high degrees of perforation. However, and due to the fact that its execution can be easier than other layouts since it can be built by two conventional scooter cylinder kits, the pistons of which would be connected by a solid rod (which would be the only custom-manufactured part), it has been the main layout that research groups have been using in their linear alternator projects. In fact, Phoenix Machinery have built in 2006 a fully functioning linear alternator that was based on this engine layout. Although it wasn't clear if they reached a high enough efficiency, they were able to overcome some of the control challenges of these engines. However, the aforementioned mechanical limitations didn't allow them to run their engine for a long enough duration.
Figure II.11 : Dual Piston Layout[8]
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Figure II.12 : Phoenix Machinery's Free Piston Alternator
In addition to the other two layouts, a third layout, the opposed piston free piston engine, has been proven to be the most successful. In fact, it was the layout that was applied to Pescara's most successful free piston engines. It consists of two sliding pistons that are moved apart by one central combustion. On each end, a pneumatic bounce chamber is formed by the rebound pistons and the cylinder heads. These two bounce chambers, which are connected through an equalizing tube, serve as the main rebound system of these engines. These engines feature an opposed piston uniflow scavenging that overcomes the emission problem that engines with crossflow scavenging suffer from. It is also an important feature since it allows this engine to feature uniflow scavenging without the inconvenience and complexion of having an exhaust valve installed. Another main advantage that this layout features is the fact that it is both statically and dynamically balanced, which allows it to be totally vibration-free. In fact, General Motors engineers used to demonstrate this feature by balancing a nickel on a running GMR 4-4 'Hyprex' engine, which adopts this same
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configuration[17]. Another advantage of this type of engine is that it features a reduced heat transfer since it lacks a cylinder head on the top of the combustion chamber[8]. However, these engines feature a main challenge since they require a synchronization linkage for a proper operation, since they belong to the opposed piston type. This configuration has been mainly used as the main layout of air compressors, gasifiers, and some linear alternators, which includes the Colgate engine that claims to achieve piston synchronization through electromagnetic coupling[10].
Figure II.13 : Opposed Piston Engine Layout[8]
Figure II.14 : SIGMA GS-34 Slider Assembly[9] MAKHLOUF-HADDAD
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II-3 Rebound Systems One of the main requirements on all of the aformentioned free piston engine layouts (except for the dual piston configuration) is the absolute need for an energy storage system that replaces the conventional flywheel (which serves as a kinetic energy storage system) that is found on all other engines, and that enables both the piston bounce-back operation, and the continuous operation of the engine. Although most of the free piston engines' rebound systems consist of either hydraulic and pneumatic energy accumulators, all energy accumulation systems that can be practically applied to these engines will be discussed in this section. One of the first rebound systems that comes to mind is a mechanical spring, which stores elastic energy that is later used for the bounce-back operation. This system has been featured on some Stirling free piston engines. However, it has been found that due to the high frequencies of free piston engines (which can reach 60 hz) [8], and that due to the high loads that the pistons are subjected to during the combustion process, it is a subject to a very early fatigue failure, which makes its use impractical[18]. Another rebound system can be used exclusively on linear alternators, which consists of using some of the energy stored in the batteries during the expansion stroke to compress the gases during the compression stroke, since a linear alternator is a reversible machine that can be used as a motor. This imposes a need for a highly accurate control and the use of switches with very high switching frequency. However, batteries, like mechanical springs, have a limited life cycle, which would reduce their life to a very short time due to the high frequency that these engines reach. One of the solutions to such a problem is the use of a separate rebound circuit MAKHLOUF-HADDAD
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that is independent of the charging circuit of the batteries and that includes super capacitors that accumulate the necessary energy for the bounce-back operation. These have a life cycle that is long enough for such a system. However, they can be a quite expensive solution. Hydraulic and pneumatic energy accumulation are the two forms of energy storage systems that are usually used in free piston engines. Each has its own characteristics. In fact, a hydraulic energy system usually consists of a series of accumulators which are divided into two categories based on their stored pressures : high pressure accumulators and low pressure accumulators[8]. High pressure accumulators are generally connected through a check valve at the bottom dead center of the slider that is fixed to the piston while low pressure accumulators are connected in a very similar way at the top dead center[8]. On the compression stroke, the pressure difference between the two accumulators drives the piston back to the top dead center, while the working liquid is compressed into the high pressure reservoir during the expansion stroke. Such a system is generally integrated into a wider hydraulic circuit, where the engine is used as the central pump[8]. It has the advantage of allowing the engine to be highly controllable which helps increase its efficiency. Such a system can be found on the INNAS Chiron[12], which is a hydraulic pump that uses a hydraulic circuit as its rebound system. However, hydraulic systems are known to have a slow response time and to take a big space because of the fact that liquids are incompressible. They can also be pollutant in case infiltration occurs into the engine. They can however withstand high loads.
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Figure II.15 : INNAS Chiron Hydraulic Circuit[8]
Figure II.16 : INNAS Chiron External Layout[12]
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On the other hand, pneumatic systems, and though they might be less efficient due to the heat transfer that occurs when they are compressed, and though they cannot withstand high loads as much as hydraulic systems can, have several practical advantages over hydraulic systems. In fact, pneumatic systems are cleaner. Therefore, and in case infiltration occurs, the engine's emission would be unaffected. In addition, and due to their compressibility, the pneumatic accumulators that are used for the bounce-back operation have a significantly smaller size than those used in hydraulic systems, which enables them to be included on the ends of the engine thus reducing the size of the system (they actually consist of the piston in itself, the cylinder head, and the cylinder walls), and moreover, these accumulators, which are commonly known as bounce chambers or air cushions, are all of the high pressure type, since air is compressed to a pressure that is high enough to drive the piston back without the need of a second low pressure reservoir, thus reducing the number of bounce chambers to one in single piston engines, and to two in opposed piston engines, and thereby eliminating the need for a complicated pneumatic circuit in contrast to that of hydraulic rebound systems, which was a factor that limited the operational application of their respective engines to hydraulic pumps. The pneumatic system is therefore reduced to a simple equalizing tube that ensures an equal pressure in both bounce chambers, in addition to an air recovery system in case a significant blow-by occurs. Free piston engines with a pneumatic rebound system have a wider field of applications, ranging from air compressors to gasifiers and alternators[8]. However, the fact that their stroke length cannot be as controllable as that of hydraulic engines denies this type of engines to operate as efficiently at all frequencies. Therefore, they tend to operate at a determined regime[8].
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Figure II.17 : Pescara Free Piston Compressor[5]
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II-4 Advantages Of Free Piston Engines
Throughout this section will be recapitulated some of the most notable advantages that free piston engines have over other types of engines. Some of these advantages have been briefly mentioned in the previous sections, one of which being the lighter weight that free piston engines have, which is more than an advantage for free piston engines : it is the main cause that lead to the invention of this type of engines, as it was discussed earlier. This advantage has enabled a multitude of applications for free piston engines in the maritime and aerospace fields back in the 1930s, especially that conventional rotational turbo-compressors and jet engines were still in a very early development stage when free piston engines were becoming more and more common back then[8]. Another advantage that free piston engines have is the simplicity of their design compared with the designs of other conventional engines, which was due to the fact that these engines lack any rotating systems. That advantage is especially found in single and dual piston engines, the designs of which can be very simple. It is less significant in opposed piston engines, especially that they require a synchronizing mechanism that can complicate their design quite a bit[8]. That last advantage implies another, which is the fact that frictional losses are way smaller than those of other types of engines, which is due to the fact that fewer parts are in motion in such an engine. This fact also implies that the mechanical efficiency of these engines is increased. In addition to the increase in mechanical efficiency of these engines, the fact MAKHLOUF-HADDAD
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that the stroke length of such an engine is variable can be used as a factor to increase the thermal efficiency of these engines, especially that of spark ignition engines. In fact, and as it is observed on conventional gasoline internal combustion engines, the efficiency is higher on a certain rotational speed than it is on other (usually between 3000 and 4000 rpm). That is due to the fact that on different rotational speeds, different compression ratios are needed for the combustion to be optimal. However, and due to the crank-slider mechanism that most engines have, the stroke length is constant on all the speed regimes of the engine, which implies a constant compression ratio. That led many engine manufacturers to develop variable compression ratio engines, which require complicated linkages and mechanisms, thus implying a further inconvenience. Free piston engines already have variable strokes lengths that are not limited to a constant value by any linkage (even the synchronizing linkages featured on opposed piston engines do not limit the stroke lengths of their respective engines to a certain constant value), which reduces the task of having a variable compression ratio to the proper control of the ignition of the gases, and at most to the control of the fluid motion of the rebound systems, and thus, higher thermal efficiencies can be observed in these engines[8]. A variable stroke length also implies a multi-fuel operation, which was impossible on conventional engines due to the fact that each fuel has its own required compression ratio range. Moreover, homogeneous charge compression ignition, which is a form of compression ignition (that doesn't require a spark) in which a gasoline-diesel fuel mixture is injected to the combustion chamber during the compression stroke (thus combining the Otto and Diesel cycles), would be possible. Other advantages include less fuel consumption, a better fuel-air mixture which is due to the high speed that is featured around the top dead center, and a MAKHLOUF-HADDAD
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reduced heat transfer loss due to the high speed expansion featured in these engines, which reduces the time available for heat loss, and also limits the formation of temperature-dependent pollutants such as NOx[8].
II-5 Starting Systems
One of the main challenges that free piston engines have is the fact that they cannot be “cranked over several revolutions”[8] as it is the case with other internal combustion engines, which implies the use of unconventional starting systems. Pneumatic free piston engines were started by the impulsive introduction of air into the bounce chambers, which drove the engine towards the top dead center[8]. These engines had to achieve a steady-state operation right on the first stroke since that mode of starting was only valid for the first stroke only. Removing the introduced air volume was the main challenge of this feature[8]. Although a one stroke starting process was featured on these engines, it wasn't reported that it was a serious inconvenience[8]. These engines featured a staring reservoir that contained enough compressed air for this operation. These can be seen on the following figure[9].
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Figure II.18 : SIGMA GS-34 Power Plant[9] Multiple stroke starting processes are featured on hydraulic engines and linear alternators, which are reversible. In fact, an external pump can be controlled to provide the circuit with the fluid motion necessary for the operation of hydraulic free piston engines especially that these are generally integrated into a closed hydraulic circuit[8]. Linear alternators are also reversible electric machines[20][21]. Therefore, the same alternator can be used as an electric motor to generate a multiple stroke starting process by simply reversing the current passing through the coils[8]. No mechanical reciprocating system has been noted to have been used for the starting of pneumatic free piston engines, which is quite remarkable since many factors, including low temperatures and high altitudes, can impose a multiple stroke starting process.
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III- Kinetic And Thermodynamic Simulation
After having reviewed most of the notable free piston engines that were built throughout history, it was found that opposed piston pneumatic free piston engines were the most successful and that they were the only engines to have been able to compete commercially, mostly through the Pescara SIGMA GS-34 engines. Therefore, it was decided that it was the best choice as a basis for the design of the free piston engine that is described throughout the rest of this document. In fact, the engine in question is an opposed piston spark-ignition free piston engine with pneumatic bounce chambers that is based on the SIGMA design. It features two standard pistons on each side that are connected through a rigid connecting rod. The two sub-assemblies that are formed each by the two aforementioned pistons, which are of different sizes, and the connecting rod, are the main sliding elements of the engine. As it can be seen on the following picture, the small piston is in direct contact with the combustion chamber gases. A larger piston is selected for the bounce chamber side to decrease its pressure . A third space is formed by the large piston and the combustion cylinder transverse walls. It is known as the compression chamber, and it is used a a scavenge pump, which allows the working fluid to enter the combustion chamber at a higher pressure, which is essential for the scavenge operation of two-stroke engines, and also serves as a supercharger. Two Reed check valves are located on both ends of this space. During the expansion stroke, pressure decreases in this space, thus allowing an atmospheric pressure airfuel mixture to enter this space. It is later compressed to the point where it exceeds the pressure of the scavenge reservoir surrounding the combustion cylinder. MAKHLOUF-HADDAD
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At that point air is allowed into the scavenge reservoir through the Reed valve, thus maintaining a pressure that is “super-atmospheric” (it is usually a 1.8 bar pressure)[22]. Note that the bounce chambers are considered to be closed spaces where air is subjected to a nearly isentropic compression until the slider comes to rest. The force due to the compressed gases in the bounce chamber later pushes the sliders towards the top dead center of the engine, where ignition occurs, and thus the cycle is repeated.
Figure III.1 : Diagrammatic Sketch Of A Free Piston Gas Generator[9]
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Figure III.2 : Reed Valve[23]
Each sliding element is subjected to a multitude of forces that are identical on both sides due to the fact that this engine is perfectly symmetrical, and that the sliders are connected through a synchronizing mechanism. The resulting sum of these forces generates the kinematic characteristics of the sliders. Throughout this section will be detailed the kinetic and thermodynamic studies and simulations that have been performed to determine the operating parameters of the engine in question.
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III-1 Kinetic Characteristics Of The Sliders
Each of the two sliders, as discussed earlier, is subjected to a multitude of forces that are shown on the following free body diagram. Each of these forces will be discussed in the following table. The sum of these forces is obviously equal to the acceleration of the slider multiplied by its mass according to the second law of Newton.
ΣF = Ms * d2(x)/dt
(Eq. III.1)
This equation is the main differential equation that generates the motion of these sliders. The solution of this equation is a function of time representing the position of the slider with respect to time. Therefore, it was modeled on SIMULINK and a MATLAB program has been written to automatically assign the corresponding value of each parameter. This numerical aspect of the study will be detailed later on.
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Figure III.3 : Slider Free Body Diagram[24]
Symbol Description Fc
Force due to the pressure of the gases present in the combustion chamber.
Fb
Force due to the pressure of the air inside the bounce chamber.
Fcomp
Reaction force of the scavenge pump.
Ffric
Friction force on the slider.
Falt
Laplace force on the slider in case the engine is also a linear alternator. Table 1 : Forces Acting On The Sliders Note that the wide arrow represents the motion of the slider. Many of these forces' expressions will be determined later on while discussing
the thermodynamic cycles that are respective each of the engine chambers. The Laplace force that is induced on the slider by the coils will be discussed later on in a detailed study that was performed on a linear alternator free piston engine. Therefore the only force that can be determined in this section is the friction force.
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The friction force occurs mainly on the side of the engine, between the piston rings and the cylinder walls[22]. It is mainly due to the shear stress that occurs in the lubricant that is located between the two of them. Therefore[22]: Ffric = τs * Ar
(Eq. III.2)
with : - τs : shear stress occurring in the lubricant between the rings and the cylinder walls. - Ar : side area of the piston rings Noting that: Ar = π * B * h with : - B : Piston Bore - h : Piston Ring Height
and[22]:
τs ≈ μ * v / c with : - μ : dynamic viscosity of the lubricant - v : instantaneous velocity of the slider - c : piston ring-cylinder wall clearance
The expression of Ffric becomes: Ffric = π * B * h * μ * v / c
(Eq III.3) [22]
The previous expression has been entered into the numerical simulation model that will be detailed later on.
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III-2 Thermodynamic Characteristics Of The Free Piston Engine As it was shown earlier, and as shown on figure III.1, each of the three main chambers of the engine has its own thermodynamic cycle. Throughout this section will be shown and explained the P-V diagrams of each cycle, which will help in determining the expressions of the forces that are due to each of the different chambers' pressures. In fact, the two-stroke Otto cycle can be applied to the fluids of the combustion chamber. The different processes of this thermodynamic cycle will be briefly detailed based on its P-V diagram that is shown on the following figure.
Figure III.4 : Standard Spark-ignition Pressure-Volume Diagram[22] MAKHLOUF-HADDAD
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Process 1-2 : isentropic expansion. At any point of this process, the combustion chamber pressure is [25]: Pc = P1 * (V1/V) k
with k = 1.4
(Eq. III-4)
Due to the obvious fact that the piston surface is constant: Pc = P1 * (x1/x) k
with x the position of the slider.
(Eq. III-5)
Note that the previous expression will be the one included for this process in the numeric simulation of the engine. Process 2-3 : the exhaust blowdown. During this process, the exhaust ports are uncovered by the piston. The pressure difference between the combustion chamber gases and the atmospheric air induces the motion of the gases that exit the engine according to Bernoulli's Equation. That fact has been taken into account in the numeric SIMULINK model of the exhaust process, thus allowing a simulation of the pressure variation with respect to time, which is affected by the aforementioned fact in addition to the expansion that occurs simultaneously with the blowdown. Note that the expression of the Bernoulli equation is[26]: (vf2) / ρ + g * z + P / ρ = Constant
(Eq. III-6)
Process 3-4-5: the admission process. During this process, inlet ports are uncovered by the piston, and a fresh air-fuel mixture enters the combustion chamber and pushes the remaining combustion products out through a process known as scavenging. During this process, Pc is considered to be constant and equal to the MAKHLOUF-HADDAD
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pressure of the scavenge reservoir, which is usually between 140 and 180 KPa[22]. Process 5-6: final scavenging process. After the piston recovers the inlet ports of the engine, and before it covers the exhaust ports, some of the remaining combustion products are driven out during this process. Pc remains constant throughout this process as well. Process 6-7: isentropic compression. At any point of this process, the combustion chamber pressure is [25]: Pc = P6 * (V6/V) k
with k = 1.4
(Eq. III-7)
And therefore: Pc = P6 * (x6/x)k
with x the position of the slider.
(Eq. III-8)
Process 7-8: constant volume combustion process. The combustion process is the main process that provides the cycle with the energy that is extracted from the engine. Due to the fact that it is a spontaneous process[25], the states of the working fluids are generally determined at the beginning and at the end of this process, and the state of the fluid during that process is disregarded and considered unable to be determined. Thus, the state at the end of this process has been determined based on the standard optimal end of combustion states of standard spark ignition internal combustion engines.
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Note that due to the different expressions that Pc takes in all of the aforementioned processes, one SIMULINK model cannot be sufficient to simulate the engine cycle, which led to the creation of several SIMULINK models for each of the aforementioned processes, and to the creation of a Matlab program that assigns the initial values of the parameters of each of the processes at the beginning of its respective simulation. In addition to the combustion chamber, the compression chamber has its own thermodynamic cycle. The following diagram illustrates the cycle in question.
Figure III.5 : Schematic Diagram Of The Compression Chamber Cycle Process 1-2: isentropic expansion. During this process, both the compression chamber inlet and scavenge reservoir outlet reed valves are closed. At any point of this process, the combustion chamber pressure is [25]: Pcomp = P1 * (V1/V) k MAKHLOUF-HADDAD
with k = 1.4
(Eq. III-9) 34
And therefore: Pcomp = P1 * (x1/x) k
(Eq. III-9)
Process 2-3: compression chamber admission. During this process the inlet reed valve opens, and the Pcomp is atmospheric at any time. Process 3-4: isentropic compression. During this process, both the compression chamber inlet and scavenge reservoir outlet reed valve are closed. At any point of this process, the combustion chamber pressure is : Pcomp = P3 * (V3/V) k
with k = 1.4
(Eq. III-10)
And therefore: Pcomp = P3 * (x3/x)k
(Eq. III-11)
Process 4-1: scavenge reservoir admission. During this process the outlet reed valves are opened, and Pcomp is considered to be equal to the scavenge reservoir pressure at any time.
In contrast with the two previous chamber, air in the bounce chamber is either isentropically compressed or expanded depending on the direction of motion of the slider. And since the bounce chamber is nearly a closed volume, the expression at any time during the cycle is[25]: MAKHLOUF-HADDAD
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Pb = P1 * (V1/V)k
with k = 1.4
(Eq. III-12)
And therefore:
Pb = P1* (x1/x)k
(Eq. III-13)
Figure III.6 : Schematic Diagram Of The Bounce Chamber Cycle
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Note that the forces corresponding to each of the aforementioned pressures is equal to the product of the pressure and the area of the piston that is in contact with the chamber, such that: Fc = Pc * A1 with A1 : Area of the small piston
(Eq. III-14)
Fb = Pb * A2 with A2 : Area of the large piston
(Eq. III-15)
Fcomp = Pcomp * (A2 - A1)
(Eq. III-16)
III-3 Simulation Models All of the aforementioned equations have been modeled using SIMULINK. As it was mentioned earlier, each model represents the differential equation that generates the motion of the slider. This differential equation is essentially Newton's second law, where each of the aforementioned forces are summed according to equation III-1. Due to the fact that the expression of each of these forces is different for each of the thermodynamic processes of the cycle, the simulation requires a multitude of SIMULINK models. These models are simulated according to their respective orders in the whole cycle, a task that is performed by a Matlab program that makes sure this order is respected, and assigns the initial values for each of the models, thus making sure that the simulation is continuous throughout its phases. The Matlab code of this program can be found in Appendix A. On the following pages will be presented each of the SIMULINK models that represent the thermodynamic cycle of the free piston engine. MAKHLOUF-HADDAD
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Figure III.7 : First Expansion Phase SIMULINK Model
This model represents the expansion of the combustion products that takes place between the end of the combustion process and the opening of the inlet reed valve.
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Figure III.8 : Second Expansion Phase SIMULINK Model
This model represents the expansion process right after the inlet reed valve opens, which occurs when Pcomp reaches the atmospheric pressure. During this process, Pcomp is constant and equal to the atmospheric pressure.
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Figure III.9 : Exhaust SIMULINK Model MAKHLOUF-HADDAD
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Note that the previous model is that of the exhaust process, which occurs right after the exhaust ports are uncovered. Note that in addition to the expansion of the combustion products, the working fluid motion that occurs out of the exhaust is taken into account in this model, which generates the instantaneous pressure drop in the combustion chamber, which is an effect that is governed by the Bernouilli equation that was discussed earlier (Eq. III-6).
Figure III.10 : First Admission Phase SIMULINK Model MAKHLOUF-HADDAD
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The previous model is that of the admission process that occurs after the admission ports are uncovered. Note that the admission process has been divided into two : the first is that of the admission that occurs before the bottom dead center is reached. It is represented by the previous model. The second is that of the admission that takes place after the bottom dead center is reached, and through which starts the compression of the compression chamber mixture. This process is modeled on the following diagram.
Figure III.11 : Second Admission Phase SIMULINK Model
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Figure III.12 : First Compression Phase SIMULINK Model
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Figure III.13 : Second Compression Phase SIMULINK Model
The two previous models correspond to the compression process of the cycle. Note that throughout the first phase, the outlet reed valve is still closed and the compression of the compression chamber is still ongoing. After P comp reaches the value of the pressure of the scavenge reservoir, the reed valve in question would open, thus letting the mixture into the reservoir, a process that is model by the second model. MAKHLOUF-HADDAD
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Note that three additional models have been created since the reed valves are not bound to open in the exact processes that were shown earlier. The Matlab source code has been implemented with various tests to predict the exact process during which each reed valve opens, and thus allowing it to select the proper model at the proper time. These drawings have not been shown among the previous diagrams for clarity reasons and since the opening schedules according to the final simulation performed are those of the diagrams that were previously shown. The additional diagrams can be found in appendix A. Also note that in all the previous diagrams, all the compression and expansion processes have been considered as polytropic processes with a polytropic coefficient equal to 1.3, thus taking into account the heat transfer occurring during each of these processes[25].
III-4 Simulation Results
Throughout this section will be shown and discussed the results of the previously described simulation. Note that after having modeled the engine, and programmed the corresponding Matlab program, a great number of simulation runs have been performed. The following results are those of the final run which is considered to have provided the most optimal results. Some of the notable inputs that were entered were the minimum pressure of the bounce chamber, which was optimized after a series of runs, and found to be 1.5 bars, the scavenge reservoir pressure, which was selected to be 1.8 bars based on the scavenge pressure range of commonly availabe two-stroke engines [22]. In addition, the bores of each of MAKHLOUF-HADDAD
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the pistons have been entered. These have been initially selected to be 45 mm and 90 mm. Based on that initial choice, two standard pistons that are available on the market have been selected with close dimensions to the ones required. The small piston that has been selected has a diameter of 40 mm, and the large one is a 92 mm diameter piston. The sizes of these pistons were the ones included in the final run of the engine simulation. Other inputs can be found in appendix A.
Figure III.14 : Piston Position With Respect To Time Note that according to the previous diagram, many parameters can be extracted, including the stroke length of the engine, which was found to be 59 mm, and the duration of the cycle, which was found to be around 40 ms. Note that at around 17 ms, the slider is brought to rest by the pressure force of the bounce chamber, which in turn drives it to its initial position at the top dead center, which is located at 70 mm from the origin that was specified in the simulation parameters. MAKHLOUF-HADDAD
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Figure III.15 : Piston Velocity With Respect To Time According to this graph, the maximum velocity of this slider is found to be almost equal to 5 m/s, which has proved to be an inconvenience that was considered in the design of the synchronization mechanism that will be discussed later. It can also be inferred from the previous graph that the velocity of the slider can be interpolated into a sinusoidal function, which in turn shows that the motion of the sliders is nearly a periodic sinusoidal one. Note that the instantaneous velocity of the slider is 0 at the same moment where the slider comes to rest and the bounce back operation is started (at 17 ms). Another important feature of the free piston engine that was mentioned earlier can be seen on this graph, which is the fact that the piston velocity at the top dead center is not null, which is not the case in conventional engines where the piston is brought to rest as it belongs to a crank-slider mechanism, MAKHLOUF-HADDAD
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and which is an advantage of free piston engines that has been discussed earlier.
Figure III.16 : Combustion Chamber Pressure With Respect To x This graph represents the thermodynamic cycle that occurs in the combustion chamber of the engine. It has been found that this cycle complies with the two-stroke Otto cycle that has been shown earlier. At the top dead center of the cycle can be seen a major discontinuity, which is the combustion process of the engine that is assumed to be a spontaneous constant volume heat addition process and that is determined by its initial and final states[22][25][19]. The positions of the exhaust and inlet ports can also be seen on this graph, which are located respectively at 27 mm and 17.5 mm from the selected origin.
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Figure III.17 : Bounce Chamber Pressure With Respect To x
It can be seen on the previous graph that the maximum pressure that takes place inside the bounce chamber is equal to 4.75 bars, which occurs at the bottom dead center of the engine. In addition, the fact that the expression of the pressure of the bounce chamber is the same throughout the cycle can be verified by the continuous hyperbolic form obtained through the simulation.
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Figure III.18 : Compression Chamber Pressure With Respect To x On the following table will be shown some additional results that were calculated by this simulation. Parameter
Value
Rated Frequency
25 Hz
Compression Ratio
7.14
Thermal Efficiency
44.56%
Mean Cycle Pressure
13.175 bars
Work Produced Per Cycle
142.4 J
Rated Power Output
3.2 Kw
Ignition Advance
4.5 ms
Table 2 : Additional Results Calculated By The Simulation MAKHLOUF-HADDAD
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In addition to this simulation, a simulation of a linear alternator that is based on the Stirling Colgate free piston engine has been performed, since that engine was considered to be one of the bases of the design of the free piston engine in question due to the fact that its inventor claims that piston synchronization is achieved through electromagnetic coupling[10], which enormously simplifies the design especially that one of the main challenges that it incorporates is the design of the synchronization mechanism as it will be discussed in the following section. In fact, and as it can be seen on the following figure, this permanent magnet linear alternator, which incorporates two magnets that are fixed on the rebound pistons, has two coils surrounding the cylinders. When the magnets move through the coils, a variable magnetic field is created, thus inducing an electric current in the coils. The coils are in series with a capacitive circuit (30) which is built such that the circuit becomes a resonant RLC series circuit having a frequency equal to the frequency of the engine[10]. Therefore, and due to the fact that the same current passes through both coils, the induced Laplace force (F alt in this case), which is dependent on this current as it can be seen in the following equation[21], will be exactly the same on both sliders, thus creating the synchronization mechanism necessary for such an engine.
Falt = il ^ B
with : - i : induced current
(Eq. III-17)
- l : equivalent length of each of the coils - B : magnetic field of the magnets
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Figure III.19 : Colgate Alternator Layout A simulation that included a finite element simulation on COMSOL Multiphysics that determined the instantaneous magnetic field density that was generated by the motion of the permanent Neodymium magnets through the coils[27], and a Matlab simulation that included several SIMULINK diagrams that modeled both the kinetic and electric aspects of such an engine, in addition to a Matlab program similar to the one already described, has been performed. This simulation will not be shown in detail in this document since a free piston linear alternator was abandoned by Phoenix Machinery, and thus it will not be used in the design of the engine. However, and because it was already performed, it can be found along with its results in Appendix B.
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IV- Main Design
Based of the simulation results that were shown earlier, and based on the Pescara free piston engine, a spark-ignition free piston engine was designed. The output of this engine is intended to be extracted throughout a turbine that expands the exhaust gases generated by the engine. This turbine would be thereby coupled to an alternator that in turn generates the power required. The basis of the design was the standard available pistons that have been selected. Two 40 mm pistons and two 92 mm pistons have been used in this project. These pistons have been divided into two sets of pistons, each set including one 45 mm piston and one 92 mm piston. For each set of pistons, a central connecting rod has been conceived. This connecting rod was connected on each end to one of the pistons, and thus the sliders have been formed. The combustion cylinder has been designed such that its inlets and exhaust ports would comply with the aforementioned simulation results. Being made out of aluminum (ALUMEC79) due to its high thermal conductivity, it features a series of fins that were intended to increase the heat transfer rate of the cylinder outer walls, which is essential especially that this engine is an air cooled engine. It also features a 10 mm spark-plug located in the middle of the combustion chamber. The big cylinders are also made of aluminum. On their ends are fixed the bounce chamber covers that ensure that the bounce chamber is closed. Each of these features a 16mm thread that is intended for the connection of the communication tube that equalizes the pressure in both these chambers. A negligible blow-by occurs through the piston rings. Therefore, a bounce chamber volume conservation system MAKHLOUF-HADDAD
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has been conceived for the bounce chamber. This system makes sure that the air volume dissipated through the rings is compensated. It includes a pneumatic accumulator, a pressure regulating valve and a check valve that is connected to the pressure equalizing tube of the engine. An electric compressor provides the accumulator with its required pressure. This compressor is controlled such that it operates whenever pressure drops under a certain level, which in this case is 5 bars. Compression is stopped once the pressure reaches 7 bars. Note that a pressure drop of 0.1 bars each 30 mins occurs in the bounce chamber, which implies a limited operation time for the electric compressor. Note that the check valve ensures that air would not be transferred to the bounce chamber unless a pressure drop occurs, and denies the return of the air.
Figure IV.1 : Bounce Chamber Volume Control System Reed check valves have been selected for the scavenge pump control operation. A housing has been designed for each of these four reed valves. Two of these valves are connected to the compression chamber, while the other two are connected to the scavenge reservoir. The former two are connected on their other ends to a central carburettor where a fuel-oil mixture is pulverized into the inlet air.
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Both the big and small cylinders have been designed such that they would be properly centered during the assembly operation. Note that cast iron sleeves are intended to be inserted into both the big and small cylinders to ensure less friction in the operation of the pistons. However, the main challenge in the design of this engine remains that of the synchronizing linkage. In fact, this linkage has to ensure that the linear motion of the sliders is maintained, and that the two sliders are properly synchronized. Two synchronizing mechanisms have been designed for this purpose. A representative drawing of the first one can be seen in the following figure. It has been abandoned due to some of the complex aspects that it incorporates, especially in the sliders that the central link includes.
Figure IV.2 : Early Draft Of The Synchronization Mechanism MAKHLOUF-HADDAD
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The second one is based on the standard crank-slider mechanism. However, in this case, it consists of two connecting rods on each end that are each connected to a sliding bar that is fixed to the main slider of the engine on one end, and to a central common link on the other. The central link is fixed to an axis that rotates inside an external bearing arrangement. However, the motion of this link is not a full rotation, but rather an oscillating one. The degree of freedom of this mechanism according to the Kutzbach-Grübler equation[28] is equal to one, which is the degree of freedom required that makes it fully constrained once the engine is in operation. Note that this mechanism is based on the mechanism used by Pescara in his early opposed piston compressor that was shown previously[6]. It has the advantage of providing an external access to the synchronization mechanism, which will prove to be helpful for the starting operation. To maintain the sliding bars in a linear motion throughout the whole process, a linear guide has to be included in the engine assembly, which is one of the topics that were investigated the most, especially that the linear speed of the sliders reaches 5 m/s, which is a critical speed on almost all of the commercially available linear guides. In fact, many high speed linear bearings cannot even reach a limit of 3 m/s, which is an enormously high linear speed in industrial applications[31][32]. Therefore, and after a thorough search on every linear guide ever made, it was found that the best solution was to locally design and manufacture linear plain bearings out of sintered bronze (SAE 841), to which has been added powdered graphite, which according to the Bosch Automotive Handbook can withstands high speeds that can reach 20 m/s [29]. The design of these bushings has been based on many of the parameters of commercially available bushings. Two bushings on each side are needed for a proper support of the bars. However, and due to the limited space on such an engine, only one bushing has been used on each side. However, these MAKHLOUF-HADDAD
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bushings have been designed with a length that exceeds the required minimal length of operation (which was found to be 10 mm) by 2.5 times, thus overcoming the problem stated earlier, and allowing the bushing to have a higher Pv limit[30]. The connections between the linkages have been designed to include needle bearings, which can also be found in jet-ski engines. The bearings selected have been found to have a life that exceeds 100000 hours according to the SKF Online Bearing Calculator. However, these bearings are usually in a steady-state operation where a constant rotational speed is maintained once it is reached, which is not the case in this application especially that cyclic accelerations and decelerations occur continuously during the operation of the engine. However, this oscillating motion is taken into account by multiplying the life of the bearings by 0.8, which reduces the life of these bearings to 80000 hours, which is more than enough since a two stroke engine's life usually doesn't exceed 1000 hours (even if the results were exaggerated by the tool provided by SKF, they would still exceed the required conditions by a far large number). Note that the report of the bearing life calculation can be found in appendix C. The final three-dimensional design can be found on the next page. Note that the shop drawings of each of the 32 parts that form this engine can be found in appendix D and that the stress analysis simulations of each of the parts can be found in appendix E. In addition to the aforementioned elements, some of the elements that belong to the starting system of the engine and others that belong to the ignition system can be seen on the following figure. These elements will be discussed on the next two sections of this document.
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Figure IV.3 : Free Piston Engine Final Design MAKHLOUF-HADDAD
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V- Starting System
As it was discussed earlier, all of the pneumatic free piston engines throughout history were supposed to achieve a steady-state operation on the very first stroke after they are started. However, such a feat proves to be difficult even on the most advanced conventional internal combustion engines, especially when it is a cold start operation, which usually requires several strokes before a continuous series of ignitions is achieved. Since the designed engine doesn't belong to neither the linear alternator nor the hydraulic pump type of free piston engines, which, as discussed earlier, are the only free piston engines where a multi-stroke starting operation is possible, it requires a mechanical starting system where a reciprocating motion is possible. As it was discussed earlier, the synchronization mechanism that has been designed for this engine features the possibility of external coupling through its central link, which allows an external starting mechanism to be coupled to the engine. However, and due to the fact that the motion of the central link is an oscillating one, a conventional electric starter can't be used on this particular engine. Therefore, a mechanical linkage that converts a rotational motion into a reciprocating one is needed for such an engine, and such a mechanism is required to be disengaged once the starting operation is complete. Two designs have been considered for the starting system of this engine. The first one consists of a crank-rocker four bar linkage with a clutch. The second consists of a scotch-yoke mechanism, that converted the rotational motion of the starting MAKHLOUF-HADDAD
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motor into a linear reciprocating motion of a rack, which in turn transferred its oscillating motion to a pinion that was fixed to the central link.
Figure V.I : Scotch-yoke Mechanism[33] A crank-rocker linkage has first been designed for the system such that the rocking motion of the central link would be equal to 36 degrees, which was conform to the motion of the pistons of the engine, which was limited to a maximum stroke of 70 mm. However, a pulley reduction system was still needed to provide the central link with its required range of motion, which added an inconvenience to the design of this system. Another main disadvantage of that system was that it requires a clutch for the disengagement operation. Other disadvantages include a high risk of fatigue failure thus requiring thicker linkages which increases the costs of manufacturing, in addition to a requirement for a spacious frame on which the mechanism would have been mounted, which would make the engine less compact. An early representative three-dimensional draft for the design of such a mechanism can be found on the following figure.
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Figure V.2 : Early Draft Of The Crank-rocker Starting System The other starting mechanism, which was the one adopted in the final design, consists of a rack and pinion system that is driven by a scotch-yoke mechanism. A module two rack is fixed to the sliding element of the scotch-yoke mechanism, and a 46 tooth pinion is fixed to the rocking link of the synchronization mechanism. The sliding part of this system is allowed to rotate around the eccentric drive of the system thus allowing a disengagement operation once the starting operation of the engine is complete, and thus the inclusion of a clutch into the design would not be needed anymore. The eccentric drive of the system features an eccentricity of 7 mm, which is equal to half of the stroke length traveled back and forth by the rack. This eccentric shaft is fixed by a cross-locating bearing arrangement, which enables the MAKHLOUF-HADDAD
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use of a multitude of driving systems to be fixed on its end. The design of this system can be found on the next figure.
Figure V.3 : Rack And Pinion Starting System
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VI- Engine Electronic Control Unit
One of the main features that differentiates the free piston engine that has been designed from the Pescara free piston engine is that the former requires an ignition control unit especially that it is a spark-ignition engine, in contrast with Pescara's compression ignition free piston engine. This unit however has to be conceived especially for this type of engine, for free piston engines cannot be mounted with neither mechanical ignition units (distributors), nor conventional engine electronic control units (ECUs) that require the use of crank sensors due to the fact that they require a full rotational motion to operate properly, which is a features that free piston engines lack. Therefore, a linear ignition control unit has been designed for this engine, which consists of proximity sensors, a microcontroller that is implemented with the algorithm used to control the ignition, an ignition transistor that breaks the current of the coil whenever a spark is to occur, an electronic circuit where all the components are connected together and are provided with their rated voltages and currents, in addition to the ignition coil, the spark plug and the battery. This unit is based on an ignition control unit developed by Phoenix Machinery in 2006. However, and due to the fact that the latter belongs to a dual piston engine which is entirely different from the currently designed engine, the ignition control unit developed for this engine is different from the one designed in 2006. Throughout this section will be detailed all the steps that were taken in the design of this unit, in addition to the parameters that are crucial to the ignition process and that were included in the algorithm implemented on the microcontroller. MAKHLOUF-HADDAD
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VI-1 Ignition Sensors
As it was stated earlier, conventional pick-up sensors cannot be used on this engine due to the lack of rotating elements on such an engine. Therefore, a different type of sensors was considered for the ignition operation. It was found that due to the availability of an uncovered sliding bar in the synchronization mechanism of the engine, proximity sensors could be used for the sensing operation. Due the high frequencies that are reached during the operation of such an engine, proximity sensors having a high switching frequency were required for a proper operation of the engine, which implied the use of inductive proximity sensors, which proved to be useful especially that the components that were supposed to be detected were iron rod ends that were designed to feature a sensing rectangular surface that was separated from the surface of the bars by 10 mm, which is more than enough according to most of the sensor catalogs that were considered to prevent the sensors from continuously detecting the bar. It was found after a thorough search that the OMRON E2A-S08KN04 M8 sensor was one of the most suitable for the application in question. Some of the most important characteristics of this sensor can be found in the following table. Note that although it might be obvious that only one sensor would be used since this is a mono-cylindric engine, two sensors of this type are needed for a proper operation, which will be explained later on. Also note that one of the reasons that lead to the selection of this particular type of sensors is that it is locally available, and that it has been used by Phoenix Machinery previously which confirms that they are suitable for this application. MAKHLOUF-HADDAD
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Cylinder type sensing head size Type Sensing method Sensing distance Setting distance Differential distance
M8 Unshielded Inductive type 4 mm -10% to +10% 0 to 3.2 mm 10% Max. of sensing distance Ferrous metal (Sensitivity lowers with non-ferrous Sensing object metals.) Standard sensing object Iron 12*12*1mm Response frequency DC: 1 kHz (average) Power supply voltage 12 to 24 VDC ripple(p-p) :10% Max. Operating voltage range 10 to 32 VDC Current consumption 10 mA Max. Control output (Output type) PNP open collector output Control outpu (Switching capacity) 0 to 200 mA Indicator Operation indicator(yellow) Operation mode NO
Table 3 : Characteristics Of The OMRON E2A-S08KN04[34] The position of each of these sensors is critical for a proper ignition operation, which is a factor that will be explained later on. The sensors are supplied with a 12 V DC voltage. Their output is connected to the input ports of the microcontroller through opto-couplers that ensure that the input voltage of the controller doesn't exceed its rated value of 5V. These opto-couplers will be discussed later on.
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VI-2 Microcontroller Selection And Ignition Algorithm
The central component of the ECU is the microcontroller, which is the main component that controls the ignition operation. This microcontroller is implemented with a control algorithm that is specific to the engine. After having reviewed some of the microcontrollers used in popular ignition kits that are currently being developed worldwide, it was found that an Arduino Mega 2560 platform, which the basis of a popular open source ECU project named Speeduino[35], is the most suitable for this project especially that it features a 16-bit timer and that it is simple to program due to the fact that Arduino platforms are very well documented[36]. The following flowchart represents the algorithm which the aforementioned microcontroller was programmed to execute. Note that the Arduino source code implemented on the Arduino Mega board can be found in Appendix F. The ignition operation represented by this algorithm is similar to that of Capacitive Discharge Ignition (CDI) units that are found on two-stroke motorcycle engines, and that feature a constant ignition timing advance, which is featured on most of the smaller two-stroke engines (engines with less than 200 cc capacity) and that is also featured on this free piston engine since it is a 150 cc engine[22]. The average timing advance has been determined by the simulation that was detailed in section III. The calculation methodology of this parameter will be detailed at the end of this section.
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One of the sensors is fixed right on the position on which the ignition signal is sent by the microcontroller to the ignition transistor. This position is calculated by the numerical simulation of the engine based on the aforementioned timing advance. As soon as the aforementioned signal is received, the transistor breaks the current of the primary winding, thus inducing a 35000 V voltage on the terminals of the spark plug that is powered by the secondary winding, which induces the required spark[29]. The other sensor is located such that it is reached before the first one during the compression stroke. Its operation is included in a subsystem that makes sure that even though the first sensor is covered twice during the cycle (one time during the compression stroke and another in the expansion stroke), ignition only occurs one time, which prevents misfire. Its exact position is not as necessary as that of the first sensor. Note that a variable ignition timing requires in itself several months of research to allow the creation of a proper ignition map that optimizes the combustion process of the engine to the greatest extents possible. However, the effect of such an ignition on small engines is negligible which is why most of the commonly available commercial engines feature a constant ignition timing advance[22]. Also note that a delay of 2.5 ms takes place between the beginning of the ignition and its end to take into account the dwell time of the coil (the time it takes the RL circuit of the coil to fully charge/discharge)[29].
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Figure VI.1 : Ignition Algorithm Implemented On The Microcontroller
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The following methodology was used in the numeric simulation to calculate the timing advance required. The combustion process consists of three phases: flame formation, flame propagation, and flame termination. The first two phases take some time to occur, which is the time that is compensated by the ignition advance featured on all internal combustion engines[22]. Therefore, the duration of these two phases along with the dwell time of the coil is the timing advance required for the engine. This timing advance is usually expressed in terms of angular degrees on most engines. It will be determined in terms of time for this free piston engine because it is a linear engine. This timing advance will be determined at a frequency of 25 hz, which is the simulation frequency of this engine. The position of the ignition sensor required for this timing advance will be determined at the aforementioned frequency through a subroutine implemented in the Matlab program, and this position will be considered to be the average position that will be used on all the operating frequencies of the engine. The timing advance required for flame formation and flame propagation on a conventional internal combustion engine running at 1800 rpm is 18 degrees[22]. 1800 rpm are the equivalent of a 30 hz free piston engine operation. Therefore, at 25 hz and for a dwell time of 2.5 ms [22]: Tadv = 0.0025 + (30/25)*((1/30) * (18/360)) = 4.5 ms
(Eq. VI.1)
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According to the numeric simulation of the engine, the position of the sensors corresponding to the timing advance previously calculated would be 61 mm from the origin of the simulation. Therefore, in terms of mm, the ignition advance would be 9 mm on this engine.
VI-3 Power transistor
Due to the fact that the ignition operation requires breaking the circuit of the primary winding of the ignition coil in order to induce the required current in the secondary coil, a switching component with a high switching frequency is required to drive the ignition coil, which in this case is a transistor. This transistor has to withstand high voltages of around 300 V. Among many of the power transistors that were considered during the selection procedure, and which are almost all of the Darlington NPN type, the one chosen was the HGTP14N36G3VL transistor, which is one of the transistors that are specially manufactured as ignition drivers. It is rated at 14 A and 360 V. This transistor's gate is connected to the output pin of the microcontroller. An intermediate opto-coupler is used between the two since the output current of the microcontroller is not sufficient for a proper ignition operation. This opto-coupler along with those of the input sensors will be discussed in the following section. Note that the collector of this transistor is connected to the coil and the emitter is connected to the ground.
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VI-4 Ignition Circuit An electronic circuit has been designed that incorporates all the ignition system components. It has the role of connecting all the components together, and preventing their damage by making sure every one of them is provided with its rated electric characteristics. The latter feature is ensured through the voltage regulating circuit featured in the circuit, which provides the circuit with the two required voltages. Therefore, both 12 V and 5 V supplies are provided for each of their respective components. Opto-couplers are used whenever a communication between two differently rated components is required. In fact, on both the inputs and outputs of the microcontroller, a difference between the rated electric characteristics of the connected components can be found, which requires opto-couplers on each of these connections. In fact, the power voltage of the sensors is 12 V and the rated voltage of the microcontroller communication pins is 5V, which requires the use of opto-couplers, in which the LEDs are powered by the sensor output signal, and a 5 V voltage supply is provided to its phototransistor. Moreover, the rated current of the output of the microcontroller is not sufficient to drive the ignition coil driver, which also requires an opto-coupler that is powered by a 5 V voltage on its phototransistor end. It was found that Vishay SFH618 opto-couplers are suitable for the required aforementioned operations. MAKHLOUF-HADDAD
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A schematic diagram and the printed circuit boards of the aforedescribed circuit have been designed. These designs can be found on the following figures.
Figure VI.2 : Schematic Diagram Of The Ignition Circuit
Figure VI.3 : Power Transistor Circuit PCB Layout
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Figure VI.4 : Main Ignition Electronic Circuit PCB Layout
In addition to all the aforementioned components, a 10 mm spark plug has been used in this engine, along with a 2.5 ms dwell ignition coil and a 12V battery, which serves as the main power source of the ignition system.
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VII- Conclusion
Throughout this document were detailed all the steps that have been taken in the study and the design of a linear spark-ignition free piston engine. The different mechanical and thermodynamic aspects of most of the free piston engine applications that took place throughout history, including that of the Pescara SIGMA GS-34 on which the design of the free piston engine in question is based, were presented in detail throughout the literature review section. The results of a thorough numerical study that takes into account the kinetic and thermodynamic characteristics of the designed free piston engine were detailed. These show some of the characteristics that differentiate free piston engines from other types of internal combustion engines, which include a longer stroke, a slower compression stroke and a high piston velocity around the top dead center of the engine. This study also shows that the rebound system that was selected for the engine can ensure a complete return of the piston to its relative top dead center, which is one of the initial challenges that are met during the design of such an engine. One of the most important features that resulted from this study was the high thermal efficiency of around 45% that this engine features compared to that of other conventional spark-ignition internal combustion engines, which is limited to 30 % . Several challenges have been met throughout the design process of this engine, many of which were due to the fact that every moving component featured on this engine has a reciprocating motion, and to the relatively high frequencies that can be reached on these engines. The design of the synchronization mechanism featured on MAKHLOUF-HADDAD
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opposed piston engines can be complicated due to the aforementioned operation conditions. Moreover, an unconventional starting system has been designed for this engine to accommodate the reciprocating motion of the synchronization mechanism. In addition, the unique mode of operation of free piston engines requires a customized electronic ignition control unit that can provide the engine with a properly timed ignition, and that is well adapted to the linear aspect of this engine. Such a unit had to be designed from scratch although its design falls beyond the scope of mechanical engineering. However, it is an essential element in sparkignition engines which has to be included in this work. It can be concluded from this report that free piston engines are in fact more efficient than other types of engines, which explains the renewed interest in these engines that many international automotive and energetic developers are having right now especially that the slightest efficiency improvements can make the biggest difference. A very important local commercial success can also be achieved by free piston engines due to the fact that Lebanon, and though it is doesn't have an automotive manufacturing sector, suffers from a great electric power distribution problem due to the fact that the daily electric power generated doesn't match the current overall daily need by a far margin. Since a solution to this problem isn't predicted to be available in a near future of ten years, free piston engines, and due to their compact size and to their high efficiency, low consumption, low emission levels and low noise generation especially when they are of the properly balanced opposed piston type, can be installed in every domestic real estate thus compensating the aforementioned power deficit as an alternative to the local private generators that are distributed throughout MAKHLOUF-HADDAD
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the country, which form a relatively expensive and non-environmental solution. Nevertheless, the required presence of a synchronization system on the engine in question can be one of the inconveniences that might shadow many of a free piston engine's advantages, due to the fact that the design of such a system decreases the simplicity of a free piston engine, which is one of the essential advantages that are sought to be achieved by free piston engines. Therefore, future works should focus on the opposed piston design because of all the advantages it features, and most importantly on the elimination of such a mechanical synchronization system, which was claimed to be achieved by Stirling Colgate through electromagnetic coupling[10]. Such a free piston linear alternator has been investigated throughout this work, and was found to be very promising as it extremely simplifies the design and execution of free piston engines. These alternators should be also implemented with electronic fuel injection, which would enormously increase their efficiency, and which was investigated throughout the design of this free piston engine, but was not accomplished due to the limited duration that was imposed. Moreover, the power extraction method that is to be featured on the free piston engine described throughout this document, which consists of a turbine mounted on the exhaust of the engine and which is coupled to an alternator should be featured on the aforementioned linear alternator, thus creating a turbine compounded free piston linear alternator which would thus feature a heat recovery system that not only compensates the power losses featured on linear alternators, but also might increase the efficiency of free piston engine to unprecedented levels that can exceed 50 %. Such an engine has been theoretically investigated in 2014 by Chan-ping Lee and was MAKHLOUF-HADDAD
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found to be an impressive free piston engine design [24]. Such an engine, and due to its very high efficiency and its extremely simple design and execution, can be, without any exaggeration, the basis of the industrial revolution of the twenty-first century.
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References [1] Butler E., Griffin C.& Co. , “Evolution Of The Internal Combustion Engine” , Inc., London, 1912. [2] Lichty L., “Internal Combustion Engines” , 6th Edition, McGraw-Hill, Inc., New York, NY, 1951. [3] http://www.freikolben.ch [4] US Patent 1,657,641, United States Patent Office, Janyary 31, 1928. [5] US Patent 1,950,063, United States Patent Office, March 6, 1934. [6] US Patent 1,798,697, United States Patent Office, March 3l, 1931. [7] UK Patent 212,924, United Kingdom Patent Office, June 12, 1925. [8] Mikalsen R., Roskilly A.P., “A review of free-piston engine history and applications”, Applied Thermal Engineering, Volume 27, Issues 14-15, Pages 2339-2352, 2007. [9] Pescara C., “Histoire Des Pistons Libres Pescara”, La Gazette, Toulouse, January 2013. [10] US Patent 3,234,395, United States Patent Office,February 8, 1966. [11] http://www.freikolben.ch/37401/index.html [12] Achten PAJ, van den Oever JPJ, Potma J, Vael GEM. , “Horsepower with brains: The design of the Chiron free piston engine”, SAE Paper 2000-01-2545, 2000. [13] Van Blarigan, P., "Advanced Internal Combustion Electrical Generator", NREL/CP-57030535, 2001. [14] Kosaka, H., Akita, T., Moriya, K., Goto, S. & Co., “Development of Free Piston Engine Linear Generator System Part 1 - Investigation of Fundamental Characteristics”, SAE Technical Paper 2014-01-1203 doi:10.4271/2014-01-1203, 2014. [15] http://www.beetron.ch [16] http://www.libertine.co.uk/ [17] Underwood A.F., "The GMR 4-4 “HYPREX” engine –A concept of the free-piston engine for automotive use", SAE Transactions 1957:65:377–391, 1957. [18] Walker G., Senft J.R., “Free Piston Stirling Engines”, Springer-Verlag, Inc, Berlin, Heidelberg, 1985. [19] Heywood J. B., “Internal Combustion Engine Fundamentals”, McGraw-Hill, Inc., New York, NY, 1988. MAKHLOUF-HADDAD
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[20] Chapman J.R., “Electric Machinery Fundamentals”, 5th Edition, McGraw-Hill, Inc., New York, NY, 2012. [21] Boldea I., Nasar S.A., “Linear Electric Actuators And Generators”, Cambridge University Press, Inc., Cambridge, 1997. [22] Pulkrabek W. W., “Engineering Fundamentals Of The Internal Combustion Engine”, Prentice Hall, Inc., New Jersey, NJ, 2007. [23] http://www.torvergata-karting.it/article/articleview/76/1/9/ [24] Lee C., “Turbine-Compound Free-Piston Linear Alternator Engine”, Dissertation, University of Michigan, 2014. [25] Borgnakke C., Sonntag R.E. ,“Fundamentals Of Thermodynamics”, 7th Edition, John Wiley & Sons, Inc, New Jersey, NJ, 2009. [26] Munson B.R., Young D.F. & Co. ,“Fundamentals Of Fluid Mechanics”, 6th Edition, John Wiley & Sons, Inc, New Jersey, NJ, 2009. [27] “Voltage Induced in a Coil by a Moving Magnet”, COMSOL Multiphysics 4.4 Documentation, 2013. [28] Norton R. , “Design Of Machinery”, McGraw-Hill, Inc., New York, NY, 1999. [29] “Bosch Electronic Automotive Handbook”, Robert Bosch GmbH, 2002. [30] http://www.reliablebronze.com/catalog-design-param-841.php [31] Budynas, Nisbett , “Shigley’s Mechanical Engineering Design”, 8th Edition, McGraw-Hill, Inc., New York, NY, 2006. [32] Chevalier A. , “Guide Du Dessinateur Industriel”, Hachette, Paris, 2004. [33] http://web.mae.ufl.edu/tribology/Laboratory/Wear/Mechanisms.html [34] http://www.ia.omron.com/product/item/e2a_7198b/ [35] http://www.speeduino.com [36] http://www.arduino.cc/en/Main/arduinoBoardMega2560
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Appendix A : Numeric Simulation Of The Free Piston Engine Throughout this appendix will be found the remaining SIMULINK diagrams of the numeric simulation, in addition to the Matlab program that assigns the initial values of each of the diagrams, and makes sure each simulation run occurs at the right order and at the right moment.
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admission2.mdl
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admission3.mdl
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admission.mdl
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compression2.mdl
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compression.mdl
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exhaust1.mdl
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exhaust.mdl
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expansion2.mdl
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expansion.mdl
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Matlab Program: FPE.m clc; clear; m=4; R=0.287; Pcm=180000; Patm=101325; S=0.07; BC=0.03; CC=0.007; K2=1.3; A1=(pi*(0.04)^2)/4; A2=(pi*(0.092)^2)/4; A3=A1; Aex=(pi*(0.04)^2)/4; Fr=500; B=0; K1=1.3; Exx=(0.05); Ex=S+CC-Exx; Pcci=(Patm)*(Exx/CC)^K1; Tcci=707/(1826000/Pcci); Pccf=10111000/(1826000/Pcci); C2=((Patm*1.5)*(A2*(BC+S))^K2); Mgc=(Pcci*CC*2*A1)/(R*Tcci); K1=1.3; C1=(Pccf*(A1*2*CC)^K1); C3=(Pcm*((A2-A3)*CC)^K1); sim('expansion',[0 0.03]); i=1; while p3(i) > Patm, i=i+1; end tst1=x(i); if tst1 > Ex, ts1=time(i); xs1=x(i); vs1=v(i);
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sim('expansion',[0 ts1]); Fplt; K1=1.3; C1=(Pccf*(A1*2*CC)^K1); sim('expansion2',[ts1 0.03]); i=1; while x(i) > Ex, i=i+1; end ts2=time(i); xs2=x(i); vs2=v(i); ps2=p1(i); sim('expansion2',[ts1 ts2]); Fplt; else i=1; while x(i) > Ex, i=i+1; end ts1=time(i); xs1=x(i); vs1=v(i); sim('expansion',[0 ts1]); Fplt; K1=1.3; C1=(Pccf*(A1*2*CC)^K1)/(Mgc); sim('exhaust1',[ts1 0.03]); i=1; while p3(i) > Patm, i=i+1; end ts2=time(i); xs2=x(i); vs2=v(i); sim('exhaust1',[ts1 ts2]); Fplt; end K1=1.3; C1=(Pccf*(A1*2*CC)^K1)/(Mgc); sim('exhaust',[ts2 0.03]); i=1; while x(i) > 0.0175, i=i+1; end ts3=time(i); xs3=x(i); vs3=v(i); sim('exhaust',[ts2 ts3]);
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Fplt; sim('admission',[ts3 0.03]); i=1; while v(i) < 0, i=i+1; end ts4=time(i); xs4=x(i); vs4=v(i); sim('admission',[ts3 ts4]); Fplt; K1=1.3; C3=(Patm*((A2-A3)*(CC+S-xs4))^K1); sim('admission2',[ts4 0.04]); i=1; while x(i) < Ex, i=i+1; end tst=p3(i); if tst < Pcm, ts5=time(i); xs5=x(i); vs5=v(i); sim('admission2',[ts4 ts5]); Fplt; K1=1.3; C1=(Pcci*(A1*2*CC)^K1); C3=(Patm*((A2-A3)*(CC+S-xs4))^K1); sim('compression',[ts5 0.04]); i=1; while p3(i) < Pcm, i=i+1; end ts6=time(i); xs6=x(i); vs6=v(i); sim('compression',[ts5 ts6]); Fplt; else i=1; while p3(i) < Pcm, i=i+1; end ts5=time(i); xs5=x(i); vs5=v(i); sim('admission2',[ts4 ts5]); Fplt; K1=1.3;
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sim('admission3',[ts5 0.04]); i=1; while x(i) < Ex, i=i+1; end ts6=time(i); xs6=x(i); vs6=v(i); sim('admission3',[ts5 ts6]); Fplt; end K1=1.3; C1=(Pcci*(A1*2*CC)^K1); sim('compression2',[ts6 0.1]); i=1; figure (7) plot(time,x); hold on; figure (8) plot(time,v); hold on; figure (9) plot(time,a); hold on; while x(i) < S, i=i+1; end ts7=time(i); xs7=x(i); vs7=v(i); sim('compression2',[ts6 ts7]); Fplt; frequency=1/ts7; compratio=(Pcci/Patm)^(1/K1); effth=1-1/(compratio)^(K1-1); Vh=(Exx-CC)*A1*2; lambda=Pccf/Pcci; Phi=0.92; Pi=Phi*((Patm*compratio^K1)*((lambda*(1-compratio^(1-K2))/(K2-1))-((1-compratio^(1-K1))/(K1-1))))/ (compratio-1); Li=Pi*Vh; Ni=Li*frequency; i=1; Tign=ts7-(0.0025 +((30/frequency)*((1/30) * (18/360)))); while time(i) < Tign, i=i+1; end Xign=x(i); frequency compratio
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effth Pi Li Ni Ex Exx xs3 xs4 Xign Vh Pcci Tcci
Fplt.m: figure (1) plot(time,x); title('Piston Position With Respect To Time'); xlabel('Time (s)'); % x-axis label ylabel('Position (m)'); % y-axis label hold on; figure (2) plot(time,v); title('Piston Velocity With Respect To Time'); xlabel('Time (s)'); % x-axis label ylabel('Velocity (m/s)'); % y-axis label hold on; figure (3) plot(time,a); title('Piston Acceleration With Respect To Time'); xlabel('Time (s)'); % x-axis label ylabel('Acceleration (m/s2)'); % y-axis label hold on; figure(4) plot(x,p1); title('Combustion Chamber Pressure With Respect To x'); xlabel('Position (m)'); % x-axis label ylabel('Combustion Chamber Pressure (Pa)'); % y-axis label hold on; figure(5) plot(x,p2); title('Bounce Chamber Pressure With Respect To x'); xlabel('Position (m)'); % x-axis label ylabel('Bounce Chamber Pressure (Pa)'); % y-axis label hold on; figure(6) plot(x,p3); title('Compression Chamber Pressure With Respect To x'); xlabel('Position (m)'); % x-axis label ylabel('Compression Chamber Pressure (Pa)'); % y-axis label hold on;
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Appendix B : Simulation Of A Free Piston Linear Alternator
Throughout this appendix will be found one of the SIMULINK diagrams of the numeric simulation of an opposed piston linear alternator that is based on the Colgate engine. In this diagram, it can be seen that a simulation diagram of the electric RLC circuit that includes the coils that surround the moving permanent magnet of the alternator has been added to the admission2.mdl diagram that can be found in Appendix A, and that the effects of each of the two systems on the other is taken into account by connecting both diagram on the corresponding spots ( the resulting Laplace force that is induced by the circuit is added to the sum of the forces of the kinetic simulation, and the velocity of the slider, which is a part of the expression of the electromotive force, is connected to the circuit diagram). The system obtained is a two-degree of freedom differential equation. Note that only one diagram has been shown since the same modification can be found on all the other diagrams that can be found in appendix A. In addition, the Matlab program that assigns the initial values of each of the diagrams, and makes sure each simulation run occurs at the right order and at the right moment, the results of the simulation, and a COMSOL Multiphysics finite element analysis that determines the magnetic field distribution of the permanent magnet with respect to time and position of the slider, can be found in this section.
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admission2.mdl
Gain
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time
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a
Clock
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uv -K1 Math Function 2 Constant2
Product
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-1 Gain 5
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B Gain 8 Fr
Idot
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Km
I
1 s
e
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Matlab Program: FPE-ELEC.m clc; clear; m=5; R=0.287; mu0=1.256637061e-6; roco=2.13e-8; Tcci=707/1.4; Pcci=1826000/1.4; Pcm=182500; Pccf=10111000; Patm=101325; S=0.05; BC=0.02; CC=0.007; Br=1.2; murc=1.07*mu0; hm=0.007; hs=0; ks=1.1; g=0.001; gm=8e-3; Dm=0.09; N=100; Vt=12*sqrt(2); fest=36; Rcc=roco*((N^2)/(0.8*4*Dm)); Rc=Rcc; Rload=10; L1=(mu0*pi*Dm*S*N^2)/(2*ks*gm); L=2*L1; C=(L*(2*pi*fest)^2)^(-1); Bm=Br/(1+(murc/mu0)*((2*ks*g)/(hm+hs))); Km=pi*Dm*N*Bm;
K2=1.3; A1=0.0016; A2=A1*4; A3=A1; Aex=64/10000; Fr=500; B=0;
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K1=1.3; Exx=(((Pcci/Patm)^(1/K1))*CC); Ex=S+CC-Exx; C2=(Patm*2)*(A2*(BC+S))^K2; Mgc=(Pcci*CC*2*A1)/(R*Tcci); K1=1.3; C1=(Pccf*(A1*2*CC)^K1); C3=(Pcm*((A2-A3)*CC)^K1); sim('expansion',[0 0.03]); i=1; while p3(i) > Patm, i=i+1; end tst1=x(i); if tst1 > Ex, ts1=time(i); xs1=x(i); vs1=v(i); Is1=I(i); Idots1=Idot(i); sim('expansion',[0 ts1]); Fplt; K1=1.3; C1=(Pccf*(A1*2*CC)^K1); sim('expansion2',[ts1 0.03]); i=1; while x(i) > Ex, i=i+1; end ts2=time(i); xs2=x(i); vs2=v(i); ps2=p1(i); Is2=I(i); Idots2=Idot(i); sim('expansion2',[ts1 ts2]); Fplt; else i=1; while x(i) > Ex, i=i+1; end ts1=time(i); xs1=x(i); vs1=v(i); Is1=I(i); Idots1=Idot(i); sim('expansion',[0 ts1]);
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Fplt; K1=1.3; C1=(Pccf*(A1*2*CC)^K1)/(Mgc); sim('exhaust1',[ts1 0.03]); i=1; while p3(i) > Patm, i=i+1; end ts2=time(i); xs2=x(i); vs2=v(i); Is2=I(i); Idots2=Idot(i); sim('exhaust',[ts1 ts2]); Fplt; end K1=1.3; C1=(Pccf*(A1*2*CC)^K1)/(Mgc); sim('exhaust',[ts2 0.03]); i=1; while p1(i) > Patm, i=i+1; end ts3=time(i); xs3=x(i); vs3=v(i); Is3=I(i); Idots3=Idot(i); sim('exhaust',[ts2 ts3]); Fplt; sim('admission',[ts3 0.03]); i=1; while v(i) < 0, i=i+1; end ts4=time(i); xs4=x(i); vs4=v(i); Is4=I(i); Idots4=Idot(i); sim('admission',[ts3 ts4]); Fplt; K1=1.3; C3=(Patm*((A2-A3)*(CC+S-xs4))^K1); sim('admission2',[ts4 0.04]); i=1; while x(i) < Ex, i=i+1;
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end tst=p3(i); if tst < Pcm, ts5=time(i); xs5=x(i); vs5=v(i); Is5=I(i); Idots5=Idot(i); sim('admission2',[ts4 ts5]); Fplt; K1=1.3; C1=(Pcci*(A1*2*CC)^K1); C3=(Patm*((A2-A3)*(CC+S-xs4))^K1); sim('compression',[ts5 0.04]); i=1; while p3(i) < Pcm, i=i+1; end ts6=time(i); xs6=x(i); vs6=v(i); Is6=I(i); Idots6=Idot(i); sim('compression',[ts5 ts6]); Fplt; else i=1; while p3(i) < Pcm, i=i+1; end ts5=time(i); xs5=x(i); vs5=v(i); Is5=I(i); Idots5=Idot(i); sim('admission2',[ts4 ts5]); Fplt; K1=1.3; sim('admission3',[ts5 0.04]); i=1; while x(i) < Ex, i=i+1; end ts6=time(i); xs6=x(i); vs6=v(i); Is6=I(i); Idots6=Idot(i); sim('admission3',[ts5 ts6]); Fplt; end
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K1=1.3; C1=(Pcci*(A1*2*CC)^K1); sim('compression2',[ts6 0.1]); i=1; figure (14) plot(time,x); hold on; while x(i) < S, i=i+1; end ts7=time(i); xs7=x(i); vs7=v(i); Is7=I(i); Idots7=Idot(i); sim('compression2',[ts6 ts7]); Fplt; frequency=1/ts7; compratio=(Pcci/Patm)^(1/K1); effth=1-1/(compratio)^(K1-1); Vh=(Exx-CC)*A1*2; lambda=Pccf/Pcci; Phi=0.92; Pi=Phi*((Patm*compratio^K1)*((lambda*(1-compratio^(1-K2))/(K2-1))-((1-compratio^(1-K1))/(K1-1))))/ (compratio-1); Li=Pi*Vh; Ni=Li*frequency; i=1; Tign=ts7-((0.00204*800/(1800))+(0.00204*800*8/(1800*22))); while time(i) < Tign, i=i+1; end Xign=x(i); frequency compratio effth Pi Li Ni L Rc C Bm xs3 Ex Xign
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Fplt.m: figure (1) plot(time,x); title('Piston Position With Respect To Time'); xlabel('Time (s)'); % x-axis label ylabel('Position (m)'); % y-axis label hold on; figure (2) plot(time,v); title('Piston Velocity With Respect To Time'); xlabel('Time (s)'); % x-axis label ylabel('Velocity (m/s)'); % y-axis label hold on; figure (3) plot(time,a); hold on; figure(4) plot(x,p1); title('Combustion Chamber Pressure With Respect To x'); xlabel('Position (m)'); % x-axis label ylabel('Combustion Chamber Pressure (Pa)'); % y-axis label hold on; figure(5) plot(x,p2); title('Bounce Chamber Pressure With Respect To x'); xlabel('Position (m)'); % x-axis label ylabel('Bounce Chamber Pressure (Pa))'); % y-axis label hold on; figure(6) plot(x,p3); hold on; figure(7) plot(time,I); title('Induced Current With Respect To Time'); xlabel('Time (s)'); % x-axis label ylabel('Current (A)'); % y-axis label hold on; figure(8) plot(time,e); title('Induced Electromotive Force With Respect To Time'); xlabel('Time (s)'); % x-axis label ylabel('EMF (V)'); % y-axis label hold on; figure(9) plot(time,Pelec); title('Extracted Electric Power With Respect To Time'); xlabel('Time (s)'); % x-axis label ylabel('P (W)'); % y-axis label hold on;
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figure(10) plot(time,Felec); title('Laplace Force Acting On The Piston With Respect To Time'); xlabel('Time (s)'); % x-axis label ylabel('Laplace Force (N)'); % y-axis label hold on; figure(11) plot(time,Vout); hold on; figure(12) plot(time,Vind); hold on; figure(13) plot(time,Iload); hold on;
COMSOL Multiphysics Simulation Results:
Simulation Model
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Magnetic Field Distribution
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Simulation Results
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Appendix C : SKF Bearing Life Calculator Report
Throughout this appendix will be found the detailed calculation report generated by the SKF bearing life calculator. Note that many of the inputs of the calculations have been exaggerated as a mean of safety precaution.
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SKF Bearing Calculator Calculation summary report Published on 2015-07-15 12.44.51 GMT
SKF General Conditions for technical assistance and advice (available at www.skf.com) shall apply to this report. SKF accepts no variation of any of these conditions unless confirmed in writing by SKF. ® SKF is a registered trademark of the SKF Group. © SKF Group 2013 The contents of this publication are the copyright of SKF and may not be reproduced, duplicated, copied, transferred, distributed, stored, modified, downloaded or otherwise exploited for any commercial use without the prior written approval of SKF.
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Table of Contents 1.
Designation: NA 4900 1.1 Bearing life
2.
Designation: 6000 2.1 Bearing life
3.
Designation: 6202-2Z 3.1 Bearing life
1. Designation: NA 4900
Type: Needle roller bearing
Bearing Data d
D
B
C
C
10.0 mm
22.0 mm
13 mm
8.8 kN
10.4 kN
1.1
0
Bearing life
Input Parameters F
0.2 kN
n
3000 r/min
Operating temperature Bearing outer ring
80 °C
r Radial load i Rotational speed of the inner ring
η specification method c
Cleanliness classification(recommended)
® SKF is a registered trademark of the SKF Group. © SKF Group 2013
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Lubricant type and cleanliness
Normal cleanliness (e.g. shielded bearing) 2 27 mm /s
Viscosity at 40 °C
Result L
497800 hour
a
0.3
10mh SKF rating life SKF SKF life modification factor a
SKF
κ Viscosity ratio
0.42
P Equivalent dynamic bearing load
0.2 kN
η
0.06
ν
2 17.3 mm /s
L
>1000000 hour
C/P Load ratio
44
c Factor for contamination level 1 Required kinematic viscosity for κ=1 10h Basic rating life
2. Designation: 6000
Type: Deep groove ball bearing
Bearing Data d
D
B
C
C
10.0 mm
26.0 mm
8 mm
4.75 kN
1.96 kN
0
® SKF is a registered trademark of the SKF Group. © SKF Group 2013
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Bearing Data
2.1
Bearing life
Input Parameters Select bearing internal radial clearance
Normal internal radial clearance
F
0.2 kN
F
0.1 kN
n
3000 r/min
Operating temperature Bearing outer ring
80 °C
r Radial load a Axial load i Rotational speed of the inner ring
η specification method c
Cleanliness classification(recommended)
Lubricant type and cleanliness
Normal cleanliness (e.g. shielded bearing) 2 27 mm /s
Viscosity at 40 °C
Result
® SKF is a registered trademark of the SKF Group. © SKF Group 2013
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L
6730 hour
a
0.27
10mh SKF rating life SKF SKF life modification factor a
SKF
κ Viscosity ratio
0.45
P Equivalent dynamic bearing load
0.289 kN
η
0.07
ν
2 16.3 mm /s
L
24700 hour
C/P Load ratio
16.4
c Factor for contamination level 1 Required kinematic viscosity for κ=1 10h Basic rating life
3. Designation: 6202-2Z
Type: Deep groove ball bearing
Bearing Data d
D
B
C
C
15.0 mm
35.0 mm
11 mm
8.06 kN
3.75 kN
3.1
0
Bearing life
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Input Parameters Select bearing internal radial clearance
Normal internal radial clearance
F
0.2 kN
F
0.1 kN
n
3000 r/min
Operating temperature Bearing outer ring
80 °C
r Radial load a Axial load i Rotational speed of the inner ring
η specification method c
Cleanliness classification(recommended)
Lubricant type and cleanliness
Normal cleanliness (e.g. shielded bearing)
Grease used in the bearing
MT47 2 70.0 mm /s 2 7.3 mm /s
Viscosity at 40 °C Viscosity at 100 °C
Warning The calculation is only valid for horizontal shaft, inner ring rotation and moderate vibrations. For deviating operating conditions, please contact the SKF application engineering service.
Result L
151100 hour
a
1.56
10mh SKF rating life SKF SKF life modification factor a
SKF
κ Viscosity ratio
0.93
P Equivalent dynamic bearing load
0.311 kN
η
0.15
ν
2 13.8 mm /s
c Factor for contamination level 1 Required kinematic viscosity for κ=1
® SKF is a registered trademark of the SKF Group. © SKF Group 2013
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L
96700 hour
L
33500 hour
C/P Load ratio
25.9
10h Basic rating life 10 Capped bearing grease life
® SKF is a registered trademark of the SKF Group. © SKF Group 2013
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Appendix D : Free Piston Engine Execution Drawings
Throughout this appendix will be found a detailed bill of material that includes all the standard and manufactured parts that are included in this project, followed by each of the 32 execution drawings of the parts of this project.
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S
Division/Dept: M.MAKHLOUF F.HADDAD
R&D Department
Designation
Technical specifications
Prepared by:
Item CENTRAL SYNCHRONISING LINK Support 1 CONNECTING LINK LINEAR GUIDE BOUNCE CHAMBER COVER CONNECTING PIN 1 SYNCHRONISATION SHAFT ROD END 1 FLANGE PISTON ROD BOUNCE CHAMBER CYLINDER COMBUSTION CYLINDER BEARING HOUSING 1 SCOTCH-YOKE SLIDER LINEAR GUIDE CASE PLATE 1 CASE PLATE 2 CASE PLATE 3 ROTATION ARM STARTING SYSTEM FLOOR BASE STARTING SYSTEM WALL 1 STARTING SYSTEM WALL 2 ECCENTRIC SHAFT VALVE HOUSING COVER VALVE HOUSING COVER ROD END 2 BEARING SUPPORT BEARING HOUSING 2 CENTRAL SHAFT 1 CENTRAL SHAFT 2 SENSOR PLATFORM RACK PINION NEEDLE BEARING BALL BEARING 1 BALL BEARING 2 PISTON 1 PISTON 2 REED VALVE
Approved by:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40
Date:
pcs pcs pcs pcs pcs pcs pcs pcs pcs pcs pcs pcs pcs pcs pcs pcs pcs pcs pcs pcs pcs pcs pcs pcs pcs pcs pcs pcs pcs pcs pcs pcs pcs pcs pcs pcs pcs pcs pcs pcs
Unit
Date:
Catalog reference
Signature:
Brand required
Signature:
R.T.F R.T.F SKF SKF SKF
M2 M2 ; T23 NA 4900 6000 6202-2Z 40mm 92mm ATSUGI
Function
Bill of Material DES/BOM/30
Bill of Material
Section / Assembly # 40FPE000000 40FPE000000 40FPE000000 40FPE000000 40FPE000000 40FPE000000 40FPE000000 40FPE000000 40FPE000000 40FPE000000 40FPE000000 40FPE000000 40FPE000000 40FPE000000 40FPE000000 40FPE000000 40FPE000000 40FPE000000 40FPE000000 40FPE000000 40FPE000000 40FPE000000 40FPE000000 40FPE000000 40FPE000000 40FPE000000 40FPE000000 40FPE000000 40FPE000000 40FPE000000 40FPE000000 40FPE000000 40FPE000000 40FPE000000 40FPE000000 40FPE000000 40FPE000000 40FPE000000 40FPE000000 40FPE000000
1/JUN/2015
Qty of parts 2 1 4 4 2 8 4 2 2 2 2 1 4 1 2 2 2 2 1 1 2 1 1 1 4 4 2 1 2 1 1 2 1 1 8 2 4 2 2 4
Part # 10FPE000001 10FPE000002 10FPE000003 10FPE000004 10FPE000005 10FPE000006 10FPE000007 10FPE000008 10FPE000009 10FPE000010 10FPE000011 10FPE000012 10FPE000013 10FPE000014 10FPE000015 10FPE000016 10FPE000017 10FPE000018 10FPE000019 10FPE000020 10FPE000021 10FPE000022 10FPE000023 10FPE000024 10FPE000025 10FPE000026 10FPE000027 10FPE000028 10FPE000029 10FPE000030 10FPE000031 10FPE000032 20FPE000033 20FPE000034 30FPE000001 30FPE000002 30FPE000003 30FPE000004 30FPE000005 30FPE000006
Wiring Sheet # Sub-assembly # 40FPE000000 40FPE000000 40FPE000000 40FPE000000 40FPE000000 40FPE000000 40FPE000000 40FPE000000 40FPE000000 40FPE000000 40FPE000000 40FPE000000 40FPE000000 40FPE000000 40FPE000000 40FPE000000 40FPE000000 40FPE000000 40FPE000000 40FPE000000 40FPE000000 40FPE000000 40FPE000000 40FPE000000 40FPE000000 40FPE000000 40FPE000000 40FPE000000 40FPE000000 40FPE000000 40FPE000000 40FPE000000 40FPE000000 40FPE000000 40FPE000000 40FPE000000 40FPE000000 40FPE000000 40FPE000000 40FPE000000
Rev. #
Assembly/Section #: Revision # :
0FPE
40FPE000000
Rev.:1
Job#:
RDT
Rev. Date:
Remarks
PRS/ORS #
Spare Part
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Appendix E : Autodesk Inventor Stress Analysis Reports
Throughout this appendix will be found the detailed reports of the stress analysis finite element calculations that were performed on each of the parts that form the engine. Note that these reports have been automatically generated by the Autodesk Inventor Stress Analysis tool.
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Stress Analysis Report Analyzed File: Autodesk Inventor Version: Creation Date: Simulation Author: Summary:
Spur Gear11.ipt 2015 SP1 (Build 190203100, 203) 7/10/2015, 2:33 PM User
Project Info (iProperties) Summary Author User
Project Part Number Designer Cost Date Created
Spur Gear1 User $0.00 5/28/2015
Status Design Status WorkInProgress
Physical Material Density Mass Area Volume
Steel 7.85 g/cm^3 0.58884 kg 20325.2 mm^2 75011.5 mm^3 x=-0.00000578626 mm Center of Gravity y=0.0000131034 mm z=37.0046 mm Note: Physical values could be different from Physical values used by FEA reported below.
Simulation:1 General objective and settings: Design Objective Simulation Type Last Modification Date Detect and Eliminate Rigid Body Modes
Parametric Dimension Static Analysis 7/8/2015, 1:29 PM No
Mesh settings: Avg. Element Size (fraction of model diameter) Min. Element Size (fraction of avg. size) Grading Factor Max. Turn Angle
MAKHLOUF-HADDAD
0.1 0.2 1.5 60 deg
149
Create Curved Mesh Elements
Yes
Results Parametric Configuration:1 Result Summary Name Volume Mass Displacement Safety Factor
Minimum Maximum 75012.1 mm^3 0.588845 kg 0 mm 0.0235165 mm 6.72447 ul 15 ul
Figures Displacement
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Safety Factor
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Stress Analysis Report
Analyzed File: Autodesk Inventor Version: Creation Date: Simulation Author: Summary:
Part36.ipt 2015 SP1 (Build 190203100, 203) 7/10/2015, 2:30 PM User
Project Info (iProperties) Summary Author User
Project Part Number Designer Cost Date Created
Part36 User $0.00 5/22/2015
Status Design Status WorkInProgress
Physical Material Density Mass Area Volume
Generic 1 g/cm^3 0.241463 kg 39705.7 mm^2 241463 mm^3 x=0.0000000022446 mm Center of Gravity y=38.6472 mm z=0.0000000000430052 mm Note: Physical values could be different from Physical values used by FEA reported below.
Simulation:1 General objective and settings: Design Objective Simulation Type Last Modification Date Detect and Eliminate Rigid Body Modes
Parametric Dimension Static Analysis 7/3/2015, 10:58 AM No
Mesh settings: Avg. Element Size (fraction of model diameter) 0.1 Min. Element Size (fraction of avg. size) 0.2
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Grading Factor Max. Turn Angle Create Curved Mesh Elements
1.5 60 deg Yes
Results Parametric Configuration:1 Result Summary Name Volume Mass Displacement Safety Factor
Minimum Maximum 241463 mm^3 0.65195 kg 0 mm 0.0473067 mm 3.77985 ul 15 ul
Figures Displacement
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Safety Factor
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Stress Analysis Report
Analyzed File: Autodesk Inventor Version: Creation Date: Simulation Author: Summary:
Part15.ipt 2015 SP1 (Build 190203100, 203) 7/10/2015, 6:37 PM User
Project Info (iProperties) Summary Author User
Project Part Number Designer Cost Date Created
Part15 User $0.00 4/4/2015
Status Design Status WorkInProgress
Physical Material Density Mass Area Volume
Generic 1 g/cm^3 0.739955 kg 234503 mm^2 739955 mm^3 x=22.3278 mm Center of Gravity y=105.882 mm z=-0.0000318816 mm Note: Physical values could be different from Physical values used by FEA reported below.
Simulation:1 General objective and settings: Design Objective Simulation Type Last Modification Date Detect and Eliminate Rigid Body Modes
Parametric Dimension Static Analysis 7/10/2015, 6:36 PM No
Mesh settings: Avg. Element Size (fraction of model diameter) 0.1 Min. Element Size (fraction of avg. size) 0.2
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Grading Factor Max. Turn Angle Create Curved Mesh Elements
1.5 60 deg Yes
Results Parametric Configuration:1 Result Summary Name Volume Mass Displacement Safety Factor
Minimum Maximum 739955 mm^3 5.80865 kg 0 mm 0.0026513 mm 11.5893 ul 15 ul
Figures Displacement
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Safety Factor
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Stress Analysis Report
Analyzed File: Autodesk Inventor Version: Creation Date: Simulation Author: Summary:
Part14.ipt 2015 SP1 (Build 190203100, 203) 7/10/2015, 6:35 PM User
Project Info (iProperties) Summary Author User
Project Part Number Designer Cost Date Created
Part14 User $0.00 4/3/2015
Status Design Status WorkInProgress
Physical Material Density Mass Area Volume
Generic 1 g/cm^3 0.198419 kg 46071.9 mm^2 198419 mm^3 x=-0.0000000169427 mm Center of Gravity y=5 mm z=0 mm Note: Physical values could be different from Physical values used by FEA reported below.
Simulation:1 General objective and settings: Design Objective Simulation Type Last Modification Date Detect and Eliminate Rigid Body Modes
Parametric Dimension Static Analysis 7/10/2015, 6:33 PM No
Mesh settings: Avg. Element Size (fraction of model diameter) 0.1 Min. Element Size (fraction of avg. size) 0.2
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Grading Factor Max. Turn Angle Create Curved Mesh Elements
1.5 60 deg Yes
Results Parametric Configuration:1 Result Summary Name Volume Mass Displacement Safety Factor
Minimum Maximum 198419 mm^3 0.535732 kg 0 mm 0.0761728 mm 1.66431 ul 15 ul
Figures Displacement
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Safety Factor
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Stress Analysis Report2 Analyzed File: Autodesk Inventor Version: Creation Date: Simulation Author: Summary:
synchronizatin stress analysis1.iam 2015 SP1 (Build 190203100, 203) 7/10/2015, 6:53 PM User
Project Info (iProperties) Summary Author User
Project Part Number Designer Cost Date Created
synchronizatin stress analysis1 User $0.00 4/16/2015
Status Design Status WorkInProgress
Physical Mass Area Volume
1.30561 kg 365864 mm^2 1305610 mm^3 x=33.4183 mm Center of Gravity y=29.5539 mm z=-24.1601 mm Note: Physical values could be different from Physical values used by FEA reported below.
Simulation:2 General objective and settings: Design Objective Simulation Type Last Modification Date Detect and Eliminate Rigid Body Modes Separate Stresses Across Contact Surfaces Motion Loads Analysis
Parametric Dimension Static Analysis 7/10/2015, 6:52 PM No No No
Mesh settings: Avg. Element Size (fraction of model diameter) Min. Element Size (fraction of avg. size) Grading Factor Max. Turn Angle
MAKHLOUF-HADDAD
0.1 0.2 1.5 60 deg
169
Create Curved Mesh Elements Use part based measure for Assembly mesh
No Yes
Results Parametric Configuration:1 Result Summary Name Volume Mass Displacement Safety Factor
Minimum Maximum 1305600 mm^3 5.47931 kg 0 mm 0.0993369 mm 1.40172 ul 15 ul
Figures Displacement
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Safety Factor
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Stress Analysis Report Analyzed File: Autodesk Inventor Version: Creation Date: Simulation Author: Summary:
excentrique.ipt 2015 SP1 (Build 190203100, 203) 7/10/2015, 2:36 PM User
Project Info (iProperties) Summary Author User
Project Part Number Designer Cost Date Created
Part9 User $0.00 5/28/2015
Status Design Status WorkInProgress
Physical Material Density Mass Area Volume
Generic 1 g/cm^3 0.0238963 kg 9158.02 mm^2 23896.3 mm^3 x=0.0000000000983883 mm Center of Gravity y=-59.1829 mm z=-0.447159 mm Note: Physical values could be different from Physical values used by FEA reported below.
Simulation:1 General objective and settings: Design Objective Simulation Type Last Modification Date Detect and Eliminate Rigid Body Modes
Parametric Dimension Static Analysis 7/10/2015, 2:35 PM No
Mesh settings: Avg. Element Size (fraction of model diameter) Min. Element Size (fraction of avg. size) Grading Factor Max. Turn Angle
MAKHLOUF-HADDAD
0.1 0.2 1.5 60 deg
174
Create Curved Mesh Elements
Yes
Results Parametric Configuration:1 Result Summary Name Volume Mass Displacement Safety Factor
Minimum Maximum 23896.3 mm^3 0.187586 kg 0 mm 0.368055 mm 1.41244 ul 15 ul
Figures Displacement
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Safety Factor
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Stress Analysis Report
Analyzed File: Autodesk Inventor Version: Creation Date: Simulation Author: Summary:
Part2.ipt 2015 SP1 (Build 190203100, 203) 7/10/2015, 2:27 PM User
Project Info (iProperties) Summary Author User
Project Part Number Designer Cost Date Created
Part2 User $0.00 3/12/2015
Status Design Status WorkInProgress
Physical Material Density Mass Area Volume
Generic 1 g/cm^3 0.702994 kg 177635 mm^2 702994 mm^3 x=-0.304108 mm Center of Gravity y=-0.103671 mm z=0.00669375 mm Note: Physical values could be different from Physical values used by FEA reported below.
Simulation:1 General objective and settings: Design Objective Simulation Type Last Modification Date Detect and Eliminate Rigid Body Modes
Parametric Dimension Static Analysis 7/10/2015, 2:24 PM No
Mesh settings: Avg. Element Size (fraction of model diameter) 0.1 Min. Element Size (fraction of avg. size) 0.2
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Grading Factor Max. Turn Angle Create Curved Mesh Elements
1.5 60 deg Yes
Results Parametric Configuration:1 Result Summary Name Volume Mass Displacement Safety Factor
Minimum Maximum 702991 mm^3 5.51848 kg 0 mm 0.00695989 mm 3.08133 ul 15 ul
Figures Displacement
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Safety Factor
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C:\Users\User\Desktop\fyp\Part2.ipt
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Appendix F : Arduino Source Code2I7KH(QJLQH&RQWURO8QLW Throughout this appendix will be found the Arduino Source Code that has been implemented on the Arduino Mega board.
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Arduino Program : FPE_IGNITION.ino const int Sensor1Pin = 2; const int Sensor2Pin = 3; const int IgnitionPin = 6; //IgnitionPin = 13 for testing the ignition with the built-in LED int Sensor1State = 0;
// current state of Sensor1
int Sensor2State = 0;
// current state of Sensor2
int LastSensor2State = 0;
// previous state of Sensor2
void setup() { // initialize the Sensor1 Pin as a input: pinMode(Sensor1Pin, INPUT); // initialize the Sensor2 Pin as a input: pinMode(Sensor2Pin, INPUT); // initialize the Ignition Pin as an output: pinMode(IgnitionPin, OUTPUT); // initialize serial communication: Serial.begin(9600); }
void loop() { // read the sensor input pins: Sensor1State = digitalRead(Sensor1Pin); Sensor2State = digitalRead(Sensor2Pin); if (Sensor2State == HIGH) { LastSensor2State = 1; } // used to prevent post-combustion ignition
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if (LastSensor2State = 1 && Sensor1State == HIGH ) { digitalWrite(IgnitionPin, HIGH); delay(2.5); digitalWrite(IgnitionPin, LOW); LastSensor2State = 0; } else { digitalWrite(IgnitionPin, LOW); } }
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