abstract This paper represents a new inside-look of the working process and expectable performances performances and ideas of forwardly innovative innovative ways of increasing the efficiency of the (ICE) Internal Internal Combustion Combustion engines. Fulfilling the new Legal requirements , focused on significant emission and fuel consumption reductions , Additional manufacturing cost reductions will be essential to maintain, or better grow the business in a very competitive environment. environment. In the following research , we will explore some of the engineering solutions made to seek the ultimate IC-Engine .. a closer view of Internal Combustion Engines for the Future .
1.Introduction. The Laperouze Report, adopted by European Parliament in February 2009, demands a 25-40% reduction in emissions by 2020. Reducing fuel consumption is an important part of this, and fuel injection technology has a key part to play in Injection Systems for IC . now, the question is "Will the internal combustion engine be able to cope with these challenges also in the future?" Under this strict circumstances of environment and consumer harsh demands , Customers are very focused on total cost of ownership, which is determined by such factors as price, fuel consumption (and fuel price), maintenance cost, as well as reliability and durability. Environmental demands will also act as a constriction of the developments of (ICE) as a result of The legal requirements for exhaust emissions and fuel economy , as well as the CO2 emission reduction commitment of the European car industry , there are major differences in the future development priorities between diesel and gasoline engines. As a conclusion With modern machinery industry developing, the application of internal combustion engine is getting wider and research direction is towards high-power, high speed and strong loads. With minimal environmental effects and with optimal customer satisfaction . The focus for future gasoline engine development will be on fuel economy improvements through improved combustion systems and reduced throttle losses at part load operation. This can be achieved through Downsizing in combination with boosting offers and additional potential. Internal combustion engines still have a huge potential to deal with the challenges of the future. In comparison with alternative power-train concepts, at least for the next 20 years, the internal combustion engine should be able to maintain its advantages regarding high power density, low manufacturing cost, recyclability, long driving distance between two refueling events, well established fuel supply infrastructure, and its capability to use a wide variety of fuels.
1-NEW IC ENGINE CONCEPT WITH VARIABLE PISTON MOTION (VPM).
1.Main features. The main feature of this new IC engine concept is the realization of variable movement of the piston. With this unconventional piston movement it is easy to provide variable compression ratio, variable displacement and combustion during constant volume. These advantages over standard piston mechanism are achieved through synthesis of the two pairs of non-circular gears. Presented mechanism is designed to obtain a specific motion law which provides better fuel consumption of IC engines. The results show that combustion during constant volume, variable compression ratio and variable displacement have significant impact on improvement of fuel consumption. Relatively low efficiency of today`s internal combustion engine is the consequence of several factors. First, ordinary spark ignition (SI) internal combustion engines during running at low loads have their thermal efficiency reduced due to the effect of the throttle valve that controls the engine load and by the fact that the compression starts at low pressure Conventional IC engines are based on a relatively simple solution to achieve a thermodynamic cycle while providing mechanical power. While the performance, emissions and reliability of IC engines have been improved significantly, the fundamental principle of crank-rod-piston slider mechanism still remains largely unaltered. In theory, the most efficient thermodynamic cycle for IC engines is the Otto cycle , which consists of isentropic compression and expansion processes and constant volume heat addition and rejection processes . It is generally known that the most important parts of the cycle which determine the efficiency are the constant volume heat addition at high compression ratios . This fact provides the highest thermal potential of the various possible thermodynamic cycles which are suitable for IC engines, and the subsequent expansion process, which converts the thermal potential into work. In reality, neither conventional spark ignition nor compression ignition or even the modern developed homogeneous charge compression ignition or controlled auto ignition combustion processes, can achieve the efficiency level suggested by the ideal thermodynamic cycles . Only the Otto cycle delivers theoretical maximum thermal efficiency. The traditional design of internal combustion engines using a simple slide-crank mechanism gives no time for a constant volume combustion which significantly reduces the cycle efficiency . Variable piston motion (VPM) IC engine is not only able to provide variable compression ratio and displacement but also with this concept it is easy to achieve dwell angle at top dead center (TDC) and bottom dead center (BDC). With piston dwell at bottom dead point more complete expansion can also be achieved.
2.A Closer Look a.NCG VPM IC engine has a two pairs of non-circular gears (NCG). A NCG is a special gear design with special characteristics and purpose. While a regular gear is optimized to transmit torque to another engaged member with minimum noise and wear and with maximum efficiency, a non-circular gear's main objective might be ratio variations, axle displacement oscillations and more.
In fact this feature of NCG is very important for synthesis of mechanism where is intermittent-motion required. This intermittent-motion mechanism combines circular gears with noncircular gears in a planetary arrangement. With such planetary differential gear it is possible to achieve very complex movement, where toroidal piston is able to provide motion with variable displacement and variable compression, also because of the characteristics of NCG, piston dwell at TDC and BDC is also feasible. b. Dwell Angle
Dwell time or dwell angle is important fact during combustion process. In conventional engine this dwell angle can be changed due to variations of ratio between connecting rod and crank radius. Piston dwell at TDC and at BDC are often mentioned, it should be noted that strictly, there is no dwell period in ordinary mechanism. The piston comes to rest at precisely the crank angle that the crank and rod are in line (TDC and BDC), and is moving at all other crank angles. At crank angles which are very close to the TDC and BDC angles, the piston is moving slowly. It is this slow movement in the vicinity of TDC and BDC that give rise to the term piston dwell. If the piston dwells longer near top dead center and ignition is initiated properly, there will actually be a longer period of time for the pressure created during combustion to press against the top of the piston. This process occurs within the engine and its part of the thermodynamic cycle of the device. c. Unconventional piston motion-new four stroke cycle
the new unconventional piston motion law will be presented. With this movement, the piston is able to make such motion where heat addition can be done during piston dwell. The design geometry creates a pause or dwell in the piston’s movement at the TDC and the BDC, while the output shaft continues to rotate for up to 35 degrees. Adding these constant volume dwell cycles improves fuel burn, maximizes pressure, and increases cylinder charge. Fuel burn can be precisely controlled by maintaining a minimum volume (TDC piston dwell) throughout the burn process, containment maximizes pressure and burn efficiency. Furthermore, holding the piston at maximum volume (BDC piston dwell) provides additional time for the cylinder to fully charge before closing the intake valves. The design creates unconventional four stroke cycle process. This unconventional cycle consists of the following strokes and processes.
Working process The first stroke consists of forced and free intake. During the forced intake, piston travels from TDC to BDC, which draws fresh mixture into the cylinder. This part of the stroke is the same as the intake stroke in the ordinary IC engines, the second part is the free intake. After the piston comes into BDC, it stops there for a while, this dwell time depends on the optimization of the intake process. However, it is very important that the piston dwell does not last longer or shorter than the optimal calculated value. After the piston comes into BDC, the column of fresh gases continues to flow into the cylinder by inertia, until the intake valve closes. In this way the intake volumetric efficiency is increased. The second stroke consists of the compression process and a combustion during constant volume. In the first part of this second stroke, the piston travels from
BDC to TDC. The ignition occurs at TDC without any spark advance, thus saving the accumulated energy of the flywheel. Ignition begins when the piston is stopped at the TDC, while the piston stop lasts for the time calculated by optimization to complete combustion and prevent any back pressure caused by the spark advance. Consequently, the use of energy obtained from the fuel is maximized and the fuel consumption is decreased. The third stroke is an expansion stroke, during which the piston comes from TDC to BDC like in a standard mechanism but with the exception that piston again makes a dwell in BDC. In this new unconventional four stroke cycle, the entire expansion stroke occurs between TDC and BDC. Compared to standard IC engine, in the new piston motion movement there is no exhaust valve opening advance, which determines loss of possibly resulting work. In the second part of this third stroke, the piston comes on BDC and stays in the same position for a while. During this time high-pressure gases are spontaneously evacuated, while the piston is stopped at the BDC. The last stroke is exhaust stroke, during which the exhaust gas is actually a low pressure gas, so the piston will not require a big pumping effort going up towards TDC. In the last phase of exhaust stroke, exhaust gases can freely leave compression volume. At the same time intake valves slowly open and fresh charge comes into the cylinder, while the piston is still in the dwell mode at TDC
Basic parts of the VPM engine are: 1-engine block, 2-engine head, 3-toroidal piston, 4-intake manifold, 5-exhaust manifold, 6-camshaft, 7-valve, 8-valve spring, 9-housing, 10-flywheel, 11-noncircular gear, 12- noncircular gear, 13-noncircular gear, 14-noncircular gear, 15-stepper motor, 16- stepper motor, 17- crankcase.
-
2-Rotating Liner Engine(RLE)
1.(RLE) Design Objectives
the design objective is developing a new cylinder liner and head seal design that will lead to reduced piston assembly friction and wear in conventional piston engines. With a Rotating Liner Engine (RLE), the cylinder liner rotates and a unique hydrodynamic face seal replaces the conventional head gasket. Its application in heavy-duty diesel engines is expected to improve efficiency and reduce fuel consumption by 3 to 7% (depending on operating conditions), and prolong engine life by a factor of two to three times. 2. The Traditional Approach to the Lubrication Challenge new techniques were developed to reduce the intensity of the metallic contact and its consequences. First, multi-weight oils allowed a low viscosity for a cold start while permitting higher viscosity at high temperature conditions. Also, better design of pistons skirts and piston rings, along with zinc and lead based lubricant additives were developed that were able to tolerate higher metallic contact pressure with reduced friction and wear. These improvements generally stayed ahead of increases in peak pressure for thermodynamic efficiency improvements, resulting in continuous improvement in both engine life and friction. Still, this metal-to-metal contact persists, with the piston assembly of a modern diesel accounting for 50 to 60% of total mechanical losses. This has a significant impact on total energy consumption because of the wide application of IC engines in use today. However, very high peak pressure of a diesel engine also leads to high specific load, so that total engine friction losses are generally only about 10% of total thermodynamic power at full load. At less than full load, engine friction accounts for a larger portion of thermodynamic combustion power, which is defined to as “indicated” power. At idle, friction accounts for 100% of indicated power. In truck applications, the operating conditions constantly change between high load, low load or idle
3.The RLE solution RLE technology is a new approach to this problem. Instead of relieving the effects of metallic contact close to the TDC area, cylinder liner rotation is expected to nearly eradicate it. Our research has shown that cylinder rotation will allow hydroplaning of the piston rings in areas where the slow piston motion fails, especially at TDC. - (SVE) Sleeve valve engine In discussing rotating cylinder liners, many engineers remember Sleeve Valve Engines (SVE’s). These engines were developed by the Ricardo laboratories prior to World War II, and were used extensively during the war for high output spark ignited aircraft engines. In SVE’s the conventional valve train was replaced by a ported cylinder liner that moved along an elliptical path. Intake and exhaust ports aligned at the proper timing with ports on the block, achieving the four stroke cycle. At TDC compression-expansion, the sleeve motion was purely rotational. The cylinder head gasket was replaced by set of piston rings that sealed the moving sleeve valve and cylinder head. The objective of the SVE design was similar to modern trends in diesel design, namely the removal of red-hot exhaust valves would improve the detonation performance of the
supercharged (spark ignition) engine, allowing higher operating pressures and thermodynamic output. It was understood that extra parts would add more mechanical friction than the simple poppet valves, but it was expected that additional thermodynamic power would more than compensate for slightly more mechanical friction. However, when the first Ricardo SVE was tested against a similar poppet valve engine, it was found that the mechanical friction of the SVE was significantly lower, both under motoring (no combustion) and firing conditions. The rotary motion of the sleeve was believed to be responsible for reducing friction in the piston assembly by nearly eliminating the metallic contact of the piston rings around TDC. In fact, an experimental SVE diesel engine achieved record fuel efficiency due to reduced friction. This record was not broken until many decades later when turbocharged diesels appeared.
-Due to the performance of the SVE’s, Ro lls Royce, the largest British aero engine manufacturer, also developed two high output SVE’s as well as an experimental two stroke ultra-high power SVE. However, before these new engines were put in large scale production, jet engines displaced all large piston aircraft engines. Within 24 months, all research in piston aero-engines, including SVE’s two stroke development, ceased in England, and the piston lubrication advantages of SVE’s rotary sleeve valve was forgotten. -Extinction of the SVE design was not due to an inability to compete with conventional engine design; it was due to the disruptive nature of jet engines. While the SVE could have propagated to other markets due to the inherent friction advantage, this friction benefit was never sufficiently quantified. The reason for the lack of interest in the SVE friction reduction by the aero engine manufacturers was probably because the thermodynamic advantage of knock suppression was considered of greater importance for their high specific power spark ignition engines.
The RLE advantages Unlike the ported SVE which cannot meet modern emissions regulations, the RLE reduces metallic contact during high pressure combustion and can meet modern emissions regulations. The RLE uses conventional poppet valves that are known to make a small contribution to total engine friction. The relatively high friction sleeve valve is replaced by a lower drag, purely rotating liner without axial motion and since the liner is decoupled from valving, its speed can be optimized for friction reduction. Since the combustion chamber is conventional, modern clean combustion technologies will be used in the RLE. This will allow RLE technology to be applied to existing IC engine designs. The outside of the rotating liner is lubricated hydrodynamically (like crank bearings), resulting in negligible wear. This is similar to the SVE experience. Based on empirical engine friction models and bearing theory, friction reduction due to liner rotation is about 5 to 10 times higher than the viscous drag of the rotating liner. Total piston assembly friction will be reduced by more than half at full load, at the expense of a relatively low rotating liner drag, and a slightly higher production cost of the engine. However, in commercial and industrial markets, the added production cost will be quickly compensated by the fuel savings. The benefit of the RLE in terms of percentage improvement in fuel consumption and absolute fuel savings depends on operating conditions of the engine. In applications where low load is frequent, the percentage improvement will be higher, while in a generator engine operating at full load, the percentage improvement will be lower since the importance of engine friction diminishes at the higher loads. In Class 8 trucks for example operating at an average EPA duty cycle, we estimate that fuel economy will improve by approximately 7% which leads to a payback period of approximately 18 months from fuel savings alone. For on-site generation, we estimate that stationary engines operating at full and constant load will only improve by about 3% -The key technical challenge to the success of RLE technology is the seal between the rotating liner and cylinder head. Instead of conventional piston rings used in SVE’s (Figure 3) which add another blow by path, a gapless face seal design has been developed. This seal achieves low friction, low wear, and very low leakage. Research at the University of Texas at Austin, funded by several sources including the Department of Energy, solved the challenge of lubricant delivery to the RLE face seal. This research achieved hydrodynamic seal lubrication (no metallic contact, no wear) while preventing contamination of the combustion chamber by the seal lubricant. This seal was tested on a single cylinder light duty gasoline engine designed and developed by RLE Technologies, Inc. personnel at the University of Texas engine lab under the supervision of Dr. Ron D. Matthews, Head of the General Motors Foundation Combustion Sciences and Automotive Research Laboratories. Practically zero gas and oil leakage and low seal friction were confirmed. Also, during motoring testing of the RLE, friction of the rotating liner was measured via a rotating torque cell on the driving mechanism. This measurement proved that liner rotation minimizes metallic contact in the TDC area. Testing also indicated significant friction reduction of the RLE prototype compared to a similar gasoline engine with a conventional cylinder, albeit at these low pressure conditions
Figure 3. The RLE prototype at the University of Texas. The seal can be seen in a single cylinder engine, converted from a 4 cylinder automotive engine. Only the second cylinder from the left is active. All other throws are balanced with bob weights.
Figure 4. Section of RLE’s design for a high pressure diesel engine. This design has been developed with the aid of finite element analysis software that combines pressure and thermal distortions with hydrodynamic solutions.
3-The free piston linear alternator 1.Introduction The development of a high efficiency, low emissions electrical generator will lead to establishing a path for renewable hydrogen based fuel utilization , The electrical generator is based on developed internal combustion engine technology. It is able to operate on many hydrogen-containing fuels. The efficiency and emissions are comparable to fuel cells (50% fuel to electricity, ~ 0 NO x). This electrical generator is applicable to both stationary power and hybrid vehicles. It also allows specific markets to utilize hydrogen economically and painlessly. Two motivators for the use of hydrogen as an energy carrier today are: 1) to provide a transition strategy from hydrocarbon fuels to a carbonless society and 2) to enable renewable energy sources. The first motivation requires a little discussion while the second one is self-evident. The most common and cost effective way to produce hydrogen today is the reformation of hydrocarbon fuels, specifically natural gas.
2.background and initial researches Electrical generators capable of high conversion efficiencies and extremely low exhaust emissions will no doubt power advanced hybrid vehicles and stationary power systems. Fuel cells are generally considered to be ideal devices for these applications where hydrogen or methane are used as fuel. However, the extensive development of the IC engine, and the existence of repair and maintenance industries associated with piston engines provide strong incentives to remain with this technology until fuel cells are proven reliable and cost competitive. In addition, while the fuel cell enjoys high public relations appeal, it seems possible that it may not offer significant efficiency advantages relative to an optimized combustion system. In light of these factors, the capabilities of internal combustion engines have been reviewed. In regards to thermodynamic efficiency, the Otto cycle theoretically represents the best option for an IC engine cycle. This is due to the fact that the fuel energy is converted to heat at constant volume when the working fluid is at maximum compression. This combustion condition leads to the highest possible peak temperatures, and thus the highest possible thermal efficiencies.
OTTO Cycle maximum utilization Edson (1964) analytically investigated the efficiency potential of the ideal Otto cycle using compression ratios (CR) up to 300:1, where the effects of chemical dissociation, working fluid thermodynamic properties, and chemical species concentration were included. He found that even as the compression ratio is increased to 300:1, the thermal efficiency still increases for all of the fuels investigated. At this extreme operating for instance, the cycle efficiency for iso-octane fuel at stoichiometric ratio is over 80%.
Caris and Nelson (1959) investigated the use of high compression ratios for improving the thermal efficiency of a production V8 spark ignition engine. They found that operation at compression ratios above about 17:1 did not continue to improve the thermal efficiency in their configuration. They concluded that this was due to the problem of non-constant volume combustion, as time is required to propagate the spark-ignited flame.
(HCCI) Combustion -Homogeneous charge compression ignition combustion could be used to solve the problems of burn duration and allow ideal Otto cycle operation to be more closely approached. In this combustion process a homogeneous charge of fuel and air is compression heated to the point of auto ignition. Numerous ignition points throughout the mixture can ensure very rapid combustion . Very low equivalence ratios ( ~ 0.3) can be used since no flame propagation is required. -HCCI combustion has been shown to be faster than spark ignition or compression ignition combustion. And much leaner operation is possible than in SI engines, while lower NO x emissions result. -Most of the HCCI studies to date however, have concentrated on achieving smooth releases of energy under conventional compression condition (CR ~ 9:1). Crankshaft driven pistons have been utilized in all of these previous investigations. -In order to maximize the efficiency potential of HCCI operation much higher compression ratios must be used, and a very rapid combustion event must be achieved. Recent work with higher compression ratios (~21:1) has demonstrated the high efficiency potential of the HCCI process.
Fig 1 - This extreme case of non-ideal Otto cycle behavior serves to emphasize how much can be gained by approaching constant volume combustion.
-Engineering solution. The free piston linear alternator has been designed in hopes of approaching ideal Otto cycle performance through HCCI operation. In this configuration, high compression ratios can be used and rapid combustion can be achieved
The linear generator is designed such that electricity is generated directly from the piston. oscillating motion, as rare earth permanent magnets fixed to the piston are driven back and forth through the alternator coils. Combustion occurs alternately at each end of the piston and a modern two-stroke cycle scavenging process is used. The alternator component controls the piston’s motion, and thus the extent of cylinder gas compression, by efficiently managing the piston’s kinetic energy thro ugh each stroke. Compression of the fuel/air mixture is achieved inertially and as a result, a mechanically simple, variable compression ratio design is possible with sophisticated electronic control.
-The advantages of combination of the HCCI combustion process and the free piston geometry 1-the compression ratio of the engine is variable; this is dependent mainly on the engine’s operating conditions (e.g., fuel type, equivalence ratio, temperature, etc.). As a result, the desired compression ratio can be achieved through modification of the operating parameters, as opposed to changes in the engine’s hardware. 2-the mechanical friction can be reduced relative to crankshaft driven geometries since there is only one moving engine part and no piston side loads. Also, combustion seems
to be faster than in conventional slider-crank configurations. Further, the unique piston dynamics (characteristically non- sinusoidal) seem to improve the engine’s fuel economy and NO x emissions by limiting the time that the combustion gases spend at top dead center (TDC) (thereby reducing engine heat transfer and limiting the NO x kinetics). 3-High compression ratio operation is better suited to the free piston engine since the piston develops compression inertially, and as such there are no bearings or kinematic constraints that must survive high cylinder pressures or the high rates of pressure increase (shock). The use of low equivalence ratios in the HCCI application should further reduce the possibility of combustion chamber surface destruction 4-The free piston design is more capable of supporting the low IMEP levels inherent in low equivalence ratio operation due to the reduction in mechanical friction.
3-Technical specifications The overall length of the generator is 76 centimeters, its specific power is 800 watts per kilogram, and it has a power density of 800 watts per liter. Hydrogen based renewable fuels such as bio-gas (low BTU producer gas H 2-CH4-CO), ammonia (NH 3), methanol (CH4O), and/or hydrogen (H 2) can be used directly. The alternator consists of moving rare earth permanent magnets and stationary output coils and stator laminations. The design is similar to a conventional rotary brushless DC generator and has an efficiency of 96%. The magnet assembly is fabricated from 10 degree arc magnet segments, which are magnetized in a linear direction.
1-VARIABLE PISTON MOTION (VPM) [1] Ozcan, H., Yamin, J.A.A., Performance and emission characteristics of LPG powered four stroke SI engine under variable stroke length and compression ratio, Energy Conversion and Management 49, (2008), pp. 1193 –1201 [2] Kutlar, O.A., Arslan, H., Calik, A.T., Methods to improve efficiency of four stroke, spark ignition engines at part load, Energy Conversion and Management 46, (2005), pp. 3202 –3220 [3] Pešić, R., Automobilski oto motori sa minimalnom potrošnjom, monografija, Kragujevac 1994 [4] Wirbeleit, F.G., Binder, K., Gwinner, D., Development of piston with variable compression height for increasing efficiency and specific power output of combustion engines, Society of Automotive Engineers, paper no 900229, (1990) [5] Adams, W.H., Hinrichs, H.G., Pischinger, F., Adamis, P., Schumacher, W., Walzer, P., Analysis of the combustion process of a spark ignition engine with a variable compression ratio, Society of Automotive Engineers, paper no 870610, (1987) [6] Heywood, J.B., Internal combustion engines fundamentals, McGraw-Hill Book Company, 1988 [7] Andresen, B., Salamon, P., Berry, R.S., Thermodynamics in finite time, Physics Today 9, (1984), pp.62 –70
2-Rotating Liner Engine(RLE) Based on the papers of: (RLE)A New Approach to Reduce Engine Friction and Increase Fuel Economy in Heavy Duty Engines Dimitrios Dardalis, PhD Chief Technology Officer RLE Technologies, Inc.
3-The free piston linear alternator Achten, P. A. J. 1994. .A R eview of Free Piston Engine Concepts,. SAE Paper 941776. Alperstein, M., Swim , W. B. and Schweitzer, P. H. 1958. .Fumigation Kills Smoke . Improves Diesel Performance,. SAE Transactions, vol. 66, pp.574 . 588. Baruah, P. C. 1988. .A Free Piston Engine Hydraulic Pump for an Automotive Propulsion System,. SAE Paper 880658. Braun, A. T. and Schweitzer, P. H. 1973. .The Braun Linear Engine,. SAE Paper 730185. Caris, D. F. and Nelson, E. E. 1959. .A New Look at High Compression Engines,. SAE Transactions, vol. 67, pp. 112-124. Christensen, M., Johansson, B. and Einewall, P. 1997. .Homogeneous Charge Compression Ignition (HCCI) Using Isooctane, Ethanol, and Natural Gas . A Comparison With Spark Ignition Operation,. SAE Paper 972874. Christensen, M., Johansson, B., Amneus, P. and Mauss, F. 1998. .Supercharged Homogeneous Charge Compression Ignition,. SAE Paper 980787.
