AIR ENGINE WITH LOAD TEST
CONTENTS 1
CHAPTER NO
DESCRIPTION
PAGE NO
1
ABSTRACT
3
2
INTRODUCTION
3
3
WORKING PRINCIPLE
4
5
COMPONENTS’ DETAILED EXPLANATION 5.1 How Compressed Air Can Fuel engine 5.2 Air Car Disadvantages
10 11
6
PNEUMATIC SYSTEMS 6.1 INTRODUCTION 6.2 SUPPLYING COMPRESSED AIR
17
7
ADVANTAGES
52
8
APPLICATIONS
53
9
CONCLUSION
53
13
REFERENCES
54
2
22
1. Abstract:
This project work deals with the Compressed-air engine is a pneumatic actuator that creates useful work by expanding compressed air. They have existed in many forms over the past two centuries, ranging in size from hand held turbines up to several hundred horsepower. Some types rely on pistons and cylinders, others use turbines. Many compressed air engines improve their performance by heating the incoming air, or the engine itself. Some took this a stage further and burned fuel in the cylinder or turbine, forming a type of internal combustion engine. There is currently some interest in developing air cars. Several engines have been proposed for these, although none have demonstrated the performance and long life needed for personal transport.
2. Introduction:
A compressed-air vehicle is powered by an air engine, using compressed air, which is stored in a tank. Instead of mixing fuel with air and burning it in the engine to drive pistons with hot expanding gases, compressed air vehicles (CAV) use the expansion of compressed air to drive their pistons. One manufacturer claims to have designed an engine that is 90 percent efficient. Compressed air propulsion may also be incorporated in hybrid systems, e.g., battery electric propulsion and fuel tanks to recharge the batteries. This kind of system is called hybrid-pneumatic electric propulsion. Additionally, regenerative braking can also be used in conjunction with this system.
3
WORKING PRINCIPLE
Today, internal combustion engines in cars, trucks, motorcycles, aircraft, construction machinery and many others, most commonly use a four-stroke cycle. The four strokes refer to intake, compression, combustion (power), and exhaust strokes that occur during two crankshaft rotations per working cycle of the gasoline engine and diesel engine. The cycle begins at Top Dead Center (TDC), when the piston is farthest away from the axis of the crankshaft. A stroke refers to the full travel of the piston from Top Dead Center (TDC) to Bottom Dead Center (BDC). 1. INTAKE stroke: On the intake or induction stroke of the piston , the piston descends from the top of the cylinder to the bottom of the cylinder, reducing the pressure inside the cylinder. A mixture of fuel and air is forced by atmospheric (or greater) pressure into the cylinder through the intake port. The intake valve(s) then close. 2. COMPRESSION stroke: With both intake and exhaust valves closed, the piston returns to the top of the cylinder compressing the fuel-air mixture. This is known as the compression stroke. 3. POWER stroke.: While the piston is close to Top Dead Center, the compressed air– fuel mixture is ignited, usually by a spark plug (for a gasoline or Otto cycle engine) or by the heat and pressure of compression (for a diesel cycle or compression ignition engine). The resulting massive pressure from the combustion of the compressed fuel-air mixture drives the piston back down toward bottom dead center with tremendous force. This is known as the power stroke, which is the main source of the engine's torque and power. 4. EXHAUST stroke: During the exhaust stroke, the piston once again returns to top dead center while the exhaust valve is open. This action evacuates the products of combustion from the cylinder by pushing the spent fuel-air mixture through the exhaust valve(s). In our project we have to modified these four strokes into totally two stoke with the help of inner CAM alteration. In air engine we can design a new CAM which is operate only Inlet stroke and exhaust stroke. Actually in four stroke engine the inlet and exhaust valve opens only one time to complete the total full cycle. In that time the piston moving from top dead center to bottom dead center for two times. A stroke refers to the full travel of the piston from Top Dead Center (TDC) to Bottom Dead Center (BDC). In our air engine project, we have to open inlet and exhaust valve in each and every stroke of the engine so that it will convert the four stroke engine to two stroke engine by modifying the CAM shaft of the engine.
4
Introduction and Mental Set Two cycle engines are generally simpler in design and contain fewer components than 4cycle engines. As an example, most 2-cycle engines have no intake and exhaust valves. The 2-cycle engine method of operation is different than the 4-cycle engine but many of the components are the same. Let=s look at some similarities and differences between 2cycle and 4-cycle engines. Discussion 1. A.
Produce transparency 1 from text. 2-cycle engines have these parts common to 4-cycle engines
2. A.
Produce transparency 2 from text. Common parts are: $ cylinder head $ cylinder $ crankcase $ piston $ connecting rod $ crankshaft $ flywheel $ CDI ignition $ carburetor $ exhaust muffler
3. 2-cycle engines use a carburetor along with a reed valve or piston portal to admit fuel/air mixture into the crankcase of the engine. 4. Main parts of a 2-cycle engine. A. Cylinder/cylinder head. Depending on the engine application, the cylinder may separate from the crankcase and be a single casting, combining the cylinder, cylinder head, and intake and exhaust ports, or it may be separate parts. B. Commonly, most cylinder head/cylinder units bolt onto the crankcase and are sealed by a gasket at that point. This means that the piston and rings are installed from the bottom of the cylinder. 5
5. A.
Create transparency 3 or parts of 3a from text. The cylinder provides a tube so a piston will travel in a linear
B. C.
The cylinder must seal the gases for combustion. The cylinder often contains intake fuel and exhaust gas passages called ports.
6.
Crankcase A. Most 2-cycle small engines have a crankcase that is split, and often is an important frame part of a piece of equipment. Show an example of a chainsaw from transparency 3/3a. B. The crankcase will provide a solid bearing surface where a nonfriction bearing (like rollers or needles) will be installed. The crankshaft will ride on this surface. C. The up and down (linear) motion of the piston is transferred by the crankshaft into rotary motion in the crankcase.
7.
Crankshaft A. The crankshaft transmits power to do work. It is an expensive cast or forged steel unit and it is precision machined and balanced to the engine. B. It is often timed to the particular engine. C. The crankshaft works with the flywheel to store energy during the compression stroke which allows the engine to continue operating. To do this, the crankshaft has four main parts. Create transparency 4. $ Journals - machined surfaces that must be inspected for bearing surface wear when overhaul. $ Crank pin or connecting rod - must be inspected as well. $ Throws - offsets which support the crankpins and provide leverage to rotate the crankshaft. $ Counterweights - a balance to the throws, opposite the crank pins. D. Bearings and bushings are often used in the crankshaft/ connecting rod area and may be a plain bearing or an anti-friction bearing, such as needle or ball bearing.
8.
Connecting Rod A. The connecting rod is the piece of the engine that converts linear motion to rotary motion. B. It must be strong, but light. 6
C.
The connecting rod links the piston to the crankshaft. (transparency 4). 1. The piston pin or wrist pin goes into the eye while the cap and cap bolts connect the rod to the crankshaft. 2. At rebuild, the rod and crankshaft connection must be checked along with the piston/rod combination.
9. Piston A. The piston is a cast or forged item machined with grooves to fit a cylinder. B. It has lands, or grooves that accept piston rings. The rings expand and push out against the cylinder wall to provide a seal for the combustion gases. The rings are cast of hardened steel and are measured during engine removal. C. The wrist pin and its retaining locks connect the piston to the connecting rod by connecting through the piston body and eye of the connecting rod. D. Display and discuss transparency 4. 10. The 2-cycle engine A. The best description of a 2-cycle engine is to say that the fuel/air mix is moved by the high pressure created by the piston in the crankcase. B. A 2-cycle engine must have oil mixed with gasoline in the proper ratio for long life and efficient operation. C. A 2-cycle engine must have a clean muffler through which exhaust gases flow through. If the muffler is clogged, and exhaust cannot pass gases through, the engine will not run. D. The carburetor is connected to the crankcase. The oil in the fuel/air mix lubricates the engine=s internal parts. E. A reed valve may be used to help the fuel/air mix compress more in the crankcase. F. The two-cycle engine has 2 cycles; a compression stroke and a power stroke. G. As the piston moves upward, compressing a fuel/air charge in the cylinder, a low pressure area is created in the crankcase. 1. The low pressure area increases until the piston moves past the intake port, or until there is enough pressure to pull the reed valve open. When this happens, the fuel/air mixture is pulled through the carburetor. H. The piston is now at the top of the cylinder. Ignition occurs, and the piston moves down. This back pressure compresses the fuel/air mix. As soon as the piston covers the intake port, or closes the reed valve, the mixture is compressed further.
7
I. The piston moves down further, compressing the fuel/air mixture until a transfer port is uncovered by the piston. The mixture moves rapidly up the port, into the cylinder, pushing the exhaust gases out of the exhaust port and filling the cylinder with the explosive fuel/air mix.
11.
*0 *1 *2 *3 *4 *5
12.
Carburetion A. The carburetors used on small 2-cycle engines work the same way as 4-cycle carburetors. B. The 4-cycle and 2-cycle engines share: throttle plate choke plate fuel/air mixture needles, often a high and low mixture venturi diaphragm gaskets C. Air moves from high to low pressure areas. D. When air is restricted, a low pressure area is created as airspeed increases. This allows for fuel to be pumped. E. Demonstrate using information from 4-cycle engines. Ignition System A. Most all 2-cycle engines have a sold-state ignition system. B. 2-cycle ignition systems operate on the same electromagnetic theories as 4-cycle ignition systems (use transparency from 4-cycle lesson). C. The flywheel is used in the creation of an electric spark and it is also used to force air through the housing to cool the motor.
8
How Compressed Air Can Fuel engine
The laws of physics dictate that uncontained gases will fill any given space. The easiest way to see this in action is to inflate a balloon. The elastic skin of the balloon holds the air tightly inside, but the moment you use a pin to create a hole in the balloon's surface, the air expands outward with so much energy that the balloon explodes. Compressing a gas into a small space is a way to store energy. When the gas expands again, that energy is released to do work. That's the basic principle behind what makes an air car go. The first air cars will have air compressors built into them. After a brisk drive, you'll be able to take the car home, put it into the garage and plug in the compressor. The compressor will use air from around the car to refill the compressed air tank. Unfortunately, this is a rather slow method of refueling and will probably take up to two hours for a complete refill. If the idea of an air car catches on, air refueling stations will become available at ordinary gas stations, where the tank can be refilled much more rapidly with air that's already been compressed. Filling your tank at the pump will probably take about three minutes The first air cars will almost certainly use the Compressed Air Engine (CAE) developed by the French company, Motor Development International (MDI). Air cars using this engine will have tanks that will probably hold about 3,200 cubic feet (90.6 kiloliters) of compressed air. The vehicle's accelerator operates a valve on its tank that allows air to be released into a pipe and then into the engine, where the pressure of the air's expansion will push against the pistons and turn the crankshaft. This will produce enough power for speeds of about 35 miles (56 kilometers) per hour. When the air car surpasses that speed, a motor will kick in to operate the in-car air compressor so it can compress more air on the fly and provide extra power to the engine. The air is also heated as it hits the engine, increasing its volume to allow the car to move faster
Air Car Advantages One major advan¬tage of using compressed air to power a car's engine is that a pure compressed air vehicle produces no pollution at the tailpipe. More specifically, the compressed air cars we're likely to see in the near future won't pollute at all until they reach speeds exceeding 35 miles per hour. That's when the car's internal air compressor will kick in to achieve extra speed. The motor that runs this air compressor will require fuel that'll produce a small amount of air pollution. 9
Some fuel (you can use eco-friendly biofuels or fossil fuels) will also be used to heat the air as it emerges from the tank. The newest compressed air engines also offer drivers the option of using fossil fuels or biofuels to heat the air as it enters the engine. Nonetheless, this technology represents a marked improvement over cars powered by internal combustion engines that produce significant amounts of pollution at any speed. Air cars are also designed to be lighter than conventional cars. The aluminum construction of these vehicles will keep their weight under 2,000 pounds (907 kilograms), which is essential to making these vehicles fuel efficient and will help them go faster for longer periods of time. Another advantage of air cars is that the fuel should be remarkably cheap, an important consideration in this era of volatile gas prices. Some estimates say that the cars will get the equivalent of 106 miles (171 kilometers) per gallon, although compressed air will probably not be sold by the gallon. A more meaningful estimate is that it may take as little as $2 worth of electricity to fill the compressed air tank, though you'll also need gasoline to power the electric motor that compresses air while driving The vehicles themselves also will be relatively cheap. Zero Pollution Motors, which plans to release the first air cars in the United States and estimates a sticker price of about $17,800, which would make these cars affordable to budget-conscious American buyers Air Car Disadvantages While an air car produces no pollution running on already compressed air in its tank, pollution is nonetheless produced when the air is compressed, both while the car is moving and while it's being refueled. As we mentioned earlier, the vehicle's air compressor will probably run on gasoline, and this gas will produce pollution when burned. The air compressor at the gas station will probably be powered by electricity. The production of that electricity may or may not pollute, depending on how that electricity is generated. For example, coal-powered electricity could produce substantial amounts of pollution. Cleaner sources of electricity, such as nuclear power or hydropower, will result in far less pollution. According to the Web site Gas 2.0, an air car in the United States would create about .176 pounds of carbon dioxide emissions per mile based on the average mix of electric power sources during refueling. By comparison, a Toyota Prius Hybrid, which combines a battery-powered electric motor with an internal combustion engine, generates about 0.34 pounds of carbon dioxide per mile. So, while the air car is not quite pollution free, it still represents an improvement over one of the most popular hybrid cars on the market Distance could also become a disadvantage, depending on your travel habits. The distance that an air car can cover without refueling is crucial because very few filling stations will have 10
compressed air pumps available at first. If you only plan to use your air car for short commutes -distances less than 100 miles --will be fine. However, the one-to-two hour wait for the car's builtin air compressor to compress a tank full of air could become a problem on cross-country trips. Zero Pollution Motors -- the American arm of MDI and the company likeliest to produce the first air car for the U.S. market -- aims to have a car available soon able to travel between 800 and 1,000 miles on one tank of air plus 8 gallons of gas Early prototypes, however, have traveled distances closer to 120 miles -- good enough for your daily commute, but not quite adequate for longer trips What will happen if an air car suffers damage in an accident? After all, compressed air tanks can be dangerous. To reduce this danger, the air tanks are made of carbon fiber and are designed to crack, rather than shatter, in a crash. This crack would allow the "fuel" to escape harmlessly into the surrounding air. Manufacturers feared that air escaping from one end of the tank could produce a rocket-like effect and propel the car on a jet of air. The valve on the cars' fuel tanks has been placed on the side to minimize this effect. Despite these precautions, there is some concern that the air cars' lightweight construction might make it difficult for them to pass stringent American safety requirements and that this could hold up the arrival of air cars in the U.S. marketplace. Other factors have come to the forefront as well, and we'll learn about those next.
Air Cars in the Marketplace India's Tata Motors will likely produce the first air car in the marketplace in the next few years. Tata Motors' air car will also use the CAE engine. Although Tata announced in August 2008 that they aren't quite ready to roll out their air cars for mass production, Zero Pollution Motors still plans to produce a similar vehicle in the United States. Known collectively as the FlowAIR, these cars will cost about $17,800. The company, based in New Paltz, N.Y., says that it will start taking reservations in mid-2009 for vehicle deliveries in 2010. The company plans to roll out 10,000 air cars in the first year of production [source: Max]. MDI also recently unveiled the joystick-driven AirPod, the newest addition to its air car arsenal. Although the AirPod generates a top speed of only 43 mph, it's also extremely light and generates zero emissions. Major automobile makers are watching the air car market with interest. If the first models catch on with consumers, they'll likely develop their own air car models. At present, a few smaller
11
companies are planning to bring air cars to the market in the wake of the MDI-based vehicles. These include: •
K'Airmobiles -- French company K'Air Energy has built prototypes of an air-fueled bicycle and light road vehicle based on the K'air air compression engine
•
Air Car Factories SA -- This Spanish company has an air car engine currently in development. The company's owner is currently involved in a dispute with former employer MDI over the rights to the technology
•
Initially, the MDI cars will be the only air vehicles on the market. However, MDI has reportedly licensed the technology to manufacturers in a dozen different countries, so air cars should be available around the world soon.
Teachers’ Introduction
Pneumatics is used extensively in industry as well as in many everyday applications. As a method of completing tasks it has many distinct advantages in terms of energy consumption, cost and safety. It is important therefore that students gain an understanding of the benefits of pneumatics as well as the obvious limitations.
When the students have completed this unit of work they should be able to: • •
interpret pneumatic systems and circuit diagrams describe the operation of pneumatic systems
•
pipe-up/construct pneumatic systems
•
have an appreciation of safety requirements when operating pneumatic systems
•
perform calculations to determine cylinder pressure, piston force and area
•
evaluate pneumatic systems. 12
Structure
This unit is split into three distinct sections: • •
Section 1 − Pneumatic systems Section 2 − Electronic control
•
Section 3 − Programmable control.
It is recommended that these sections be delivered in this order. This provides the student with a natural progression through the course. The content of the unit is set out comprehensively so that teachers do not require the use of additional notes or textbooks. It allows pupils to move at their own pace in many areas but it must be stressed that these unit notes should not be used as an open-learning pack. It will be necessary to deliver many important lessons at crucial times.
The materials are intended to be non-consumable; however, this is at the discretion of each centre. A consumable project report template has been included for each section of work to provide a structure for reporting work on assignments.
Section 1 − Pneumatic systems
This section is concerned primarily with the basic components and operation of pneumatic circuits. It covers topics such as cylinders, valves, AND/OR control, time delays, air bleeds, and automatic and sequential circuits. A section of the unit is also dedicated to relevant calculations involving force, pressure and area.
13
Wherever possible, use should be made of computer simulation. Throughout these teaching materials, reference will be made to the FluidSIM package produced by Festo Didactic, but other packages could be used. Such software not only provides the facility to construct pneumatic circuits and test them but also to run video clips showing practical uses of pneumatic systems. This is invaluable to the teaching of this unit as it provides the students with a reference point in the real world. The simulations also enhance the practical aspect of this unit.
Problem solving Students will be required to design, construct and evaluate pneumatic systems to given specifications. A report template has been included to allow a common approach to solving problems. This will help students lay out their work in an appropriate way as well as preparing them for the format of the internal assessment. It also provides students with a detailed record of their work.
Problem solving is presented in the form of assignments. It is anticipated that much of the designing will be completed using simulation software; however, it is also important that students develop a knowledge of real components and the necessary expertise in connecting components together.
A series of homework tasks has been included. These contain a range of questions taken from the whole course. The teacher should ensure that homework tasks are issued at an appropriate time to coincide with work in class. It may also facilitate the issue and marking of homework if these tasks are completed on consumable photocopied sheets. Again, this is at the discretion of the centre. Alternatively, these questions could be used for revision purposes.
Section 2 − Electronic control
It is recommended that this section be completed after Applied Electronics. This will allow students to extend the work done in this area and demonstrate their understanding further by controlling pneumatic circuits. It also provides excellent opportunities for integration and a facility to extend the problem-solving aspect of the course. 14
Where appropriate, students should make use of a report sheet to record their solutions to the problems set out in the assignments.
Section 3 − Programmable control
It is recommended that this section be completed after Programmable Control. This will provide the opportunity for students to develop their knowledge and understanding of control as well as their problem-solving skills. In addition, it provides and excellent opportunity for integration and allows the students to revisit pneumatics, helping to keep this area of study fresh in their minds.
It is recommended that students make use of a report template to provide a structure for reporting work on assignments.
Resources
The majority of resources required to complete this unit are the same as those being used in Technological Studies at present.
• •
Single-acting spring return cylinders Double-acting cylinders
•
3/2 push-button spring return valves
•
A variety of 3/2 valves with different actuators
•
5/2 pilot air-operated valves
•
Solenoid valves 15
•
Reservoir
•
Flow restrictor valves
•
Circuit simulation software
In addition, the following are required for completion of sections 2 and 3.
• •
Microswitches Stamp controller
•
Inputs module
•
Output driver
•
Modular electronic boards
Teachers are also encouraged to use any other available resources such as videos and interactive CD-ROMs. External This unit of work and the exercises within will prepare the pupils for any pneumatic questions that appear in the 90-minute exam at the end of the course. It will enable all pupils to gain the knowledge and understanding required and give them suitable practice in reasoning and numerical analysis. Section 1: Pneumatic Systems Introduction Pneumatics is something that you probably know very little about yet come across every day without even realising it. Some examples of everyday pneumatic systems are shown below. How many do you recognise?
16
Figure 1
Pneumatics is also used a lot in industry and you would expect to see pneumatic systems in factories, production lines and processing plants. It can be used to do lots of different jobs such as moving, holding or shaping objects.
17
MOVE
HOLD
FORM
PROCESS
Figure 2 Every one of these pneumatic systems makes use of compressed air. Compressed air is quite simply the air that we breathe forced or squashed into a smaller space. We can use the energy stored in this compressed air to do things. To understand how compressed air is able to do things, let’s think of a ball. If we blow up the ball so that it is full, it will contain a lot of compressed air. If we bounce the ball, it will bounce very high. However, if the ball is burst then the compressed air will escape and the ball will not bounce as high. Quite simply, the ball bounces because it is using the energy stored in the compressed air.
Figure 3
18
Basically, all pneumatic systems make use of compressed air to do work. We can show this in a systems diagram.
Compressed air
Pneumatic system
Work
Figure 4 Advantages of pneumatics
There are usually lots of different ways to carry out a task, so it is important to understand some of the reasons for choosing pneumatic systems.
Clean Pneumatic systems are clean because they use compressed air. We know already that this is just the air we breathe forced into small spaces. If a pneumatic system develops a leak, it will be air that escapes and not oil. This air will not drip or cause a mess and this makes pneumatics suitable for food production lines.
Safe Pneumatic systems are very safe compared to other systems. We cannot, for example, use electronics for paint spraying because many electronic components produce sparks and this could cause the paint to catch fire.
It is important, however, that we look after and maintain the different components. It is also important that we follow the correct safety rules.
Reliable 19
Pneumatic systems are very reliable and can keep working for a long time. Many companies invest in pneumatics because they know they will not have a lot of breakdowns and that the equipment will last for a long time.
Economical If we compare pneumatic systems to other systems, we find that they are cheaper to run. This is because the components last for a long time and because we are using compressed air. Many factories already have compressed air for other reasons.
Flexible Once you have bought the basic components, you can set them up to carry out different tasks. Pneumatic systems are easy to install and they do not need to be insulated or protected like electronic systems.
Assignment 1 1. Give three examples of the everyday use of pneumatics. 2. Choose one of your examples from question 1. Draw a system diagram and describe how it makes use of compressed air. 3. What is compressed air? 4. Think about blowing up a balloon. What happens to the balloon if you let it go? Why does this happen? 5. Give two reasons why pneumatic systems are used in industry.
20
Supplying compressed air
We know already that pneumatic systems need compressed air to make them work. A bicycle pump can produce compressed air. This is all right for inflating the tyres on your bicycle, but can you imagine trying to blow up all the tyres on a lorry using this? You would soon become tired, exhausted even.
In order to supply pneumatic systems with compressed air we use a machine called a compressor. Compressors come in lots of different shapes and sizes but they all work in the same way.
Figure 5
A pump that is driven by a motor, sucks in air from the room and stores it in a tank called the receiver. You will be able to hear the compressor when it is running. Sometimes though, it will stop because the receiver is full.
Ask your teacher to see the compressor that will be supplying your compressed air.
Not everyone in your class could connect directly to the compressor, as this is not practical. Instead, a pipe takes the compressed air from the receiver to various points around the room. We 21
would normally connect a device called a manifold to these points. The manifold lets us connect lots of components to the compressed air. It also lets us switch our circuits on and off.
ON
OFF
Pneumatic Systems 1 Pneumatic systems A pneumatic system is a system that uses compressed air to transmit and control energy. Pneumatic systems are used in controlling train doors, automatic production lines, mechanical clamps, etc (Fig. 1).
22
(a) Automobile production lines
(b) Pneumatic system of an automatic machine
Fig. 1 Common pneumatic systems used in the industrial sector
(a) The advantages of pneumatic systems Pneumatic control systems are widely used in our society, especially in the industrial sectors for the driving of automatic machines. Pneumatic systems have a lot of advantages.
(i) High effectiveness Many factories have equipped their production lines with compressed air supplies and movable compressors. There is an unlimited supply of air in our atmosphere to produce compressed air. Moreover, the use of compressed air is not restricted by distance, as it can easily be transported through pipes. After use, compressed air can be released directly into the atmosphere without the need of processing.
(ii) High durability and reliability Pneumatic components are extremely durable and can not be damaged easily. Compared to electromotive components, pneumatic components are more durable and reliable.
(iii) Simple design The designs of pneumatic components are relatively simple. They are thus more suitable for use in simple automatic control systems. (iv) High adaptability to harsh environment Compared to the elements of other systems, compressed air is less affected by high temperature, dust, corrosion, etc.
23
(v) Safety Pneumatic systems are safer than electromotive systems because they can work in inflammable environment without causing fire or explosion. Apart from that, overloading in pneumatic system will only lead to sliding or cessation of operation. Unlike electromotive components, pneumatic components do not burn or get overheated when overloaded.
(vi) Easy selection of speed and pressure The speeds of rectilinear and oscillating movement of pneumatic systems are easy to adjust and subject to few limitations. The pressure and the volume of air can easily be adjusted by a pressure regulator.
(vii) Environmental friendly The operation of pneumatic systems do not produce pollutants. The air released is also processed in special ways. Therefore, pneumatic systems can work in environments that demand high level of cleanliness. One example is the production lines of integrated circuits.
(viii) Economical As pneumatic components are not expensive, the costs of pneumatic systems are quite low. Moreover, as pneumatic systems are very durable, the cost of repair is significantly lower than that of other systems.
(b) Limitations of pneumatic systems Although pneumatic systems possess a lot of advantages, they are also subject to many limitations.
(i) Relatively low accuracy
24
As pneumatic systems are powered by the force provided by compressed air, their operation is subject to the volume of the compressed air. As the volume of air may change when compressed or heated, the supply of air to the system may not be accurate, causing a decrease in the overall accuracy of the system.
25
(ii) Low loading As the cylinders of pneumatic components are not very large, a pneumatic system cannot drive loads that are too heavy.
(iii) Processing required before use Compressed air must be processed before use to ensure the absence of water vapour or dust. Otherwise, the moving parts of the pneumatic components may wear out quickly due to friction.
(iv) Uneven moving speed As air can easily be compressed, the moving speeds of the pistons are relatively uneven.
(v) Noise Noise will be produced when compressed air is released from the pneumatic components.
(c) Main pneumatic components Pneumatic components can be divided into two categories: 1. Components that produce and transport compressed air. 2. Components that consume compressed air. All main pneumatic components can be represented by simple pneumatic symbols. Each symbol shows only the function of the component it represents, but not its structure. Pneumatic symbols can be combined to form pneumatic diagrams. A pneumatic diagram describes the relations between each pneumatic component, that is, the design of the system.
2 The production and transportation of compressed air 26
Examples of components that produce and transport compressed air include compressors and pressure regulating components.
(a) Compressor A compressor can compress air to the required pressures. It can convert the mechanical energy from motors and engines into the potential energy in compressed air (Fig. 2). A single central compressor can supply various pneumatic components with compressed air, which is transported through pipes from the cylinder to the pneumatic components. Compressors can be divided into two classes: reciprocatory and rotary.
27
(a) Compressor used in schools (b) Compressor used in laboratories
(c)
Pneumatic symbol of
a compressor
Fig. 2
(b) Pressure regulating component Pressure regulating components are formed by various components, each of which has its own pneumatic symbol: (i)
Filter – can remove impurities from compressed air before it is fed to the pneumatic components. (ii) Pressure regulator – to stabilise the pressure and regulate the operation of pneumatic components (iii)
Lubricator – To provide lubrication for pneumatic components
28
(a) Pressure regulating component
(b) Pneumatic symbols of the pneumatic
components within a pressure regulating component Fig. 3
29
3 The consumption of compressed air Examples of components that consume compressed air include execution components (cylinders), directional control valves and assistant valves.
(a) Execution component Pneumatic execution components provide rectilinear or rotary movement. Examples of pneumatic execution components include cylinder pistons, pneumatic motors, etc. Rectilinear motion is produced by cylinder pistons, while pneumatic motors provide continuous rotations. There are many kinds of cylinders, such as single acting cylinders and double acting cylinders.
(i) Single acting cylinder A single acting cylinder has only one entrance that allows compressed air to flow through. Therefore, it can only produce thrust in one direction (Fig. 4). The piston rod is propelled in the opposite direction by an internal spring, or by the external force provided by mechanical movement or weight of a load (Fig. 5).
Fig. 4 Cross section of a single acting cylinder
30
Fig. 5 (a) Single acting cylinder
(b) Pneumatic symbol of a
single acting cylinder The thrust from the piston rod is greatly lowered because it has to overcome the force from the spring. Therefore, in order to provide the driving force for machines, the diameter of the cylinder should be increased. In order to match the length of the spring, the length of the cylinder should also be increased, thus limiting the length of the path. Single acting cylinders are used in stamping, printing, moving materials, etc.
31
(ii) Double acting cylinder In a double acting cylinder, air pressure is applied alternately to the relative surface of the piston, producing a propelling force and a retracting force (Fig. 6). As the effective area of the piston is small, the thrust produced during retraction is relatively weak. The impeccable tubes of double acting cylinders are usually made of steel. The working surfaces are also polished and coated with chromium to reduce friction.
Fig. 6 Cross section of a double acting cylinder
(b) Pneumatic symbol of a double Fig. 7 (a) Double acting cylinder
acting cylinder
(b) Directional control valve Directional control valves ensure the flow of air between air ports by opening, closing and switching their internal connections. Their classification is determined by the number of ports, 32
the number of switching positions, the normal position of the valve and its method of operation. Common types of directional control valves include 2/2, 3/2, 5/2, etc. The first number represents the number of ports; the second number represents the number of positions. A directional control valve that has two ports and five positions can be represented by the drawing in Fig. 8, as well as its own unique pneumatic symbol.
Fig. 8 Describing a 5/2 directional control valve
33
(i) 2/2 Directional control valve The structure of a 2/2 directional control valve is very simple. It uses the thrust from the spring to open and close the valve, stopping compressed air from flowing towards working tube ‘A’ from air inlet ‘P’. When a force is applied to the control axis, the valve will be pushed open, connecting ‘P’ with ‘A’ (Fig. 9). The force applied to the control axis has to overcome both air pressure and the repulsive force of the spring. The control valve can be driven manually or mechanically, and restored to its original position by the spring.
Fig. 9 (a) 2/2 directional control valve
(b) Cross section
(c) Pneumatic symbol of a 2/2 directional control valve
(ii) 3/2 Directional control valve A 3/2 directional control valve can be used to control a single acting cylinder (Fig. 10). The open valves in the middle will close until ‘P’ and ‘A’ are connected together. Then another valve will open the sealed base between ‘A’ and ‘R’ (exhaust). The valves can be driven manually, mechanically, electrically or pneumatically. 3/2 directional control valves can further be divided into two classes: Normally open type (N.O.) and normally closed type (N.C.) (Fig. 11). 34
Fig. 10 (a) 3/2 directional control valve
(b) Cross section
35
(a) Normally closed type
(b) Normally open type
Fig. 11 Pneumatic symbols (iii) 5/2 Directional control valve When a pressure pulse is input into the pressure control port ‘P’, the spool will move to the left, connecting inlet ‘P’ and work passage ‘B’. Work passage ‘A’ will then make a release of air through ‘R1’ and ‘R2’. The directional valves will remain in this operational position until signals of the contrary are received. Therefore, this type of directional control valves is said to have the function of ‘memory’.
(a) 5/2 directional control valve
(b) Cross section
(c) Pneumatic symbol
Fig. 12 5/2 directional control valve
(c) Control valve A control valve is a valve that controls the flow of air. Examples include non-return valves, flow control valves, shuttle valves, etc. 36
(i) Non-return valve A non-return valve allows air to flow in one direction only. When air flows in the opposite direction, the valve will close. Another name for non-return valve is poppet valve (Fig. 13).
Fig. 13 (a) Non-return valve (b) Cross section
(c) Pneumatic symbol
(ii) Flow control valve A flow control valve is formed by a non-return valve and a variable throttle (Fig. 14).
Fig. 14 (a) Flow control valve
(b) Cross section
37
(c) Pneumatic symbol
(iii) Shuttle valve Shuttle valves are also known as double control or single control non-return valves. A shuttle valve has two air inlets ‘P1’ and ‘P2’ and one air outlet ‘A’. When compressed air enters through ‘P1’, the sphere will seal and block the other inlet ‘P2’. Air can then flow from ‘P1’ to ‘A’. When the contrary happens, the sphere will block inlet ‘P1’, allowing air to flow from ‘P2’ to ‘A’ only.
Fig. 15 (a) Shuttle valve
(b) Cross section
38
(c) Pneumatic symbol
空氣輸入
排氣
4 Principles of pneumatic control (a) Pneumatic circuit Pneumatic control systems can be designed in the form of pneumatic circuits. A pneumatic circuit is formed by various pneumatic components, such as cylinders, directional control valves, flow control valves, etc. Pneumatic circuits have the following functions: 1. To control the injection and release of compressed air in the cylinders. 2. To use one valve to control another valve.
(b) Pneumatic circuit diagram A pneumatic circuit diagram uses pneumatic symbols to describe its design. Some basic rules must be followed when drawing pneumatic diagrams.
(i) Basic rules 1.
2.
A pneumatic circuit diagram represents the circuit in static form and assumes there is no supply of pressure. The placement of the pneumatic components on the circuit also follows this assumption. The pneumatic symbol of a directional control valve is formed by one or more squares. The inlet and exhaust are drawn underneath the square, while the outlet is drawn on the top. Each function of the valve (the position of the valve) shall be represented by a square. If there are two or more functions, the squares should be arranged horizontally (Fig. 16).
Fig. 16 3/2 directional control valve
Fig 17 3/2 directional control valve 39
(normally closed type) 3.
4.
(normally closed type)
Arrows "↓↖" are used to indicate the flow direction of air current. If the external port is not connected to the internal parts, the symbol “┬” is used. The symbol “⊙” underneath the square represents the air input, while the symbol “▽” represents the exhaust. Fig. 17 shows an example of a typical pneumatic valve. The pneumatic symbols of operational components should be drawn on the outside of the squares. They can be divided into two classes: mechanical and manual (Fig. 18 and 19).
(a) Vertical piston lever
(b) Pulley lever
(c) Unilateral pulley lever
Fig. 18 Mechanically operated pneumatic components
(a) Standard
(b) Lever
(c) Button
(d) Pull & push
Fig. 19 Manually operated pneumatic components 5.
Pneumatic operation signal pressure lines should be drawn on one side of the squares, while triangles are used to represent the direction of air flow (Fig. 20).
Fig. 20 Pneumatic operation signal pressure line
(ii) Basic principles
40
Fig. 21 shows some of the basic principles of drawing pneumatic circuit diagrams, the numbers in the diagram correspond to the following points:
Fig. 21 Basic principles of drawing pneumatic circuit diagrams
1. When the manual switch is not operated, the spring will restore the valve to its original position. 2. From the position of the spring, one can deduce that the block is operating. The other block will not operate until the switch is pushed. 3. Air pressure exists along this line because it is connected to the source of compressed air. 4. As this cylinder cavity and piston rod are under the influence of pressure, the piston rod is in its restored position. 5. The rear cylinder cavity and this line are connected to the exhaust, where air is released. (iii) The setting of circuit diagrams When drawing a complete circuit diagram, one should place the pneumatic components on different levels and positions, so the relations between the components can be expressed clearly. This is called the setting of circuit diagrams. A circuit diagram is usually divided into three levels: power level, logic level and signal input level (Fig. 22).
41
Fig. 22 Power level, logic level and signal input level
42
The basic rules of circuit diagram setting are as follows:
1.
2.
In a pneumatic circuit, the flow of energy is from the bottom to the top. Therefore, the air supply unit should be put at the bottom left corner.
The work cycle should be drawn from left to right. The first operating cylinder should be placed at the upper left corner.
43
3.
4.
Power control valves should be drawn directly under the cylinder controlled by them, forming a power unit.
Control cylinders and operational valves (signal components) driven by power control valves should be placed at the lower levels of the diagram.
5.
6.
Assistance valves, such as those with logic functions (for example, memory, ‘AND’, ‘OR’, ‘NOT’, delay, etc), can be put between the pneumatic components and the power control valves.
Use the line which represents the connecting pipe to connect all the air supply unit and the pneumatic components to complete the pneumatic circuit. Check carefully the circuit and the logic of the operation before use to avoid any accident. 44
5 Different kinds of basic circuits A basic circuit is a pneumatic circuit designed to perform basic tasks, such as flow amplification, signal inversion, memory, delay, single acting cylinder control, double acting cylinder control, etc.
(a) Flow amplification Cylinders with a large capacity require a larger flow of air, which can be hazardous to users. It is unsafe to manually operate pneumatic directional control valves with large flow capacity. Instead we should first operate manually a small control valve and use it to operate the pneumatic control system with large flow capacity. This is called flow amplification, which can greatly ensure the safety of the operators. During operation, valves with large flow capacity should be placed near the cylinder, while valves with smaller flow capacity should be placed on control boards some distances away. Fig. 23 shows a basic flow amplification circuit. Notice how different components are placed on different levels.
Fig. 23 Flow amplification system
45
(b) Signal inversion The pneumatic diagram in Fig. 24 shows how directional control valves can be switched. When operating control valve , control valve will stop producing pressure output. When control valve ceases operation and is restored to its original position, control valve will resume its output. Therefore, at any given time, the pressure output of control valve is the exact opposite of that of control valve .
Fig. 24 Signal inversion system (c) Memory Function Memory is a common basic function. It can keep a component at a certain state permanently until there is a change of signals. Fig. 25 shows a memory function circuit. When control valve is operated momentarily (that is, pressed for a short time), the output signal of the 5/2 directional control valve will be set to ON. The signal will stay that way until control valve is operated momentarily and generates another signal to replace it, causing it to stay permanently at OFF.
46
Fig. 25 Memory function circuit
(d) Delay function A pneumatic delay circuit can delay the operating time of the next control valve. Its principle of operation involves the use of an orifice to slow down the flow of air and control the time of pneumatic operation. Delay functions can be divided into two classes: ON-signal delay and OFF-signal delay.
(i) ON-signal delay Fig. 26 shows the circuit diagram of an ON-signal delay circuit, which delays the output of the next control valve. When control valve is operated, the one way flow control valve will slow down the flow of air, thus delaying the signal output of the outlet of control valve (A), resulting in a persistent ON-signal. The time when control valve will be restored to its original position is not affected.
47
Fig. 26 Circuit diagram of an ON-signal delay circuit (ii) OFF-signal Delay Fig. 27 shows the circuit diagram of an OFF-signal delay circuit, which delays the output of the next control valve. This circuit is similar to an ON-signal delay circuit. The only difference is that the one way flow control valve is connected in the opposite direction. Therefore, when control valve is operated, the outlet of control valve (A) will continue to output signals. However, when control valve is restored to its original position, the release of air is slowed down by the one way flow control valve, resulting in a persistent OFF-signal.
Fig. 27 Circuit diagram of an OFF-signal delay circuit (e) Single acting cylinder control Single acting cylinders can be controlled manually. However, they can also be controlled by two or more valves. This is called logic control. Examples of logic control include ‘OR’ function, ‘AND’ function, ‘NOT’ function, etc.
(i) Direct control and speed control
48
If a single acting cylinder is connected to a manual 3/2 directional control valve, when the control valve is operated, it will cause the cylinder to work (Fig. 28). Therefore, the circuit allows the cylinder to be controlled manually.
Fig. 28 Direct control of a single acting cylinder The only way to change the extension speed of the piston of a single acting cylinder is to restrict the flow of air at the inlet and use the spring to determine the speed of retraction. Therefore, a one way flow control valve is placed in the circuit to control the speed. (ii) OR Function The single acting cylinder in Fig. 29 can be operated by two different circuits. Examples include manual operation and relying on automatic circuit signals, that is, when either control valve or control valve is operated, the cylinder will work. Therefore, the circuit in Fig. 29 possesses the OR function. However, if the output of two 3/2 directional control valves are connected through the port of a triode, the air current from control valve will be released through the exhaust of control valve , and so the cylinder will not work. This problem can be solved by connecting a shuttle valve to the port of the triode.
49
Fig. 29 Circuit diagram of an OR function circuit
(iii) AND Function Another name for an AND function is interlock control. This means control is possible only when two conditions are satisfied. A classic example is a pneumatic system that works only when its safety door is closed and its manual control valve is operated. The flow passage will open only when both control valves are operated. Fig. 30 shows the circuit diagram of an AND function circuit. The cylinder will work only when both valve and are operated.
50
Fig. 30 Circuit diagram of an AND function circuit (iv) NOT Function Another name for a NOT function is inverse control. In order to hold or lock an operating conveyor or a similar machine, the cylinder must be locked until a signal for cancelling the lock is received. Therefore, the signal for cancelling the lock should be operated by a normally open type control valve. However, to cancel the lock, the same signal must also cancel the locks on other devices, like the indication signal in Fig. 31. Fig. 31 shows how the normally closed type control valve can be used to cut off the normally open type control valve and achieve the goal of changing the signal.
51
Fig. 31 Circuit diagram for a NOT function circuit
(f) Double acting cylinder (i) Direct control The only difference between a single acting cylinder and a double acting cylinder is that a double acting cylinder uses a 5/2 directional control valve instead of a 3/2 directional control valve (Fig. 32). Usually, when a double acting cylinder is not operated, outlet ‘B’ and inlet ‘P’ will be connected. In this circuit, whenever the operation button is pushed manually, the double acting cylinder will move back and forth once.
.ADVANTAGES 1. compressed air to store the energy instead of batteries. Their potential advantages over other vehicles include: 2. Reducing pollution from one source, as opposed to the millions of vehicles on the road. 3. Transportation of the fuel would not be required due to drawing power off the electrical grid. This presents significant cost benefits. Pollution created during fuel transportation would be eliminated. 4. Compressed air technology reduces the cost of vehicle production. 5. There is no need to build a cooling system, fuel tank, Ignition Systems or silencers. 6. The mechanical design of the engine is simple and robust. 52
7. Low manufacture and maintenance costs as well as easy maintenance. 8. Compressed-air tanks can be disposed of or recycled with less pollution than batteries. 9. The tank may be able to be refilled more often and in less time than batteries can be recharged, with re-fueling rates comparable to liquid fuels. 10. Lighter vehicles would mean less abuse on roads resulting in longer lasting roads. 11. The price of fueling air powered vehicles will be significantly cheaper than current fuels. 12. Refueling can be done at home using an air compressor
DISADVANTAGES 1. Like the modern car and most household appliances, the principal disadvantage is the indirect use of energy. 2. The temperature difference between the incoming air and the working gas is smaller. In heating the stored air, the device gets very cold and may ice up in cool, moist climates. 3. Refueling the compressed air container using a home or low-end conventional air compressor may take as long time.. 4. Tanks get very hot when filled rapidly. It very dangers it some time bloused. 5. Only limited storage capacity of the tanks. So we not take drive on long time.
APPLICATIONS 1. Two wheeler Application 2. Four wheeler Applications Conclusion: On the whole, the technology is just about modifying the engine of any regular IC engine vehicle into an Air Powered Engine. The Air Powered Engine technology is cheaper in cost and 53
maintenance, can be easily adapted by the masses and it doesn’t cause any kind of harm to the environment. Instead, its widespread use will help mankind in controlling the serious problem of global warming. It surely is the “Futuristic Mode of Transport
REFERENCES [1] Sullivan, M. World's First Air-Powered Car: Zero Emissions by Next Summer, Popular Mechanics http://www. popularmechanics. com/automotive/new_cars/4217016.html (June 2008 issue), [2] Harley, M.; Ford, G.M. Considering Joint Engine Development, http://www.autoblog.com/2008/08/04/fordgm-considering-jointengine- development, (accessed Aug 2008). [3] From Wikipedia, the Free Encyclopedia. Compressed-Air Car, http://en.wikipedia.org/wiki/Air_car (accesed June 2008). [4] Russell, C. The Air Car becomes a Reality, http://cambrown. wordpress.com/2007/03/27/the-air-car-becomes-a-reality/ (accessed May 2007). [5] Hamilton, T. Technology Review, The Air Car Preps for Market, http://www.technologyreview.com/Energy/20071 (accessed January 2008). 54
[6] Bonser, K., HowStuffWorks, How Air-Powered Cars Will Work, http://auto.howstuffworks.com/air-car.htm (accessed June, 2008). [7] Haliburton, M.-S. Pure Energy Systems News, Engineair’s UltraEfficient Rotary Compressed-Air Motor, http://pesn.com/2006/05/11/9500269_Engineair_CompressedAir_Motor/ (accessed June, 2008). [8] Richard, M.G. The Air-Powered Motorcycle by Jem Stansfield, http://www.instructables.com/id/Air-powered-bicycle (accessedApril 2008). [9] Chen, P.X. Researchers Develop Air-powered Motorcycle
55
