Analytical Determination of the Performance Parameters of CompressedAir vehicle Abhijith.R abhijith.rajan@acetvm.com Sivaprakash.SC shivaprakash.sc@acetvm.com Akhil.BS akhil.bs@acetvm.com Arun.S Assistant professor in Mechanical Engineering arun.s@acetvm.com 1. Abstract This paper gives a brief description of working and the determination of performance parameters of compressed air vehicle. At the time of developing the compressed air vehicles, control of parameters of compressed air like temperature, energy release, Ecofriendly and emission control have to be mastered for development of a safe, light and cost effective compressed air vehicle for upcoming generation. In this work, a detailed analytical study of the various performance parameters of the Compressed air vehicle is done using equations developed and modified from that of a normal internal combustion engine. Performance analysis and the analytical determination of various parameters are done using the method of dimensional analysis. The equation for work done by an air compressed engine is obtained and its actual and theoretical efficiency is determined using the thermodynamic analysis. 2. Introduction Compressed air engine is defined as the pneumatic motor that creates useful work by expanding the compressed air and thus converting the potential energy into motion. Compressed air which is used as the fuel in compressed air engine is stored in a tank at high pressure. Compressed air engines use the expansion of previously compressed air to drive the piston; this is the main advantage of compressed air engine over internal combustion engine.compressed air vehicle is a light utility vehicle. Compressed air vehicle can be said as a green environmental protection vehicle with near zero pollution as they do not emit any toxic gases and with the help of this, will be able to conserve limited fuel such as petrol and diesel for the future generation. 3. Working This working of the engine is similar to that of a diesel engine. At the end of the compression stroke, a very high-pressure air at the room temperature is injected into the cylinder. Injection of air is done by electro-mechanical injection. System is governed by the cam shaft dwell during which the piston also dwells. As the air in cylinder is hot and the compressed air mixes with the externally injected compressed air, injected at relatively higher pressure comparing to the inside pressure, the mixture tries to attain a common equilibrium temperature. As the temperature of the mixture falls down and expansion of the compressed air takes place. During expansion the pressure of the mixture of hot and cold compressed air imparts a very heavy blow on the head of the piston, which is then set to the motion and the engine runs. No combustion will take place; 36
as it is the expansive forces, which make the engine run. Compressed air technology makes the engine both non-polluting and economical. Unlike electric or hydrogen powered vehicles, compressed air vehicles are inexpensive and do not have a limited driving range. Compressed air vehicles are affordable economically and have a performance rate such that stands up to current standard limits. Compressed air technology reduces the cost of vehicle production by about 20%, due to the absence of cooling system, lubrication system, fuel tanks ignition system or silencers. Engine size and weight is also considerable reduced due to minimum number of components in a CAV. The price of filling compressed air in the air tanks is very economic compared to the use of petrol or diesel engines. By using rechargeable batteries, the electrical energy required for compressing the air can be minimized considerably. To sum up, they are nonexpensive vehicles that do not pollute the environment and are easy to get around in cities as well as in towns and villages. The main emission benefits of introducing the zero emission technology are obvious and at the same time efficiency of these vehicles need to be improved and this type of engine can be used in future generation and thus be able to reduce pollution rates and control the usage of limited fuels like petrol and diesel. 4. Symbols and Notations Used W out : Work output from CAE W in : Work input to compressor P a : initial pressure P b : pressure after compression (=P 3 ) P d: final pressure after expansion V a : initial volume or stoke volume (V s )V b : volume after compression V c : volume after heat input T a : initial temperature of air before compression T b : temperature after compression T c : temperature after heat addition C p : specific heat at constant pressure C v : specific heat at constant volume γ: adiabatic index r; compression ratio η CAE ; efficiency of CAE Q 1 ; energy of compressed air from compressor Q 2 ; energy released from CAE h 1 = initial enthalpy of compressed air h 2 = final enthalpy of compressed air (after 5. Block diagram for air compressed engine. C: compressor E: engine E 1,E 2 :Energy 6. Efficiency of compressed air engine 6.1. P-V Diagram of CAE 37
6.2. T-S Diagram of CAE T 2 = final temperature of compressed air (after Energy output from the engine, E 2 E 2 = h 4 -h 1 = C P (T 4 -T 1 ) Work output from the CAE =E 1 -E 2 The efficiency of CAE, η CAE η CAE = W out /E 1 = 1- (E 2 /E 1 ) η CAE = 1-[(T 4 -T 1 )/ (T 3 -T 2 )] Let the compression ratio be r r = v 1 / v 2 Assuming both the compression and expansion ratios are equal. From P-V diagram Consider the process 1-2 (Adiabatic process) There are mainly four strokes in the CAE, namely: i. Suction stroke ii. Compression stroke iii. Expansion or power stroke iv. Exhaust stroke Corresponding to each stroke there are four processes in the pv diagram of CAE i. Adiabatic compression ii. Constant pressure energy addition iii. Adiabatic expansion iv. Constant volume energy rejection Due to the insulation of the cylinder wall the process such as compression and expansion are assumed to be adiabatic. Hence there is no heat flow through the cylinder wall during the process. The energy input to the engine, E 1 E 1 = (h 2 -h 1 ) =C P (T 2 -T 1 ) h 1 = initial enthalpy of compressed air h 2 = final enthalpy of compressed air (after T 1 = initial temperature of compressed air PV γ =constant P 1 V 1 =P 2 V 2 (V 1 /V 2 ) γ =P 2 /P 1 r γ = P 2 /P 1 r= (P 1 /P 2 ) γ TV γ-1 =constant T 2 =T 1 (r) γ-1 Consider the process 2-3 Pressure=Constant P 2 =P 3 (V 2 / T 2 )= (V 3 /T 3 ) T 2 =T 3 (V 2 /V 3 ) Consider the process 3-4 TV γ-1 =constant T 3 V γ-1 γ-1 3 =T 4 V 4 T 3 /T 4 = (V 4 /V 3 ) γ-1 T 3 =T 4 (V 4 /V 3 ) γ-1 38
T 3 =T 4 (r) γ-1 Consider the process 4-1 Volume=Constant (P 1 /T 1 )= (P 4 /T 4 ) T 4 = (T 1 P 4 )/P 1 Work done W=E 1 -E 2 W= C P [(T 4 -T 1 )-(T 2 -T 1 )] Theoretical Efficiency η CAE = Wout/E 1 η CAE = 1- (E 2 /E 1 ) η CAE = 1-[(T 4 -T 1 )/ (T 3 -T 2 )] η CAE = 1- by substituting values of γ η CAE = 1 - η CAE = 1- Actual Efficiency The actual power output from CAE, Power output= (mep *LAN)/60 mep=(p 2 +P 4 )/2 ; mep =mean effective pressure LA=V s, stroke volume Power output= [(P 2 +P 4 )V s. N]/120 The actual input power to the compressor, but if we are using an electric motor to drive the compressor, then the input power will be Power input= voltage *current DC motor) The actual efficiency of the system will be, η act =Power output/power input η act =[(P 2 +P 4 )V s N]/120VI (using a 7. Applications 1. Mopeds Jem Stansfield, an English inventor had converted a regular scooter to the compressed air moped. This has been done by including the scooter with a compressed air engine and air tank. 2. Buses and Locomotives MDI makes Multi CATs vehicle that can be used as buses or trucks. RATP has also already expressed an in-terest in the compressed-air pollution-free bus. Advantages of CAE: 1.Major advantage of using compressed engine is that the pure compressed air vehicle produces no pollution at the tailpipe end. 2. Use of renewable fuel. 3. Compressed-air technology reduces the cost of vehicle production by almost 20%, because there is no need to build a cooling system, fuel tank and the Ignition systems or silencers. 4. Air is non-flammable. 5. The engine can be massively reduced in size and shape. 6. Manufacturing and maintenance costs is very less. 7. The air tank may be refilled more often and in less time than batteries can be recharged, with refilling rates when comparing to liquid fuels. 8. Lighter vehicles cause less damage to roads, resulting in lower maintenance cost. 9.The price of filling air powered vehicles is significantly cheaper than petrol, diesel or biofuel used in engines. If electricity is cheap, then the compressing air will also be relatively cheap. 8. Conclusion Primethe analytical determination of the performance parameters of a compressed air engine (CAV) is done theoretically by considering the thermodynamic properties of air which is the working fluid in this engine. The efficiency and work output are determined and calculated. The actual efficiency of CAV is also determined by including the input 39
electrical power to the electric motor which is used as themover in running the compressor which is providing the compressed air to the engine. The equations of CAV are found to be similar to that of a diesel engine, since the only change from diesel engine is that instead of supplying fuel by means of a fuel injector in a diesel engine, the CAV is supplying compressed air at the end of the compression stroke. 9. References [1] N Govind, S Sanyasi Rao, and Manish Kumar Behera., International Journal and Magazine of Engineering, Technology, Management and Research, 210-215, 2014 [2] Negre Guy and Negre Cyril, Compressed Air - The Most Sustainable Energy Carrier for Community Vehicles, Speech in front of assembly at Kultur gathered for Fuel Cells World, Tuesday 29th June 2004. [3] Atcitty, S., Ranade, S., Gray-Fenner, Amber, Summary of State-of-the-Art Power Conversion Systems for Energy Storage Applications- Sandia National Laboratories - Report SAND98 2019, 1998. [4] Guey Nyger, MDI The Compressed air Engine Barcelona, Spain, 2002 [5] Internet website, www.theaircar.com 40