Analysis And Experimental Research Of The Working Characteristics On Four-stroke Compressed Air Engine

Nowadays,the new energy vehicles on the market have their own obvious disadvantages in terms of energy conservation and environmental protection as well as energy sources.Therefore,it is urgent to study the energy saving and environmental protection of green car power.The research of this thesis is derived from the enterprise key project entrusted by Saic-GM-Wuling automobile co.LTD in China.A four-cylinder four-stroke gasoline engine has been improved and innovated,and a new four-cylinder four-stroke reciprocating piston type compressed air engine(CAE)is presented.In this paper,the key theoretical problems and tests of F-s CAE are studied,and the detailed content of this paper shows as follows:(1)The composition and working principle of F-s CAE are analyzed.On this basis,the mathematical model of the working process of the F-s CAE is established,including the thermodynamic model and the dynamic model.Under the condition of the basic hypothesis,the thermodynamic differential equations are constructed,which are based on the first law of thermodynamics.Simultaneously,the thermal process of each stage is analyzed.Relevant boundary conditions and constraint equations are established,and the working process is calculated and solved by Matlab/Simulink.(2)Based on CFD,the numerical simulation of the F-s CAE is carried out.The physical model is established and the engine cylinder is meshed by using the dynamic mesh technology.Based on the basic control equation,the turbulence model is established and the initial conditions and boundary conditions are analyzed.The fluid dynamics software Fluent is used to simulate the working process of the F-s CAE,and the variation rules of air pressure,air temperature and other state parameters in the cylinder are obtained.By comparing the CFD simulation results with the theoretical analysis results,the correctness and the feasibility of the model and results are verified,which lay a foundation for subsequent theoretical and experimental analysis.(3)Based on the mathematical model of the working process,the working characteristics of the F-s CAE are simulated and analyzed by numerical calculation.The working parameters and port timing parameters are analyzed,including rotational speed,supply pressure,supply temperature,cylinder wall temperature,intake advance angle,intake sustain angle and exhaust advance angle.The P-V indicator diagram,mean effective pressure,average effective torque,effective torque of the whole machine,compressed air consumption of single cylinder and work efficiency of the F-s CAE are obtained,the effects of various parameters on the performance indicators are studied and the performance characteristics of the F-s CAE are verified scientifically.(4)Based on the working characteristics of the F-s CAE,and the second law of thermodynamics,the exergy loss and utilization are analyzed,the mathematical model of the exergy analysis is set up and the exergy balance of each working phase is analyzed,the exergy of the compressed air fowing into the cylinder,the exergy of the air fowing into the cylinder during the intake stroke,the exergy of the air fowing out of the cylinder during the exhaust stroke,the exergy of the piston work,the exergy of the system caused by heat transfer between the air and the cylinder walls,the increment of exergy of the system,the exergy loss caused by irreversibility and the exergy effciency are discussed under the different working parameters and the port timing parameters.(5)The overall design of the four-cylinder F-s CAE system is carried out,and the structure and principle of each subsystem are described in detail.On this basis,the development system of electric control ECU of the CAE is established based on the V-type development mode,and the 32-bit MPC5634 microcontroller is used as the micro-control unit to develop the rapid prototype controller.Matlab/Simulink control system model is established,and the model is transformed into executable target code and is written to the fast prototype controller based on the real time workshop(RTW).Simultaneously,the performance and function of the system are tested by the measuring and calibrating system.Based on the established system test platform,the F-s CAE experimental bench is set up and the bench experiment is researched.The speed characteristic,power characteristic and related port timing parameters of the F-s CAE under different working conditions are discussed.It is found that the power performance of the F-s CAE on real vehicle can reach the desired effect,and the increase of supply pressure can significantly improve the dynamic performance in actual road conditions,and it has a broad application prospect.