Thermodynamic Cycle Simulation Analysis Of High Efficiency Gasoline Engine With Electric Supercharger

In order to reduce dependence on non-renewable energy and air pollution,changing energy utilization Structure and exploiting new energy and energy-saving technology has become the consensus of all countries.More and more stringent vehicle fuel consumption and emission regulations have been introduced.Meanwhile,decision and technical approaches to improve engine thermal efficiency have been successively formulated by automotive manufacturers in the world.Based on the thermodynamic principle and numerical cyclic simulation method,this paper aims at combining the latest electric supercharger Technology,exploring innovative technological approaches to improve the thermal efficiency of gasoline engine,and analyze the expected results.The goal of this paper is to solve the problem of low thermal efficiency at medium and low loads.The specific work and conclusions are as follows:Firstly,according to the actual geometry parameters of a 2.0L gasoline engine,combining with the concept of concurrent test and simulation,this paper establishes GT-POWER simulation model of four cylinder naturally aspirated gasoline engine,and the model is calibrated and verified by experiments.In the software simulation,an electric supercharger model is built with the special drive module and the compressor module.A knock simulation model of gasoline engine was built to predict and evaluate knock combustion caused by electric supercharging.At the same time,the throttle PID control simulation model is established to adjust the engine performance output.Based on the simulation model of four cylinder gasoline engine,an electric supercharger model of four cylinder gasoline engine was established,in combination with the model of electric supercharger,gasoline engine knock model and PID control model.Based on the principle of thermodynamics,the innovative technical approach of electric supercharging and no return Miller cycle is put forward by this chapter,to solve the problems poor fuel economy of gasoline engine at the partial load.The no return Miller cycle is achieved by closing the valve early,the expansion ratio is greater than the compression ratio,and makes the intake gas vacuum expand and cool down.Thermal efficiency is suppressed while knock is suppressed.When the electric supercharger is used to increase the pressure of Intake manifold,it makes the variation of air pressure ratio have nothing to do with the engine speed and load,and solve the problem of reduced power for running the Miller cycle.The final scheme is,closing intake valve early to realize Miller cycle without backflow,and the intake valve lift curve is IVC468oCA(72oCA before BDC),the electric supercharger is Rotrex-C15-20,the geometric compression ratio of gasoline engine is 12.5063(keep the effective compression ratio 9.3766 unchanged).The final result is,the Rotrex-C15-20 electric supercharger matches the gasoline engine very well.The whole scheme makes the effective thermal efficiency of gasoline engine is greatly improved at the low load.The overall lift is maintained at 5%~8% and the maximum effective thermal efficiency is increased by 11.47%.The innovative scheme of Variable Miller cycle with electric supercharging is presented.Based on the principle of electric supercharger,it controls the intake charge of gasoline engine intelligently.Through VVT adjust the intake valve closing time,scheme obtain the adjustable equivalent Miller cycle(Miller Cycle)effect,which includes that the effective compression ratio is less than the geometric compression ratio and the expansion ratio is greater than the effective compression ratio.The final scheme is,the intake valve lift curve is IVC490-IVO386 oCA and electric supercharger does not work.In order to improve fuel economy at low load condition,the gasoline engine works with larger geometric compression ratio(fixed value 15.4225)and larger effective compression ratio(variable 15.15).Under high load condition,VVT causes the valve lift curve to move left at 40 oCA while electric supercharger works.The gasoline engine change to work with large geometric compression ratio(fixed value 15.4225)and small effective compression ratio(variable value 9.3766,the same with the original curve).The whole scheme can avoid the occurrence of gasoline engine knock.The final result is,the matching between Rotrex-C15-20 and the gasoline engine is reasonable.Design of large geometric compression ratio of gasoline engine(15.4225)is realized by the whole scheme.The fuel economy has been further improved at the partial load,and maximum effective thermal efficiency increase by 12.41%.The two schemes are compared and analyzed.Scheme 1 is electric supercharger with no back-flow miller cycle.Scheme 2 is electric supercharger with VVT and variable effective compression ratio.Scheme 1 is slightly better than scheme 2 with the feasibility and dynamic output at high speed and high load.Scheme 2 realizes the design of large geometric compression ratio of gasoline engine(15.4225),and expands the high efficiency interval under middle and low load.Moreover,the overall thermal efficiency and maximum thermal efficiency of scheme 2 are also better than the scheme 1.The fuel economy of gasoline engine is greatly improved by the Scheme 2.All factors are taken into consideration and the final conclusion is: scheme 2 is better than the scheme 1.