Experimental Research On Pumping Losses And Miller Cycle Performance Of SI Engine Based On Fully Hydraulic Variable Valve

Fully hydraulic variable valve system(FHVVS)can realize maximum valve lift,valve opening duration and’valve timing continuously variable,instead of traditional SI engine throttle to control engine load and realize Unthrottled SI engine.EIVC can greatly reduce the pumping loss at part load,improve the fuel economy of the engine and improve the mechanical efficiency of the engine.The simulation results show that Miller cycle can reduce the temperature and pressure at the end point of engine compression and improve the anti-deflagration performance of engine.The high efficiency of engine can be achieved by using Miller cycle to turbocharging and improving the compression ratio under the condition of heavy load.The main research contents are as follows:(1)The FHVVS mechanism is installed on the BJ486EQ SI engine,and the test bench is built and collected for test.FHVVS-equipped test prototype can realize unthrottled SI engine on the premise of keeping the engine cylinder head unchanged.The data acquisition system is used to collect the engine speed,cylinder pressure,air intake,fuel consumption and other parameters in the process of engine test.(2)The one-dimensional simulation model of SI engine is established and calibrated by gt-power simulation software.BJ486EQ based on the main.technical parameters of SI engine,SI engine working fluid flow characteristics and heat transfer,heat transfer and combustion in cylinder characteristic,etc.,built the simulation model,through compares the simulation data and experimental data shows that the simulation value and experiment value error is small,basic maintain error within 5%,satisfies the requirement of engine model calibration.(3)The pumping loss and mechanical efficiency of the engine under different load control modes at the same speed and different loads were studied.It is found that unthrottled SI engine can greatly improve the pumping loss and mechanical efficiency and the two improvements are more obvious at part load.Compared with the throttle SI engine,the pumping loss is improved by 77.1-81.1%and the mechanical efficiency is increased by 3.6-10.2%.(4)The use of Miller cycle in SI engines and matching with high turbocharging and compression ratio have great advantages.Miller cycle can improve the deflagration tendency of engine caused by high compression ratio,reduce the temperature and pressure of engine compression end point,and achieve high efficiency of gasoline engine.In medium and small load conditions,the thermal efficiency of engine can be improved by increasing geometric compression ratio and temperature and pressure of engine compression end point without considering deflagration effect.