Heat Release Rate Modelling For Combustion In High Compression Ratio Miller Cycle Gasoline Engine

Miller cycle is one of the critical techniques for achieving high-efficient combustion of high compression ratio gasoline engine,greater improvement can be achieved when implementing with exhaust gas dilution.However,highly diluted combustion under high compression ratio will weaken the control of spark timing over combustion process,which will add the complexity of combustion control.Losing control of combustion phasing will lead to abnormal combustion like knock or misfire,compromising the thermal efficiency.Based on a Miller cycle gasoline engine with compression ratio up to 13.4,along with GT-POWER simulation,models for predicting in-cylinder initial condition before combustion together with predictive combustion model were established,making it possible for the re-construction of in-cylinder pressure,achieving the prediction of diluted combustion process in high compression ratio Miller cycle engine?Firstly,in order to study Miller cycle's effect on high compression ratio gasoline engine,experiments were carried out under 2000r/min and 3 different fixed fueling rate.Studies show that Miller cycle will reduce pumping loss and dilute the charge through exhaust gas re-breathing from intake port,which caused the instability of flame propagation and increased the auto-ignition prossiblity,reducing the control abilitiy of sparktimg over combustion phasing.At part load,the increased Miller cycle effect and advancd sparktiming will lead to complex changing patterns of combustion phasing.Secondly,residual exhaust gas mass and in-cylinder thermal state estimation model were established for the prediction of initial boundary condition before combustion.Results show that the absolute deviation of residual exhaust gas mass fraction were less than 3%,the deviation of temperature inside cylinder at intake valve closure were less than 4.6%,which indicates that the models were well established.Finally,through the regression analysis of simulation results,predictive heat release rate model for combustion control was established.Simulation results show that within 25 operating points form 1000³000r/min,the deviation in RMSE of predicted CA50 or CA10-90 were less than 1.5°CA,the deviation of predicted IMEP_gross of SI combustion were less than 4%.The experiment results show that within 6 operating points,the average deviation of predicted CA50 was 1.3°CA,and the average deviation of predicted CA10-90 was 1.9°CA.The average deviation of predicted IMEP_gross was2.9%?In all,the residual exhaust gas mass fraction and combustion prediction model has great potential for combustion optimization and cylinder pressure prediction,which paves the way for the combustion control in high compression ratio engine operating with Miller cycle.