Control-oriented Modeling Of TGDI Gasoline Engine Gas Exchange Process

The thermal efficiency is the main research focus in the international combustion engine due to energy shortage and environment protection.At present,the development trend of gasoline engines in passenger cars is VVT(Variable Valve Timing),gasoline direct injection(GDI),turbocharging and small displacement technology,which can meet the emission regulations and take into account both power and economy.The structure and control strategy of the turbocharged direct injection gasoline engine equipped with DVVT(Dual Variable Valve Timing)technology are more complex.In order to optimize and develop DVVT control strategy rapidly,a controlled object model is established,which is mainly used in DVVT control strategy for optimization test of ventilation process and estimation of catalytic temperature.The optimization process of DVVT control strategy is developed,and the rapid verification of DVVT control strategy in the model is realized to ensure its reliability and stability,as well as high temperature protection of catalysts and high efficient catalysis.Firstly,the in-cylinder air exchange process of TGDI(Turbocharged Gasoline Direct Injection)engine with DVVT technology is analyzed in detail.The gas in the process of air exchange is divided into three parts,including fresh air in cylinder,scavenging or return flow and residual exhaust in cylinder.This paper investigated the generation conditions of scavenging or recirculating flow,the influence of scavenging or recirculating flow on fresh air and residual exhaust in cylinder,and the relationship between gas quantities in cylinder at the time of valve closing.The working process of TGDI engine is simplified for establishing a mathematical model.The mathematical models can calculate the residual exhaust and partial pressure of the residual exhaust gas in cylinder,including the fresh air in cylinder,the fresh impulse scavenge or the exhaust return flow during the valve overlap period,and whether or not the valve overlap angle exists.According to the mathematical model,the corresponding average model was established by using MATLAB/Simulink software.Secondly,the energy transfer process from engine exhaust pipe to three-way catalytic converter is analyzed in detail in this paper.It is divided into two parts: the front part of the catalytic converter and the catalytic converter.According to the mechanism of heat transfer and generation,the heat transfer loss in front of the catalytic converter,the heat transfer loss in the catalytic converter and the heat release in the redox reaction are calculated.According to the mathematical model,a corresponding average model was established using MATLAB/Simulink software.Finally,a simulation model of gasoline engine is established by GT-power software based on a real TGDI engine.The GT-power simulation model is verified by the measured data of the test bench,and the accuracy of GT-power is verified.The accuracy of the Simulink model is verified by comparing the built and debugged Simulink model with the engine bench data and GT-power simulation data.It is shown that the model can realize the calculation of in-cylinder air exchange process and the estimation of temperature in catalytic converter.