Study On Characteristics Of Gas System And Control Strategy In A Turbocharged GDI Engine

With the increasingly strict emission regulation and demand for power performance, small gasoline engine with high power performance has become the focus of research. Turbocharged GDI engine has the potential of improving power per liter, reducing fuel consumption and emissions, but it also has the problems of insufficient intake air mass at low speed and slow transient response.This paper analyzed the law of combustion heat release rate in a 2.0L turbocharged GDI engine. By studying scavenging properties at low-speed full-load conditions and optimizing wastegate control strategy at transient conditions, to improve intake air mass in steady state and transient response property.Firstly, this paper studied effect of matching different compressors on steady-state simulation model, and take GT20 C210 A compressor as the final choice. Based on knock mode, studied the effect of temperature after intercooler on knock.Based on experiment data of pressure in-cylinder, combustion heat release rate has been analyzed. According combustion information in different conditions, correction formula of combustion model has been calculated by fitting, which can be used for correcting combustion model in condition without experiment data.By analyzing intake and exhaust pressures fluctuation in steady conditions at full load, this paper compared the change of pressure difference and scavenging parameter, determined the range of scavenging can be used is 1000~2700 r/min. In the range, scavenging coefficient is more than 1.02, scavenging mass per cylinder is more than 20 mg. Taking intake air mass as the optimization goal, optimized VVT in full load condition has been proposed.By studying the effect of different wastegate closing durations and result of PD control strategy, optimized control strategy was determined. That is, when working condition starts to change, to close wastegate. When turbocharger speed is more than 165000r/min, to control wastegate by PD strategy, where P parameter is-0.03, D parameter is-0.005. By the strategy, transient response properties of engine and turbocharger were increased obviously. Besides, it can avoid the overshoot phenomenon of turbocharger speed.