直喷汽油机恒转速增转矩工况燃烧与排放

Combustion and Emissions of Direct Injection Gasoline Engine in Constant-speed and Increasing-torque Conditions

摘要:

在一台直喷汽油机（GDI）上，利用发动机瞬态控制和测试系统，研究恒转速增转矩工况下节气门切换幅度和切换耗时对发动机燃烧与排放动态响应的影响，并通过基于比例积分（PI）调节的过量空气系数（λ）闭环控制和节气门超调策略优化瞬态工况的燃烧和排放.试验结果表明：在恒转速增转矩工况，发动机工作参数相对于节气门的变化有一定的滞后，切换时间越长各参数与节气门变化的跟随性越好；切换幅度较大时，各参数稳定性较差；进气的响应特性是影响发动机瞬态工况下燃烧与排放的主要因素.在所研究的工况下，过量空气系数闭环控制的最优PI(比例值、积分值)组合为P=0.08/I=0.5；进气门超调策略可以更有效地减小进气响应的滞后时间，使燃烧更充分，降低颗粒物数量浓度和碳氢（HC）排放.

Abstract:

The combustion and emissions of a gasoline direct injection (GDI) engine were studied during constant-speed and increasing-torque conditions by transient engine control and measuring system. The effects of transient throttle switching duration and amplitude were investigated. The close-loop λ proportion and integral(PI) control for fuel injection strategy and the throttle overshoot strategy were tried to show their potentials to improve the transient combustion and emissions. The results revealed there were different degrees of time lags for engine working parameters compared with throttle opening, and the longer switching duration would shorten the lags. The stabilities of the working parameters became worse when the switching amplitude was larger. The response characteristic of intake air was thought to be the major factor that affected the transient combustion and emissions. In this paper, the combination of P=0.08/I=0.5 was the best to shorten the time lag with throttle opening and reduce the particulate number and hydrocarbon (HC) emissions. Compared with PI optimization strategy, the throttle overshoot strategy could be more efficient to shorten the intake response delay, making more fully combustion and reducing particulate number and HC emissions in the transient conditions.