低压EGR对GDI增压汽油机外特性下性能和排放影响

通过一款涡轮增压汽油直喷(gasoline direct injection,GDI)发动机低压废气再循环(exhaust gas recirculation,EGR)的试验,研究了EGR率和点火提前角的综合作用对增压GDI发动机的燃烧、缸压、排放和油耗等方面的影响。结果表明,在GDI增压发动机中加入EGR后,由于废气的稀释和热容作用,使缸内燃烧持续期增大,排气温度下降,燃烧相位也发生了改变。这对发动机外特性的有利影响是油耗减少,CO和NO_x排放也明显减少;不利影响是EGR的加入提高了增压发动机的排气压力,导致泵气损失增加。此外,总碳氢(total hydro carbons,THC)排放也有所增加。在GDI增压汽油机中使用EGR系统并配合点火角的调节能够有效提高热效率,降低NO_x排放。

Effect of LP EGRon Performance and Emissions of a Turbocharged GDI Engine at Full Load

The effect of low pressure EGR(Exhaust gas recirculation) and ignition timing on performance and emissions of a turbocharged GDI engine at full load was investigated experimentally, including in-cylinder pressure, emissions and fuel economy changed with rate of EGR. Results show that the use of EGR leads to an increase in combustion duration, a decrease in exhaust gas temperature and a change in combustion phase due to the EGR dilution effect. The positive effect is the decrease in fuel consumption and emissions of CO and NOx. The negative influence is the increase of THC emission and the exhaust pressure, resulting in an increase in pump losses. Hence a turbocharged GDI engine using EGR system and with ignition angle adjustment can improbe thermal efficiency and reduce NOx emissions.