Effects of I-EGR and Pre-Injection on Performance of Gasoline Compression Ignition (GCI) at Low-Load Condition

Abstract

Gasoline compression ignition (GCI) has been considered as a promising combustion concept to yield ultra-low NO_X and soot emissions while maintaining high thermal efficiency. However, how to improve the low-load performance becomes an urgent issue to be solved. In this paper, a GCI engine model was built to investigate the effects of internal EGR (i-EGR) and pre-injection on in-cylinder temperature, spatial concentration of mixture and OH radical, combustion and emission characteristics, and the control strategy for improving the combustion performance was further explored. The results showed an obvious expansion of the zone with an equivalence ratio between 0.8~1.2 is realized by higher pre-injection ratios, and the s decreases with the increase of pre-injection ratio, but increases with the increase of i-EGR ratio. The high overlap among the equivalent mixture zone, the high-temperature zone, and the OH radical-rich zone can be achieved by higher i-EGR ratio coupled with higher pre-injection ratio. By increasing the pre-injection ratio, the combustion efficiency increases first and then decreases, also achieves the peak value with a pre-injection ratio of 60% and is unaffected by i-EGR. The emissions of CO, HC, NO_X, and soot can also be reduced to low levels by the combination of higher i-EGR ratios and a pre-injection ratio of 60%.