Optimizing gasoline compression ignition engine performance and emissions: Combined effects of exhaust gas recirculation and fuel octane number

Abstract Gasoline compression ignition (GCI) is a highly feasible way to obtain high efficiency and low emissions simultaneously without many modifications of standard diesel engines. Exhaust gas recirculation (EGR) is an indispensable technology to achieve high efficiency and low emissions. A series of experimental studies were carried out to investigate the co-effect of EGR and fuel octane number on GCI combustion and emissions under all loads. Four primary reference fuels (PRF) with the research octane number of 90, 80, 70 and 60 were applied in this paper, which were denoted as PRF90, PRF80, PRF70 and PRF60. The results showed that high efficiency and low NO x emissions could be obtained under all loads by adjusting fuel octane number and EGR rate. PRF70 obtained the indicated thermal efficiency of above 47% by using the EGR rate of 30% and 40% under 6 bar and 8 bar, respectively. The increase in the EGR rate could decrease the oxygen content, thus reducing the NO x emissions. The EGR rate of 30% under 4–6 bar and the EGR rate of 40% under 8–12 bar could reduce the NO x emissions to below 300 ppm and 500 ppm, respectively. The effect of EGR on particle emissions was different under different loads. The increasing EGR rate reduced the particle emissions under low and medium loads, but increased the particle emissions under high loads due to the low volumetric efficiency. In addition, PRF90 with lower reactivity produced more methane, isopentane and aldehyde emissions than other fuels.