Combustion and particle number emissions of a direct injection spark ignition engine operating on ethanol/gasoline and n-butanol/gasoline blends with exhaust gas recirculation

The combustion and particle number (PN) emissions of a direct injection spark ignition engine (DISI) operating on ethanol/gasoline and n-butanol/gasoline blends with exhaust gas recirculation (EGR) were studied in this paper. Firstly, the effect of EGR and fuel evaporation on charge cooling was investigated. The results indicate that both the addition of EGR and alcohol show evident charge cooling effect. The 0-10% mass fraction burned (MFB) combustion duration increases with increasing EGR rate and increasing charge cooling ability of fuels. As the EGR rate is increased from 0% to 20%, the 10-90% MFB combustion duration is prolonged by 25.5-38.9% for alcohol/gasoline blends, and 64.1% for gasoline. As alcohol is introduced, the 10-90% MFB combustion duration decreases. The addition of ethanol or n-butanol improves the combustion stability. The anti-knock ability mainly depends on the octane number and charge cooling effect of fuels, as well as EGR. Either ethanol/gasoline blends or EGR is beneficial to improve the anti-knock ability. However, n-butanol/gasoline blends show degraded anti-knock ability. Combined with EGR, it is possible to overcome the negative effect of n-butanol on knock. Furthermore, the effects of EGR rate and alcohol content on PN emissions were investigated. It is found that the peak particle number concentration gradually decreases and its distribution shifts toward smaller size with increasing EGR rate. Similarly, the increasing alcohol content in the blends results in decreased peak particle number concentration and higher proportion of finer particles.