Knock characteristics of SI engine fueled with n-butanol in combination with different EGR rate

Knock is one of the main obstacles for optimizing combustion process of SI engines fueled with alternative biomass fuel n-butanol. In this paper, knock characteristic of SI engine fueled with n-butanol and RON 92 gasoline is studied on a single cylinder SI engine. The onset timing, intensity and frequency of knock for these two fuels at different EGR rate are compared. Additionally, the effects of different compression ratios and intake pressures on knock intensity of SI engine are also studied and results are presented. The study results show that EGR can decrease knock intensity and delay knock onset timing due to its cooling and dilution effects. It is observed under a low EGR rate of 3%, knock intensity of n-butanol is significantly reduced whereas combustion pressure has negligible change. The probability distribution of n-butanol knock intensity is more concentrated compared with that of gasoline under a given EGR rate, which indicated n-butanol had smaller combustion variations. The application of EGR on high intake pressure and high compression ratio n-butanol engine can effectively suppression knock combustion.