An experimental study on the influence of EGR rate and fuel octane number on the combustion characteristics of a CAI two-stroke cycle engine

Having the higher power-to-weight ratio feature of two-stroke cycle engines and higher thermodynamic efficiency of controlled auto-ignition (CAI) combustion proposes a promising concept for future internal combustion engines. The control of start of auto-ignition (CA10) and its cyclic variation are major issues that should be addressed. The research to date has tended to focus on the influence of internal EGR (In-EGR) utilization on the combustion characteristics of CAI two-stroke cycle engine rather than external EGR (Ex-EGR) utilization. This experimental study aims to investigate the influence of Ex-EGR incorporated with In-EGR utilization on the combustion characteristics and the cyclic variability of a single-cylinder CAI two-stroke cycle engine using different fuel octane number (ON). Engine's combustion-related parameters were examined statistically associated with Coefficient of Variation (COV) and Standard Deviation (STD). It is perceived that the significant CAI combustion parameters, including HRRmax, θHRRmax, LTHR, θLTHR, CA10, CA50, MFB and TCA10 are strongly correlated to variation of In/Ex-EGR and fuel ON and they suggest an effective means to control CAI combustion phasing and cyclic variability. Furthermore, CA10 and its cyclic variability exhibited that are more sensitive to altering Ex-EGR compared to altering In-EGR.