Experimental characterization of ethanol controlled auto-ignition in a single-cylinder research engine

This article reports an experimental analysis of combustion, fuel consumption and pollutant emissions parameters in a single-cylinder research engine operating on spark-ignition (SI) and controlled auto-ignition (CAI), fueled with ethanol. A methodology was developed and comprehensively described to allow the engine, originally designed for SI, to reliably and repeatedly transition to CAI, at a 14.2:1 compression ratio. Initially, spark-assisted compression ignition (SACI) was achieved at 4.0 bar IMEP, 1900 rpm, λ = 2.02, demonstrating a 4.34 % higher indicated fuel conversion efficiency than spark ignition at the same operating point. Homogeneous charge compression ignition (HCCI) was attained at two loads (3.0 and 3.5 bar IMEP) and two speeds (1900 and 2500 rpm), with an intake air temperature of around 270 °C. The advanced combustion mode resulted in higher in-cylinder pressure rise rates and heat release rates. It also demonstrated a significant 21.93 % decrease in indicated specific ethanol consumption, an 80 % reduction in combustion duration, lowered exhaust levels of CO and CO 2 , and almost negligible NO X emissions. Thus, this research showcases the significantly enhanced efficiency of the HCCI engine at low loads when compared to conventional spark ignition, leading to a strong foundation for the adoption of advanced combustion modes and biofuels.