Early Pilot Injection Strategies for Reactivity Control in Diesel-ethanol Dual Fuel Combustion

This paper examines the diesel-ethanol dual fuel combustion at medium engine loads on a single-cylinder research diesel engine with a compression ratio of 16.5:1. The effect of exhaust gas recirculation (EGR) and ethanol energy ratio was investigated for the dual fuel combustion to achieve simultaneously ultra-low NOx and soot emissions. A medium ethanol ratio of about 0.6 was found suitable to meet the requirements for mixing enhancement and ignition control, which resulted in the lowest NOx and soot emissions among the tested ethanol ratios. A double-pilot injection strategy was found competent to lower the pressure rise rate owing to the reduced fuel quantity in the close-to-TDC injection. The advancement of pilot injection timing tended to reduce the CO and THC emissions, which is deemed beneficial for high EGR operations. The reactivity mutual-modulation between the diesel pilot and the background ethanol mixture was identified. The experiments confirmed that the background ethanol mixture could delay the ignition of the diesel pilot. The background ethanol can suppress the low-temperature heat release of the diesel pilot. With the close-to-TDC pilot as a reliable ignition source, the combustion phasing was controlled by the reactivity modulation of the cylinder charge through coordinated adjustment of the fuel quantity of the early injection diesel pilot and the port injection ethanol.