An optical diagnostics investigation on the effect of pilot injection dwell time and injection pressure on combustion characteristics and soot emissions in a single-cylinder optical diesel engine

The present work investigates the effect of the injection dwell time and injection pressure on soot reduction potential in an optical single-cylinder light-duty diesel engine. The engine operated under a double-injection scheme under low load and low engine speed conditions. The conducted experiments considered two different dwell times for three different injection pressures. The fuel quantity of the main injection was adjusted to maintain the same indicated mean effective pressure (IMEP) value among all cases considered. Findings were analyzed via means of pressure trace and apparent heat release rate (AHRR) analyses, as well as a series of optical diagnostics techniques, namely high-speed imaging and planar laser-induced incandescence (pLII). The combination of dwell time and injection pressure substantially affects charge reactivity and soot oxidation potential. The analysis suggests that a shorter dwell time combined with a higher injection pressure can lead to an enhanced potential for engine-out particulate reduction by creating an in-cylinder environment that promotes soot oxidation. Overall, results indicate that a close-coupled pilot and main injection scheme can reduce soot levels, albeit while increasing specific fuel consumption by up to 12% to maintain the same engine power output levels