Towards identifying flame patterns in multiple, late injection schemes on a single cylinder optical diesel engine

Abstract

The work investigates the effect of various post-injection strategies on the flame patterns in a Ricardo Hydra optical single cylinder light duty diesel engine, operated in a partially premixed combustion mode (PPC), under low load (IMEP: ca. 2.3 bar) low speed (1200 rpm) conditions. The effect of postinjection fuel amount (12 and 24% of the total fuel quantity per cycle) and post-injection timing (0, 5, 10 deg aTDC) are investigated via pressure trace analysis and optical measurements. Flame propagation is captured by means of high speed flame natural luminosity imaging and of CH* , C2 * and OH* line-of-sight chemiluminescence measurements. Results indicate that post-injections suppress mixture reactivity but enhances oxidation, and that a larger amount of fuel and/or later post injection, leads to higher levels of natural luminosity, indicating possible higher soot-out emissions, while post injection close to the main combustion event appears to have a beneficial effect on the soot oxidation processes.