Abstract
A clean premixed Diesel combustion strategy, called low temperature combustion (LTC), was able to achieve very low nitrogen oxide emissions (<35 ppm) through use of exhaust gas recirculation (12.1% inlet oxygen), and reduced particulate matter (PM) emissions (<0.05 FSN) through advanced fuel injection timing (-24°aTDC). When varying the injection timing by relatively small increments, large changes in PM mass and number emissions were measured within the premixed LTC regime. A discrepancy is investigated between expected reductions in PM emissions by simple fuel-air premixing and combustion temperature metrics, and actual PM emissions measurements when advancing the fuel injection timing earlier than -24°aTDC. For these earlier injection timings, particle numbers were seen to increase in two distinct particle size modes, whereas only one particle size mode existed at the minimum PM emissions -24°aTDC injection timing. Additional parameters from a 1D free fuel spray model were used to suggest new information that could explain the cause of these unexpected increases in PM. Using 0D and 1D calculations, the engine-out particle size and number emissions are analyzed to better understand their sensitivity to changes in the fuel injection timing within the early injection timing LTC regime. © 2011 Elsevier Ltd. All rights reserved.
