Effect of fuel oxygen on the trade-offs between soot, NOx and combustion efficiency in premixed low-temperature diesel engine combustion

The effect of fuel oxygen on the trade-offs between soot, nitric oxides (NOx) and combustion efficiency in a premixed low-temperature combustion (LTC) mode using boost, single late injection and cooled exhaust gas recirculation (EGR) is investigated in a single cylinder diesel engine. NOx, carbon monoxide (CO) and hydrocarbon (HC) emissions are dominated by intake dilution level (EGR rate), and not affected by fuel oxygen. For fuels with 0% and 7% fuel oxygen, soot exhibits a maximum at moderate intake dilution. When high intake dilution is used to reduce soot, combustion efficiency drops, demonstrating a soot versus combustion efficiency trade-off. When fuel oxygen is increased to 15%, soot is very low (maximum filter smoke number (FSN) < 0.15) at all test EGR dilution levels. Thus, a defeat of the NOx versus soot trade-off is realized, and low NOx, low soot and high combustion efficiency are achieved at moderate intake dilution using fuel with 15% oxygen.