Effect of Fuel Ignitability on the Stable Operating Range of Premixed Diesel Combustion

Abstract

The effects of fuel ignitability on the stable operating range of premixed low temperature diesel combustion (LTC) were investigated. With the intake oxygen concentration set at 14% and the injection timing at 30 °CA BTDC, the operating load range is almost unchanged for fuels with cetane number above 40; while with cetane number below 40 both the high and low load limits increase significantly with decreasing cetane numbers, the low load limit increases more steeply, resulting in a narrowing of the load range. When keeping the combustion phasing constant at TDC by controlling the injection timing, smoke emission limits at the higher load operation for high ignitability fuels and abrupt combustion for low ignitability fuels become problems, but a decrease in the intake oxygen concentration is effective to expand the high load limit. The low load limit can be expanded with the combustion phasing held constant at TDC, and it can be further expanded when increasing the intake oxygen concentration, at the expense of increases in NOx emissions however. Finally, the effects of fuel ignitability on the range of injection timings for stable LTC operation are also examined.