Some effects of fuel autoignition quality and volatility in premixed compression ignition engines

Previous work has shown that it may be advantageous to use gasoline type fuels with long ignition delays compared to today's diesel fuels in compression ignition engines. In the present work we investigate if high volatility is also needed along with low cetane (high octane) to get more premixed combustion leading to low NO_x and smoke. A single-cylinder light-duty compression ignition engine is run on four fuels in the diesel boiling range and three fuels in the gasoline boiling range. The lowest cetane diesel boiling range fuel (DCN = 22) also has very high aromatic content (75%vol) but the engine can be run on this to give very low NO_x (< 0.4 g/kWh) and smoke (FSN < 0.1) e.g. at 4 bar and 10 bar IMEP at 2000 RPM like the gasoline fuels but unlike the diesel fuels with DCNs of 40 and 56. If the combustion phasing and delay are matched for any two fuels at a given operating condition, their emissions behaviour is also matched regardless of the differences in volatility and composition. However the same high aromatic, low cetane, diesel fuel can match different gasoline fuels depending on operating conditions - a result in line with previous understanding of autoignition quality from HCCI and knock studies.