Extension of the Lower Load Limit of Gasoline Compression Ignition with 87 AKI Gasoline by Injection Timing and Pressure

Previous work has demonstrated the capabilities of gasoline compression ignition to achieve engine loads as high as 19.5 bar BMEP with a production multi-cylinder diesel engine using gasoline with an anti-knock index (AKI) of 87. In the current study, the low load limit of the engine was investigated using the same engine hardware configurations and 87 AKI fuel that was used to achieve 19.5 bar BMEP. Single injection, “minimum fueling” style injection timing and injection pressure sweeps (where fuel injection quantity was reduced at each engine operating condition until the coefficient of variance of indicated mean effective pressure rose to 3%) found that the 87 AKI test fuel could run under stable combustion conditions down to a load of 1.5 bar BMEP at an injection timing of −30 degrees after top dead center (°aTDC) with reduced injection pressure, but still without the use of intake air heating or uncooled EGR. A 0.4% concentration (by volume) of 2-Ethylhexyl Nitrate (EHN) was added to the 87 AKI test fuel to test the effects of increased reactivity on the minimum load attainable and injection timing at which it would occur, while maintaining similar physical mixing properties. The results showed that a 0.4% EHN addition caused the minimum attainable load to be reduced to 1.3 bar BMEP at a slightly delayed injection timing of −24 °aTDC. Effects of the minimum load level, injection timing, injection pressure, and fuel reactivity on auto-ignition, combustion phasing, specific fuel consumption, and gaseous emissions are also discussed.