Engine performance and octane on demand studies of a dual fuel spark ignition engine with ethanol/gasoline surrogates as fuel

For gasoline preparation, it is necessary to control the fuel's octane number, which often affects production costs. Ethanol is widely used as gasoline alternative fuel with high octane number. In this paper, based on a modified dual fuel spark ignition engine, studies of port injection of ethanol and direct injection of gasoline surrogates (toluene reference fuel) were conducted. The results revealed that when direct injection of toluene reference fuel with research octane number of 90, with the increase of ethanol injection ratio, the flame development duration and rapid combustion duration were prolonged (about 2 degrees CA and 3 degrees CA, respectively). Meanwhile, nitrogen oxide emissions, total hydrocarbon emissions, ethane, isopentane, cyclohexane, olefins and aromatics gradually decreased. For direct injection of fuels with different research octane number and port injection ratio of ethanol fixed at 21%, even when the research octane number of gasoline surrogates was as low as 75, the combustion history and engine efficiency were close to those of fuel with research octane number of 95. In particular, the indicated thermal efficiency of dual fuel spark ignition mode with direct injection of fuel with research octane number of 75 combined with 35% ethanol ratio was similar to that of direct injected spark ignition mode fueled with research octane number of 95 under respective knock limited spark timings.