Simulation based investigation of achieving low temperature combustion with methanol in a direct injected compression ignition engine

Low temperature combustion concepts used in compression ignition engines have shown to be able to produce simultaneous reduction of oxides of nitrogen and soot as well as generating higher gross indicated efficiencies compared to conventional diesel combustion. This is achieved by a combination of premixing, dilution and optimization of combustion phasing. Low temperature combustion can be complemented by moving away from fossil fuels in order to reduce the net output of CO ₂ emissions. Alternative fuels are preferably liquid and of sufficient energy density. As such methanol is proposed as a viable option. This paper reports the results from a simulation based investigation on a heavy-duty multi-cylinder direct injection compression ignition engine with standard compression ratio. The engine was simulated using two different fuels: methanol and gasoline with an octane number of 70. The primary objective of the study was to find the optimal engine settings which maximized the brake efficiency for the engine. A secondary objective was to find the optimal injection strategy and combustion mode that would result if the brake efficiency was targeted. Comparing methanol with gasoline, the brake efficiency was on average 5.5% higher with methanol. This increase stemmed from a reduction of in-cylinder exhaust loss which was due to higher specific heats and favorable combustion phasing. Furthermore there was a significant difference in the optimal injection strategy comparing methanol and gasoline. Due to the higher octane number of methanol, all the fuel could be injected before the start of combustion. Consequently, an injection strategy typical for the low temperature combustion concept partially premixed combustion resulted. The injection strategy with gasoline, on the other hand, was similar to what is typically found in conventional diesel engines.