Study on combustion characteristics of a methanol-diesel dual-fuel compression ignition engine

There is an increasing interest in applying methanol to diesel engines so as to achieve fuel diversity and reduce engine emissions. Dual-fuel application is the most promising method, but its combustion characteristics have been less extensively studied. In this paper, with the measured cylinder pressures of the engine operated on pure diesel and on dual fuel (methanol-diesel), the engine combustion characteristics are investigated. The increase in methanol mass fraction lowers the polytropic index of compression and the temperatures at BDC and TDC, as well as the oxygen concentration in the mixture. This prolongs the ignition delay under the same engine load and speed condition by comparison with diesel operation. The combustion heat release rate changes from dual-peak mode to single-peak mode. The centre of the heat release rate curve moves near to TDC under high load conditions, which indicates a better fuel economy. The high methanol mass fraction will realize a simultaneous reduction in both smoke and NOx, under all the operating conditions. Meanwhile, the NOx smoke trade-off curve disappears in combustion of the dual fuel, but CO and HC increase.