Impact of dissociated methanol gas direct injection strategy on performance of port-injection methanol engines under dilution combustion condition

Methanol is the most promising carbon-neutral alternative fuel for the future. This paper studies the impact of DMG (dissociated methanol gas) double injection parameters in a methanol port injection engine to enhance the improvement of DMG on methanol dilution combustion performance. Additionally, it seeks to understand the optimization results of DMG direct double injection parameters for combustion performance at different DMG blending ratios. Optimizing DMG double injection parameters can effectively shorten CA10-IG (crank angle corresponding of 0 %–10 % heat release) and CA90-CA10 (crank angle corresponding of 10 %–90 % heat release), and reduce HC (hydrocarbons) and CO (carbon monoxide) emissions, BSFC (brake specific fuel consumption) and COVIMEP (coefficient of variation of indicated mean effective pressure), while slightly rising NOx (nitrogen oxides) emissions. As DMG blending ratio rises, optimization results of first and second injection timings remain constant, while second injection ratio decreases, reaching 40 %, 20 %, and 20 % at blending ratios of 10 %, 15 %, and 20 %. Moreover, DMG double injection extends the dilution combustion limit compared to single injection. At blending ratios of 10 %, 15 %, and 20 %, double injection reduces BSFC by 2.8 %, 1.4 %, and 1.2 % at the dilution combustion limit compared to single injection.