Study On The Characteristics Of Dissociated Methanol Gas/diesel Engine

Methanol is a clean alternative fuel with great potential.In the application of methanol fuel,it is a feasible,reliable and practical method to obtain dissociated methanol gas by catalytic dissociation of methanol using waste heat from engine exhaust.H₂ contained in dissociated methanol gas is conducive to clean and efficient combustion of the engine.At present,most researches focus on the application of dissociated methanol gas in SI engine,but there are few researches on the application of dissociated methanol gas in compressed-ignition engine.Therefore,a diesel engine is taken as the research object in this paper to carry out the numerical simulation study on the characteristics of the diesel engine fueled with dissociated methanol gas.The three-dimensional combustion model of diesel engine was established,where the detailed chemical reaction mechanism was applied.On this basis,the effects of dissociated methanol gas on the combustion and emission characteristics of diesel engines under different methanol substitution ratios were studied.The results show that compared with the original engine,the engine cylinder pressure increases and the temperature rises after the addition of dissociated methanol gas.High temperature region has also been broaden due to dissociated methanol gas.Engine power and economic performance increase.Soot and CO emissions decreased significantly.NO emission increases with the increase of methanol substitution ratio,and HC emission decreases when methanol substitution ratio exceeds10%.The engine characteristics under different initial pressure,initial temperature,injection timing and EGR rate were studied.The results show that when the initial pressure increases,the peak cylinder pressure increases,the peak temperature decreases slightly,and the engine power and economic performance increase.Soot,CO and HC emissions all decreased to varying degrees,while NO emissions increased slightly.When the initial temperature increases,the peak pressure and temperature level in the cylinder increase,but the excess air coefficient in the cylinder decreases,and the engine power and economy also decrease.Soot,NO,CO and HC emissions all increased.When the injection time is delayed,the peak pressure and temperature level in the engine cylinder both drop,the effect of fuel and air mixture in the cylinder becomes worse,the engine power and economy both drop.Soot,CO and HC emissions all rise,and NO emissions fall.When EGR is adopted,the peak pressure and temperature level in the cylinder both decrease.Soot,CO and HC emissions all increase,and NO emissions significantly decrease.However,excessive EGR rate will significantly reduce the engine's power performance and economy.The comparison between the dissociated methanol gas/diesel engine and the original engine shows that the dissociated methanol gas/diesel engine can achieve better comprehensive performance in terms of power performance,economy and main pollutant emission by adopting the EGR rate of about 5%-6%.