Study On Combustion Characteristics Of Coal To Liquid/Dimethyl Carbonate

The China’s oil dependence on foreign countries has already exceeded70%.For national energy security,the search of alternative oil clean fuel is one of the main directions of automobile engine technology research.China’s coal-to-oil industry has a large scale and output,but the problems of too high chemical methane value and poor combustion efficiency of coal-to-oil oil need to be solved urgently.The dimethyl carbonate has low value and high oxygen content,which has the potential to improve engine combustion performance as an additive.Therefore,the influence of the dimethyl carbonate on the coal to oil/mixed combustion engine.The test was conducted on a 4-cylinder high-pressure common-rail engine.Under different loads(20%～70%),the effects of dimethyl carbonate blending ratio(0%～30%),the injection advance angle(0~oCA～30~oCA)and pre-injection rate(0%～30%)on engine combustion and emission were studied.The main conclusions are as follows:(1)With the increase of load,the engine cylinder pressure and peak release rate rise,and the release rate curve gradually shows bimodal distribution.When the proportion of dimethyl carbonate is more than 20%,the peak pressure in the engine cylinder is lower than that of pure coal and MT10due to its high vaporization latent heat.At the fixed oil injection time,with the increase of load,the CA50 combustion phase is gradually delayed,and the effective thermal efficiency increases.When dimethyl carbonate is added,the effective thermal efficiency is further improved.Increasing the mixing ratio of dimethyl carbonate can effectively reduce CO,THC and sweet emissions,while greatly reducing the total particle concentration of the engine.(2)With the increase of the pre-injection rate,the peak pressure increases,the peak pre-injection release rate increases,the peak main spray release rate decreases,and the CA50 is advanced.The peak cylinder pressure of MT30 is the largest,which is because the addition of high proportion of dimethyl carbonate increases the latent heat of the mixed fuel,extends the flame lag period,and increases the proportion of premixed combustion,so the burst pressure is higher.Increasing the pre-injection rate and coupling the high proportion of dimethyl carbonate,the engine can obtain higher effective thermal efficiency,lower CO,THC emission and total particle number concentration.The engine has the lowest total particle number concentration of dimethyl carbonate with 30%addition rate and 20%pre-injection rate.(3)Increasing the injection advance angle,the peak pressure in the cylinder and the main injection discharge rate of the engine rise,but the peak value of pre-injection release rate shows a trend of rising first,and then decreasing.Appropriate increase in the ratio of the injection advance angle and dimethyl carbonate can further improve the effective thermal efficiency of the engine and reduce CO,THC,Soot and total particle emissions.When the injection advance angle is 5～10°CA and,the mixing ratio of the lowest THC emission is 5～15%.