Simulation Study On Performance Of Low Temperature Combustion In Diesel Engine Fueled With Biodiesel

In order to solve the problem of energy shortage and meet increasingly stringent emission regulations,it is quite urgent to develop alternative clean fuels for internal combustion engines and strictly control pollutants from internal combustion engines.As a renewable energy with many advantages,biodiesel has been widely studied and applied in the world in recent years.However,there are still some problems such as high NO_x emission when biodiesel is used in diesel engines.As a new combustion mode,low temperature combustion is capable of reducing both NO_x and soot emissions,now it has become one of the research focuses in the field of internal combustion engines.Therefore,when biodiesel is used in diesel engine,higher NO_x emission can be reduced by converting combustion mode into low temperature combustion.In this paper,4JB1 turbocharged diesel engine is taken as the research object.Firstly,performance of diesel engine fueled with diesel and biodiesel were compared in order to provide theoretical basis for low temperature combustion of diesel engine fueled with biodiesel.It was found that the diesel engine fueled with biodiesel produced higher NO_x emission.In order to reduce NO_x emission,the combustion mode needs to be changed to low temperature combustion.Based on the fact that low temperature combustion usually requires a higher EGR rate and is subject to load limitations,so the effects of EGR on diesel and biodiesel under low-load conditions were studied in this paper.Based on the results of EGR and the characteristics of 4JB1 diesel engine,the timing and pressure of fuel injection were selected as auxiliary means to realize low temperature combustion.Finally,the low temperature combustion of biodiesel was realized by three means.The results show that:(1)When the diesel engine burned the same amount of biodiesel and diesel,the output torque of biodiesel was lower than that of diesel.Under the same working condition,the brake specific fuel consumption and NO_x emission of biodiesel were higher than that of diesel,but the emissions of soot,CO and HC were lower.(2)The use of EGR can reduce the NO_x emission of biodiesel,but the deterioration effect of EGR on soot,HC and CO emissions was greater than the optimization effect of biodiesel.At the maximum EGR rate at low load,the brake specific fuel consumption of biodiesel was lower than that of diesel engine.(3)Late injection timing can also reduce the NO_x and soot emissions of biodiesel,but excessive delaying fuel injection further deteriorated the lower economy of biodiesel and increased CO and HC emissions.At this time,the optimization effect of biodiesel on CO and HC emissions was not strong.(4)Under the synthetic action of low EGR rate and late injection timing,NO_x and soot emissions were reduced by 54.36%and1.36%respectively compared with diesel engine,which shows that the low temperature combustion of biodiesel was realized.And the brake specific fuel consumption was reduced by 0.08%compared with the original engine at this time,but CO and HC emissions were seriously deteriorated.(5)Simply increasing injection pressure can reduce soot,CO and HC emissions,and slightly improve the economy of biodiesel.The increase of NO_x emission of biodiesel compared with diesel was smaller under higher injection pressure,but the NO_x emission of biodiesel was still higher than that of diesel.(6)Under the synthetic action of low EGR rate and high injection pressure,NO_x and soot emissions were reduced by 8.57%and 9.98%respectively compared with diesel engine,which shows that the low temperature combustion of biodiesel was realized.But the brake specific fuel consumption,CO and HC emissions increased slightly.