Simulation Research On The Effect Of Multiple Stage Injections On Diesel Engine Fueled With B20 Biodiesel

In the face of severe environmental pollution and energy crisis,biodiesel is regarded as an alternative fuel with good development prospects for its excellent properties and renewability.In this paper,petrochemical diesel blend with 20%biodiesel(B20)was used to study the effects of multiple-stage injection and variable intake timing on engine performance.Engine performance when fueled with 100%petrochemical diesel(B0)was taken as an reference.Based on the 4JB1 diesel engine,operating parameters of the engine was not changed except for the fuel type.When fueled with B20 and B0,the power and emission properties under external characteristic was compared and analyzed.According to the characteristic that NO_x emission was higher when fueled with B20,this paper took 1800r/minfull load as the operating condition when fueled with B0 and B20 separately and adopt three different injection strategies:single-stage injection,pilot-main injection and main-post injection.The effects of main injection timing,pilot injection quantity,pilot injection timing,post injection quantity and post injection timing was investigated.Based on this,pilot-main-post injection strategy was used and appropriate injection parameters was selected to improve the trade-off relation betweenNO_x and soot emission.According to the fact thatNO_x emission from engine fueled with B20 under multiple-stage injection was still higher than original engine,this paper tried to solve the problem through early intake valve closure.The results show that:(1)Under single-stage injection strategy,NO_x emission can be reduced by properly reducing the fuel injection advanve angle.(2)Using pilot-main injection strategy can reducedNO_x emission.NO_x emission decrease at first and then increase as the delay of pilot injection timing and as the increase of the pilot injection quantity.There exist the optimum pilot injection timing and pilot injection quantity which can prevent torque and brake specific fuel consmption(BSFC)of the engine from major deterioration and at the same time,NO_x emission can be the lowest but soot emssion increased.(3)Using main-post injection strategy can reduced soot emission.Soot emission decrease at first and then remain unchanged as the delay of post injection timing.With the increase of post injection quantity,soot emission decrease butNO_x emission increase.It is necessary to consider the compromise relationship of engine performances to select the post injection parameters.(4)Considering comprehensive performances of the engine under pilot-main-post injection strategy,the optimal pilot injection timing is 25~?CAbefore main injection and the optimal pilot injection quantity is 2mg.The optimal post injection timing is35~?CAafter main injection and the optimal post injection quantity is 2mg.Using the above injection parameters,the emission ofNO_x and soot is lower when compared to those from single-stage injection.However,when using multiple-stage injection and fueled with B20,theNO_x emission is still higher than that of the original engine fueled with B0.(5)Under single-stage injection strategy,theNO_x emission increase at first and then decrease with the delay of intake valve closure timing,and soot emission decrease at first and then increase with the delay of intake valve closure timing.The relationships between intake valve closure timing,NO_x emission and soot emission under multiple-stage injection are similar to those of single-stage injection,but the emission values are different.(6)Using multiple stage injection strategy and couple with varaible intake timing when fueled with B20,NO_x emission of the engine is 3.74%lower than that of the original engine fueled with B0,and soot emission is 11.26%lower than that of the original engine fueled with B0.