The Analysis Of Influencing Factors Of Transient Performance Of Diesel Engine Under Medium And High Load

As an important part of the internal combustion engine industry,diesel engines are widely used in heavy machinery such as trucks and military equipment.However,in the face of increasingly severe energy and environmental problems,research on energy-saving and emission reduction of internal combustion engines is particularly important.Moreover,the diesel engine is mostly operated in transient operation,the combustion and emission performance of the diesel engine will deteriorate under transient operation.In order to improve the deterioration of diesel engine under transient operation,this paper takes CA6 DL diesel engine as the prototype with high-pressure common rail,and builds the three-dimensional simulation model of diesel engine with STAR-CD commercial software.Aimed at the typical transient process that based on the constant speed of 1650r/min and the load linearly increases from 10% to 100% within 5s,50% load and 75% load(hereinafter referred to as B50,B75)are selected as simulated calculation conditions.Firstly study the effects of single factor adjustment of injection and intake parameters on the transient performance and the microscopic field in the cylinder of the diesel engine,and then develop the strategy of combining the injection and intake parameters to optimize the transient performance of the diesel engine.The research results are as follows:1.Under medium and high load,compared to the steady operation of the original machine,the fuel evaporation rate is lower under the transient operation,and the combustion phases of CA10,CA50,CA90 have lag to a certain degree,the oxygen drive energy and total drive energy are much lower than the steady state conditions.Eventually,the indicated thermal efficiency is reduced,the smoke emissions are deteriorated,and the NOx emissions are lower than the steady state conditions.By increasing fuel injection pressure,pre-injection timing and reducing initial gas temperature in the cylinder,the indicated thermal efficiency is increased and the SOOT emissions are reduced.Although increasing the temperature of the gas in the cylinder can increase the thermal atmosphere in the cylinder,the retardation period is shortened and the mixing quality of the mixture is decreased.Therefore,the retardation period is a core factor affecting the in-cylinder combustion and emission performance compared with the temperature.2.In the medium and high load,based on the original machine and under the same crank angle,as the load increases,the longer the SOOT generation island increases,the SOOT production increases,and the spike temperature of the equivalence ratio-temperature increases for the duration of T>2000K,so NOx emissions increase.The variation trend of the volume ratio of SOOT generation zone is similar to that of ?>2 volume ratio.It is considered that the amount of SOOT formation depends mainly on the amount of concentrated gas in the cylinder.The volume ratio of NOx formation zone is similar to that of high temperature zone,so the generation of NOx is mainly affected by temperature.In the medium and high load,the thermal atmosphere in the cylinder is high.At this time,when reduce the temperature of the cylinder gas,the effect of simultaneously reducing the equivalence ratio and the temperature in the cylinder can be achieved,thereby achieving the effect of simultaneously reducing SOOT and NOx emissions.3.When the single factor adjustment boundary condition reaches the limit,the multi-factor coupling adjustment can better improve the transient performance of the diesel engine,even exceeding the steady state value.Considering the compromise between SOOT and NOx emissions and the improvement of economy,the “160-9.5” strategy under B50 and the “160-7.5” strategy under B75 conditions are selected for the optimal coupling strategy of the injection pressure and injection time.Compared with the transient original machine,the cumulative SOOT rate is 21.5% and 32.9% of the original machine respectively;the NOx peak is increased by 15% and 10% respectively;the indicated thermal efficiency is increased by 3.2% and 3.5% respectively.On this basis,coupling the initial gas in the cylinder is continued to be studied,and the "160-9.5-665" strategy under the B50 operation and the "160-7.5-650" strategy under the B75 operation are finally determined as the optimal strategy.At this time,compared to the transient original machine,the cumulative SOOT rates were 13.0% and 30.2% of the original machine respectively;the NOx emission peaks increased by 11% and 4.8% respectively;the indicated thermal efficiency increased by 4.9% and 5.1% respectively.