Optimization Of Combustion Process For Diesel Engines Of Non-Road Mobile Machinery

With the continuous strengthening of China’s infrastructure construction and the acceleration of the urbanization process,the use of diesel engines for non-road mobile machinery continues to increase.Compared with road diesel engines,non-road mobile machinery diesel engines are relatively backward,and the resulting pollutant emissions have a huge impact.Therefore,pollution prevention and emission reduction for diesel engines for non-road mobile machinery are urgently needed.In this paper,an optimization study on a diesel engine combustion system for R4105ZD non-road mobile machinery is carried out.The original machine uses an electronically controlled unit pump fuel system.The bench test results show that the emission results can meet the requirements of the third-stage regulations when no post-treatment system is installed,but cannot meet the requirements of the non-road fourth-stage emissions regulations.A simulation model of the diesel engine combustion system was established based on CONVERGE software,and the validity of the model was verified based on the cylinder pressure and pressure increase rate curves.Using the verified simulation model and numerical simulation,the influencing factors of the in-cylinder combustion process were optimized,and the effects of key structural parameters,fuel injection parameters,and intake system parameters on the performance and emission characteristics of the diesel engine were investigated,And then provide guidance for parameter matching of diesel engine combustion system for non-road mobile machinery.The simulation analysis results of the structural parameters of the combustion chamber show that when the penetration distance of the oil beam is small,as the diameter-to-depth ratio increases,the squeezing and reverse squeezing in-cylinder intensity in the compression process decreases,the combustion rate decreases,and the Soot generation increases;when the oil When the beam penetration distance is large,the influence of the diameter-depth ratio on the combustion process and emission characteristics is inversely regular.As the height of the central boss of the combustion chamber is reduced,the oil beam can more easily reach the center of the combustion chamber,so that the air utilization rate in the combustion chamber is improved,the Soot generation amount is reduced,and the NOx generation amount is increased.The sensitivity of the combustion process and emission characteristics to the diameter-to-depth ratio,the indentation inclination angle,the pit radius,and the height of the boss sequentially decrease.The analysis results of the injection parameters show that:the injection time is advanced,the injection pressure is increased and the injection hole diameter is reduced,which increases the premixed combustion amount in the cylinder,the peak instantaneous heat release rate increases,the combustion center of gravity moves forward,and the cylinder The maximum combustion temperature is increased,Soot emissions are reduced,and NOx emissions are increased,but the reasons for the decrease in Soot are slightly different.The fuel injection is in advance to improve the Soot oxidation rate,and the injection pressure is increased and the diameter of the injection hole is reduced to improve oil and gas mixing.quality.Increasing or decreasing the optimal matching relationship between the injector’s detection distance and injection angle and the combustion chamber structure will lead to the deterioration of the quality of the mixed gas in the cylinder,thus leading to an increase in Soot emissions.The simulation results of the influence of the intake air parameters on the engine performance and emission characteristics show that under the same intake air volume,the intake air swirl ratio increases,which promotes the acceleration of the oil-gas mixing rate and the combustion rate,advances the combustion center of gravity,and shortens the combustion duration.Increasing the intake swirl ratio improves the uniformity of the mixture and reduces carbon emissions,but results in increased NOx emissions.The simulation results of the effect of EGR rate on engine performance and emission characteristics show that as the EGR rate increases,the in-cylinder combustion temperature decreases,the combustion rate slows,the combustion center of gravity shifts backward,the combustion duration extends,and the peak instantaneous heat release rate decreases.The amount of production increases and the amount of NOx production decreases.The simulation results of the influence of the intake air temperature on the engine performance and emission characteristics show that:the intake air temperature is lowered,the actual intake air volume in the cylinder increases at the same intake pressure,which is beneficial to reduce the mixture concentration and reduce the in-cylinder Soot generation,and The amount of NOx generated decreases due to the decrease in combustion temperature.