Optimization Research Of Combustion And Emission Of Vehicle Diesel Engine With Multi-strategy Synergy

Vehicle diesel engines have the advantages of high thermal efficiency and high power,but the emission of pollutants has attracted the attention of the entire industry as relevant regulations become more and more stringent.In order to solve the problem of excessive pollutant emissions,many new emission reduction technologies are used in the field of diesel engines.Based on CFD with CONVERGE software,numerical simulation is carried on for a vehicle diesel engine.The research involves the selection of air passage type,intake air humidification,fuel injection advance angle,fuel injection pressure,Miller cycle and the above strategies.Studies have shown that the combined port is better than the straight port in improving the combustion in cylinder,and the maximum reduction of NOx emissions in the cylinder with the combined port intake humidification is 85.09%,which is better than the maximum reduction of 70.66% with straight port.The airway soot emission increases with the increase of humidification degree,and the combined airway soot emission is higher than that of the straight airway.Increasing the fuel injection advance angle and fuel injection pressure can increase the peak temperature and peak pressure in the cylinder.Under the two strategies,the indicated fuel consumption rate ISFC is reduced by 7.38% and 10.9% respectively compared with the original.But the NOx emissions increase as the fuel injection advance angle increases,and the SOOT emissions increases first and then decreases.As the fuel injection pressure increases,the SOOT emission gradually decreases.In this paper,in order to study the influence of Miller cycle on the combustion and emission of vehicle diesel engine,four early closing schemes and two late closing schemes are designed.With the increase of Miller degree,there is a trend of first decrease and then increase.Under the 10°CA scheme of late intake valve closing,the oil and gas mixing state is the best,and the late intake valve closing helps to improve the fuel consumption level of the engine.Based on the above strategies,taking NOx,SOOT emission and fuel economy as the evaluation indicators,the best optimization scheme is obtained: combined air passage,the water mass fraction in the intake air is 5.2%,the injection pressure is 1900 bar,and the injection advance angle is 12 °CA,the closing time of the intake valve is delayed by 20°CA compared with the original machine,this scheme keeps the emission at a lower level and can avoid the deterioration of fuel consumption.