Research On The Optimization Of Zonal Combustion System With Spray Impingement Of Diesel Engine

Facing the huge pressure of energy shortage and environmental pollution,the emission regulations of non-road diesel engines are increasingly stringent.It is urgent to optimize and upgrade non-road diesel engines with lower cost and simpler technologies to meet tougher emission requirements.The reasonable matching of the diesel engine combustion system among fuel?fuel injection system?,air?air motion?,chamber?combustion chamber?has an important impact on the combustion process.The optimization of the diesel engine combustion chamber is sought to seek a rational organization between fuel and air.On the one hand,it can increase utilization of air.On the other hand,it can improve the spray distribution and atomization in the combustion chamber and promote the rapid mixing of fuel and air simultaneously,which improves the quality of the mixture in the cylinder.Taking the aspects above into account,the non-road diesel engines can achieve efficient and clean combustion.Therefore,the non-road diesel engine combustion system has great potential in the rational optimization and match among fuel,air,chamber,which has important practical value.This paper,based on a four-cylinder non-road diesel engine,proposed a new combustion collision to guide the spray impingement through the optimization design of the combustion chamber structural.Firstly,the influence of grid size and time step of the model on cylinder pressure was investigated,while the simulation results of cylinder pressure,heat release rate and emissions were verified comparing with experimental results.Secondly,focusing on the in-cylinder air motion,spray development,mixture formation and combustion emission process,the combustion process of the diesel engine was numerically simulated by AVL FIRE software.Finally,on the base of the orthogonal design method,the optimal combination plan of combustion system parameters?injection nozzle angle,injection pressure,injection timing and swirl ratio?under different evaluation indexes(Soot emission,NO emission,cylinder pressure peak P_max and F)was explored.Multidimensional numerical simulation was carried out under 2200r/min and 100%load conditions for the original engine system and spray impingement combustion zonal system with different chambers.The results showed that the spray impingement zonal combustion system can effectively improve the utilization of air in the cylinder,increase the diffusion of spray and the contact area of fuel and air,making the more reasonable distribution of fuel.In addition,the new system improves the atomization quality of fuel and speeds up the mixing rate of fuel and air,which can form the more uniform mixture to perfect combustion and reduce Soot emission.Compared with the original engine,the spray impingement zonal combustion system has a shorter ignition delay period and a lower peak heat release rate.With the decrease of the opening degree of the collision stage,the starting timing of combustion is advanced,while the peak in-cylinder pressure and heat release rate gradually decrease,which can reduce premixed combustion and increase diffusion combustion.Beyond that,the average in-cylinder temperature and cumulative heat release rate are both higher during the whole combustion process.On the other face,as the opening degree of the collision stage increases,the NO emission increases while the Soot emission decreases.With the help of orthogonal design method to carry out multi-parameter collaborative optimization on the spray wall-impingement partition combustion system,the influence of each parameter on the combustion process and emission performance was explored.The results showed that when Soot emission is taken as the optimization target,the nozzle angle and injection pressure are the main influencing factors,and the optimal parameter optimization combination plan is:nozzle angle of 154°,injection pressure of 110MPa,injection timing of 347°CA,swirl ratio of 2.When NO emission is taken as the optimization target,the injection timing and swirl ratio are the main influencing factors,and the optimal parameter optimization combination plan is as following:injection nozzle angle of 152°,injection pressure of 90MPa,injection timing of 351°CA,swirl ratio of 1.2.When F value is taken as the optimization target,swirl ratio and nozzle angle are the main influencing factors.The optimal parameter optimization combination plan is:nozzle angle of 154°,injection pressure of 90MPa,injection timing of 347°CA,swirl ratio of 2.When P_max is taken as the optimization target,the injection timing and injection pressure are the main influencing factors,and the optimal parameter optimization combination plan is:injection nozzle angle of154°,injection pressure of 110MPa,injection timing of 347°CA,swirl ratio of 2.