| With the rapid development of society,energy shortage and environmental pollution is becoming more and more serious.Therefore,it is an inevitable trend to optimize the internal combustion engine and improve its economy and environmental protection.The domestic research on diesel engine started relatively late,and the research and development of many injection technologies and the improvement and optimization of injection systems are based on relatively mature injection systems abroad.For the optimization of diesel fuel injection system,how to increase the combustion efficiency,reduce the emission of harmful substances and improve the control accuracy is the first direction we need to consider.Aiming at the above problems,this paper studies and optimizes the high-pressure common rail electronic fuel injection system of diesel engine with the support of the key research and development project of Zhejiang Province and the National Natural Science Foundation of China.The focus of this research is to optimize the key structure of the injector nozzle.The main research contents are as follows:(1)The composition and working principle of diesel fuel injection system are introduced,including low pressure system and high pressure system.The research status of diesel engine system domestic and abroad has been analyzed,and the mathematical model of key structure in high pressure system is established.On this basis,the three-dimensional geometric model of key structure nozzle of injector has been established.(2)The flow field characteristics inside the nozzle were analyzed in detail.The threedimensional model is processed by Fluent/Ansys software.The three-dimensional flow field of the nozzle was established by meshing,solving area and setting of relevant parameters.The nephogram of pressure,velocity and gas volume fraction flow field is analyzed,and the existing problems of the original nozzle are found out.Firstly,the oil pressure in the pressure chamber is on the low side.Inhomogeneity will lead to poor fuel injection characteristics;secondly,low flow rate in the nozzle will lead to low flow rate,which will affect the performance of diesel engine;finally,there is cavitation phenomenon between the edge of pressure chamber and the upper edge of nozzle,which will not only affect the flow characteristics,but also lead to cavitation.(3)RSM response surface analysis method is introduced in detail,five key nozzle parameters affecting injection characteristics are determined,and the target response which can reflect the flow characteristics of the nozzle is determined,and the maximum mass flow rate and pressure in the pressure chamber are determined.Based on iSight software,the experimental data points are designed through the composite design of CCD center in DOE test design.On this basis,the relationship between the key structural parameters of five nozzles and the target response is analyzed by response surface method.(4)The second generation genetic optimization algorithm(NSGA-II)is introduced in detail.Based on the NSGA-II algorithm in the optimization module of i Sight,the multiobjective optimization is carried out.The optimization results are analyzed and the optimal value of this optimization is finally determined.Compared with the parameters before and after optimization,the optimized nozzle core top radius decreased by 10%,the nozzle angle increased by 9%,the nozzle diameter increased by 22%,the pressure chamber ball diameter decreased by 22%,and the needle valve seat cone angle decreased by 3%.After optimization,the mass flow rate of the nozzle increased by 37.5%,and the pressure of the pressure chamber increased by 39.8%.It can be found that the flow characteristics of the nozzle have been greatly improved.(5)The three-dimensional model of the optimized model is established,and the threedimensional flow field of the optimized model is established.The comparison and analysis with the three-dimensional flow field of the original model further verifies the reliability of the optimization. |
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