Study On Structure Parameters Optimization Of Common Rail System For Gasoline Direct Injection Engine

Gasoline Direct Injection engine(GDI engine)with the advantages of high thermal efficiency,low fuel consumption has become a key technology of energy-saving and emission reduction,which the engine manufacturers must master.The common rail system is the core composition of direct injection engine.Its main function is to pressurize low pressure fuel pressure into high pressure fuel and spray atomized fuel into the cylinder under the ECU precise control.The prerequisite of direct injection engine maintaining high performance is that the common rail system has a stable rail pressure.The rail pressure fluctuation will affect fuel injection quantity and affect the performance of engine ultimately.Comparing with the high pressure common rail system installed in the diesel engine,the pressure of GDI engine common rail system is relatively low and the common rail volume is relatively small,so the effect of rail pressure fluctuation on fuel injection is more obvious.Therefore,reducing the pressure fluctuation of common rail system becomes a key job of GDI engine research.There are many factors causing the rail pressure fluctuation,including the selection of common rail system structure parameters and common rail pressure control algorithm,of which properly selecting the structure parameters of GDI engine common rail system is a important mean to reduce the rail pressure fluctuation.Therefore,the main content of this article is using the improved genetic algorithm to optimize structure parameters of GDI engine common rail system to reduce rail pressure fluctuation caused by structure parameters and reduce the calibration workload of structure parameters of common rail system.The details of the work are as follows:Firstly,this paper analyzes the working principle of GDI engine common rail system.According to the physical structure and liquid volume elastic and flow formulas,the mathematical and GT-suite model are developed and the dynamic characteristics are analyze.Considering the structure parameters optimization of GDI engine common rail system needed to guarantee the stability of common rail pressure at each working point.Therefore,the rail pressure control system is designed based on the strategy of feedforward and feedback.Finally the effectiveness of control system is verified.Then,the influence of diameter of high pressure pump plunger,common rail volume and aspect ratio,damping orifice diameter,injector orifice diameter and Injector oil chamber volume on rail pressure fluctuation and rise time are analyzed based on the mathematical and GT-suite model of GDI engine common rail system,Which laid a foundation for structure parameter optimization.Finally,an improved genetic algorithm based on sequential quadratic programming and genetic algorithm is proposed and used to optimize the plunger diameter,common rail pipe diameter and length,damping orifice diameter,injector orifice diameter considering common rail pressure fluctuation and rise time as objective function.Then,the optimized structure parameters of GDI engine common rail system are obtained.In order to verify the performance of the optimized structure parameters,the optimized structure parameters are compared with before optimization in rail pressure fluctuation and rise time.The simulation results show the effectiveness of optimization method proposed in this paper.In this paper,a series of work on the optimization of structure parameters of GDI engine common rail system are carried out,but some of the follow-up work needs to be improved in the further.Firstly,In the actual production,the requirements of common rail system structure parameters optimization need meeting the purpose of not only reducing the pressure fluctuation,but also introducing more optimization targets and constraints according to the actual needs.In addition,this article mainly optimizes several key common rail system structure parameters.Other structure parameters need to be optimized referring to the idea of this article.