Study On Ejector Design And Simulation Optimization For Increasing Engine EGR Rate

In the face of increasingly stringent emission regulations and the need to improve engine reliability,the use of exhaust gas recirculation(EGR)technology in engines has become a common technical route.Under the condition of low speed and high torque,the existing turbocharged engine will have the problem that the exhaust gas is difficult to mix into the intake air,resulting in insufficient EGR rate,which has a negative impact on pollutant emission reduction and engine reliability.It is necessary to improve this problem.In this paper,a scheme of using the ejector to improve the EGR rate of the engine is proposed,and the design and optimization of the ejector are carried out.Firstly,the derivation and analysis are carried out in combination with the working principle of the ejector,and the method of iteratively solving the maximum ejection coefficient is obtained.The program is written and the software for the conceptual design of the ejector is made.After testing,the software is relatively reliable and can be used to guide the ejector designing.Using this software to analyze the layout of the engine and the ejector.It is found that the design scheme of introducing the engine exhaust gas from the front of the vortex into the secondary gas as the ejector is feasible.And the boundary conditions of the ejector are determined.Then the structural parameters of the ejector are designed and modeled,and the accuracy of the mathematical model and calculation method of CFD calculation are verified.The effects of pressure,temperature,diffuser outlet angle,diffuser length,mixing section diameter,mixing section length,nozzle outlet to mixing section distance,nozzle length and throat length on the ejection coefficient are studied,and the influence rules of working condition parameters and structural parameters on the ejection coefficient are revealed.Five structural parameters that are sensitive to the ejection coefficient are determined.A highprecision response surface mathematical model for the interactive analysis and optimization of ejector parameters is established by D-optimal sampling method.The axial size of the ejector is reduced to 79.2% by genetic algorithm,and the required ejection coefficient can be met at the same time.