Numerical Evaluation Method Of Turbocharger Performance Matching For A GDI Gasoline Engine

With the increasingly stringent emission and fuel consumption requirements,the small-displacement direct-injection turbo-charged gasoline engine has become one of the key points in the development of global power system.However,due to the factors of high thermal load,easy to knock,speed and load vary widely and the turbocharging technology is applied to the gasoline engine too short,how to ensure that the reasonable matching for turbocharger and gasoline engine on the condition of steady-state and transient are the key and difficult points for the matching research of the turbocharger of gasoline engine.This paper aims at exploring a reasonable turbocharger matching scheme for a direct-injection gasoline engine based on the steady state and transient condition of the engine by numerical simulation.The main work and conclusions are as follows:Firstly,the full load thermodynamic model for direct injection turbocharged gasoline engine is established by the actual geometric parameters and bench test data,and the part load thermodynamic model is established on the basis of the full load thermodynamic model.These models are calibrated by using the relevant test data,the maximum deviation is within 5%.It is shown that the full load thermodynamic model and the part load thermodynamic model can better characterize the steady-state performance of the engine.These two models can be used to calculate the steady-state matching of turbocharger and engine.In order to evaluate the steady-state matching characteristics of turbocharger and engine,a numerical evaluation method of three-line condition is proposed.Based on the principle of this method,the steady-state thermodynamic model is used to research the matching characteristics of the original turbocharger and engine.According to the problems found in the research,two new turbochargers are selected.Compared with the original turbocharger,the engine adopts two new turbocharger matching schemes,the overall performance is improved to different degrees,and the turbocharger P matching scheme is the most obvious.After matching the turbocharger P,the surge margin of the compressor at 1200r/min engine speed increased by 30.2%,the joint operation curve of the compressor and the engine is expanded efficiently,the external characteristic turbine efficiency and torque increased by 5.8% and 3.9% respectively.In order to compare the transient response characteristics of two new turbocharger matching schemes,a numerical evaluation method of constant speed and variable torque is proposed.Based on the principle of this method,the part load thermodynamic model is extended to the transient thermodynamic model.The transient response characteristics of two new turbocharger matching schemes are studied by using the transient thermodynamic model based on the ideal condition of engine constant speed and variable torque.The research indicated that,in the transient process of the engine constant speed and rising torque ideal condition,the boost pressure,torque and turbine speed of the engine under the turbocharger P matching scheme are more rapid.However,in the transient process of the engine constant speed and dropping torque ideal condition,although the transient response characteristics of the boost pressure,torque and turbine speed of the engine under the two new turbocharger matching schemes are basically identical,but the running characteristics of the turbocharger matching scheme P more stable.In the matching schemes of two new turbocharger,the transient response characteristics of the turbocharger P matching scheme are better.Based on the evaluation result of the three-line engine,the turbocharger P can replace the original turbocharger to match the engine.