Study On The Performance Improvement Of GDI Engine With Controllable Turbocharging Technology

In this paper,the design of the mechanism is carried out on the basis of the idea “control mechanism of twin diaphragm box gasoline engine bypass valve”.The effect of bypass valve opening on engine performance was studied by using simulation calculation method,and the optimization of bypass valve opening was carried out to optimize the engine performance.At the same time,due to the variation of the opening of the bypass valve,the engine torque fluctuated,and the joint control strategy of throttle valve and bypass valve is proposed to reduce the fluctuation of engine torque.There are three parts included in this paper.Part 1,Design the parts of the structure on the basis of the control mechanism of twin diaphragm box gasoline engine bypass valve.The specific components include the upper and lower shell of the twin diaphragm box,spring,diaphragm,putter,rocker,etc.,and the selection of materials for these parts,determination of the processing technology,strength and rigidity check.Through design of the dimensions of each part,draw the parts drawing and twin diaphragm box assembly drawing,and using CATIA software established the 3D model of each components included the diaphragm box assembly model,diaphragm box and supercharger assembly model.Part 2,The influence of the bypass valve opening on the performance of the engine was studied by using the established EA111 model.The main research condition is different rotational speed for the same load conditions,and the same speed for the different loads,the main performance evaluation indexes include the engine fuel consumption rate and brake mean effective pressure.Under different loads at different speeds utilizing economy and power performance as the main goal to optimize the by-pass valve opening.The main conclusions are as follows:1).Under the condition of same load and different speeds,the opening of the bypass valve has a certain effect on engine performance.At the small load,due to the increasing of the bypass valve opening,the average effective pressure increases gradually.The higher the speed of engine,the greater influence on the average effective pressure it has.Fuel consumption decreases gradually with the by-pass valve opening increases.With the increase of engine speed,the trend is more obvious,this is mainly because the engine exhaust back pressure is relatively larger at the small load.At the large load,the average effective pressure of the engine decreases rapidly with the opening of the bypass valve,and the faster engine speed is,the faster decrease rate of the average effective pressure.The opening of bypass valve has less effect on the fuel consumption rate at low speed,but the effect will be obvious at high engine speed,this is mainly because the by-pass valve opening leads to low working efficiency of the turbocharger.2).Under different load conditions at the same speed,the mean effective pressure change rate is not obvious with the increase of the by-pass valve opening at low speed,mean effective pressure change rate increases with the increase of the load.The specific fuel consumption rate and mean effective pressure have the same change trend.At mid-high speed and small load,the mean effective pressure change rate increases gradually,the average effective pressure gradually decreases with load increasing.3).The performance of the engine can be improved by optimizing the opening of the bypass valve.With the increase of engine load,the diameter of the optimal bypass valve decreases gradually at the same speed.Similarly,with the increase of engine speed,the optimal bypass valve decreases gradually at the same load.Meanwhile,in order to ensure the engine power under the large load condition,the optimal bypass valve should not be too large.Part3,The engine joint simulation platform was established through Matlab/Simulink and GT-Power,Studied the influence of the change rate of the bypass valve diameter on the torque fluctuation of the engine.On the basis of the optimum bypass valve opening rate,four different bypass valve opening characteristics were studied,which are concave,convex,concave and convex?inclined type.As the change of bypass valve opening during high speed load has great influence on engine torque,a large torque fluctuation affects the power output of the engine,so the joint control strategies for throttle and bypass valve were proposed to improve engine torque fluctuation.The results are just as bellow:1.The closing rate of the bypass valve should be reduced with the increase of the load,and the decrease rate of the bypass valve will minimize the influence of the engine torque fluctuation.The bypass valve should be changed followed with the convex line at low speed and low load,and the torque fluctuation of the engine will be smaller.The bypass valve should be changed followed with convex or oblique line at the high speed load.2.When the throttle and by-pass valve opening change follow with linear type,and the throttle and the by-pass valve opening linear reduced,when the by-pass valve opening decrease rate increases,the corresponding throttle opening decrease rate should be increased,so that is more conducive to the engine torque's recovery.When the by-pass valve opening changes in a linear,throttle opening changes in a nonlinear,and decrease rate of throttle opening is relatively small,the opening of the by-pass valve should be changed followed with concave and convex line and diagonal line,engine torque fluctuation will be smaller and recovery time will be shorter.When the throttle changes with nonlinear,the smaller opening of the by-pass valve and throttle change rate is,the bigger fluctuation of the engine torque,the opening of the by-pass valve change follows with concave and convex line or diagonal lines,which is advantageous to engine torque.