Research Of Fuel Injection And Mixture Formation During Staring Process On A Gasoline Direct Injection Engine

Compared to PFI engine,GDI engine has higher charging efficiency and compression ratio,and dynamic response fast.As GDI engine emits smaller particles and this is particularly the case for unburned hydrocarbon emissions where 60 to 80% of these occur in the cold start portion of the driving cycle.In order to be able to give full play to the advantages of GDI engine,we have to get high-quality mixture in the cylinder,so it is necessary to fully understand the spray characteristics of the injector and the formation of mixed gas.To study the spray characteristics of a multi-hole injector,this paper has finished some experiments by means of a constant volume chamber and optical engine experimental platform,and established a cylinder direct injection engine calculation model through the Fire software.Based on the calculation model,some simulation study on the formation process of GDI engine in-cylinder mixture under different starting conditions has been finished.Based on the constant volume chamber,the effects of environmental back pressure and temperature,fuel injection pressure,fuel injection pulse width,different blending ratio methanol gasoline and ethanol gasoline on spray cone angle and penetration distance are mainly studied.The results show that:(1)When the back pressure in the constant volume chamber increases,both spray cone angle and penetration distance gradually reduced.The influence of the increase of the back pressure of the environment has a great influence on the penetration distance,and the influence on the spray cone angle is small.The larger environmental back pressure is not conducive to the evaporation of fuel.(2)The spray cone angle decreases gradually with the increase of the ambient temperature,and the spray cone angle decreases slightly with the increase of the temperature.Spray penetration distance decreases with the increase of ambient temperature.(3)For different fuel injection pulse width,the development trend of spray cone angle is similar,and the cone angle is very close,and there is no obvious gap.As the pulse width increases,the penetration distance continues to increase.So the fuel injection pulse width has larger impact on the distance and the effect on the spray cone angle is small.(4)As the injection pressure increases,the spray cone angle is gradually reduced and the penetration distance increases.(5)When the proportion of ethanol blending is low,with the increase of the proportion of ethanol,spray cone angle and the penetration distance decreases.(6)When the proportion of methanol blending is low,with the increase of the proportion of methanol,spray cone angle increases,through the penetration distance decreases.Based on the optical engine,the influence of the engine speed and the fuel injection pressure on the spray characteristics are studied by using the high speed camera as the shooting means.In the study of the spray cone angle,the right half of the spray angle is relatively clear,the measurement error is small,so choose the right half cone angle as the object of study.The results show that:(1)In the cold starting process,with the increase of the engine speed,the right half of the spray angle increases,the penetration distance has a decreasing trend,but this trend is not obvious.(2)The penetration distance and the right half of the spray increases as the injection pressure increases.So the increase of the injection pressure is conducive to the evaporation of the fuel.In the simulation calculation,the influence of injection pressure and engine speed on the formation of mixed gas is analyzed.The results show that:(1)At the same speed and different injection pressure,with the fuel injection pressure increases,the cylinder velocity field distribution has a certain difference,but the difference is small.The difference is mainly due to the instability and randomness of the in-cylinder airflow motion and the disturbance of the fuel injected into the cylinder to the cylinder airflow under different injection pressures.In the staring process,the increase of the fuel injection pressure is conducive to the formation of mixture which is easy to be fired in the cylinder,but not the higher injection pressure brings the better results.(2)With the increase of the engine speed,the velocity and intensity of the flow field in the cylinder are strengthened.When the engine speed range is low,the higher the speed,the better the quality of the mixture formed in the cylinder.This is mainly due to the strong flow field in the cylinder to promote the evaporation of the fuel and movement,which is conducive to be fired and burning.