Simulation Study On The Mixture Formation And Fuel Impingement Process In A Direct Injection Gasoline Engine

Compared with intake port injection gasoline engine, direct injection gasoline engine which is an important direction for the development of gasoline has obvious advantages in the aspects of fuel economy, power and cold start. However, due to fuel injection in the cylinder, the less time of mixture formation and the inevitable fuel impingement phenomenon, particulate matter and hydrocarbon emissions increase. By reasonable matching spray and flow field can improve the uniformity of mixture distribution and greatly reduce the amount of fuel impinging on the wall.In this paper, the experimental devices of shooting spray image and testing spray particle size were used to test the spray angle, penetration and particle size respectively. The injector which was tested is a six holes injector. And the spray model is calibrated using the experimental data. Then the spray process was simulated using the AVL-Fire software studied the influence of different injection angle,injection time, dual injection and injector holes number on the mixture formation and fuel impingement. Finally, improved the original intake port and designed a high tumble ratio intake port using the UG software. And studied the influence of different tumble ratio on the flow field, kinetic energy, mixture distribution and fuel impingement.The results of this study indicate that more fuel sprays and gathers in the lower part of the cylinder and this is harmful for the formation of a homogeneous mixture when the injection angle is 33°. The fuel distributes more reasonable in the cylinder when the injection angle is 23°. It could improve the mixture formation. The injection time sooner, the more conducive to the mixture formation used single injection. But at the same time, the amount of fuel impingement increases as the distance of piston and injector shorten. With the injection time delay, the amount of fuel impingement reduces, but the mixture distribution in cylinder deteriorated. Especially at the ignition time, the fuel accumulates at the below injector. The dual injection can effectively improve the above situation. When the injection time or the injection fuel in the second injection is different the result is also different. The later injection time or the more injection fuel in the second injection, the less fuel impingement. But the mixture distribution uniformity is poor and the fuel accumulates in the below injector at the ignition time. Seven holes injector has bigger spray angle and shorter penetration. So it could improve the mixture distribution and fuel impingement situation.The flow and the turbulent kinetic energy are stronger in the high tumble ratio engine and the region of high turbulent kinetic energy closer to the center of the combustion chamber. It could be conducive to the spread of flame, reduce the knock and improve the combustion stability. The high tumble ratio also could improve the mixture distribution, decrease the fuel impingement and speed up the oil filmevaporation. It is conducive to the formation of homogeneous mixture at the ignition time. And the oil film quality, thickness and area are less.