Simulation Study On Combustion Process Of 4102 DI Diesel Engine

Because of the increasingly shortage of petroleum resource and the rise of oil costs,as well as stringent exhaust emission standards, advancing thermal efficiency and reducing exhaust matter of internal combustion engine become focus recently. The fuel economy of diesel engine is 20～30% better than gasoline engine, so it develops rapidly recently, but its major problems are the higher level of NOX and PM emission. The combustion process has decisive effects on the power, economy and emission performance of internal combustion engine, so it is very important for advancing thermal efficiency and reducing emission to improve the combustion process of diesel engine.At present, the research of the diesel combustion progress is based mainly on experimental method and numerical simulation. The experimental method has not satisfied requirement of the model diesel design. For some decades now, with the development of computer technology and computational fluid dynamics, numerical simulation becomes very important method for the research of the diesel combustion. Numerical simulation is not only used to forecast engine overall performances, but also reconstruct the fluid flow process, the charge of the turbulence, the space distribution of the fuel particles, combustion process, heat-transfer process and temperature field in the cylinder. Numerical simulation has become the necessary method for the research of in-cylinder combustion process. In this paper the CFD simulation software AVL FIRE is introduced to simulation combustion process of 4102 DI diesel engine in connection with the fuel injection advance angle and nozzle hole cone angle of fuel injection system. First the geometric model and mathematical model are built, and then based on the fuel injection system parameters of the original diesel; the combustion process of the diesel is simulated.Through the simulation and analysis, it is concluded that: with the increase of the fuel injection advance angle, the ignition delay period become longer, the maximum temperature and pressure and heat release rate are increased, and the crank angles of their peaks are also proposing; the oxynitride(NOX) is increased and the soot is decreased; the velocity field and diesel concentration field are not changed obviously, it is thought that the temperature and pressure are the main causes to effect the combustion process; it is found that in the bottom of the combustion chamber the diesel concentration is larger, it disadvantages the form of the air-fuel mixture and would lead the exhaust of soot to increase. With the increase of the nozzle hole cone angle, the maximum heat release rate and the maximum temperature and the maximum pressure are all increased, but the crank angles of their peaks and the ignition delay period are without change; the emission of NOX is increased, and the soot is decreased. Through the analysis of the diesel concentration field, it is found that the diesel concentration is decreased in the bottom of the combustion chamber with the increase of the nozzle hole cone angle; this is favor of the form of the air-fuel mixture.