Abstract:Exhaust Gas Recirculation(EGR) is a common way to control in-cylinder NOx production and is used in most modern direct injection diesel engines. However the influence of EGR on NOx and Soot is not perfectly understood. In order to analyze the characteristics of EGR, a model of diesel engine based on the GT-POWER is established. Based on the basic structure of diesel engine, the model is a 1D fluid-dynamic engine cycle simulation model of TDI diesel engine with EGR system. The influences of EGR on combustion of the diesel engine are investigated in a constant inlet boost pressure and constant inlet air fuel ratio condition. In the condition of constant inlet boost pressure and constant EGR temperature, along with the rise of the EGR ratio, the rise ratio of the in-cylinder pressure reduces, the highest in-cylinder pressure drops, the start of combustion delays, the peak rate of heat release becomes higher. The EGR makes the Soot lifts and the Brake Specific Fuel Consumption comes down. In the condition of constant air fuel ratio and the EGR temperature, in the wake of the rise of EGR ratio, the in-cylinder pressure becomes higher, which makes the start of heat release shifting to an early time. The delay of heat release due to EGR is compensated by the rise of in-cylinder pressure. The characteristics of the inert gases in the exhaust gases become a secondary factor. EGR reduces the combustion efficiency. The rate of heat release becomes lower. The combustion temperature of in-cylinder comes down. The small EGR ratio can improve the emission. So, the effect of EGR at different boundary conditions is different. The control strategy of EGR with air fuel ratio as the controlling target is defective. One should adopt the control strategy with both inlet air mass flow and EGR ratio as controlling targets. In the condition of constant EGR ratio, the rise of EGR temperature shortens the ignition delay. The start of combustion shifts to an early time, and the rate of heat release comes down. The in-cylinder temperature and the emission of NOx rise, however, the emission of Soot improves. Dynamic property and economical efficiency deteriorate. In order to make a perfect EGR control system, the EGR temperature should also be controlled.