The Study Of EGR Effect On Di Disel Engine Combustion

With the issues of energy and environment becoming increasingly prominent, people pay attention to the economical efficiency and emission performance of engine more and more. The most fundamental way to increase the economical efficiency and emission performance of engine is improving the combustion. In the paper, indicator diagram, relative intensity of combustion, high-speed CCD photographs and other methods are used to study the effect of exhaust gas recirculation (EGR) on DI Disel Engine Combustion with the simulation experiment on Constant Volume Combustion Bomb (CVCB), and Chemkin4.11 software was used to study the effect of H2O on DI Disel Engine Combustion.In this paper, the method of using CVCB to simulate the Top Dead Center (TDC) combustion of disel engine and realizing EGR by multiple injection or addition of water is feasible. The combustion result detected by homemade Light intensity sensor is same as the result detected by indicator diagram. In the visible range, the wavelength choice of sensor has no effect on combustion characteristics.At all of different initial pressure, temperature, the increment of EGR rate can extend the ignition delay, slow down the rate of fuel combustion and the maximum relative intensity, as a result, the maximum combustion temperature was reduced. When EGR rate is smaller than 5%, the time when the maximun relative intensity rise rate turns up is same as or even ahead of the time when the maximum heat release rate turns up; but when the EGR rate is larger than 5%, the appearance of the maximun relative intensity rise rate will be significantly delayed. In other words, the time of sharp increase in temperature is later than the rapid increase in heat release rate. When the EGR rate is high enough(40%), the brilliant flame will not turn up, the method based radiation intensity will no longer apply.To add H2O in intake will promote oxidation reaction of fuel, reduce the ignition delay, improve combustion stability, and also inhibit pyroreaction, reduce the maximum combustion temperature. It is mainly due to the reason that H2O reduces the lower temperature by increasing of heat capacity in the combustion zone and i OH,Hi ionization out from H2O promotes the oxidation of CO at low temperature.The effect of real EGR on combustion is mainly due to the dilution of EGR gas and the temperature effect. Dilution can increase the ignition delay, slow down the oxidation rate of the fuel, and reduce the maximum combustion temperature. The intake temperature caused by EGR gas will increase the oxidation rate of fuel and the maximum temperature. It can improve the combustion stability in idle speed, low-load and cold start; but it will increase the NOX emissions in normal and heavy load. The increasing of heat capacity by EGR gas will deduce the maximum combustion temperature, but the effect is weaker than dilution effect and temperature effect.