Design And Experimental Study Of The New EGR System

In this day, the world energy shortage and the environmental pollution are very serious. Though the diesel is popular because of its high thermal efficiency, high power, high torque and high reliability, the stringent emissions regulation requires good performance of the diesel. The EGR has been widely used in diesel to the combustion which can achieve high efficiency and low emissions currently, including HCCI、PCCI etc.Overcoming the inadequacies of the high pressure EGR and low pressure EGR, this paper designed a new EGR system and EGR apparatus using the gas jet principle based on the traditional low pressure EGR, and studied the influence of the special apparatus to the system EGR rate.According to the problems of the traditional high pressure exhaust gas recirculation and low pressure exhaust gas recirculation. This paper designed a new EGR system,on one hand,it can avoid the pollution which the exhaust gas brings to the compressor and intercooler in the low pressure EGR system;on the other hand, the designed new system can solve the malpractice that the high pressure EGR need the pressure difference which lies between the exhaust and intake air to realize EGR rate at the low speed or low load conditions. At the same time, this system can ease the burden of the after-treatment equipment, because the exhaust gas flows before the after-treatment equipment.The dedicated EGR device is based on the venture effect and jet pump principle to solve the difficult that it is too hard to realize the pressure difference at low speed or low load. First of all, select the range of the device structure size according to the jet pump structure and decide the size, and verify the accuracy of the model through the test. Secondly, optimize the structure size to get the maximum EGR rate using the FLUENT software.The pressure operating range of this dedicated device is wider than the pressure range of venture tube. But it is limited by the pressure scope. Through simulation, it is devoted to studying the influence that the pressure difference between the air inlet pressure and the mixed gas outlet to the EGR rate when the exhaust gas is constant; and when the pressure difference is constant,the influence of the change of exhaust gas to the EGR rate. The results show, when the pressure of exhaust gas is constant, the EGR rate in this system increases as the pressure difference increasing; when the air pressure and the mixed gas pressure are constant, the EGR rate increases with the exhaust gas increasing.Finally, making the device into real and access to the engine for test, the paper study the change characteristic of the threshold of the EGR rate under different conditions. The test results show:the threshold of EGR rate decreases gradually as the load increasing at the same speed; and the threshold of EGR rate decreases gradually with the speed increasing at the same load.