Development Of EGR System For Turbocharged Diesel Engine And Its Experimental Study

With the rapid development of automobile industry, pollution caused by automobile exhaust emissions has the serious influence to the human survival environment. To the diesel engine, exhaust gas recirculation(EGR) technology which can optimize the combustion process has become one of the most important methods that control NOx emissions of diesel engine. For turbocharged diesel engine, it's especially important to choose EGR circuit and equipment for diesel engine realizing EGR. Therefore, in this paper, based on DK4 A turbocharged diesel engine, the design of Jet-Type EGR device and circuit which based on the principle of venturi and variable EGR rate was carried out. The CFD method was used to optimize the design. The engine test bench with EGR loop was established, and effect of this EGR loop on performance of diesel engine was explored.In this paper, numerical computations were carried out with CFD software Fluent. Meanwhile, in order to get the reliability of the simulation model, a confirmatory experiment was conducted. The simulation analyzed the gas flow field of EGR device with different structure parameters, and the influence of structural parameters and boundary conditions on the maximum achievable EGR rate(EGRmax) were explored. The results show that the shorter of the air inlet diameter, the higher of the EGRmax. EGRmax will get higher when the exhaust gas inlet pipe move inward, and the value of contraction angle has no effect on EGRmax. The lower of the differential pressure between exhaust gas inlet and outlet, the more difficult to realize EGR. Decreasing the value of contraction section width, contraction angle and diffusion section angle are benefit of the mix of air and exhaust gas. The longer of air inlet diameter and the shorter of the contraction section width will bring a large energy loss. On the basis of the final simulation results, taking into account the size conditions of engine test bench, the final size of EGR device was confirmed, and the device objects was manufactured.In order to investigate the influence of diesel performance that come from EGR device and loop, a part of low load conditions were selected in experiments. The pressure characteristics of boundary and the effect of EGR system on engine's performance, fuel economy and emissions test with different EGR rates was conducted. The test results show that:The pressure at the inlet and outlet of the EGR device would increase with the increasing of engine speed and loads, but the differential pressure between exhaust gas inlet and outlet would reduced, which caused the decreasing of EGRmax. When the differential pressure came to-0.02 bar, the function of EGR could not be realized. When the exhaust gas inlet pipe moved to 15 mm inward, the capability of EGR device was enhanced obviously. By adjusting the relative position of exhaust gas inlet pipe, the purpose of regulating EGRmax could be achieved. The EGRmax increased with the exhaust gas inlet pipe moved inward, and decreased with it moved outward. Both the maximum cylinder pressure and the heat release rate peak declined with the increasing of EGR rate, and the corresponding crank angle was retarded. The brake specific fuel consumption(BSFC) of engine increased with the increasing of EGR rate. Under the same EGR rate, BSFC increased with exhaust gas inlet pipe moved inward, decreased with it moved outward. With the increasing of EGR rate, engine's NOx emissions decreased sharply, and the trends of carbon smoke emission was opposite.