Research On EGR System Development And Optimization Technique For Diesel Engine

The use of exhaust gas recirculation system can make the emission of nitrogen oxides in the exhaust gas content significantly reduced.For an engine,only the matched EGR system can effectively achieve the role of energy conservation.As important components of the EGR system,EGR cooler and EGR valve will affect the engine working conditions and emissions of pollutant content.And the EGR rate distribution of the engine intake pipes will affect the stability of the engine operation.This paper builds a one-dimensional simulation model of a truck diesel engine based on the software GT-power.The experimental results verified the accuracy of the model.According to the different working conditions of the diesel engine,EGR rates and EGR temperatures of the diesel engine at different rotational speeds and different loads are studied.The paper summarizes the influence law on the dynamic performance,economic performance and emission performance of the diesel engine,and based on this series of simulation results,the overall evaluation of the impact on the engine performance,the different working conditions under the best EGR rates and the best EGR cooling temperatures of the MAP for the subsequent EGR system in the development of various components to provide a theoretical support.Based on the simulation results of GT-power,the maximum heat load point of the EGR cooler is determined,and the boundary conditions of the EGR cooler are determined by the corresponding parameters of this condition.Two different types of cooler structures,such as shell-and-tube cooler and plate-fin cooler,are established.The simulation results shows that the cooling effect of plate fin cooler better.But it is also easier to form carbon deposition.According to the cooling effect and the situation of carbon deposition,the original plate-fin cooler is optimized,and the heat transfer simulation is carried out according to the structure of different fin layers.Compared with the simulation results,the six-layer finned cooler structure can not only make the exhaust gas to achieve the desired temperature,but also for the carbon situation has the best improvement effect.In order to reduce the carbon deposition during the operation of the EGR valve,the EGR system selects valve that works before the cooler to reduce the deposition of the charcoal by high temperature.Through the flow simulation of the EGR valve with different structure.the flow of the EGR valve inlet and outlet on both sides of the stem is determined according to the results.Based on the results of the EGR valve,the flow rate of the EGR valve with different throat diameters and different maximum valve lifts is analyzed.The results show that the nozzle has a diameter of 22mm and the maximum lift of the valve is 13mm.The local loss of the valve is minimum.Based on the experimental results,the simulation is verified.The experimental and simulation results are in the range of 5%under different flow conditions.Finally,the flow distribution analysis of the intake pipe model of the EGR intake pipes at different positions is carried out.The uniformity of the exhaust gas distribution in the six intake manifolds is compared with each other,and the position uniformity of the EGR inlet pipe is located on the same side of the manifold opening well.The model is further optimized to calculate when the intake pipes and the intake manifolds are at different angles.According to the simulation results,when the angle between the intake pipe and the intake manifold is 50°,the flow manifold has the best flow uniformity.