High Pressure Common Rail Diesel EGR Control Strategy

With the purpose of preventing air pollution, many countries have issued regulations restricting the amount of NOx in the vehicle exhaust. Nowadays, the Exhaust Gas Recirculation (EGR) is the most effective method to reduce the emission of NOx. But the emission of PM will increase while reducing NOx. In order to find a compromise and get the best EGR rate, we should precisely control the EGR valve according to the engine speed and load when we are conducting the EGR. In addition, for diesel engines, the exhaust pressure is lower than intake pressure in some operating conditions, it's hard for the exhaust gas flow into the intake pipe. The control system studied could raise the exhaust pressure by controlling TVA, so the exhaust is forced into intake pipe, and EGR is completed. Recirculate gas with high temperature will do harm to the power property, the economic efficiency and the emission performance of the diesel engine, and system with EGR will raise fuel pressure within common-rail diesels. Based on these ill effects, an EGR cooler is installed before the EGR valve in this system, in order to reduce the temperature and pressure of the exhaust gas recirculated.Based on situations above, this thesis takes the common-rail diesel as subject, uses the ASCET Software Development Platform of ETAS company and the method combining the structuring and modular, and proposes a new control strategy of EGR innovatively. The engine speed, amount of fuel injected, temperature of intake gas and the cooling fluid, amount of intake gas of each cylinder, pressure of atmosphere and gas supercharged are all considered and used to modify the value of TVA, in order to agree with the true condition of the engine, and to control the NOx emission more precisely. The system is divided into five control module. The feedforward control module could solve the problem of response and send out values of EGR valve and TVA valve, complete the open-loop control; Expected value calculation module and the adaptive control module could complete the close-loop control and send out the value of EGR valve and TVA valve according to the current condition of the engine. Monitoring and closure module could supervise the engine and send out the default value when error occurs; Calculation module of the cooling valve could control the switching to adjust the temperature of the blow-back. Finally, modules of this system is simulated using the well calibrated parameters, such as the speed, amount of fuel injected, temperature, mass of air and MAP values of EGR. The result shows that the EGR control strategy is correct and the function of these modules are feasible, so we are convinced that this control system could control EGR precisely.