Study On Optimization Methods Of EGR Controlling Parameters

Diesel engines have many advantages such as high thermal efficiency, strong power, high reliability, and good durability. However, the emission of diesel engines has been widely criticized all the time. NOx and Soot exhausted from diesel engine acting on human and atmospheric enviro N·ment cause considerable damage. Especially in northern China full of serious haze, Emissions of motor vehicles i MPact on the enviro N·ment and society seriously.The generation and emissions of NOx is affected by cylinder temperature, oxygen concentration, reaction time, engine fuel injection parameters, intake parameters, combustion chambers and other relevant parameters. Exhaust gas recirculation(EGR) technology used currently is one of the most effective measures to reduce NOx. However, it has a negative iMPact on the different levels of power, fuel economy, and emissions. Numerous studies have demonstrated that cold EGR technology and flexible high-pressure injection technology have significant function on improving diesel engine emissions and reducing fuel consumption rate. But most of the research is combined with only one or two parameters rather than all parameters considered in optimization design with different conditions.This paper focuses on a small-displacement electronically controlled high-pressure and common-rail diesel engine to research the combustion and emissions with the change of the EGR rate, EGR temperature, main injection advance under synergy angle, and injection pressure, combining EGR with fuel injection technology and referring to DIPulse combustion model built in GT-Power. The EGR control parameters, injection parameters for cylinder pressure, transient heat release rate peak, and emissions relation are also explored. Ultimately, the paper shows the optimal matching of all the parameters based on the changes of all performance and the genetic algorithm for optimization. The paper shows theoretical basis for the later control strategy design of EGR. This main research work of this paper is as follows:This paper focuses on a high-pressure and common-rail diesel engine to build the EGR system and the test bench. Rearching the relation of EGR under different conditions with the combustion and emission characteristics of the the diesel engine. Test data is recorded to establish and check the engine model.Building DIPulse combustion model and machine model in GT-Power to analyze the effects of various experimental parameters in the combustion process; Researching the relationship of different EGR rate, EGR temperature, the main injection timing and fuel injection pressure in typical conditions and cylinder combustion status and emission through the calibration of empirical parameters.Building the genetic algorithms in Matlab, multi-objective optimization problem is transformed into a target more constrained optimization problem. The constraint boundary is reflected in the model through the establishment of penalty function. Finally, Combine Matlab with GT-Power to find EGR parameters and injection parameters combinations in all conditions. In this way, we can meet the emission requirements.The results shows that higher EGR rate in small load at low speeds can be effective to reduce NOx. Besides, advancing the fuel injection phase and increasing injection pressure can curb Soot caused by EGR and make up for torque loss. However, lower EGR rate in high load at high speeds can be effective to retarded injection for maintaining stable torque output.