Study On Parameter Optimization Of Air-path System Of Commercial Vehicle Diesel Engine And Its Control Strategies

Today,energy saving and emission reducing have become the key focus for combustion engine technology progress.In the research and development of advanced diesel engine,the air-path system plays an important role in the comprehensive improvement of diesel engine performance.A well-designed air-path system can improve economy of the engine and reduce emissions.In this thesis,a commercial vehicle diesel engine which equipped with EGR system and VGT system was taken as the research object,and a reaserch was carried out for control parameter optimization and control strategy development.Firstly,a working process simulation model of commercial vehicle diesel engine was established by GT-Power,and accuracy of model was verified.Combined with the advantages of GT-power in engine performance calculation and MATLAB/Simulink in data transmission and control calculation,a coupling platform of GT power and Matlab/Simulink was developed which can be used to optimize control parameters.Based on this platform,considering emission requirements and aiming at fuel consumption,EGR valve effective area and VGT rack position were optimized by single objective genetic algorithm.Finally,the optimal parameter maps of EGR valve effective area,VGT rack position,intake manifold mass flow and boost pressure were obtained.Diesel engines equipped with EGR system and VGT system introduce inherent feedback loops from exhaust manifold to intake manifold,which causes the highly nonlinear dynamic behavior of air-path system.In order to analyze and design the engine control system,a third-order nonlinear control-oritend model of air-path system for commercial vehicle diesel engine was established.There were some unknown parameters in the model,and multi-objective genetic algorithm was used to identify these parameters.In order to solve the control problem of the nonlinear system,the third-order nonlinear model of air-path system was transformed into the quasi linear parameter varying model,and the nonlinear problem was transformed into the quasi linear problem by this method.In the quasi linear parameter varying model,intake manifold pressure and exhaust manifold pressure were ragarded as state variables and also ragarded as time-varying parameters,and EGR valve effective area and VGT rack position were regarded as control inputs.In this thesis,the tracking performance of boost pressure and intake manifold mass flow was taken as target,and model-based control method was used to control the air-path system of diesel engine with multivariable.Model predictive control algorithm was designed in this research,which is a control method that deals with the optimal control and constrained systems,with its three characteristics of predictive model,receding horizontal optimization and feedback correction.The simulation results of the coupling platform of MATLAB/Simulink and GT-power showed that the control scheme designed in this thesis can achieve better control effect at low and medium speed of diesel engine.There are 49 figures,19 tables and 118 references.