The Influence Of Air-Fuel Ratio Control On The Dynamic Characteristics Of Marine Dual Fuel Engine

With the increasingly stringent emission regulations of IMO,clean diesel / natural gas dual fuel engine is gradually applied in the field of shipbuilding.However,the operation area of dual fuel engine is limited by knock and misfire.Compared with diesel engine,its dynamic characteristics are poor,which limits its application.At present,the measures to improve the dynamic characteristics of dual fuel engine mainly include improving engine structure,optimizing air-fuel ratio control strategy and blending fuel.In the air-fuel ratio control,the traditional throttle is mainly used to control,which brings the problem of unable to control accurately.In the thesis,the control method of air-fuel ratio is extended,and the dynamic process of dual fuel engine is optimized by using the exhaust gas by-pass and the coordinated control of throttle and exhaust gas by-pass.According to the basic principle of dual fuel engine working process,the thesis establishes the steady-state model of dual fuel engine in GT-power software,and compares the parameters of model simulation results with test data to verify the accuracy of host model,which can be used for subsequent research.Then,the balance models of governor,load and shafting are established and verified in Matlab/Simulink software,which can be used for later research Research on control strategy of continuous air-fuel ratio.In the thesis,by studying the influence of throttle and exhaust gas by-pass on the dynamic process of dual fuel engine,it is concluded that both throttle and exhaust gas by-pass have a good regulating effect on the air-fuel ratio.The control effect of throttle on the whole dynamic process is more balanced,but the response speed of throttle is not as fast as that of exhaust gas by-pass.exhaust gas by-pass has a strong regulating effect in the initial stage of regulation.By optimizing the controller parameters,the dynamic process of dual fuel engine can be further improved.According to the working characteristics of the throttle and the exhaust gas by-pass,the thesis improves the cooperative control strategy.The throttle is used as the main controller,and the bypass valve is used as the auxiliary controller(it works when the air-fuel ratio deviation exceeds the specified value).The improved cooperative control strategy gives full play to the advantages of the throttle in regulating the intake flow and the ability of the exhaust gas by-pass to bypass the exhaust flow quickly to ensure the air-fuel ratio The stability of the system.On the basis,fuzzy control theory is used to optimize the throttle controller,which can effectively improve the dynamic process of dual fuel engine.The thesis studies the working characteristics of throttle and exhaust gas by-pass,cooperatively controls the air-fuel ratio,optimizes the dynamic process of dual fuel engine,and provides some reference for the operation and design of dual fuel engine.