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In the process of coal-bed gas engine working, air-fuel ratio fluctuation is ofen caused by working condition transition and changes of coal-bed gas parameters, such as the concentration, the pressure and the temperature. Then it would cause coal-bed gas engine to run unsteadily, and even flameout. Therefore, the research on air-fuel ratio control key technologies of coal-bed gas engine has great realistic significance and practical application value for ensuring the engine run steadily, improving coal-bed gas utilization efficiency, reducing coal-bed gas emission pollution degree, and even propelling the work of energy saving and emission reduction.Firstly, in view of air-fuel ratio change caused by coal-bed gas parameter change and the working condition change of coal-bed gas engine, the mixer structure of coal-bed gas engine is optimized. In the process of optimization, the mixer coal-bed gas valve port model is built by using the theory of hydrodynamics, and its flow characteristics is researched and analysed. As the same time, a coal-bed gas valve port with quasi-linear flow characteristics is designed by using piecewise linear modeling method. So the response speed of air-fuel control is improved, and its accuracy and real time are also ensured.Secondly, based on the fuel oil engine mean value model and considering the characteristics of coal-bed gas engine, the mean value model of pre-mixing coal-bed gas engine is presented, and its simulation model, which contains mixed gas formation subsystem, gas intake subsystem and crankshaft power output subsystem, is built by using Simulink software. This lays a good foundation for the research and simulation on air-fuel ratio control strategy of coal-bed gas engine.Thirdly, in order to decrease the adverse effects to air-fuel ratio control brought by coal-bed gas concentration disturbance, and the large pure time-delay existed in signal response of methane transducer, a suitable flow control scheme is proposed for coal-bed gas supply system. By appropriate designing and disposing the coal-bed gas pipeline, the adverse effect produced by the methane transducer signal response is decreased. Based on this, the flow control model of coal-bed gas supply system for coal-bed gas engine is bulit, and the flow control strategy of gas supply system based on incremental PID control and fuzzy-PID control are researched and simulated. This restrains the effect to air-fuel ratio control, which caused by coal-bed gas component change, and lays a foundation for the steady running of coal-bed gas engine.Finally, By analyzing air-fuel ratio control characteristics of pre-mixing coal-bed gas engine and according to its working condition changes, a air-fuel ratio control scheme used in pre-mixing coal-bed gas engine is proposed. According to this scheme air-fuel ratio control strategies based on incremental PID control and fuzzy-PID control, which used in transient working condition and steady working condition, are researched and simulated. The simulation result shows that the air-fuel ratio control sheme has optimal control effect, and preferable stability and robustness.
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