Research And Simulation On Co-combustion Strategy Fuzzy Control Method Of LNG/Diesel Dual Fuel Engine

In the ship transport industry,in order to effectively control exhaust pollution and adjust the energy structure,inland river ships in our country have already begun to steadily promote the operation and application of “oil to gas” technology since 2010.Using nature gas in the ship engine as an alternative fuel is the main technical approach.The technical characteristics of the first generation LNG/diesel dual fuel engine were that the prototype diesel was retrofitted to inlet manifold dual fuel engine by simple installation of LNG fuel supply and electronic control system without significantly changing original structure.The supply and control of LNG fuel have direct impact to the engine performances in the system.Traditional co-combustion strategy is determined by bench test,and made into MAP forming open-loop control.The formulation of this kind of co-combustion strategy control method depends on bench test,which is not accurate.And the final co-combustion strategy control method is only for the engine with the same model and same technical conditions,which is not generic.Meanwhile the cost is high and the development period is long.This paper is specific to the inlet manifold LNG/diesel dual fuel engine retrofitted by marine Z6170 diesel engine.Fuzzy adaptive regulating PID control based on feedforward is used to the co-combustion strategy control after comprehensively analyzing the characteristics of engine modern control theory.First,based on the control method,the paper sets air-fuel ratio as the control target and designs the fuzzy adaptive regulating PID controller.Fuzzy PID controller uses the deviation and deviation rate of change between actual air-fuel ratio and target air-fuel ratio as input.After the process of variable fuzzification,fuzzy synthesis reasoning and fuzzy operation,self-turning function of PID control parameters is achieved.Then,the paper uses Simulink module in Matlab to establish engine model,including intake model and fuel model.And fuzzy control module in Simulink is used to establish fuzzy PID controller model which is applied to the engine model to obtain the simulation model of fuzzy self-turning PID control.Finally,the paper simulates the fuzzy self-turning PID control method,and analyzes the simulation results between fuzzy self-turning PID control method and conventional PID control method.Simulation results show that,whether in steady state conditions,or in the transient conditions of sudden increase and reduction above the load.Compared to conventional PID controller,the fluctuation numbers and vibration amplitude in the output waveform of fuzzy self-turning PID controller are reduced to varying degrees,and the response time can be reduced by about 2~7 s,therefore,the adaptive ability,stability,and sensitivity of fuzzy self-turning PID controller are better.Fuzzy self-turning PID control method can be well adapted to the un-linearity change of engine air-fuel ratio.The controller adaptively adjusts the PID control parameters according to the condition information so that it adjusts the amount of natural gas injection,which can make air-fuel ratio achieve target air-fuel ratio quickly and accurately.And co-combustion strategy adaptive control in LNG/diesel dual fuel engine can be achieved finally.