Modeling And Optimization Of Fuel Mode Switching For Marine Dual-Fuel Main Engine

Due to the worldwide strain on oil resources and increasingly stringent anti-pollution emission regulations for ships,the diversification of ship power sources has become a future trend in the development of ships.Natural gas dual-fuel engines are gaining more and more attention in the marine main engine sector due to their good emission performance and excellent economy.A major advantage of marine natural gas dual-fuel engines over conventional diesel engines is that they can be switched between diesel and gas modes to meet emission and power requirements,taking into account the specific operating conditions of the vessel and allowing the vessel to operate at its optimum level.However,the engine is susceptible to speed fluctuations and erratic operation due to the different combustion characteristics of the two fuels when switching between fuel modes.In this thesis,taking Win GD 7X82 DF Marine two-stroke dual-fuel engine as the research object,the fuel mode switching process and its control system are studied by modeling and simulation.Firstly,the model of the dual-fuel engine was built in GT-POWER and calibrated according to the bench report provided by the engine manufacturer,and the errors of the main parameters of the model were less than 5%,meeting the requirements of simulation accuracy.Secondly,the engine control system was modeled in SIMULINK and the control logic and control method for the engine fuel mode switching operation were established and coupled with the engine model built in GT-POWER.The joint simulation model can complete the transient operation of fuel mode switching according to the rules set.Then,to address the problem of insufficient control effect of the traditional PID controller,the cuckoo search algorithm and fuzzy control principle were used to optimize the design of the controller and obtain a new type of control unit,and the optimized control system was used to study the influence of the switching time on the engine stability during the engine fuel mode switching.The simulation results show that the dual-fuel engine simulation model established in this thesis has good accuracy and reflects the changes in the performance parameters of the engine during the transient operating condition of fuel mode switching.The engine parameters fluctuate considerably during the switch from gas to diesel mode,which places high demands on the control system,while the engine parameters fluctuate more smoothly during the switch from diesel to gas mode.The fuzzy adaptive PID controller based on the cuckoo search algorithm has a better control effect on the engine speed control than the traditional PID controller and can effectively suppress the speed fluctuation during the fuel mode switching process.The speed fluctuation during mode switching can be reduced by extending the switching time appropriately.