Modeling And Simulation Study Of LNG Fuel Supply System For Marine Engines

With the increasing energy crisis and the deterioration of the ecological environment,the International Maritime Organization(IMO)has imposed increasingly stringent requirements on the emission of gases from ships,forcing shipping to take measures to meet the regulations.The use of LNG to power ships has received a lot of attention as it can reduce emissions at source while ensuring the economy.However,as LNG is stored in cryogenic liquid form,it needs to be vaporized and heated in the gas supply system to a certain temperature and pressure before it can be fed to the engine for combustion,which is a significant difference to the fuel supply system of a conventional engine.Compared to the actual system,modelling and simulation of the LNG gas supply system allows for virtual commissioning of the equipment,shortens the development cycle,reduces testing and verification costs,and reduces safety risks;in addition,based on the model,the designed system can be evaluated and the control strategy can be studied,and the optimal configuration of the equipment can be proposed to guide the subsequent system design.Therefore,it is necessary to carry out modelling and simulation studies on marine engine LNG fuel supply systems.With this background,this paper designs an LNG fuel supply system for the6M33C450-15E220 NG natural gas engine that meets the engine requirements.The whole system is divided into several different modules depending on the functions realized by each component.Theoretical design calculations of the relevant structural parameters are carried out for the main equipment and functional components in the storage,vaporization,BOG and delivery modules,such as storage tanks,submersible pumps,vaporizers and pipelines,to provide a basis for the matching selection of equipment and to provide data support for the modelling.After obtaining the structural parameters of the LNG gas supply system,the simulation model of the LNG gas supply system is built in AMESim software according to the working principle,and the parameters of temperature,pressure and flow rate at important nodes are observed to analyze the vaporization process of LNG and test the system performance to ensure that the parameters of each node are within the reasonable range,and the influence of the characteristics of the heat transfer medium on the vaporization effect is studied.The results show that the accuracy of the designed LNG gas supply system model is more than95%,which can meet the engine gas supply-demand;the flow rate and temperature of the heat transfer medium water glycol at the inlet of the vaporizer will affect the vaporization effect of the vaporizer.Therefore,its flow rate and temperature should be controlled to maintain suitable values,which is important to improve the vaporization effect and thus the engine performance.Then,to ensure the normal operation of the engine and reduce the incidence of failure,the evaluation system and method of the LNG gas supply system are studied,and a comprehensive evaluation of the performance,reliability,safety,economy,environmental protection and design redundancy is carried out for the whole process involved in the system design to verify the reasonableness of the LNG gas supply system design.On this basis,the optimal configuration of equipment is proposed,and the parameters of equipment and functional components such as heat exchangers,pipelines and related valves are adjusted to meet the requirements of gas supply flow and temperature,providing a theoretical basis for the subsequent design and optimization of the LNG gas supply system,which has engineering application value.Finally,to improve the accuracy and dynamic response of the LNG gas supply system,the control system of the LNG gas supply system is designed.Using a joint simulation approach,the designed LNG gas supply system is first validated in real-time based on a simplified model,and the controlled object model,i.e.,the LNG gas supply system model,is run in a real-time manner to accurately simulate the real controlled object.The results show that the use of PID control can effectively reduce the overshoot of the gas supply quantity and improve the system response speed.The results show that the use of PID control can effectively reduce the overshoot of the gas supply and improve the response speed of the system.This provides strong support for the subsequent integrated simulation analysis and optimization of the ship auxiliary system and power unit,and the establishment of a joint simulation platform.