In-cylinder CFD Simulation In Flexible Valve Controling Of Two-stroke Low-speed Diesel Engine

The scavenging process of marine low-speed two-stroke diesel engine is accompanied by the process of exhaust,which will directly affect the scavenging quality,and then affect the whole working process of the diesel engine.The traditional design uses a fixed cam to control the lift of the exhaust valve,which can only ensure the good ventilation of the engine under a given working condition.However,in the actual working process,the best valve parameters of the engine should be different with the change of speed and load.The flexible exhaust method can adjust the parameters of the exhaust valve flexibly,so that the parameters of the exhaust valve can be adjusted flexibly with the change of the operating conditions of the diesel engine,so as to improve the performance of the diesel engine,reduce fuel consumption,improve power and reduce emissions.In this paper,for 340 EF marine two-stroke low-speed diesel engine,a one-dimensional model of the working process in the cylinder is established and verified by GT-POWER software,and the effect of flexible exhaust on the performance of low-speed two-stroke diesel engine is studied.In order to better reveal the details of the flow in the cylinder of the lowspeed two-stroke diesel engine under the control of flexible valve,a three-dimensional geometric model of the cylinder structure and exhaust system of the 340 ef marine two-stroke low-speed diesel engine is established,and the three-dimensional simulation calculation of the working cycle of the low-speed two-stroke diesel engine is carried out by using the converse software.By changing the opening and closing phases of the exhaust valve,the development process and law of the gas flow in the cylinder are simulated,and the effect of flexible exhaust on the performance of low-speed two-stroke diesel engine is studied.Finally,a joint simulation model based on GT-POWER and mode-FRONTIER is established to optimize the lift curve of exhaust valve under different working conditions and obtain the optimal lift parameters of exhaust valve under each working condition.The threedimensional simulation of cylinder flow and spray combustion process is carried out by CONVERGE.Verify and analyze the optimal results of the valve movement under various operating conditions,and obtain the optimal control parameters of the lift of the flexible valve of 340 ef marine two-stroke low-speed diesel engine.Based on the three-dimensional CFD simulation analysis of converse,the development and variation of the flow field in the cylinder under different exhaust control parameters of lowspeed two-stroke diesel engine and the influence of flexible exhaust on NOx emission are revealed.The relevant research results provide theoretical reference for the optimization of air distribution of low-speed engine and optimal control parameters for flexible exhaust.