Simulation Study On The High Efficiency Combustion Of Marine Medium-speed Diesel Engine

Nowadays,energy saving and emission reduction has always been the mainstream direction in the world.In addition,marine pollution is becoming more and more serious,which makes the technology of energy saving and emission reduction of marine diesel engine more and more important.With the development of computer technology,using CFD to simulate the working process of internal combustion engine and to optimize and match multiple parameters has become an important means of performance development of internal combustion engine.Especially for large marine diesel engine,numerical simulation can effectively shorten the research and development process and reduce the research and development cost.This paper combines one-dimensional numerical simulation software GT-Power with three-dimensional numerical simulation software AVL-FIRE to simulate the working process,intake air flow process and combustion process in cylinder of a marine medium-speed diesel engine.Through one-dimensional numerical simulation,the efficient combustion schemes with different parameters are explored,and on this basis,the shape of intake port,injection parameters and combustion chamber profile were optimized by three-dimensional numerical simulation.Firstly,the one-dimensional numerical simulation software GT-Power is used to establish the performance calculation model of diesel engine,and the model calibration is completed according to the bench test data.On this basis,the effects of single factors such as injection timing,injection volume,compression ratio,valve timing and intake flow coefficient on engine performance are explored respectively,and three factors that have the greatest impact on engine performance are identified.The DOE test design of the engine is carried out.By adopting DOE optimization method of two-stage turbocharging,under the conditions of limiting the maximum explosive pressure,maximum pressure rise rate and NO emission,an efficient combustion scheme was found.Finally,the goal of reducing the effective fuel consumption by 8.2% was achieved,and its economy and power were improved.Then,based on the steady flow test of the intake port,the three-dimensional simulation calculation of the intake port is carried out.Through the analysis of the flow field in the intake port,the sensitive parts affecting the flow coefficient are found,and the shape of the intake port is optimized.The goal of increasing the flow coefficient from 0.588 to 0.64 under the condition that the eddy current ratio is within a certain range is achieved.At the same time,the following conclusions are drawn: The flow coefficient can be effectively increased by reducing the curvature of the inlet of the short airway and moving the bifurcation lines of the two airways backward.In addition,on the basis of engine bench test data and one-dimensional numerical simulation data,the combustion chamber model was established by using AVL-FIRE,and the appropriate spray model and combustion model were selected,and the initial and boundary conditions were set accurately.The accuracy of the calculation model was verified.The cylinder spray process,the mixing process of oil and gas and the process of combustion and emission were analyzed in detail.On this basis,in order to improve the combustion thermal efficiency and reduce emissions of diesel engines,the effects of fuel injection system parameters and combustion chamber shape parameters on the combustion and emission process of diesel engines in cylinder were investigated respectively.By comparing and analyzing the simulation results,the following conclusions are drawn: properly increasing the fuel bundle angle,selecting the appropriate aperture and number of apertures,properly increasing the combustion chamber.The throat diameter is helpful to improve the combustion thermal efficiency and emission performance of the prototype.