Research On Optimization Of Combustion System Of A Marine High Speed Diesel Engine

The design of combustion system is considered to be a very important part in the design field of internal combustion engine,especially the design of combustion chamber and injector.The combustion system will affect the combustion process of the internal combustion engine,thus affecting the power of the engine and its performance as well.The turbulent gas flow,fuel injection process,spray development and oil and gas mixing process are related to the structure of combustion chamber and injector.Therefore,by changing the structure of combustion chamber and injector will change in-cylinder parameters and engine performance.In this paper,the CFD method is used to optimize the combustion system of diesel engine.By establishing combustion simulation model,the results of different combustion chambers and injectors are compared and analyzed.Also,the effects of structure of combustion chamber and injector on combustion process and emission characteristics of diesel engine are obtained.The main objectives of this paper are carried out involving three stages.Firstly,GT-Power software is used in order to build one-dimensional combustion calculation model to analyze the one-dimensional combustion characteristics and diesel engine performance.In addition,the operation parameters are calculated as initial and boundary conditions for the establishment of three-dimensional combustion calculation model.AVL FIRE software is adopted in order to build the three-dimensional combustion calculation model of diesel engine,and the calculation model is verified by the performance test of a single-cylinder diesel engine.After that,the in-cylinder pressure,in-cylinder temperature,combustion heat release rate,pollutant emission and in-cylinder fuel distribution are carried out through calculation,and based on these results,the combustion and emission characteristics of diesel engine are analyzed.Secondly,FIRE software is adopted in order to build the calculation model.Through the calculation,the maximum explosion pressure,maximum temperature,physical field distribution and pollutant emission of combustion chambers with different structure are obtained.By comparing and analyzing the calculation results of combustion chambers with different structure,it can be concluded that the NO emission of B5 is the least,which is15.7% less than the NO emission of the prototype combustion chamber;the effect of combustion opening form on the Soot emission is the most significant,and the Soot emission of the opening combustion chamber is 89.2% less than the Soot emission of the prototype combustion chamber.Finally,the calculation model is established by FIRE software.Through the calculation,the in-cylinder pressure,in-cylinder temperature,physical field distribution and pollutant emission of injectors with different structure are obtained.By comparing and analyzing the calculation results of injectors with different structure,it can be concluded that the effect of nozzle diameter on the NO and Soot emission is the most significant,compared with the prototype combustion chamber,the NO emission of D3 is reduced by 63.1%,while the Soot emission of D1 is reduced by 97.3%.