Numerical Study On Cyclic Process Of A Low-speed Marine Diesel Engine

Marine low-speed two-stroke diesel engine is one of the most important power devices the shipping industry.It is of great significance to study the combustion and air-fuel mixing ocess in its combustion chamber.The fuel spray characteristics have a great influence on e formation of fuel-air mixing in the combustion chamber,which directly affect the mbustion efficiency.In this study,the fuel injection and combustion process in the combust amber were studied using software FLUENT.The effects of various spray parameters on e air-fuel mixing and combustion were investigated.At the same time,the air exchange ocess in the cylinder was also studied,so that the complete working process of the diesel Lgine can be simulated.It mainly includes the following aspects:Firstly,a geometric model of combustion chamber and scavenge port of a low-speed arine two-stroke diesel engine was established by using UG software,and the ICEM ftware was used for reasonable mesh division.Then,the mesh was imported into FLUENT.e compressible turbulence model,multicomponent transport model,fuel atomization model d non-premixed combustion model were involved to simulate the processes of fuel injection d combustion.Then,the influences of spray cone angle,fuel droplet diameter,injection direction and e number of nozzles on the mixing of fuel and air were numerically studied at a cold state d the effects of these parameters on combustion efficiency were discussed.The results owed that the larger spray cone angle made the mixing and combustion better in the earlier ige of the injection stage,but the combustion efficiency was reduced at the later stage of the jection.For fuel droplet diameter,smaller diameter is helpful for the mixing of fuel and air,t the spray penetration distance decreased at combustion state.The research on the nozzle rection showed that the better the nozzle direction made the space of combustion chamber ed by the fuel spray,the the higher the combustion efficiency was.In general,when other rameters remained unchanged,only increasing the number of nozzles lead to better air-fuel ixing and the improvement of combustion efficiency.Finally,the dynamic mesh technique was used to simulate the exhausting and avenging process in the diesel engine cycle.Combined with the above processes of jection and combustion,the numerical calculation of the whole cycle of diesel engine was hieved.The average temperature and pressure in the cylinder calculated by the numerical ethods were compared with the experimental results,and it was found that they were in od agreement.That verified the accuracy of the model.