Small-Bore Marine Diesel Engine Working Process Calculation

With the out-standing global energy crisis and gradually deteriorating environment,the sustainable development has attracted people's attention.Marine diesel engine is widely used as the main propulsion power in global shipping industry,the improve of combustion efficiency and reduce of emission inmarine diesel engine are the hottest research field nowadays.International MarineOrganization(IMO)has strict regulations on the emission of marine diesel engine in the Marpol73/78 Convention Annex VI.With the upcoming of tier III in the Annex VI about the NOx emission is to be put into effect.It's a great challenge for the current emission control technology.Based on a small bore marine diesel engine,numerical calculation carried out tosimulate the working process of this engine,to provide the reference for the marine engine emission certificationtest.Based on the AVL Boost and the AVL Fire simulation platform,the work process of the marine diesel engine have been analyzed.First of all,the three-dimensional model includes exhaust valve,scavenging port,cylinder and one-dimensional model which is used to acquire the initial and theboundary conditionsare built up,those modelsare based on the practical structure parameters of the original diesel engine.Then set the solver and check the simulation model at test work conditions.Based on thevalidated model,the influence of exhaust valve closing time and multi-injection strategy is tested,and the result of this research is as follows:(1)When the close of exhaust valve delayed by 5 crank angle degree on the condition of 75%load and 50%load,the generation of NOx is restrained in the combustion with almost unchanged Brake specific Fuel Consumption(BSFC).(2)On the condition of 100% load,the pilot injection leads to higher NOx emission and lower BSFC,meanwhile,the post injection has the same level in NOx emission with lower BSFC.(3)On the condition of 75% load,the pilot injection has higher NOx emission and BSFC while the post injection results inalmost NOxemission besides higher BSFC.At the same time,the influence of multi-injection consist of pilot injection,main injection and post injection is detected,small injection mass results in the decrease of NOx emission and the increase of BSFC,on the contrary,large injection mass come to the end of NOx emission as well as BSFC increase.(4)On the condition of 25% load,the pilot injection and the post injection can reduce the NOx with a rising BSFC.