The Numerical Study Of In-cylinder Emission Reduction Technology To Meet The Tier Ⅱ And Tier Ⅲ Emission Regulations In A Marine Engine

Due to environmental degradation in recent years,people are paying more attention to environmental protection,the emission regulations are becoming more stringent for marine engines in the world,and the IMO Tier III emission regulations have been carried out in 2016 for ECA(emission control area),which arise more challenges for emission control technologies.In the current study,CFD(computational fluid dynamics)simulations are used to explore the optimal in-cylinder emission reduction technology to meet Tier II and Tier III emission regulations.In this study,KH-RT spray breakup model of multi-component HFO(heavy fuel oil)is validated in a constant volume chamber using CONVERGE.Next,further optimization of fuel injection system was carried out based on the validated spray model,solution 2(nozzle number is 4 and nozzle diameter is 0.875 mm)was chosen as the optimized nozzle solution considering the economy,emissions and the difficulty of nozzle machining.Besides,based on this nozzle solution,the optimization of injection strategies on the performance and emissions are carried out to explore the optimal fuel injection strategies for different emission control area.The results show that whatever the fuel you use(HFO or diesel),the sequential injection,pilot-injection and postinjection all have the potential of simultaneously reductions of NOx emission and fuel consumption.Lower fuel consumption and NOx emission can be realized by using large and small proportion of pilot-injection with proper injection interval(main-injection and pre-injection),respectively.Fuel consumption can’t be significantly improved by post-injection strategy.Sequential injection coupled with pre-injection has the potential for further decreasing the NOx emission,but has negative effects on fuel consumption.In this paper,the optimal strategies to meet the Tier II and Tier III emission regulations are purposed based on the optimization results of injection system coupled with retarded injection timing,valve strategies and EGR.The results show that retarded injection timing,E-EVC(early exhaust valve close)and L-EVC(late exhaust valve close)can meet the Tier II emission regulation,however,deteriorated fuel consumption was observed with retarded injection timing.Light E-EVC could significantly improve the fuel consumption,while limited by max pressure.L-EVC also has the capability to reduce fuel consumption,but it is limited by the boosting capability of turbocharger.Heavy EGR combined with proper injection timing is able to meet the Tier III emission regulation while maintaining good fuel consumption.The exhaust valve strategies coupled with EGR can decrease the dependence on external EGR and won’t deteriorate fuel consumption.To summarize,the present work develops the in-cylinder emission reduction technology based on variable valve,fuel injection strategies and EGR so as to meet the Tier II and Tier III emission regulations.It can guide for the realization of highefficiency and clean combustion for marine engines and also has practical value for the development of new marine engine.