Comprehensive Performance Optimization Study Of Marine Medium-speed Diesel Engines Based On Combined Application Of EGR And Miller Cycle

Diesel engines are widely used in modern ship transportation due to their good economy and power.In recent years,with the increasing environmental pollution problem,the emission of pollutants from marine diesel engines has attracted people’s attention.The International Maritime Organization(IMO)has formulated pollutant emission standards for ships traveling on the high seas,and governments of various countries have also formulated relevant emission regulations in their territorial waters according to the actual situation.With the increasingly stringent emission regulations,researchers from various countries have carried out research on diesel engine NOx emission control technologies.Among the many emission control technologies,Miller cycle and EGR are effective technical measures to reduce diesel engine NOx emissions.In this paper,the marine medium-speed four-stroke diesel engine is taken as the object to study the influence of Miller cycle,EGR,compression ratio and hydrogen mixing on the power,economy and emission of diesel engine,in order to reduce the fuel consumption loss when reducing NOx.The main work and conclusions of this paper are as follows:Taking the marine medium-speed four-stroke diesel engine as the object,the working process model of the diesel engine is established and the model is verified.Based on the diesel engine working process model,EGR diesel engine model and Miller cycle diesel engine model were established,and the effects of EGR and Miller cycle on diesel engine performance and NOx emission were analyzed.The results show that EGR can effectively control NOx emission,NOx emission decreases with the increase of EGR rate,and fuel consumption increases with the increase of EGR rate.There is a trade-off relationship between NOx and fuel consumption.Compared with high load,low load When EGR has a great influence on fuel consumption,it is not suitable to use too high EGR rate;Miller cycle can reduce fuel consumption and NOx emission within a certain Miller degree,and there is an optimal Miller valve timing angle M40.In order to reduce NOx and fuel consumption,the impact of combined technology on NOx emissions and performance of marine medium-speed diesel engines was studied,and EGR combined Miller cycle,EGR combined Miller cycle + compression ratio,EGR hydrogen mixed Miller cycle,etc.were carried out.A study of the effect of combined technologies on engine NOx emissions and performance.The research results show that compared with using EGR alone,EGR combined with Miller cycle has better effect on NOx emission control.When the Tier Ⅱ emission requirements are met,the equivalent fuel consumption increases by 3.3 g/kWh and NOx decreases by 26.7 g/kWh compared with the original engine.%;EGR combined Miller cycle + compression ratio can improve the fuel consumption of the engine on the basis of EGR combined Miller cycle.When the compression ratio is 13.7,compared with the original engine,the diesel engine equivalent fuel consumption is reduced by 0.5 g/kWh,and NOx is reduced by 24.4 %,and reach Tier Ⅱ emission standards;EGR hydrogen-mixed Miller cycle can reduce engine NOx emissions,improve diesel combustion thermal efficiency,and improve engine economy.Compared with the original engine,the equivalent fuel consumption of the diesel engine is reduced by 1.76 g/kWh,the NOx is reduced by 28.4 %,and the emission standard of Tier Ⅱ is reached.Finally,based on the principle of genetic algorithm,this paper takes the 100% load condition as an example to optimize the four variables of EGR opening,intake bypass,compression ratio,and hydrogen content.The results show that compared with unoptimized,the optimized diesel oil consumption is reduced,the single diesel optimized fuel consumption is reduced by 1.1 g/kWh,and the diesel/pure hydrogen dual fuel fuel consumption is reduced by 0.4 g/kWh,and can meet the Tier Ⅱ emission standards.