Simulation Research On Compound Power Turbine Of Marine Low-speed EGR Diesel Engine

Diesel engine is the main power source of ocean shipping.In order to achieve green and sustainable development,it is necessary to continuously reduce its fuel consumption and emissions.Therefore,through some technical means to achieve energy conservation and emission reduction of marine diesel engine has practical value and necessity.In order to study the application effect of exhaust gas recirculation(EGR)technology and power turbine technology on marine diesel engines,this paper takes a 5-cylinder 520 mm cylinder diameter low-speed two-stroke diesel engine as the research object.The influence of EGR on the combustion and emission of low-speed engine is studied by using simulation as the main test reference,and the power turbine is matched for low-speed engine.The optimization strategy of EGR mode and EGR combined power turbine mode(referred to as ED mode)is studied,and the operation scheme of diesel engine in the whole working condition is finally obtained.First of all,in order to obtain a more accurate EGR rate of Tier III regulation,it is found through three-dimensional simulation that the increase of EGR temperature will deteriorate NOx emissions and economy,and the increase of EGR rate will reduce NOx emissions but deteriorate economy.When EGR rate is 24.6 %,NOx emission reaches Tier III standard,and fuel consumption rate increases by 4.97 g / k Wh compared with the original engine.Secondly,the influence of injection timing and exhaust bypass on the performance of the low-speed engine is studied through one-dimensional simulation under the common working conditions of the low-speed engine,so as to determine the matching power turbine.When more than 50 % load is cut into the power turbine,the injection time can be earlier than the original engine to ensure that the power of the diesel engine is the size of the original engine,the power turbine can recover part of the exhaust energy,the explosion pressure does not exceed the limit,the NOx emission is Tier II standard,and the exhaust waste heat recovery is meaningful.Finally,based on the EGR rate obtained by three-dimensional calculation,a single turbine high-pressure EGR composite power turbine system is established to study the influence of EGR fan,injection timing and bypass on system performance.The multi-objective optimization design of EGR mode and ED mode was carried out by using isight software.The results show that when NOx emission is Tier II standard,the diesel engine operates in power turbine mode at 50 % – 100 % load,and EGR mode at less than 35 %load.When the NOx emission is Tier III standard,the diesel engine operates in EGR mode under 85 % load and in EGR or ED mode under 85 % load ～ 100 % load.