Co-simulation And Design Of SCR System And Exhaust Muffler For Marine Four-stroke Diesel Engine

With the third phase emission regulations(Tier III)of the International Maritime Organization(IMO),strict limits are imposed on the content of nitrogen oxides(NO_x)in the flue gas emitted from marine diesel engines and the establishment of Chinese water emission control zone(ECA).Adding denitration purification equipment to the exhaust system of diesel engines has become an inevitable choice.SCR technology has become the first choice for reducing theNO_x emissions of marine diesel engines by virtue of its mature technical solutions and good economy.Typically SCR reactors consist of a metal shell and SCR catalysts as well as ancillary systems and equipment.The metal shell makes the exhaust pipe of the diesel engine form a sudden change in the cross section of the inlet and outlet of the SCR reactor,which has the ability to eliminate sound at medium and low frequencies.The porous structure of the SCR catalyst makes it have high frequency noise cancellation capability.At the same time,the exhaust noise of the marine diesel engine is the main noise source of the ship,and the exhaust muffler must be installed in the exhaust system of the marine diesel engine.Therefore,in the exhaust system of the diesel engine,it is a preferable measure to jointly design the SCR system and the exhaust muffler to form an integrated exhaust gas muffler.The exhaust gas purification muffler not only achieves the dual functions of denitration purification and control of exhaust noise,but also saves space.There is an integrated exhaust gas purification muffler application in the automotive field.This paper draws on the application experience of the vehicle exhaust purification muffler,and jointly simulates and designs the SCR system and exhaust muffler of the MAN9L32/40 Tier II four-stroke medium speed diesel engine hosted in a certain type of traffic supply ship.An exhaust gas purification muffler was designed.It mainly includes the following aspects.(1)Using the joint analysis method of power system,flow field and sound field,combined with commercial software GT-Power,Fluent and LMS Virtual.Lab for joint simulation,calculation of preliminary design and configuration in marine MAN 9L32/40diesel engine exhaust purification muffler pressure loss and noise reduction.The simulation results show that the pressure loss of the exhaust gas muffler is less than 2.5 kPa,a At the same time,according to the insertion loss value,it has a good sound-absorbing effect in most frequency ranges.(2)For the uneven distribution of reactants in the inlet section of the catalyst and the poor sound elimination at some frequencies for the preliminary design of the exhaust gas purification muffler,By adding a flow guiding device in the expansion section and adding a perforated pipe and a perforated plate structure in the middle section of the exhaust gas purification muffler,the purpose of optimizing the distribution of the reactants in the inlet section of each layer of the catalyst and optimizing the effect of the noise at the partial frequency is achieved,at the same time,it is analogous with the parameters of the actual ship,and the results all meet the IMO Tier III standard,the pressure loss is less than the solution of the independently configured SCR reactor and exhaust muffler.(3)For the soot blowing and replacement requirements of the SCR catalyst in the exhaust gas purification muffler,the structure of the exhaust gas purification muffler has been refined accordingly,and according to the requirements of the shipyard,the system design and key equipment selection of the auxiliary supply system of the exhaust gas purification muffler were carried out according to the supply demand of the reducing agent for the SCR reaction and the conditions on board.