Experimental And Numerical Analysis Of Marine Diesel Engine SCR System

For the past few years,the emissions of nitrogen oxides in marine diesel engines are increasingly concerned.International Maritime Organization(IMO)has developed the Tier ? standard to limit the ship's NO_x emissions.Selective catalytic reduction(SCR)technology is an effective measure to reduce NO_x emission.In the SCR system of diesel engine,the reasonable size of the catalyst and the distribution of the reducing agent have great influence on the performance of the denitrification.In this paper,targeted on the 6G60ME-C9.2 MAN diesel engine,the SCR reactor and urea injection strategy is studied.First of all,sensitivity analysis and absolute rate analysis were used to simple the chemical reaction mechanism of ammonia oxidation by using the business software CHEMKIN-PRO.The 95 step detailed chemical reaction mechanism is simplified as the 12 step basic element reaction mechanism,and the simplified mechanism is compared with the original mechanism.Then,the SCR experiment platform was designed to test the performance of SCR catalyst.By using commercial software FLUENT to simulate the process of denitrification,the numerical simulation was fitted with the experimental results to determine the site density of the catalyst.Finally,the reasonable size of the SCR reactor and the arrangement of the urea injection system were determined by using the simplified mechanism and the detailed mechanism of the other parts.In addition,the influence of the size of SCR catalyst on the denitrification rate,the influence of the angle of the expansion tube,the number of the nozzle and the distribution of the distribution of the reducing agent were studied.Through the analysis,the following conclusions are obtained:Ammonia oxidation reaction is weak in 350?.1000ppm ammonia oxidation rate is lower than 5%.The temperature has a great influence on the catalyst activity.At about 350 degrees,the activity of V2O5 catalyst increases with the increase of the temperature.The size of the catalyst has a great influence on the denitrification rate.The total denitrification rate increases,but the unit volume decreases with the increase of the volume of the catalyst.At the same catalyst volume,The total denitrification rate is similar and there is a optimal aspect ratio of length to width.The velocity distribution of the flow field has a great influence on the angle of the expansion tube.The smaller the angle of the expansion tube,the more uniform distribution of the flow field,but it will lead to the increase of the size of the expansion pipe,the design needs to be combined with the actual situation,select the appropriate angle of the expansion tube.The number of nozzles and the center distance have great influence on the uniformity of the jet.Too many nozzles,too little center distance can lead to uneven distribution of reducing agent.When the number of nozzles is constant,the distribution of the reducing agent is increased with the increase of center distance.