The Injecting Structural Parameters Optimization And Matching Performance Of SCR System For Marine Diesel Engine

With the development of shipping industry,the emissions of marine diesel engine are becoming more and more serious.The International Maritime Organization proposed MARPOL convention annex VI in order to cortrol NOx emissions from ships.SCR technology is one of the most promising technologies owing to its NOx emissions within the Tire III requirement.In this paper,a SCR system for a marine diesel engine was designed based on the matching diesel engine,including the design of structural parameters and urea nozzle structural parameters.The matching performance between SCR reactor and the diesel engine,and the matching performance between injecting structural parameters and SCR reactor were tested in the process.Firstly,3D simulation model of SCR reactor was established with AVL FIRE.The influence of structural parameters on SCR was analyzed subsequently.Then optimization results were obtained by simulation and theoretical calculation as follows: volume of SCR reactor was 0.036m3,CPSI was 400,the coating and wall thickness of the substrate were 0.01 mm,0.15 mm respectively.Secondly,the influence of SCR reactor on the performance of the diesel engine by test under D2 test cycles was conducted.The results indicated that: the back pressure of diesel engine with SCR reactor was 4.7kPa higher than diesel engine without SCR reactor;the maxium pressure of cylinder increased about 5.4% and earlier than oringnal engine;the emission performance was within the Tire III requirement after adding SCR reactor owing to the emission of NOx was 1.112g/k Wh;the economic performance changed worse owing to the fuel consumption increased about 1%.Lastly,the injecting parameters were optimized by the simulation model of SCR reactor established previously.The four injecting structural parameters were evaluated by uniformity of NH3 before catalyst and the conversion of NOx,the simulation results were obtained by simulation and orthogonal method.Then two urea nozzles were chosen according to the best simulation results of injecting parameters.The influence of different injecting structural parameters on SCR reactor was analyzed by test under D2 test cycles.The best injecting structural parameters were obtained as follows: the distance between urea nozzle and catalyst is 5 times the diameter of exhaust pipe(635mm),diameter of urea nozzle was 0.5mm,number of nozzle was 4,the injecting angle was 45°.NOx conversion was developed through urea injecting structural parameters optimization.