Simulation Study On Urea-SCR System To Reduce Nitrogen Oxide Emissions From Marine Diesel Engines

While China's marine transportation industry is developing rapidly,marine diesel engines emit substances that are harmful to the human body,the environment and the entire ecosystem,such as NOx,SOx,HC and particulate matter.Under the increasingly strict requirements of people's living environment,China's domestic and international maritime organizations have issued a series of regulations on ship emissions,requiring control of emissions of NOx from marine diesel engines.It is a very effective way to reduce the NOx emission of marine diesel engines by using Urea-SCR system(Urea selective catalytic reduction reaction system).Therefore,the in-depth study of Urea-SCR system is beneficial to control the emission of nitrogen oxides from marine diesel engines,which is beneficial to provide people with a healthy living environment is conducive to slowing down the global pollution process.Firstly,based on the main engine operating parameters and exhaust emission parameters of a marine diesel engine,the parameters of each component of the Urea-SCR system matched with the marine diesel engine are calculated,and the three-dimensional physical model of the Urea-SCR device is established,and related literature and The experiment compares the feasibility of the numerical simulation method.Secondly,the FLUENT fluid simulation software is used to explore the factors affecting urea injection.Again,the numerical simulation method is used to influence the factors affecting the catalytic reduction reaction in the SCR catalytic converter.In the end,the numerical simulation method was used to explore the influence of the installation method between the various components in the Urea-SCR system and the external geometry of the system on the entire Urea-SCR system.Through the research of this thesis,the feasibility of the numerical simulation method adopted in this thesis is verified.In addition,the six-nozzle with wall spray method,the nozzle diameter of 0.3mm,the injection speed of 10.6m/s,the higher exhaust gas temperature and lower exhaust flow rate are beneficial to improve the Urea-SCR system urea spray atomization effect;Low airspeed,high exhaust gas temperature,nitrogen to ammonia ratio around 1 and appropriately lengthened catalyst are beneficial to increase nitrogen oxide conversion rate and reduce ammonia gas leakage;smaller expansion angle is beneficial to increase ammonia gas.Distribution uniformity index,increase nitrogen oxide conversion rate and reduce system pressureloss.Properly increasing the distance between the urea nozzle and the front end surface of the SCR catalyst is beneficial to increase the ammonia gas distribution uniformity index and increase the nitrogen oxide conversion rate,but will not change the system and the pressure loss.The research work of this thesis can provide a reference for the design and research of marine diesel engine Urea-SCR system.