Study Of The Marine SCR System Reducing Agent Injection

In this thesis, based on the emission regulations of Tier ?,the main frame parameters of diesel engine and the exhaust emission data, taken a certain type of Marine diesel engine as the research object, the system that matches to the diesel engine has been designed. Moreover, the geometric model of the SCR catalytic converter has been built and the corresponding boundary conditions have been established. A stimulation has been made by the application of the discrete phase model of Fluent software to the Urea solution spray and the flow and distribution of diesel exhaust. At last, based on the uniformity evaluation index of velocity, the analysis of the simulation results has been made. Studies are carried out through the following aspects:(1) In order to improve the uniformity of Urea spray solution distribution and make it more completely contacted with the engine exhaust, the three-dimensional numerical model of the SCR reactor has been established in accordance with the emission data of diesel engine, emitted dose of Urea solution and assumed conditions. Using the discrete phase model of Fluent software, stimulated the impact of some parameters, such as the injection location and the distance of the reactor inlet nozzle, the position of jet nozzle, the reactor inlet Angle, different reactor section on the spray and the mixing uniformity of exhaust. The evenness index is concluded under different parameters by analyzing the simulation results based on the uniformity of velocity evaluation index. Then the establishment of spray parameters and reactor parameters when the Urea spray and the exhaust are mixed completely. In order to make the mixing effect of the Urea solution spray droplet and the exhaust much better, the author designed a static mixer to make a stimulation of spray and mixing conditions before and after the installation and analyze the effect of the mixer.(2) During the process of studying injection scheme of reductants of SCR system, in order to test the impact the injection effect of reducing agent on the efficiency of the SCR catalytic reduction reaction system, the author stimulated different influences of various temperatures, Re, NO entrance concentrations of NO and space velocities on catalytic conversion rate of NO on the basis of chemical reaction of single-hole way 3-D model based on the Eley-Rideal mechanism, take the V2O5 / TiO2 as the catalyst, take the data mixed by reducing agent and the exhaust as boundary conditions. Through the stimulation, the author found the main factors that affect the efficiency of catalytic reduction reaction and drew out the relation curve between the entrance concentration and the airspeed of temperature, Re, No and reaction efficiency. In addition, the analysis can verify the reliability of the reducing agent injection scheme, and can concluded the optimal catalytic reaction conditions which provide certain reference for structure optimization design of the reactor.(3)According to the simulation conclusion, the author installed the SCR post-processing system on the4102 type diesel engine. Choose the four hole nozzle, the best spray effect, when the motivation operated in a steady state, and spray the Urea aqueous solution to the exhaust duct injection along the central axis of exhaust pipe, then record the NOX content of Urea injection before and after the reactor outlet. In addition, the author conducted ESC test by applying two different catalytic reactor, the research test found because of the leaking of ammonia, when the amount of the Urea solution spray too much, the NOX value of the catalytic reactor increased instead of decreasing; when the engine exhaust temperature is too low or too high, the catalytic reaction efficiency of both catalytic reactor are low.