Numerical Study On The Injection And Mixing Processes Of Urea Solution In SCR System For Marine Diesel Engines

Diesel engines are widely used in marine power systems as the core power due to their excellent reliability and economy.With the development of society,the issue of engine pollutant emissions has received unprecedented attentions.the International Maritime Organization has increasingly higher requirements for the pollutant emissions of marine diesel engines.China is keeping up with the pace of foreign countries,formulating and rapidly iterating relevant emission regulations.As a very important pollutant in exhaust emissions,the reduction of NOx emissions require post-treatment technology.under this background,a numerical study on the urea solution jet mixing process of the SCR post-processing system was conducted in this thesis.This was performed using the CFD software CONVERGE.The main body of the research is the spray mixing process of the urea solution in the SCR system.The urea solution with a concentration of 32.5% is used as the object to study the spray pressure,the angle between the nozzle hole and the nozzle axis(hereinafter referred to as the nozzle hole angle),spray cone angle and ambient temperature.The influence of a single variable on the effect of the urea solution jet mixing process.In this paper,a simulation experiment is designed by orthogonal experiment method to explore six important factors in the spray mixing of urea solution in the SCR system,including spray pressure,nozzle number and diameter,nozzle angle,spray cone angle,ambient temperature and the distance between the mixer and the nozzle.For the influence of the injection process of the urea solution,an orthogonal table of six factors and five levels is designed,and the best combination scheme of the injection mixing system is obtained through data analysis.The results show that increasing the spray pressure and internal environmental temperature can promote the development of the urea solution spray and make the spray more uniform;increasing the number of nozzle holes can quickly improve the uniformity of the spray;increasing the angle of the nozzle hole and the axis,the spray distribution follows As the angle increases,the spray uniformity first becomes better and then becomes worse.In this paper,the orthogonal experimental design method is used to design,calculate and analyze the six factors of spray pressure,nozzle number and diameter,nozzle angle,spray cone angle,ambient temperature,and the distance between the mixer and the nozzle.The results show that in the analysis based on the uniformity of ammonia distribution,the order of influence of the six factors is as follows: spray cone angle > distance between mixer and nozzle > ambient temperature > number of nozzle holes and diameter > nozzle hole angle > injection pressure.The various factors of scheme X,the spray pressure is 0.7MPa,the number of holes is 4,the aperture is 0.0035 m,the angle between the nozzle and the axial direction is 30°,the spray cone angle is 30°,the temperature is 600 K,the distance between the mixer and the nozzle It is0.25m;in the analysis based on velocity uniformity,the order of influence of the six factors is:temperature> spray cone angle> mixer distance> nozzle number and diameter> nozzle hole angle> spray pressure;the optimized plan Y parameter: the pressure is 0.3MPa,the number of holes is 4,the aperture is 0.0035 m,the angle between the nozzle hole and the axial direction is 10°,the spray cone angle is 15°,the temperature is 700 K,and the distance between the mixer and the nozzle is 0.2m.In summary,after comprehensive factor analysis,the spray pressure is 0.7MPa,the number of holes is 4,the hole diameter is 0.0035 m,the spray hole angle is 30°,the spray cone angle is 30°,the temperature is 600 K,and the distance between the mixer and the nozzle is0.25 m is the optimal combination of multiple factors affecting uniformity.