With the objective of alleviating  emissions from marine diesel engines, a variety of selective catalyst reduction (SCR) system parameters were evaluated by numerical simulation. The simulations were developed to optimize flow conditions including the uniformity of the urea droplet distribution in the exhaust gas flow, and analyzed droplet distribution at the exhaust duct for different mixer configurations and locations. The results presented in this paper show that the parameters of several devices play an important role in improving the uniformity of the flow and urea droplet distribution. Regarding the deflector plate, the concentration uniformity increases with increased diameter ratios  When the diameter ratio of the half-sphere is 0.2, the uniformity is approximately 70%. The concentration uniformity increases with the addition of the swirler. When no mixer is installed, the  distribution focuses on the middle of the catalyst. However, the  is wildly homogeneously diffused with the addition of the mixer, swirler, and deflector plate.

selective catalyst reduction (SCR), urea solution,  conversion rate,  reduction, loss of pressure drop.