Selective catalytic reduction (SCR) systems are among the most effective methods used to reduce NO_X emissions in internal combustion engines. SCR system performance is directly related to exhaust gas characteristics such as temperature and mass flow rate. Two-stroke engines commonly used in ships have different exhaust gas temperatures compared to four-stroke engines. In low-speed two-stroke diesel engines, the gas temperature drops after the exhaust gas expand in the turbocharger turbine, affecting SCR system performance. The main objective of this study is to determine performance parameters of marine SCR systems using computational fluid dynamics (CFD). The working processes of low-pressure SCR (LP-SCR) and high-pressure SCR (HP-SCR) systems were examined comparatively. The SCR system was modeled to include urea-water solution (UWS) decomposition and catalytic reduction reactions in the study. In the designed model, the amount of injected urea-water solutions (UWS), SCR bypass valve (RBV) opening, thermolysis and hydrolysis reactions, ammonia (NH₃) slip and NO_X reduction performances were investigated. In addition, pressure drop, velocity distribution and optimal catalyst length were determined on the model. The results showed that an increase in UWS reduces NO_X emissions however increases the probability of NH₃ slip. Increasing the RBV opening also reduced the pressure loss, which was beneficial to engine performance. However, the increasing RBV opening decreased the NO_X reduction performance and increased the NH₃ slip. The optimal SCR catalyst length was determined as 1200 mm. Furthermore, in the studies carried out under the same boundary conditions, the HP-SCR system meets the IMO Tier III standard, but it was observed that the LP-SCR system could not meet the standard due to the decreasing temperature in the turbine.

选择性催化还原 (SCR) 系统是用于还原 NO _X的最有效方法之一内燃机的排放。SCR 系统性能与废气特性如温度和质量流量直接相关。与四冲程发动机相比，船舶中常用的二冲程发动机具有不同的废气温度。在低速二冲程柴油机中，废气在涡轮增压器涡轮中膨胀后气体温度下降，影响SCR系统性能。本研究的主要目的是使用计算流体动力学 (CFD) 确定船用 SCR 系统的性能参数。对低压SCR（LP-SCR）和高压SCR（HP-SCR）系统的工作过程进行了比较研究。SCR 系统被建模为包括研究中的尿素水溶液 (UWS) 分解和催化还原反应。在设计的模型中，₃ ) 研究了滑移和 NO _X还原性能。此外，在模型上确定了压降、速度分布和最佳催化剂长度。结果表明，UWS 的增加减少了 NO _X排放，但增加了 NH ₃泄漏的可能性。增加 RBV 开度也减少了压力损失，这有利于发动机性能。然而，增加 RBV 开度降低了 NO _X还原性能并增加了 NH ₃滑。最佳 SCR 催化剂长度确定为 1200 mm。此外，在相同边界条件下进行的研究中，HP-SCR 系统满足 IMO Tier III 标准，但观察到 LP-SCR 系统由于涡轮机温度降低而无法满足标准。