Large two-stroke marine diesel engines are used as the prime mover in the majority of ocean going commercial vessels and are currently facing new stringent NOx emission reductions. Selective catalytic reduction is an aftertreatment technology which is able to reduce emitted NOx at allowable levels. In most marine applications, the selective catalytic reduction system is placed on the high pressure side of the turbine, due to limitations at the exhaust gas temperature at the inlet of selective catalytic reduction system. In this article, the operation of a large two-stroke marine diesel with a selective catalytic reduction aftertreatment system, is investigated in heavy weather conditions. Operation of a vessel in heavy weather results in increased ship resistance, wave-induced ship motions, and a highly varying flow field in the propeller due to ship motions. This results in a fluctuation of propeller demanded torque and hence a fluctuation in engine load and exhaust gas temperature which may affect engine and selective catalytic reduction performance significantly. To investigate this phenomenon and taking into account the engine–propeller interaction, the entire propulsion system was modeled, namely the propulsion engine, the high pressure selective catalytic reduction system, the directly driven propeller, and the ship’s hull. A propeller model was employed to simulate the transient propeller torque demand and torque fluctuations due to ship motions. A three-dimensional six degrees of freedom panel code was used to calculate ship motions and wave added resistance in regular waves. The coupled model of the marine propulsion plant was validated against available measured data from a ship-board propulsion system on good weather conditions. The model was then used to simulate the behavior of the system during transient loading conditions in the presence of regular waves.

中文翻译：

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与选择性催化还原排气后处理系统耦合的直驱大型船用二冲程发动机在波浪中运行时的响应

大型二冲程船用柴油发动机被用作大多数远洋商船的原动力，目前正面临新的严格的 NOx 减排。选择性催化还原是一种后处理技术，能够将排放的 NOx 减少到允许的水平。在大多数船舶应用中，由于选择性催化还原系统入口处废气温度的限制，选择性催化还原系统放置在涡轮机的高压侧。在本文中，研究了具有选择性催化还原后处理系统的大型二冲程船用柴油机在恶劣天气条件下的运行情况。船舶在恶劣天气下运行会导致船舶阻力增加、波浪引起的船舶运动、由于船舶运动，螺旋桨中的流场变化很大。这会导致螺旋桨所需扭矩的波动，从而导致发动机负载和废气温度的波动，这可能会显着影响发动机和选择性催化还原性能。为了研究这种现象并考虑发动机-螺旋桨的相互作用，对整个推进系统进行了建模，即推进发动机、高压选择性催化还原系统、直接驱动的螺旋桨和船体。采用螺旋桨模型来模拟由于船舶运动引起的瞬态螺旋桨扭矩需求和扭矩波动。三维六自由度面板代码用于计算常规波浪中的船舶运动和波浪附加阻力。船用推进装置的耦合模型根据来自船载推进系统在良好天气条件下的可用测量数据进行了验证。然后使用该模型来模拟系统在规则波存在的瞬态加载条件下的行为。