OICC Press International Journal of Energy and Environmental Engineering 2251-6832 14 4 (December 2023) 2022 10 03 Negative impact of constant RPM control strategy on ship NOx emission in waves 10.1007/s40095-022-00542-0 EN Mohammad Hossein Ghaemi Faculty of Mechanical Engineering and Ship Technology, Institute of Ocean Engineering and Ship Technology, Gdańsk University of Technology, Gdańsk, 80-233, PL Hamid Zeraatgar Department of Maritime Engineering, Amirkabir University of Technology, Tehran, IR Journal Article 2022 10 03 Abstract In severe wave conditions, the ship propulsion system is loaded with high fluctuations due to external disturbances. The highly fluctuating loads enforce radical changes in the main engine torque, which in turn demands variation of the fuel rate injected into the cylinders if a constant rotational speed strategy is applied. Therefore, the temperature of gases varies to a large extent during the combustion process in the cylinders. The emitted NOx is a function of this highly fluctuating temperature. The main goal of this study is to investigate NOx emission under the aforementioned conditions when a usual constant RPM control strategy is applied in waves similar to the calm water condition. The paper presents a mathematical model of the whole system, which is applied to a selected ship both in regular waves and in calm water conditions. The results show that the sea waves, in comparison with the calm water condition, can radically increase the emitted NOx under the constant rotational speed strategy. This change can reach even 10 14 times more, averagely. The results also show that the higher the wave height the higher the emitted NOx. It is concluded that the control strategy of keeping the engine rotational speed in waves at a constant level is the most important reason for the significantly increased NOx emission in waves in comparison with the calm water condition.