Effects of torsional vibration of a propulsion shafting system and energy efficiency design index from a system combining exhaust gas recirculation and turbocharger cut out

Abstract

Recently constructed vessels are equipped with super long stroke engines to accommodate stiffer environmental regulations and to reduce fuel consumption. This is a way to reduce fuel consumption in main engines for propulsion by improving propeller efficiency and thermodynamic efficiency of the engine. However, ships intended to accommodate nitrogen oxides regulations must satisfy the Tier III regulation prescribed by the International Maritime Organization. For this purpose, the vessel should apply additional nitrogen-oxide reduction facilities. When an exhaust gas recirculation (hereafter EGR) system is applied for the exhaust gas reduction, not only is the fuel consumption increased according to the amount of EGR, but the vibration excitation force tends to increase as well. In addition, there is a limit to the engine control technology that can be applied to optimize fuel consumption under partial load, even if the ship travels in areas other than NOx emission control areas, the fuel consumption of the engine is high. Therefore, it is necessary to change the design of the ship so that fuel can be saved even in areas other than NOx emission control areas by applying the turbocharger cut out (hereafter TCCO) method. In this paper, the performance and dynamic characteristics of a marine diesel engine were compared and reviewed when applying a combined system of EGR and TCCO. Also examined were effects on the torsional vibration of a corresponding propulsion shafting system and the energy efficiency design index (hereafter EEDI) according to each operating condition of the engine applied with this system.