Analysis of Fuel Consumption in Marine Diesel Engines Using Thermodynamic Equations

Application to the Libyan Vessel “Anwar Alnase”

Abstract

Fuel injection systems in marine diesel engines are critical factors that determine combustion efficiency, fuel consumption, and operational stability of ships. This study aims to analyze the fuel injection system performance of the main engine on the Libyan tanker M.T. ANWAAR ALNASER, equipped with a MAN B&W 6S46MC-C slow-speed diesel engine rated at 7860 kW at 129 rpm, using a computational model based on the actual technical specifications of the vessel, without the need for field measurements. Thermodynamic and hydrodynamic equations were employed to calculate the total fuel mass flow, fuel distribution per cylinder, and fuel per injection stroke. The required injection pressure was determined using nozzle flow equations, considering discharge coefficients and fuel density, while the effect of injection variations and fuel viscosity on combustion stability was also analyzed. Results showed that the fuel mass per injection is approximately 30.5 g, and the required injection pressure is around 190 bar, consistent with the manufacturer’s design specifications for the MC-C engine. A 5% variation in fuel per injection between cylinders leads to noticeable power fluctuations and an increase in exhaust temperature by about 20°C, highlighting the importance of controlling fuel viscosity and maintaining injection pumps to ensure injection stability and improved atomization. The computed thermal efficiency of the engine is approximately 50%, reflecting typical performance for slow-speed marine engines running on HFO fuel.