Comparative Study on the Performance of Marine Diesel Engines Running on Diesel/Methanol and Diesel/Natural Gas Mode

Abstract

With the increasingly stringent requirements of international decarbonization regulations, the shipping industry has accelerated the pace of exploiting low-carbon fuels. Methanol is one of the most prospective substitute fuels featured with low-carbon content, clean combustion and easy storage. For marine diesel/methanol dual-fuel engine applications, a certain quantity of diesel is typically used to ensure a stable ignition and combustion. However, the combustion and emission characteristics as well as the stable operation window of marine diesel/methanol dual-fuel engines under different operating loads have not yet been well investigated. In this study, a marine diesel/natural gas dual-fuel engine was used as a prototype to develop a 3D simulation model using CONVERGE, which was then validated using experimental data under different operating loads. The validated model was then employed to investigate the effects of methanol substitution rate (MSR) on the combustion and emission characteristics under the diesel/methanol operation mode. By monitoring the abnormal combustion phenomena such as misfire and knocking, the maximum MSR under different operating conditions was identified. Finally, the engine performances of diesel/natural gas and diesel/methanol modes were compared in terms of combustion and emission characteristics. The results show that the maximum MSR tends to increase first (from 5% to 43% under operation load from 25% to 75%) and then decrease (from 43% to 20% under operation load from 75% to 100%) with increasing operating load owing to the misfire limitation at low load and knocking limitation at high load, respectively. Comparing to the prototype diesel/natural gas mode, the diesel/methanol mode exhibited a shorter combustion duration with increased NOx emissions. The results obtained from this study are expected to guide the operation management of marine diesel/methanol dual fuel engines, and thus help reduce ships’ CO2 emissions.