Simulation research on working performance of methanol/diesel low-speed engine equipped with integrated MOC + SCR aftertreatment

In response to increasingly stringent emission reduction requirements, methanol holds great potential as an alternative fuel for marine applications. This study proposes an aftertreatment system targeting pollutants emitted by methanol/diesel low-speed engines, which consists of methanol oxidation catalyst (MOC) and selective catalytic reduction (SCR). By establishing models of the methanol/diesel engine and its aftertreatment system, this research systematically analyzes the impact of the MOC + SCR aftertreatment system on engine performance and emissions under both diesel mode and methanol mode. Then, a comparative analysis of the energy balance of the engine with and without the MOC + SCR system was conducted. The results indicate that at 25%, 50%, 75%, and 100% load, the brake specific fuel consumption (BSFC) in pure diesel mode is significantly lower than that in methanol mode, while the exhaust temperature is higher than in methanol mode. After adding the MOC + SCR aftertreatment system in methanol mode, the BSFC generally increases, while the exhaust temperature generally decreases. Except at 25% load, the conversion efficiency of MOC for HC and CO can reach 100%. Under all four engine loads, the conversion efficiency of SCR for NO X can reach 100%. It can be seen that the effect of combined aftertreatment system on pollutant removal can meet ideal requirements. After installing the aftertreatment system, the engine’s brake efficiency is reduced by about 3.7% under medium and high loads, which is within an acceptable range. This study can provide fundamental theoretical and technical support for achieving ultra-low emissions in marine methanol/diesel low-speed engines.