Methanol sprays in marine internal combustion engines

Abstract

The maritime industry is a major contributor to global emissions, particularly carbon dioxide (CO₂) and nitrogen oxides (NOₓ), which has led to increasingly strict environmental regulations from organizations such as the International Maritime Organization and the Paris Agreement. These regulations are driving the search for sustainable alternatives to conventional fossil fuels in marine internal combustion engines. Methanol has emerged as a promising candidate due to its potential for renewable production, its liquid state under ambient conditions, and its ability to reduce harmful emissions compared to fuels like diesel. However, its adoption presents challenges, especially in fuel injection and mixture formation, due to its distinct physical properties such as high latent heat of vaporization, higher vapour pressure, and lower energy density. As most existing models are based on conventional fuels, there is a lack of understanding of methanol spray behaviour under realistic engine conditions.

This PhD thesis addresses these challenges by developing a computational fluid dynamics (CFD) framework using CONVERGE-CFD, incorporating both Reynolds-Averaged Navier–Stokes (RANS) and Large Eddy Simulation (LES) approaches. The framework is used to analyse methanol spray behaviour in conditions relevant to marine engines, covering both port fuel injection (PFI) and direct injection (DI). The study begins with a literature review that introduces a unified classification of methanol injection and ignition strategies, clarifying existing definitions and identifying knowledge gaps. The modelling framework is then validated using experimental data and applied to investigate atomization, evaporation, and spray dynamics under different injection conditions. Results show that while higher injection pressures improve atomization, evaporation remains limited, and spray-wall interactions play a dominant role in mixture formation.

Further analysis under direct injection conditions reveals unique spray phenomena specific to methanol, such as plume collapse and sweeping, which are successfully captured through careful model calibration. The research also examines methanol use in dual-fuel engines, highlighting the significant cooling effect caused by its high latent heat. This cooling can reduce local temperatures by up to 100 K, potentially hindering combustion and increasing variability. Overall, the study provides a validated and efficient modelling framework that improves understanding of methanol spray behaviour and supports the optimisation of methanol-fuelled marine engines, contributing to the transition toward more sustainable maritime energy systems.