Fuel oils currently employed in marine machinery systems are of the lowest grade heavy fuel oil, which is a mixture of various hydrocarbons with high concentration of sulfur, nitrogen and residual carbons as well as metal components. The combustion of marine fuel oils leads to the generation of high-concentration aerosol, i.e., MPM (Marine Particulate Matter), but the characteristics of combustion products and its contribution to MPM are not well understood yet. IMO (International Maritime Organization) is making urgent efforts to grasp the actual state of MPM emission from marine traffic, and seeking countermeasures. The present work studied the formation and decomposition of particulate matter during the spray combustion of marine heavy fuel oil with an industrial- scale stable diffusion flame, focusing on the influence of air/fuel ratio. As a result, sprayed droplets of marine fuel oil are well mixed with combustion air both inside and near the flame funnel cone. Pyrolysis reactions are dominant upstream of the flame, where a large number of unburned droplets exist contributing the formation of THC and SOF. It is shown that the formation of particulate matter is reduced by increasing the air/fuel ratio.
