In the marine engineering field, research has been conducted to reduce fuel consumption and emissions of harmful exhaust gases from medium- and low-speed diesel engines by improving supercharging performance, scavenging efficiency, and introducing electronic control technology, etc., and these technologies have been put to practical use. However, most of these technologies have been applied to newly constructed vessels, and oxygen-containing fuels such as water-emulsion fuel and DME fuel have not yet been put to practical use. In this study, the effects of heating high viscosity residual oil and mixing air into the fuel as fine bubbles on the combustion and exhaust characteristics of the fuel were investigated using a practical medium-speed marine diesel engine. As a result, the fuel consumption reduction effect was confirmed when fine air bubbles were mixed in heated residual oil, as is the case with them being blended into marine diesel oil. In particular, the maximum reduction was 7% at 75% load and 0.2L/min air volume, and the average reduction was 3.2% at 75% load. In terms of the exhaust gas characteristics of the fuel, no significant reduction in NOx was observed when microbubbles were mixed, but smoke values were reduced by up to 33%.
