Abstract
Greater part of Japanese domestic commercial ships install Low-speed, four-stroke trunk piston type engines as their primemovers enjoying its merits in fuel economy and maintenance cost.
Marine engines have been improved restlessly to be less fuel consumption, higher output, and availability of low quality fuels especially since world oil crisis.
Fuels supplied to ships recently have mainly been manufactured in catalysis process plant or distilled residues thined down by visbreaker-refined light oil because oil suppliers make their process fit to increasing market demands of lighter oils.
Fuels manufactured by these process have negative properties such as low ignition quality, long combustion period and low thermal stability that cause troubles in engines and auxiliary machineries.
Considering that there is close relationship between contamination of system oil and bad combustion inside engine, we studied system oil contamination and fuel quality comprehensively.
As a result of this study, we have establishied a guideline with which engineers are able to judge whether system oil contamination has been caused by bad combustion of engine or other reasons.
