抄録
Since oil crisis in 1973, oil price has increased and the running cost of vessels has become enormously high, which has resulted in a necessity of much more economical designs for diesel engines as well as a decrease in the optimum speed of vessels. Consequently, many vessels in service have become equipped with overpowered and less economical propulsion machinery, compared when they were first launced in service. Under such circumstances, a concept for modernizing 2-stroke engines in service has been developed. The conversion for modernization is carried out mainly by using standard components from the new L-MC engines with a smaller cylinder diameter. The modernization brings almost the same specific fuel oil consumption figures as the L-MC engines, corresponding to a reduction about 20%, by means of conversion from impulse to constant pressure tubocharging systems and increase in a stroke/bore ratio, thereby increase in maximum cylinder pressure.
The first conversion in the world has been carried out from Mitsui-B&W 10K90GF to 10K90 70MG for modernization. A reduction in specific fuel oil consumption about 30g/BHP/h {11g/MW/s} has been reached, and a good service result has been obtained after the conversion.
