Regarding SOx and NOx, a new Annex VI of the MARPOL Convention was adopted at MEPC (Marine Environmental Pollution Committee) at IMO (International Maritime Organization) in September. 1997, and the procedures of ratification have been promoted among the parties concerned. Regarding SOx, the regulations specify that the sulfur content in the fuel shall not exceed 4.5% (1.5% only for Baltic Sea). In this connection, sulfur is contained by at least 3% in 70% of the bunker oil in the world of about 85 million tons in total supply. Regarding NOx, the upper limit for the emission was specified according to the engine speed at the rated output. In this connection, the upper limit is 17 g/kWh with large low-speed engines of 130 rpm or under.
Regarding CO2, the target value for reduction of each country was specified at the above-described COP3 in December, 1997; however, in this Framework Convention, the CO2 emission from ocean-going ships is excluded from the emission by the country. Thus, not only the allotment of the reduction in emission on the use of the bunker oil but also the grasping of the present status has been insufficient. Since COP3, the UNFCCC (United Nation Framework Convention on Climate Change) has requested the IMO to grasp the present status of the global warming gas emission attributable to the operation of ocean-going ships on the global level, and its countermeasures. In response to this request, the full examination and consideration have been started in MEPC since 1999 FY.
In order to cope with these trends, it is necessary not only to improve the hardware including the increase in the thermal efficiency of the engineitself, and the improvement of the propulsion efficiency, but also to achieve the medium-to-long technological development including the software such as the improvement of the operational mode and the mean stowage ratio. In this paper, a brave try is made in predicting the future of marine main engines intended for the suppression of global warming and reduction in CO2 emission.
