There is also the possibility, in California and regions around Japan, of a demand for NOx countermeasures that go beyond even those of the proposed 2nd stage NOx regulations.

　

6.1 Effective reduction at partial loads

Effective reduction at partial loads will be more important when regional regulations on NOx have to be met by engines themselves. On the other hand, similar reduction rates of NOx emission may not be realized at every load level when overall emission reduction of a test cycle has to be reduced (see Fig.9b and 6c).

　

FiG.9 Scheme for NOx reduction for marine main diesel engine

　

In the case of SCR, denitrification efficiency decreases theoretically when the temperature of exhaust gas from a diesel engine is low. We are now considering an "absorbent-SCR catalyst" hybrid system, which absorbs NOx when the temperature of exhaust gas is low, in departure, and uses the separated urea as a deoxidization agent to denitrificate NOx in heavy load [5].

If regional control is required, for example within ports and coastal areas, technologies with a high reduction rate of NOx emission will be used only for a limited part (probably less than 5%) of the operation time of main diesel engines. This will lead to introduction of technologies which can change the reduction rate during operation. Use of water, such as water injection, and application of emulsion fuel in diesel engines will be effective since they allow the reduction relatively easily. Fuel injection adjustment mechanisms such as VIT and electronic fuel injection control technology to regulate combustion comprehensively are also promising.

　

6.2 Achievement of both NOx and C0₂ reductions

Technologies to reduce NOx emission are already mentioned above, but UNFCCC requires IMO to consider suppression of CO₂ generation. In diesel engines, there exists trade-off between NOx emission and CO₂ emission. Technological development of diesel engines to realize both improvement of thermal efficiency and reduction of NOx emission will be increasingly important from now on. Development of a super marine gas turbine, or SMGT, is under way with support from The Nippon Foundation and the Ministry of Transport, to achieve 90% reduction of NOx emission without increasing its fuel consumption more than the conventional high-speed diesel engines [6]. Their mass production will lower the cost in future.

One option could be navigation in accordance with lenient IMO regulations in waters far from lands but with reduced NOx emission in expense of thermal efficiency in coastal waters. Balance between these two should be discussed after its implications in global and regional environment and economy of the technology are assessed more thoroughly and quantitatively.

　

6.3 Application of alternative fuels and renewable energies

In the long term, development of technologies, such as navigation systems with alternative fuels and renewable energies, which have not been cost-competitive so far, may need to be addressed. A system to produce calorie rich hydrogen and carbon monoxide from natural gas and CO₂ in exhaust gas by catalyst and exhaust heat is now being developed [7].

In our country, research on sailing ships reached the level of commercialization 20 years ago, but decline of fuel price at that time prevented it. However, new materials developed since then may reduce their production cost.

Recently, fuel cells have been rapidly developed for commercialization on land. Their generation capacity, however, is not sufficient for application to main engines in ships, and further development in future is required [8].

　

6.4 Reduction of load on environment through alternative transportation and port systems

In addition to the regulation on ships, or marine engines, future options could be power supply from land during loading to tankers at large-scale sea-berth for exclusive use and the improvement of medium to small-scale engines in vehicles for loading at ports, such as straddle-carrier and transfer-crane, and pleasure boats. Reorganization of overall transportation systems would be required, including a shift from transportation by trucks to high-speed marine transportation. This shift in transportation is not necessarily successful in Japan due to the delay of modernization in the taxation system and port loading regime. There even exists a social tendency for operators to shift too less expensive transportation by trucks. However, environmental superiority of other transportation such as transportation by ships will become obvious when we evaluate quantitatively the external cost associated with transportation by trucks, for example their long-term impacts on human health and vegetation and the economic loss by heavy traffic in cities. It is necessary to compare the social cost of overall transportation systems, including TCA, and to present the result actively to society.

　

[1] Ship & Ocean Foundation, "Investigation of Vessel Exhaust Gas Effects on the Environment and its Solutions" (1999)

[2] Ship & Ocean Foundation, "Investigation of Effect to Environmental and Prevention Technology on Exhaust Emission from ships (in Japanese)" (1991)

[3] Kondo, A, and K. Yamaguchi, E. Nishikawa et al., Proceedings of the 38th annual meeting of the Japan Society for Atmospheric Environment.(1997), p340

[4] Ship & Ocean Foundation "Development of NOx Reduction Technology on Diesel Engine for Ships (in Japanese)" (1994)

[5] Ship & Ocean Foundation "Research and Development on Catalyst on for Exhaust Emission for internal trading ships (in Japanese)" (1998)

[6] Super Marine Gas Turbine Research Union (in Japanese), http://plaza18.mbn.or.jp/~smgt/

[7] Ship & Ocean Foundation "Research and Development on LNG Engine for Ships -Intermit Report- (in Japanese)" (1998)

[8] Ship & Ocean Foundation "Research and Development of fuel cell for ships (in Japanese)" (1994)

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