Kazuyuki Maeda, Yutaro Wakuri, Koji Takasaki, Shin-ichi Morishita

　

In the Shadow graph in the figure, the shadow of the light caused by the changes in density of the gas or liquid is projected on the film, and the behavior of the fuel vapor in addition to that of the liquid phase part of the fuel spray is photographed. On the other hand, in the Back diffused light, only the liquid phase part of the fuel spray is photographed. While MDO is completely evaporated before the fuel spray is impinged onto the piston, the non-evaporated core in the liquid phase of BFO is clearly impinged onto the piston.
As mentioned above, the core seems to mainly contain the residues, and evaporation is further delayed due to impingement, and a large volume of smoke is generated. Thus, when BFO is used, it is the major points to reduce the smoke by performing ignition before the fuel spray travels to the piston crown, raising the temperature of the fuel spray flame, promoting evaporation of the residues, and preventing adhesion of the fuel spray in the liquid phase.

Fig. 15 shows the section⁷⁾ of the combustion chamber of the main engine of the training ship "Tenyo Maru" belonging to National Fisheries University as an example of medium-sized engine, and the calculated value⁶⁾ of the fuel spray travel at the load factor of 12%. Because the load is low, the air density is small, and the fuel spray travel to the time is especially increased.

The ignition delay of this engine is sufficiently short (approximately 1 ms) in the normal load condition, and it is impossible from this figure that the fuel spray travels the piston crown before ignition. However, in the low load condition, the ignition delay can be increased up to approximately 2 ms, and the ignition is made immediately before impingement, and it can be expected that collision and adhesion of the residues to the piston become possible.

Thus, attention is paid to the distillation temperature distribution and the ignition delay of BFO, and the effect on the combustion and characteristics of exhaust emissions are described. In the future, the effect of the contents which are contained much in BFO (such as asphaltene and residual carbon) on the combustion and emission characteristics will be clarified.

　

Fig. 15　Section⁷⁾ of combustion chamber of medium-sized engine, and fuel spray travel (calculated value⁶⁾)

　

5. Conclusion

The experiment using the small high-speed marine diesel engine was carried out to clarify the characteristics of exhaust emissions when the residual fuel containing the residues is used. In addition, the results were applied to medium and large-sized marine diesel engines for examination. The following conclusions were obtained.

(1)　Combustion of the residual fuel is possible even in the small high-speed diesel engine, but the exhaust smoke is greatly deteriorated

(2)　When the difference in the NOx emission is examined by the fuel, comparison not by the same injection timing but by the same ignition timing is required to examine the effect of the heat release pattern.

(3)　When the fuel spray of the residual fuel containing a large amount of residues is impinged onto the piston crown during the ignition delay, a large amount of black smoke is generated, and the fuel consumption is deteriorated, leading to the increase in the C0₂ emission.

　

The authors would like to express their gratitude to the Development Institute of Mitsubishi Oil Co., Ltd., who cooperated much in this study.

　

References

1)　K. Maeda et al., Journal of the M.E.S.J., 28-1, 1993, 31.

2)　E. Nishikawa and T. Takarada, Journal of the M.E.S.J., 29-6, 1994, 412.

3)　H. Kondoh et al., Journal of the M.E.S.J., 28-11, 1993,725.

4)　N. Nakayama et al., Journal of the M.E.S.J., 30-9, 1995, 661.

5)　Y. Wakurai et al., Transactions of the JSME, 59-561(B), 1993, 1739.

6)　Y. Wakuri et al., Transactions of the JSME, 25-156, 1959, 820.

7)　K. Takasaki et al., Proc. of the 1996 Spring Technical Conference of the ASME, ICE-Vol. 26-1, 1996, 63.

　

Discussion

Minoru Hanazaki (Kawasaki Heavy Industries Ltd.)

　

[Questions]

1.　Please explain a little more in detail the definition of the fuel consumption and CO₂ emission in paragraph 3.3 and the relationship therebetween.

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