Further, combustion improvement can also be achieved by applying air swirl at an intensity below over-swirl.

Finally, side injection as used with 2-stroke marine diesel engines can improve combustion, because under these conditions the swirl can effectively supply air into the fuel-rich zone.

　

5.　Conclusions

In this study a comparison between the combustion characteristics of gas oil and bunker fuel oil is examined. The following is concluded：

1.　Experiments using the test engine shows that particulate (PM) emission, especially soluble organic fraction, increases drastically when using BFO.

2.　Observation of the spray using the rapid compression machine shows that in case of BFO a large liquid core remains within the spray which impinges unburned on the piston, when the ignition delay is long.

3.　Examination of the combustion process using a visual engine shows that：

｡?he distribution of fuel and air in the BFO spray is less homogeneous than in the GO spray, caused by the poor evaporation characteristics of the residual portion.

｡?he combination of smaller injection hole diameter and higher injection pressure improves the combustion of BFO.

4.　According to the results obtained by numerical simulation, it is essential to supply air to the fuel injected at the end of the injection duration, in order to improve the combustion of BFO.

　

Acknowledgement

The authors would like to thank to the staff and students of the Institute of Internal Combustion Engines at Hanover University and the Laboratory of Engine System at Kyushu University. Similarly, thanks are due to Associate Professor K. Maeda of the National Fisheries University, Japan, Mitsubishi Heavy Industries, Ltd. and Mitsubishi Oil, Co. Ltd. for their cooperation in the project.

　

References

　

　

　

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