And even pressure rise rate is several hundred MPa/s, the maximum pressure still can be limited to a level of just over the static rupture pressure by providing multiple rupture discs and keeping total relief area more than 0.12V2/3. Therefor NK has changed its rule to require rupture disc for arrangement shown in Figure 1 for the time being. The concerning requirements are
"An adequate rupture disc device is to be fitted at an appropriate position on the main starting manifold as an emergency, means of relieving pressure caused by explosion for direct reversing engines fitted with flame arrester".
As a matter of course, further amendments to the Rules relating to measures described in 4.1 and 4.2 are under consideration.
5. CONCLUSIONS
Summarising the results of foregoing analysis, it can be concluded that:
(1) Auto-ignition in starting air manifold of diesel engines can be caused by rapid opening of starting air stop valve, which has been neglected so far because of lack of the knowledge of such phenomenon.
(2) Elimination of the compressor lubricant and system lubricant from the air manifold will efficiently reduce the risk of compression ignition.
(3) To reduce the pressure rise rate by appropriate choice of starting air stop valve opening time and its maximum area could effectively reduces the final gas temperature.
(4) For a given maximum pressure rise rate, reduction of diameter of manifold would lead to a lower final gas temperature.
(5) Rupture disc with a sufficient area attached at air manifold may effectively limit the pressure rise to a level almost equal to the designed static bursting pressure.
(6) Film detonation and mechanism of carryover of combustibles into air manifold should be further examined in the future.
ACKNOWLEDGEMENTS
The amendment to NK-rules for requiring rupture disc as an emergency means to protect starting air system was carefully examined by the sub-committee on machinery of the NIPPON KAIJI KYOKAI Technical Committee. The authors would like to express their sincere appreciation to the chairman of the sub-committee. Professor Emeritus Shinji Hayama of the University of Tokyo for his continuous guidance.
REFERENCES
[1] MARINE PROPULSION. April 1998
[2] White, D. F., "The unintentional Ignition of Hydraulic Fluids Inside high Pressure Pneumatic systems", Journal American society of Naval Engineers, Vol.72, No.3, August, 1960
[3] Faeth G. M. and White, D. F., "Ignition of Hydraulic Fluids by rapid compression", Journal American society of Naval Engineers. Vol.73, No.3, August, 1961
[4] Semenov, N. N., Some Problems in Chemical Kinetics and Reactivity, Vol.2, Princeton University Press, Princeton, N. J., 1959.
[5] K. Terao, Combustion and detonation wave as an irreversible phenomenon, IPC Itd., 1991 (in Japanese)
[6] G. M. FAETH, auto-ignition charging processes in pneumatic systems, Naval engineers journal, December 1965
[7] G. M. Faeth, Thermal Environment of Combustibles during Pneumatic Charging Processes, Naval engineers Journal, April 1965.
[8] For example, Kennedy, R. E., G. S., and Zabetakis, M, G., "Flammability Limits of Hydrocarbons," Chemical engineering Progress, Vol. 53. No. 3, March, 1957.
[9] G. M.FEATH, Spontaneous Ignition Charging Processes in Pneumatic Systems, Naval Engineers Journal. December 1965.
[10] Kazuo Hatori, Ignition delay of single droplet of marine fuel oils in high-temperature ambient, Journal of the Marine Engineering Society in Japan. Vol.35, N0.4, 2000 (in Japanese)
[11] Toshihiro Hayashi, Characteristics of Gaseous Explosion in a Vessel with a Complex Inner Structure and Pressure Venting by Rupture Disks, Research Institute of Industrial Safety of Japan, RIIS-RR-86, 1986 (in Japanese)
