TS-119
A Study on Detonation in Starting Air Manifold of Diesel Engine
Yuzhong SONG*, Hiromi SHIIHARA** and Senichi SASAKI*
ABSTRACT
Two accidents of explosion in starting air manifold in two ships were experienced in recent years. The accidents caused the loss of manoeuvrability of the ships. One of the two accidents sparked serious public fear for marine safety after it left a VLCC tanker full up with crude oil drifted in the Tokyo bay. In this paper, the authors describe the causes of such kind of explosions and corresponding revisions of classification rules as safety measures against such accidents, after a thorough examination of several similar accidents occurred over the last two decades.
Key Words: Detonation, Explosion, Diesel Engine, Starting Device, Auto-ignition, Rapid Compression
1. INTRODUCTION
Explosions in starting air manifold of diesel engines were occasionally experienced until the early 1970s. To prevent these accidents some unified requirements (UR) have been established by International Association of Classification Societies (IACS) based on the perception that most of such accidents were caused by backfire from cylinders due to imperfect seal of starting valves. The following are the requirements:
In order to protect starting air mains against explosion arising from improper functioning of starting valves, the following devices must be fitted:
(i) an isolation non-return valve or equivalent at the starting air supply connection to each engine
(ii) a bursting disc or flame arrester in way of the starting valve of each cylinder for direct reversing engines having a main starting manifold at the supply inlet to the starting air manifold for non-reversing engines.
Devices under (ii) above may be omitted for engines having a bore not exceeding 230 mm
Accordingly, some engine builders adopted the arrangement with a flame arrester at each branch pipe leading to cylinder as shown in Figure 1.
Figure 1. An Example of Starting Air Line Arrangement Required by IACS UR
As the results of such arrangements, explosions in starting pipes have been reduced considerably.
However, it has been leaned from the investigations into recent accidents that explosion may take place without backfire, since latest investigation confirmed that the explosion occurred before fuel being injected.
Once explosions occur in air manifold of engines having an arrangement as shown in Figure 1, mechanical failure of starting systems would be caused with high possibility because of lack of pressure relief means. Mechanical failure of starting systems usually caused the loss of manoeuvrability of ships or even loss of life or personal injuries to crews. Hence the examination of the causes and corresponding preventive measures are urgently required.
Literatures show that similar accidents also occurred in ships classed with other Societies. For example, such explosion for total of 11 from 1989 through 1998 were reported on Lloyd's Register of Shipping (LR) classed ships [1].
2. SAMPLES OF ACCIDENTS
Based on NK damage database, a summary of the explosion or detonation accidents of which these causes are considered to be auto-ignition rather than backfire in the starting air lines of main engines over the past two decades is listed below in time order:
(1) In August 1973, the ship S equipped with 2 6-cylinder 4-stroke engines of 2471 kW for each engine lost the manoeuvrability due to breakage of the 2 starting air stop valves caused by explosion in starting air piping during ahead-stop-astern trial before entering the port of Kobe. The explosion almost coincided with astern order after engine stop. Fortunately only one crew was at a location above the engines at the engine room when explosion occurred, so no one was killed or injured except the hearing loss of the man at scene attributable to the exposure to explosion noise.
(2) In June 1979, the ship T equipped with a 6-cylinder 2-stroke engines of 2794 kW lost the manoeuvrability due to the breakage of the end portion of the starting air manifold caused by explosion in starting air piping during ahead-stop-astern trial before entering the port of Shanghai.
*NIPPON KAIJI KYOKAI Research Centre
1-8-3, Ohnodai. Midori-ku, Chiba 267-0056, JAPAN
Fax: +81-43-294-5896, E-mail: song_yuzhong@classnk.or.jp
**NIPPON KAIJI KYOKAI Head Office
