25th May. 06

While sailing at sea in mid Atlantic, at evening 1730 hrs, with engine room on UMS mode, an engine room alarm sounded.

On accepting the alarm and subsequently initial inspection from engine control room noticed the main engine no. 2 unit piston cooling lube oil temperature on the rise. By then engine slow down process was also activated.

Next no. 3 crank case high oil mist alarm also came on. Expecting a possible breakdown, we slowed down the engine further, and then stopped for investigation. Few days earlier, almost similar incident had occurred, the result was a cracked piston crown in Main Engine no. 1 unit.

The detailed inspection through scavenge space confirmed a similar incident had now taken place in this case too.

But this time the situation was more critical as we did not have a spare piston, which had been used in the previous case and we had had to sail out of a South American port without any spare till arrival Europe, where the spare was due to arrive.

Anyway at this time we had no option but removing the piston without rod, blank the crank case chamber, cut out fuel P/P and exhaust value actuating device, and starting air pipe and starting air distributor. After completing the job we sailed out with half ahd. speed and then moved up to full ahd. With engine room on continuous watch, we arrived safely in first European port (Lisbon), where we received the spare and after repairs sailed out with full engine power.

Probable cause that we analyzed, was that both the unit piston crowns developed the elephant skin around the fuel injector firing area, and also developed cracks on that area, which means the fuel injectors were not in good condition. Upon close inspection on the injectors we found though the injectors were atomized and at correct pressure, the atomization were not good due to the increased dia of the spray holes.

This causes the fuel to impinge on the piston crown and the excess heat caused the elephant skin to develop on the crown surface, and then the crack which finally led to the breakdown.

Another reason was to increase the running hours between the overhauling time by checking only the piston ring condition through the scavenge space, as the piston crown condition cannot be seen correctly through the scavenge space with a fine dust cover on these piston crown surfaces hiding the elephant skin as well as the crack on the surface.

Had it been opened after correct running hours stipulated by the maker, we surely could have found out the deterioration of the piston crown condition thereby the fuel injectors' condition and could possibly have avoided the situation.
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