Ignition in Crankcase

08028-0D/H5250/94.08.12

During running the atmosphere in the crankcase contains the same gases (N2-O2-CO2) in the same proportions as in the ambient air, but an intense spray of coarse oil drops is flung around everywhere. If undue friction, and thus heating, arise between sliding surfaces, or heat is transmitted otherwise to the crankcase, the heated surface will cause evaporation of the lubricating oil splashed onto it. When the oil vapours condense they form a multitude of minute drops suspended in the atmosphere, i.e. a milky white oil mist is formed, able to nourish and spread a flame if ignited. Such ignition may be caused by the same "hot spot" which produced the oil mist. If a large quantity of oil mist has developed before ignition, the burning may cause considerable pressure rise in the crankcase, forcing the relief valves to open. In a few cases, presumably when the whole crankcase has been filled with oil mist, a subsequent explosion has thrown off crankcase doors and caused fire in the engine room.

Every precaution should therefore be taken to (A) avoid "hot spots" and (B) discover oil mist in time.

A."Hot spots" in Crankcase

Overheating of bearings is a result of too bad or failing lubrication possibly caused by pullution of the lubricating oil.

It is therefore important that the lubricating oil filtration equipment is in perfect condition. Filter cartridges must not be used again, if they have been removed from the filter. Check of the oil condition by analysis is recommended.

B Oil Mist in Crankcase

Presence of oil mist may by noted at the vent pipe, which is usually fitted to the top of the engine frame.

Measures (in case of white oil mist).

Warning: Keep away from doors and relief valves on crankcase. Do not stay unnecessarily in doorways near doors of the engine room casing.

2. Leave the engine room. Shut doors and keep away from them. Make ready fire-fighting equipment.

Warning: Do not open crankcase until 10 minutes after stopping the engine. When opening up, keep clear of possible flames. Do not use naked light and do not smoke.

3. Take off all doors on one side of the crankcase. Cut off starting air. Engage turning gear, if fitted.

4. Locate the hot spot. Powerful lamps should be employed at once (in explosion-proof fittings). Feel over all sliding surfaces (bearings, liners, pistons, roller guides, etc.).

Look for squeezed-out bearing metal and discoloration by heat (blistered paint, burnt oil, heated steel).

5. Prevent further heating, preferably by making a permanent repair. Special attention should be given to ensure lubricating oil supply and satisfactory condition of the frictional surfaces involved. It is equally important to replace filter elements in time.

6. Start electrically driven lubricating oil pump and check oil flow from all bearings and splash pipes in crankcase while turning the engine through at least two revolutions. Section 502, Check 1.

7. Stop and feel over. Look out for oil mist.

Especially the frictional surfaces that caused the heating should be felt over (5-15-30 minutes after starting, and again when full load is obtained). Section 501.10, Point 2.

8. In case it has not been possible to locate the hot spot, point 8 should be intensified and repeated until the cause of the oil mist has been found and remedied. In very rare cases oil mist could be due to "atomization" of lubricating oil by the action of an air jet (for instance blow-by, or blow-by through cracked piston).

L23/30H

08028-0D/H5250/94.08.12

Description

The built-on fresh water pump in the high tempera-ture (HT) circuit is of the centrifugal type and is mounted on the front cover of the engine and is driven through a gearing.

L23/30H

The pump bearings are lubricated automatically with oil from the lubricating oil system of the engine.

If the pump leaks and the shaft sealing rings are worn, it is recommended to replace the shaft seal, see working card 516-02.00.

08028-0D/H5250/94.08.12

Note! Running troubles with the pump, apart from mechanical faults, are most often due to leaks in the suction line. It is essential, therefore, that all packings and gaskets are in order and that they are renewed when necessary. Even a tiny hole in the suction line will reduce the pump capacity.