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The main trouble to be avoided handling pistons in a marine diesel engine

How to avoid piston seizure or cracking
Piston forms the lower part of the combustion chamber. It seals the cylinder and transmits the gas pressure to the connecting rod. Below are the main troubles for piston that need to be avoided

i) Piston seizure; all too often followed by an explosion of the lubricating oil – air mixture in the crankcase.

ii) Cracking of piston crown and side walls, due to cyclic variation of pressure stress superimposed on stress due to temperature gradient.

iii) Burning of piston crown; this occurs mainly of large slow running engines

iv) Excessive lubricating oil consumption (trunk engines)



v) Sticking of piston rings by various deposits, formed by oxidation of lubricating oil and fuels leading to blow-past’ which is excessive can lead to piston seizure or scavenge fire (crosshead engines) Breaking of piston rings

vi) Scuffing of piston rings and cylinder liner


Handling piston

Fig:Handling piston



Summarized below more guidance for marine diesel engine piston handling safety procedure:
  1. Construction of 4 stroke piston

  2. For medium and high speed engines the weight of the material becomes important to reduce the stresses on the rotating parts. The high thermal conductivity of aluminium alloys allied to its low weight makes this an ideal material. To keep thermal stresses to a reasonable level cooling pipes may be cast into prevent distortion.
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  3. Piston oil cooling method - basic principle

  4. The coolant used for removing and conveying the heat from a piston may be either fresh water, distilled water or lubricating oil. Water has the ability to remove more heat than lubricating oil ( specific heat of water approximately 4 and lubricating oil 2 and temperature difference 14 deg C for water and 10 deg C for lube oil) .

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  5. Function of piston ring in a marine diesel engine

  6. The efficiency of the engine depends upon the effective sealing between the piston and liners. Leakage will reduced compression pressure and power will lost. Piston rings seal the gas space by expanding outwards due to the gas pressure acting behind them. They also spread the lubricating oil up and down the cylinder liner and transfer heat to the liner walls Three to six power or compression rings are fitted to the piston, the number depending on weather the engine operates on the 2-stroke or 4-stroke cycle.

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  7. Requirement of piston ring

  8. Piston forms the lower part of the combustion chamber in a marine diesel engine. It seals the cylinder and transmits the gas pressure to the connecting rod.

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  9. Piston designing considerations

  10. Piston forms the lower part of the combustion chamber in a marine diesel engine. It seals the cylinder and transmits the gas pressure to the connecting rod.

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    Troubles of piston to be avoided
    i) Piston seizure; all too often followed by an explosion of the lubricating oil – air mixture in the crankcase. ii) Cracking of piston crown and side walls, due to cyclic variation of pressure stress superimposed on stress due to temperature gradient.

    More .....

  11. Detection of piston overheating

  12. most common reasons of Piston running hot : i) Inadequate circulation of cooling media and or supply not sufficient. ii) Excessive deposit in cooling space (scale or carbon). iii) Lubrication not sufficient.

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