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Detection of Piston Overheating

diesel engine piston, ring, cylinder, bedplate, crankcase, bearings, crosshead, fuel pump timing, compressor, boiler, for marine engineers exams

Shatter Cooling Effect (less at slow speed) - piston go up, more pipe length, less pressure
Piston come down, more pressure

Crown damage

  • Thermal stress, mechanical loading
  • Direct oxidation
  • Catalytic oxidation
  • Wet corrosion, water in fuel
Piston Overheat due to:
  • Overloading - excessive fuel
  • Poor lubrication - friction more, heat up, water in fuel
  • Poor coolant and faulty circulation - pressure and volume, deposits, scale and carbon for oil cooled, engine running slow, no full flow of coolant.
  • Faulty injector - impingement - localized burning, star crack. Peel off layer, crazy crack
  • Leaky after burning - loop scavenging hot gas return to crown
  • Distorted liner or oversized piston - touch and friction, misaligned piston
  • Faulty piston ring - blow by of gas
  • Insufficient air from turbocharger for cooling
Detection of Piston Overheating
  • Occur at slow speed due to coolant not agitated and effectiveness reduced.
  • Rise in cooling water return temperature
  • Noise in cooling system due to vapor lock
  • Crank mist for trunk piston using splash lubrication
  • Dry patches and discolorization
  • Smoke and smell

 
Aluminum piston
  • Lose shine if overheated
  • White powder oxidized or ash from fuel

Worn groove can be deposited by argon arc method, but cannot do too many times due to weakening of material

Piston Ring Material

  • Made slightly harder than piston
  • Ring speed faster, area of contact less

Copper ring

  • Loop scavenging for long piston skirt to avoid micro seizure due to piston touching liner
Ring breakage
  • Worn piston ring grooves, not straight, blow past
  • Worn cylinder liners blow past
  • Deposits in ring grooves, blow past
  • Sticking rings blow past
  • Combustion knock. Improper timing. Inadequate cetane no. Of fuel
  • Local blow by of ring - blocked ring groove, chamfered too much, ring twisted
  • Excessive piston clearance - piston slap (move sideways)
  • Ring flutter
  • Oil of inadequate quality
  • Incorrect design of scavenging and exhaust ports, chamfer not proper. (Make narrow so that less length of ring unsupported)
  • Incorrect shape of rings - chamfer, no allowance for expansion outwards
Deposits on Piston Rings and Piston due to:
  • Improper air filtration
  • Improper fuel filtration (gas engine)
  • Wet or corrosive gas
  • Improper combustion
  • High cylinder oil feed rate
  • Worn or weak rings
  • Incorrect jacket water temperature
  • Continuous overload operation
  • Blow by of piston ring
  • High crankcase vacuum (trunk piston engine)
  • High crankcase oil level (trunk piston engine)

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