How to prevent coking

How to prevent coking


  • Coking occurs because the temperature and the oil residue time are higher than the oil stability limitations.
  • Coke formation increases dramatically as local metal contact temperatures exceed 300°C.
  • Operational factors can influence coke formation, such as hot shutdowns, which promote coke build up.
  • Obstructions to flow or directional changes cause reduction in flow rate and increases in oil residence time.
  • High post-shutdown temperatures due to conducted or convected heat increase deposition in low-drainage areas.
  • Low-clearance scavenge ports increase the likelihood of blockage due to shedding.
  • Prolonged aircraft inactivity enables moisture absorption of coke deposits, which typically shed after startup
  • Unprotected reactive metals in the oil system, such as lead, cadmium or magnesium, can increase deposits (reaction between oil and metals).
  • Low-alloy iron and copper can stimulate coke formation by catalysis.
  • Positive washing of system surfaces by high liquid oil flow reduces residence time.
  • Increased airflow in high-temperature metal contact zones reduces the amount of coke deposits formed by promoting oil volatilization.
  • Thermal insulation of supply, scavenge or vent lines in the gas path can significantly reduce deposits.


  • While deposits are not desirable, if they form, staying where they form is preferred.
  • Coke shedding can cause blockage of filters and engine oil system passageways.
  • Shedding can occur by absoprtion of moisture during prolonged shutdown periods and engine thermal cycles.
  • Cracking, crazing and lifting of deposits from formation surfaces causes more oil to be trapped, increasing coke formation.


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