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Why may fuel injector nozzles fail due to burning? Which precautions to be followed to minimise the risk of this type of failure?

05 Sep '17, 17:31

Sept. 5, 2017, 5:31 p.m.
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The burning of the nozzles of fuel injectors happens when the material is weakened by overheating. The hot combustion gas flow erodes the material.

Causes may include:

  1. Lack of cooling: some injectors are cooled by circulating water through cooling passages in the injector scale build up, contamination of the cooling system by fuel oil or restriction in cooling water flow will cause the injector to overheat. In case of oil cooled injectors, sludge accumulations may block cooling passages.
  2. Overloading of the engine: This may cause burning away of the back of the fuel injector nozzles on a two stroke uniflow scavenged engine fitted with multiple injectors. The burning fuel from one injector may impinge on the back of the next injector.
  3. Incorrect atomization: Caused by worn nozzle atomising holes, weak springs, incorrect injection viscosity, a fuel of the wrong specification for the engine. Carbon 'trumpets' may form on injector interfering further with atomization causing dribbling and overheating.

To investigate the actual cause of burning check:

  1. Is the problem common to all cylinders, or just individual units?
  2. Is the fuel injection viscosity/temperature correct?
  3. Check the test results for the fuel against the specification recommended for use in the engine.
  4. If fitted with fuel valve cooling, check flow and individual returns to tank for fuel contamination.
  5. Dismantle injector with the burnt nozzle and check cooling water spaces and spring length. Reassemble with a new nozzle, ensuring that correct size nozzles are fitted and check injection setting pressure and atomization.
  6. Check for overloading/injection faults by comparing fuel rack settings and peak pressures and looking at the out of phase cards for the cylinders; the out of phase card will give an indication of timing and burning of fuel.

To prevent fuel injector nozzles burning:

  1. Ensure correct operating procedures keeping within engine specifications.
  2. Observe log book entries to spot trends which may indicate an increase in loading due to a drop off in performance.
  3. It is important to ensure that the fuel is of the correct specification and heated to the appropriate temperature for injection viscosity.
  4. Ensure that the fuel injection equipment is in optimum condition. This includes regular checks and maintenance on fuel pumps, timing check and adjustment to compensate for wear as well as changing and overhauling the injectors at recommended intervals. 
  5. The efficiency of the turbochargers is to be maintained at the correct level by regular water washing as are the air coolers to ensure that the engine is not starved of combustion air.
  6. Regular checks on compression and peak pressures will give a guide to cylinder conditions.
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05 Sep '17, 17:51

Sept. 5, 2017, 5:51 p.m.
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