A fuel injector valve is a device which receives pressurized fuel as a liquid and sprays it into engine cylinder as a fine mist. It consists of a nozzle and nozzle holder and a  body. The nozzle has a series of small orifices around its tip used for atomizing the injected fuel. So, the purpose of injection valves is to precisely inject the fuel quantity calculated by the control unit in all engine operating states. To ensure the fuel is atomized effectively while minimizing condensation losses, a certain engine-specific distance and injection angle need to be observed.

Fuel injector valves, like any other machinery or devices that are under continuous load and stress, tend to malfunction and ultimately to fail while in service if maintenance plan is not properly followed.

Accelerated wear/damage to nozzle tips are in most cases caused by poor fuel oil
quality, fuel contamination and this will cause poor combustion which in turn will result in poor engine performance and eventually may result in major damage to the engine.

Based on experience accumulated over years, has been observed the following issues regarding fuel injection valves:

• • • Premature inspection of fuel valves, before scheduled inspection according to the Planned Maintenance Program causing maintenance induced failures and extra costs;
    • Short lifetime of fuel nozzles;
    • Broken fuel nozzle springs as a result of excessive pre-tensioning by repeatedly readjusting the opening pressure to new value causing dynamic overloading of the spring;
    • Repair/Re-condition of fuel injection valves (which is not recommended by engine makers as through recondition of fuel valve nozzles the engine SFOC dramatically increases due unsuitable fuel atomization);
    • Incorrect cleaning of nozzle tips causing damage to the injection nozzle.

As per MAN Diesel & Turbo the fuel injection valve should be operated for 8000 hrs. without removal and as per Wartsila for 6000 hrs. , unless a specific reason dictates so. To ensure safe operation, the heavy fuel oil operating instructions and treatment, including correct filtration must be strictly observed.

In case of MAN engines equipped with the latest requirement of filters, common 10μm abs. automatic back flush filter for the auxiliary engines and a 25μm abs. fuel safety filter fitted to each generator, a maintenance interval of at least 8000 hours for fuel valves can be normally expected.

Opening pressure must be adjusted according to the manufacturer’s guide lines, in order to prevent breakage of the spring.

In the above image there is no need to remove any fuel injection valves for pressure testing, adjustments or overhaul. Fuel valves should remain in engine unless other indications dictate so.

However, at the below stated indications, inspection of the fuel valves are mandatory.

• • • Deviation of more than 40°C of exhaust gas outlet temperature measured at cylinder head among cylinders.
  • In the above image low exhaust gas temperature at cylinder no. 4. If the temperature decrease is related to the fuel injection valve the cause is most likely sticking needle in fuel nozzle. In this case, fuel injection valve should be removed for checking.
  • 
  • In the above image High exhaust gas temperature at cylinder no. 4. If the temperature increase is related to the fuel injection valve the cause is most likely leaking or worn fuel nozzle. In this case fuel injection valve should be removed for checking.
    • Exhaust gas temperature inlet turbocharger has increased to 10°C below alarm limit.
    • Black smoke is observed during normal static load.

Therefore performance check is strongly recommended at least once a week.

The fuel injection valve should be cleaned from the outside without dismantling the fuel valve, check should be done in fully assembled condition. Correct cleaning procedure of the nozzle is necessary to ensure proper atomisation of the fuel in the combustion chamber.

Steel brush including rotating steel brush will destroy the nozzle spray holes and a new nozzle element is required.Consequence by using rotating steel brushes

For judgment of the fuel nozzle condition, only opening pressure and leakage should be used as criteria for acceptance or rejection. Spray pattern test should not be used as a criteria, as the test bench injection capacity is too small to produce the same condition as exits is in the engine.

Drop in opening pressure is typically caused by wear in the needle seat in the fuel injection valve or setting of the spring.
Setting of the spring cannot be avoided, however wear in the seat area is the result of wear from abrasive particles and can be reduced by proper treatment of the fuel.

In case of leakage or low opening pressure, the valve should be opened for internal check of parts. If leakage is the reason for opening the fuel valve, typically the nozzle will have to be replaced as a minimum, while a low opening pressure normally dictates a replacement of the spring. In both situations replacement of other parts may be required based on condition.

On some injector valves there is a requirement to replace the thrust piece as it tends to wear down after certain operating hours.

 

 

 

 

 

 

 

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Source and Bibliography:

• MAN Diesel video training
• MAN Diesel & Turbo Service letter SL2016-628