If the fuel pump barrel and plunger are worn out, there will be leakage between them, this will mean that after the spill Port is closed it will take longer for the pump to reach sufficient pressure to open the fuel injection valve, delaying injection.It also means that the total quantity of fuel delivered will be less than it should be for any given fuel rack setting.
The consequences are that fuel injection will start late, even if the spill timing is correct, and the maximum amount of fuel that can be injected will be less.
On some engines the smaller valve is actually mounted inside the larger one. It should be fairly easy to test if these are opening at the correct pressure, and closing tightly, unfortunatly they are often sealed units (especially on Medium speed engines) that can not be dismantled and lapped in.
The consequences are that fuel injection will start late, even if the spill timing is correct, and the maximum amount of fuel that can be injected will be less.
Symptoms
- Symptoms will be higher exhaust temperatures in relation to the load, and reduced maximum power output.
- The severity of these symptoms will be dependant on the viscosity, and therefore the temperature of the fuel, because the viscosity &
- The density of the fuel, together with the clearance between the Barrel & Plunger will determine the mass of fuel "Lost" from the fuel pump.
The best solution
- Would obviously be to change the Barrels and plungers as soon as possible.
- It is common for Engines that normally run on HFO to have problems after changing over to MDO because the reduced viscosity of the fuel causes such a large increase in leakage that the engine will no longer start.
Design factor
- Most modern fuel pumps are fitted with 2 spring loaded non return valves, the larger one, with the greater spring force opens to allow fuel to flow to the injector and closes at the end of the delivery stroke, the other opens at the end of the delivery stroke and releases the fuel pressure in the H.P. fuel pipe and injector, to prevent " dribbling" from the injector.
On some engines the smaller valve is actually mounted inside the larger one. It should be fairly easy to test if these are opening at the correct pressure, and closing tightly, unfortunatly they are often sealed units (especially on Medium speed engines) that can not be dismantled and lapped in.
- If the Non Return valves are leaking this can reduce the volume of fuel delivered IF air is drawn in from leaking discharge pipe connections, or combustion gas leaks back through the injector during the pump suction stroke.
No comments:
Post a Comment