Fuel Oil And Fuel Injector Page 11-13 Flashcards
(23 cards)
How is high viscosity fuel oil treated between the storage tank and main engine?
The fuel is stored and heated in the settling tank, allowing gravity to separate sediment and water, which is drained off as sludge every watch. It is drawn to a centrifugal separator, filtered in duplexed filters changed every watch, and cleaned to remove further particulates. The purifier heats the fuel to around 90°C to aid separation, and water and sediment are removed as the oil passes through the unit. After purification, the fuel is stored in the service tank at a high temperature, allowing more water and particulate to settle and be removed as sludge. The fuel is drawn to the booster unit via fine hot filters, circulated through heaters and a viscometer to maintain correct viscosity, and finally pressurized to around 7bar into the main fuel rail, which is trace heated with steam to maintain viscosity.
What is the purpose of treating high viscosity fuel oil?
To ensure a clean and reliable fuel supply, to prevent damage, and maintain efficiency of combustion.
How is high viscosity fuel oil treated prior to entering the main engine?
Fuel is heated to the correct temperature to reduce viscosity.
It is purified to remove any last water or remaining small particles, and then filtered to take away any solids or finer particles that the purifier couldn’t remove.
• Fuel passes to the fuel booster unit through fine hot filters, where it is heated in banks of heaters
controlled by a viscometer set to the suitable viscosity for optimum injection; passing then onto the
fuel booster pumps where the pressure is increased to around 7bar before the main fuel rail.
Describe the test which is carried out on a fuel injector after overhaul (4)
• Mount the fuel injector into the test rig. Connect the fuel injector to the test oil supply and prime the injector; this is complete when oil returns down the leak line.
• At no point should hands enter the test compartment during testing. Using the test pump deliver several quick strokes, the injector should open with a high-pitch chatter. Check that the pressure does not fall away quickly after opening. Check the opening pressure is within tolerance set by the manufacturer.
• After the opening test, allow the pressure to return to zero. Slowly build pressure until it is just below the opening pressure and check that there is no dripping or leaking from the injector nozzle
🎯Place a clean piece of paper underneath the injector nozzle and observe the spray pattern
Cross section of fuel injector
What is the process for fuel preparation when changing to fuel of lower density and viscosity?
Fuel of this type requires the purifiers to have a smaller gravity disc fitted in order to maintain the water- oil interface, finer filters are also fitted within the fuel treatment system to enable effective particle separation.
The visco-therm controller must also be adjusted in order not to over-heat the fuel reducing its viscosity too much risking carbonisation or gassing up the fuel lines.
The engine fuel injection timing must also be retarded to compensate for the less viscous fuel.
What is the first step in testing a fuel injector after overhaul?
• Mount the fuel injector into the test rig. Connect the fuel injector to the test oil supply and prime the
injector; this is complete when oil returns down the leak line.
• At no point should hands enter the test compartment during testing. Using the test pump deliver
several quick strokes, the injector should open with a high-pitch chatter. Check that the pressure does
not fall away quickly after opening. Check the opening pressure is within tolerance set by the
manufacturer.
• After the opening test, allow the pressure to return to zero. Slowly build pressure until it is just below
the opening pressure and check that there is no dripping or leaking from the injector nozzle
• Place a clean piece of paper underneath the injector nozzle and observe the spray pattern
What should be avoided during the testing of a fuel injector?
Hands should not enter the test compartment during testing.
What should be checked after the opening test of a fuel injector?
Ensure the pressure does not fall quickly after opening and that the opening pressure is within the manufacturer’s tolerance.
What is the procedure after allowing the pressure to return to zero in a fuel injector test?
Slowly build pressure until just below the opening pressure and check for dripping or leaking from the injector nozzle.
What should be done to observe the spray pattern of a fuel injector?
Place a clean piece of paper underneath the injector nozzle and observe the spray pattern.
What are the components of a fuel injector nozzle?
Pressure pin, nozzle body, nozzle needle, inlet passage, pressure chamber, spray hole, blind hole.
Why is simultaneous injection of fuel oil and starting air into a main engine cylinder undesirable?
To stop explosion at the air start manifold.
How is simultaneous injection of fuel oil and starting air prevented?
The fuel supply index is shut off via an interlocking valve while air is admitted, and an air solenoid valve blocks the fuel line until the air start button is released.
What are the effects of early injection in a two-stroke diesel engine?
Severe stress loading of piston rod, con-rod, cross head bearing, and bottom end bearings. Very high unit temperatures, cooling water, and exhaust gas. Vibration and irregular engine speed.
What are the effects of late injection in a two-stroke diesel engine?
Uneven thermal distribution throughout piston liner, causing micro-seizure and liner cracking. Heavy carbon deposits on piston and liner due to improper combustion. Fuel oil wash down due to incomplete combustion.
What is the procedure to change the fuel supply from high viscosity fuel to low viscosity fuel for manoeuvring purposes?
- Check the status of the diesel tank, i.e., quantity and quality. 2. Reduce the heat supply to the HFO heater gradually. 3. Slowly close the HFO tank valve and slowly open the diesel oil tank valve, leaving the return line to the HFO tank open. 4. Monitor the flow situation with respect to temperature and pressure. 5. Monitor the visco-therm if fitted. 6. After a suitable period of time to allow circulation of diesel oil, remove all trace heating. 7. Change over the recirculating line from the HFO tank to the diesel oil tank. 8. Monitor condition of engine, i.e., temps, pressures, sound, etc.
What is the ignition point of fuel in a two-stroke diesel engine?
Ignition of fuel occurs at TDC (Top Dead Center).
What is indicated by the peak pressure in a two-stroke diesel engine?
Peak pressure is represented as Pmi.
What does Pscay represent in a two-stroke diesel engine?
Pscay is a point in the engine cycle related to pressure.
