M/E Fuel Oil & Fuel Injection Flashcards
- With reference to high viscosity fuel:
a) Explain how it is treated between storage tank and main engine.
a) Fuel oil is held and heated within the settling tank where sludge and water is separated by gravity. Further heating takes place after it travels through course filters. The fuel is purified, removing particulate and water before being transferred to the service tank, where t is maintained at a higher temperature. Passing through hot fine filters before passing through the visco-therm where the fuel is heated to the correct viscosity. Finally passing through the booster pumps to the main engine fuel rail.
With reference to high viscosity fuel:
a) Explain how it is treated between storage tank and main engine.
b) State the purpose for the treatment.
b) To remove solid particulate to prevent damage.
To remove water to prevent emulsifying the fuel.
To reduce the viscosity of the fuel for correct injection and combustion.
b) To remove solid particulate to prevent damage.
To remove water to prevent emulsifying the fuel.
To reduce the viscosity of the fuel for correct injection and combustion.
c) Fuel of this type requires the purifiers to have a smaller gravity disk 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 less viscous fuel.
a) Describe the tests that are carried out on a fuel injector after overhaul and before it is refitted to the engine.
a) Newly overhauled injectors have a crack-off test performed on them to test their operation. The injector is mounted on a test rig and the injector is primed with calibration fluid. The pressure is then raised to test the crack/lifting pressure of the injector. The pressure is read from the rig and if within the correct pressure it is good for use, if firing too high an additional washer may be added into the injector.
c) State the stages of on board preparation of heavy fuel oil prior to use.
c) Fuel oil is transferred from storage tanks to a settling tank where it is heated and water is allowed to settle out and be drained. It is then heated to approx., 60oC and centrifuged to remove liquid containments, it is then stored in the service tank. From the service tank it is further heated to around 120oC to reduce its viscosity to around 14 cSt before being passed through fine filters to remove all debris. Its then pressurised to around 300 bar before being injected into the engine via the fuel injectors which atomise the fuel.
3.
a) State why the simultaneous injection of fuel oil and starting air into a main engine cylinder is undesirable.
a) Pressure relief valves may lift, causing hot fuel oil to spray onto hot parts of the engine. b) Starting interlocks of the air start valve in order to stop fuel supply until air is released. During manual starting, the operator will only apply fuel once the engine is up to starting speed and after the air has been closed.
a) State why the simultaneous injection of fuel oil and starting air into a main engine cylinder is undesirable.
b) Explain how simultaneous injection of fuel oil and starting air is prevented
b) Starting interlocks of the air start valve in order to stop fuel supply until air is released. During manual starting, the operator will only apply fuel once the engine is up to starting speed and after the air has been closed.
- a) State why the simultaneous injection of fuel oil and starting air into a main engine cylinder is undesirable.
b) Explain how simultaneous injection of fuel oil and starting air is prevented. c) Explain how a leaking air start valve is detected while the engine is running.
c) Hot branch of pipeline with possible paint discoloration.
Activation of air start line, bursting disk prevention device.
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a) State why the simultaneous injection of fuel oil and starting air into a main engine cylinder is undesirable.
b) Explain how simultaneous injection of fuel oil and starting air is prevented. c) Explain how a leaking air start valve is detected while the engine is running. d) Describe the actions to be taken upon discovery of a leaking air start valve.
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a) State why the simultaneous injection of fuel oil and starting air into a main engine cylinder is undesirable.
b) Explain how simultaneous injection of fuel oil and starting air is prevented. c) Explain how a leaking air start valve is detected while the engine is running. d) Describe the actions to be taken upon discovery of a leaking air start valve.
a) With respect to the fuel injection timing of a 2-stroke diesel engine, what would be the effect of:
i) Early injection
ii) Late injection
a)
i) Sever stress loading of piston rod, connecting rod, cross head bearing and bottom end bearings.
Very high unit temperature, cooling water and exhaust gas.
Vibration, irregular engine speed.
ii) Uneven thermal distribution throughout piston liner, causing micro-seizure and liner cracking.
Heavy carbon deposits on piston, liner also due to improper combustion
Fuel oil wash down due to incomplete combustion.
- Describe how the high viscosity fuel oil is prepared for delivery to the injection pumps to ensure correct conditions for combustion.
A visco-therm consists of a capillary tube inside of which a gear pump is fitted which rotates at very slow rpm. There is an outside casing provided for the capillary tube. When the oil passes through the casing, some part of the oil pass through the gear pump and its capillary, and some part of the oil passes over the capillary tube. Hence a flow difference occurs inside the casing. The oil inside the tube maintains a laminar flow and outside the tube maintains a turbulent flow. The pressure difference between outside and inside of the tube is measured which is directly proportional to the viscosity of the oil. Hence oil viscosity is maintained. The viscosity controllers act as the controller of the 3 way valve from which steam is passed into the heater or bypassed from the heater as per the position of the control valve.
