Engine systems: fuel injection, lubrication, cooling, starting, reversing and control
The systems domain tests how fuel, oil, water, air and control signals reach and leave the engine, and what happens when a parameter drifts outside its band. Questions usually link a component to its failure symptom.
Fuel injection and fuel treatment
- Jerk pumps or common rail deliver fuel at several hundred bar to over 1,000 bar; needle valve opening pressure and delivery valve behaviour set atomisation and prevent secondary injection.
- Injection is advanced to allow ignition delay. Too much advance raises peak pressure and NOx; too little raises exhaust temperature and smoke.
- Residual fuel is heated so viscosity at the injector is about 10-15 cSt, typically 130-150 °C; settling tank around 60-70 °C for separation, service tank slightly higher.
Lubrication and cooling
- System oil BN must suit fuel sulphur; two-stroke cylinder oil feed is set by the alpha factor in g/kWh and reduced as load falls.
- High-temperature fresh water at 70-90 °C serves jackets and liners; the low-temperature circuit at 30-40 °C serves charge air and lubricating oil coolers.
- Running jackets too cold causes acid corrosion of liners; expansion tanks provide static head and allow air and vapour to escape.
Starting, reversing and control
- Starting air at about 30 bar is distributed to cylinders in firing order; interlocks block starting with the turning gear engaged and cut air once the engine fires.
- Reversing shifts the camshaft or changes electronic timing so air-start and fuel timing suit the opposite rotation; the manoeuvring handle passes through an interlocked neutral.
- The governor holds speed; the overspeed trip acts independently of the governor.
Worked example
A 10,000 kW engine at 180 g/kWh burns 1,800 kg/h. HFO density is 0.985 t/m³ at 15 °C but about 0.90 t/m³ at 130 °C. Correct volume flow = 1,800/900 = 2.00 m³/h. Dividing by 0.985 instead gives 1,827 kg/h and overstates SFOC by about 1.5 %. Either correct flowmeter readings to the temperature at which density applies, or fit a mass flowmeter.
Traps
Treating the settling tank as the service tank; setting cylinder oil feed by habit rather than load and sulphur; confusing HT and LT circuits; believing the governor is also the overspeed trip; ignoring the minimum starting air pressure needed for the required consecutive starts.