There are 4 tests conducted when testing fuel injectors. Please name 3 of those tests
- Pop test / pressure setting
- Atomization / spray pattern test
- Back leakage test
- Dry sea/ dribble test
Label the fuel pump diagram found on the separate page (12 items
- Delivery valve spring
- Delivery valve
- Slot
- Spill port
- Helix
- Plunger
- Pinion
- Control sleeve
- Control flange
- Barrel
- Rack
- Inlet port
Using figure 43 of the injector, explain how high pressure fuel is injected into the combustion chamber. How is the opening pressure adjusted?
High pressure fuel is delivered from the fuel pumps by means of a double wall fuel line that connects to the injector at the inlet. As the fuel pressure in the line increases (due to the pump being actuated by the fuel cam) this high pressure is transmitted to the pressure chamber in the nozzle body by means of the fuel duct (an internally bored passageway). The increasing pressure acts on the valve seat and causes the valve to lift and atomized fuel to be injected into the cylinder. As the pressure decreases (due to the fuel pump barrel helix uncovering the spill port), the valve descends and reseats on the valve seat. This process is repeated every time the fuel pump operated.
The opening pressure is adjusted by adjusting the lifting pressure adjusting screw and repeating the pop test until the injector opens at the manufacturer’s specified pressure. The screw will exert more or less pressure on the spring, causing more or less compression, therefore changing the pressure that the valve seat will need to overcome to lift.
If the combustion pressure is low but the compression pressure is okay on a particular cylinder, what may be the issue with the cylinder combustion pressure being so low?
Insufficient fuel delivery due to blocked or leaking fuel injector, poor atomization, poor penetration into the cylinder.
Describe the purpose, construction, operation, and safety items of an electric starter fitted to a high speed diesel engine.
Purpose: provide sufficient cranking speed to produce the heat of compression for ignition of the injected fuel.
May be a direct drive or a gear reduction assembly. Direct drive: designed to generate high torque at low speeds, and low torque at high speeds. Uses a solenoid-actuated shift lever to push out the pinion to engage it with the ring gear before or just as the armature starts turning. Gear reduction starter: designed to use a smaller, higher speed electric motor to produce higher cranking torque with the same or less electrical power consumed.
Direct Drive components: starter housing, nose piece, end cap, armature, brushes, brush holders, field coils, pole shoes, solenoid, pinion gear, overrunning clutch, shift lever.
Direct drive operation: when the start button is pushed, the solenoid is energized and its hollow plunger moves axially, causing the pinion to move towards the ring gear on the engine flywheel. As the plunger closes the first stage contacts, current is supplied to the field coils and armature windings so that full battery voltage is applied to these, and the motor develops full torque. When the pinion is in full engagement with the ring gear, it is locked in position and will remain so until the start button is released or the overrun clutch operates. When the engine starts, the pinion is accelerated rapidly by the flywheel and the overrun clutch will operate to allow the pinion to accelerate at a higher rate than the armature.
Gear Reduction components: same as the direct drive but adding a gear reduction
Gear reduction operation: the armature does not drive the pinion gear directly, instead, the armature drives a small gear that is in constant mesh with a larger gear. The solenoid operation is similar to that of the direct drive starter.
Safety items: thermal over-crank protection switches open when the temperature gets too high. The starter cannot operate until it cools back down.
Sketch and describe a heavy fuel oil system that may be fitted to a cargo vessel. Please include in your answer how the fuel flows from the tanks to the main engine and any recirculation arrangements.
- Storage tank to settling tank via a transfer pump with duplex strainers fitted before it
- In settling tanks, heated to 72C or 6 below flash point (whichever is lower)
- From settling tank, through a strainer, through a steam heater to 98C, through the purifier, to a service tank
- From service tank, through flow meter to mixing tank
- From mixing tank, through strainers, to fuel pumps (duplex), steam heaters (duplex - 150 C), viscometer (that controls steam heaters), duplex filter, to main engine.
- Unused fuel is recycled to the mixing tank for reuse
