Engine Flashcards
What function does the carburettor perform?
Fuel arrives under low pressure. Mixes the fuel and air correctly and controls its delivery to the cylinders.
Fuel injection system
Where the fuel is injected into the inlet port under higher pressure to be mixed with the air after it has arrived at the cylinders.
Gravity fed systems
Where the fuel tanks are far enough above the engine to allow the fuel to flow into the engine system by gravity alone. (high wing aircraft with carburettor equipped engines)
Pressure or pump fed systems
Where the fuel tanks are not high enough to allow gravity flow, or where the engine system requires the fuel to be delivered under higher pressure. (low winged aircraft or aircraft equipped with fuel injection systems)
Detonation
If fuel becomes too hot before it is ignited by the spark plugs, there is a drastic change in the way it burns. Instead of burning at a uniform rate for a given time, it explodes releasing all of its energy in an instant. At lean mixture, high power setting resulting in hot engine.
Symptoms of detonation
- Rising cylinder head or oil temperature indication
- Significant power loss
- Engine vibration
- A ‘pinging’ sound coming from the engine
To prevent detonation
Anything that helps cool the engine will help prevent detonation. Steps:
- ensure the mixture control is in the fully rich position
- reduce engine power
- if climbing, climb at a higher IAS to improve
Alternator
The alternator can be thought of as a pump. The alternator generates electrical power and pushes it through the system. Unlike the battery, it cannot store electricity. It is driven by the engine and can supply power only when the engine is running.
The magneto
A magneto produces an electric current by spinning a magnet within a coil. This current is then boosted to produce the high voltage required for a spark hot enough to ignite the mixture.
Factors affecting the engine power output (6 factors)
The strength of the push that acts on the piston during the power stroke depends upon:
- The amount of gas that is induced into the cylinders
- The temperature reached during combustion
- The position of the throttle control
- The engine RPM
- Mixture condition
- Supercharging (turbocharging)
The octane rating of a fuel is a measure of
its resistance to detonation
The pressure exerted on the piston during the power stroke increases as the amount of gas induced
increases and combustion temperature increases.
Functions of the oil system
- It lubricates by providing an unbroken surface to support and separate adjacent metal surfaces.
- It cools by absorbing heat from the engine components and dissipating it to the airstream as it passes through the oil cooler.
- It cleans by carrying microscopic particles of carbon or metal in suspension and depositing them in the filter.
Manifold pressure
The amount of gas that gets into the cylinders depends upon the pressure in the inlet manifold before the valve opens.
Carburettor ice - conditions necessary
- most likely when temp is below about 20 degrees
- relative humidity is above 80%
What is the bus bar and what does it power?
Bus bar is a common source of electrical energy to which all of the system’s appliances are connected to including fuel pump, light, radio, flaps, nav aid.
What is an alternator failure indicated by?
Indicated by a discharge on the centre-zero ammeter and the illumination of the warning light.
Why is impulse coupling necessary and how does it work?
When the engine is turning very slowly such as during cranking for start-up, the magneto is not spinning fast enough to produce a spark. Impulse coupling is provided to overcome this. Impulse coupling is a spring mechanism which delays the spark until it gets closer to the full compression of the cylinder. As the engine turns during start up, part of the shaft turns with it, while the part that drives the magnet remains stationary. As the part of the shaft continues to turn a strong spring is wound until, at the appropriate time, a trigger releases the spring and the part that drives the magnet flicks quickly to catch up.
spark plug fouling
During long periods at taxi power and idling, the engine temperatures are low enough to allow some of the oil to remain unburnt in the cylinders. Unburnt oil pools in the lowest part of the cylinder. If this oil forms drops across the spark plug electrodes, it will conduct the high voltage current across the gap preventing the spark from occurring.
What is the function of the battery?
A battery should do nothing except start the engine. Its only function after that is to stand by in case the alternator should fail. The battery stores electrical energy for use if the alternator should fail.
What is the function of the alternator?
The alternator supplies all electrical demands of the system during flight and keep the battery fully charged.
What is the purpose and function of the cylinders?
The cylinder is made up of two parts, the cylinder head which contains valves and ports by which the fuel-air mixture enters and exits, spark plugs which ignite it, and the cylinder barrel. The cylinders are responsible for powering the four-stroke cycle of induction, compression, power and exhaust.
What is the purpose and function of the pistons?
The piston slides up and down inside the barrel in accordance with each of the strokes, to either let the mixture fill the cylinder, compress the mixture or release the mixture.
What is the purpose and function of the piston rings?
Piston rings reduce friction and form a gas-tight seal preventing high pressure gas from leaking past.
