P Piston Engine Fuel Systems Flashcards
What is the composition of AvGas?
85% carbon and 15% hydrogen
What colour is AvGas 100?
Green
What colour is AvGas 100LL?
Blue
What colour is AvGas 80?
Red
What colour is MoGas?
Black
What are the octane ratings for AvGas and AvGas 100LL?
Both are 100
Prior to flight what must the condition of the fuel sample be?
- Clear and bright
- Free of sediment
- No entrained water
What is the maximum water content of fuel?
30ppm
What can detonation cause?
Mechanical shock
What are 4 principal causes of detonation?
- Fuel with poor anti-knock properties
- Incorrect mixture (excessively weak)
- Anything that might raise the temperature (low rpm with high manifold absolute pressure)
- High engine temperature
What can pre-ignition cause?
Mechanical shock
What are the 3 principal causes of pre-ignition?
- Hot spot within the cylinder - carbon deposits on valve
- Ignition malfunction - damaged spark plug
- High cylinder temperatures
What is the ideal combustion mixture?
15:1
What ratio would a pilot use for take-off?
11:1
What ratio would a pilot use for cruise?
17:1
Which ratio do you get peak exhaust gas temperature (EGT) at?
15:1
What are the 2 types of fuel delivery?
Carburation and fuel injection
In a carburettor, what is the purpose of a pressure balance duct?
To counteract the ram effect by equalising the pressure in float chamber and the pressure at the start of the Venturi
In a carburettor, what is the purpose of a diffuser?
The diffuser allows some of the pressure in the float chamber to escape, reestablishing the pressure differential
In a carburettor, what is the purpose of mixture control?
Allows the pilot to alter the fuel constant of the charge mixture, when valve is closed the mixture is fully rich. As the valve opens pressure is equalised and less fuel flows into air flow
In a carburettor, what is the purpose of a slow running jet?
When the engine is at idle and the pressure differential isn’t significant, the slow running jet assures fuel is injected into accelerated airflow around the edge of the butterfly valve
In a carburettor, what is the purpose of a power enrichment cam?
Adds additional fuel boost when more power is requested, reducing lag
In a carburettor, what is the purpose of a accelerator pump cam?
Adds additional fuel boost when immediate acceleration is requested, by injecting fuel directly into the Venturi, reducing lag
What does fuel evaporation and pressure drop at idle throttle cause?
Cooling in the inlet tract which could lead to ice formation
What temperature can carburettor ice from at?
Any temperature so long as enough moisture is present
What does carburettor icing cause?
Stuck throttle and/or reduction in power
What are the symptoms of carburettor icing?
- Loss of rpm
- Reduced performance
- Reduced inlet manifold absolute pressure (MAP)
- Decreased exhaust gas temperature (EGT)
- Rough running
- Jammed throttle
- Engine stops
What is the 1st sign of carburettor icing with a fixed pitch propeller?
Unexplained drop in rpm
What is the 1st sign of carburettor icing with a variable pitch propeller?
Drop in MAP
What does carburettor heat do?
Takes air heated by exhaust gasses and uses it for combustion
What is indirect fuel injection?
When fuel is injected into the stream of air just before the valve
How is fuel injection powered?
By an electric pump
