Fuel Flashcards
Fuel used in aviation
AVGAS
Fuel used in cars
MOGAS
Fuel used in jet turbines
AVTUR
Differences between AVGAS and MOGAS
- AVGAS has lead, MOGAS doesn’t
- AVGAS has higher octane rating - helps delay the start of detonation
- AVGAS has better quality control, less volatile - reduces risk of vapour lock and knocking
- AVGAS = blue, MOGAS = purple/bronze,red/orange or yellow/orange.
- AVGAS is used in piston engine aircraft
- MOGAS used for cars, some microlight, homebuilt and vintage aircraft
How are octane ratings determined?
Anti-detonation properties.
The lower the octane rating number the lower the vaporisation temperature (easier to burn) and vice versa.
E.g. low octane = 91, high octane rating = Jet A-1
How can the octane rating be improved?
By adding certain amounts of tetra-ethyl lead.
What happens when the octane rating exceeds 100?
A performance number is used.
E.g. 100/130
100 = power available with a weak/lean mixture
130 = power available at a rich mixture
What happens if you use a higher grade than advised?
- Increase chance of spark plug fouling and corrosion of exhaust valves.
If specified fuel grade is unavailable - it is permitted to used the next highest grade, carefully.
What happens if you use a lower grade than advised?
- Increased risk of detonation, especially at high power settings.
Use of lower grade fuel than specified is prohibited.
What are the dangers of using MOGAS?
- Poorer quality control
- More volatile - higher chance of vapour lock, could lead to fuel starvation.
- Power output is lower, increased chanced of spark plug fouling and especially detonation.
What is the danger of having water in the fuel?
Block fuel flow through the carburettor and cause an engine failure.
What are some precautions to avoid fuel contamination?
- Fuel tanks filled up overnight, especially if expected temperature are cold or storing it for a long time.
- Drain the fuel to check for water and other impurities.
- Park the aircraft inside a hangar or if storing outside make sure to have the fuel caps secured.
When refuelling drum stocks…
- Check type, grade, and expiry dates as old fuel may have reduced anti-detonation qualities.
- Connect the bonding lead from the drum to the aircraft before opening any fuel caps and leave it in place until all fuel caps have been replaced.
- Stand drum upright but tilted slightly, and chock it with the high side position at 12 o’clock, the bung at 3 o’clock, and the vent at 9 o’clock.
- Allow the drum to stand undisturbed for at least 10 minutes prior to fuelling.
- Use a filter (preferably not a synthetic chamois due to issues creating a static charge) to refuel.
What is a gravity feed system?
- Older high wing aircraft
- Fuel is stored above the engine
- Fuel pump is not required
- Need at least 150% of the maximum flow rate
- Priming system is required
What are the disadvantages of a gravity feed system?
- Attitude changes - can cause engine failure
- Subject to vapour lock
What is a pump feed system?
- Two fuel pumps
- Fuel pump supplies the fuel pressure from the fuel tanks to the engine
- One pump is engine driven - cannot be turned off when the engine is running.
- Second pump is fitted and electric, can be turned off an on by the pilot
Monitored by the fuel pressure gauge
What is the electrical boost (auxiliary) pump?
- AKA electrical fuel pump
- Ids engine-driven pump
- Can be turned on and off inflight
What is the electrical fuel pump used for?
- To start the aircraft engine - provides fuel to the carburettor or to the fuel injection system and prime the fuel-injected engines
- Purge fuel lines to reduce vapour lock
- Provide fuel flow to the engine if the engine-driven pump fails (redundancy). Used in critical gases of flight.
What is the priming system?
Provides a positive supply of fuel to each cylinder.
- Injects raw fuel directly into the cylinders - bypasses carburettor.
What is expansion space?
Located inside the fuel tanks to allow the fuel to expand.
What are fuel vent tanks?
- So tanks can breathe and prevent the formation of a vacuum as fuel leaves the tank.
OR
- If you overfill the tanks when fuel is expanded, it has a space where the air and fuel can escape.
What are some symptoms of a blocked fuel tank?
- Fuel flow is slower
- Fuel tank can collapse or deform
What are baffles?
Dividers inside the fuel tanks to prevent fuel from rapidly moving inside due to movements of the aircraft.
Strengthens the structure and reduces fuel surging.
What are fuel sumps?
Located at the bottom of the fuel tank and functions to accumulate contamination.
Fuel in the sump is unusable.
What is a mechanical float type fuel quantity detector?
- Has an arm inside a fuel tank to measure the quantity,
What is an electronic capacitance fuel detector?
- More accurate
- More expensive
What are fuel flow metres?
- Used on modern aircraft and those with larger power plants to indicate rate of fuel consumption.
What are cross feed systems?
Is used to draw fuel from the left tank for the right engine, and vice versa
What is a Magna-stick?
Magnetic fuel-level measuring sticks used to measure the fuel quantity - stored inside the fuel tank.
