Piston Engine Fuel Systems Flashcards
Pressure Balance Duct
Venturi Effect
Ensure correct mixture ratio at high speed/low speed flights
EGT
Exhaust Gases Temp
Used for adjusting mixture ratio
Cooler when excess lean
Cool when excessive mixture due to excess fuel
Grades of AVGAS
AVGAS 100ll (Blue) - Low lead
AVGAS 100 (Green) - High Lead
AVGAS density
15 degrees about 0.72kg
Vapour Lock
Vaporise in fuel lines restricting fuel flow
Detonation definition and symptoms
Rapid combustion after burning has begun
- knocking sound
- reduce power output
- CT temp rises
- Rough running
- Damage cylinder
Causes of detonation
Fuel with poor anti knock qualities
Incorrect mixture ratio
Raising temp or pressure of mixture before burning (low rpm)
High engine temp
Definition of pre-ignition symptoms/causes
Ignition of mixture before spark plug has fired
- tendency for engine to run after shut down
- worsens with increased rpm
- weak mixture
- hot cylinder
- contaminated with carbon deposits
Octane Rating
Resistance to detonation
Power ratio/economic ratio/ideal ratio
Ideal - 15:1 (Very high combustion temp so not used)
8:1 (rich) to 20:1 (lean)
Ideal Cruise - 12:1
Economy - 17:1
EGT vs Mixture
Combustion cooler at richer mixture due to cooling effect
Cooler when mixture is very lean (Excess air in mixture)
Power Cruise - leaning mixture to achieve peak EGT then enriching more until EGT DROPS
Economy cruise - leaning mixture until peak EGT then leaning again until slight drop
Petrol vs Diesel (Carbon monoxide)
Petrol produced more carbon monoxide but less soot than diesel
Engine driven pump role
Ensure a positive supply of fuel under pressure to the carb under all engine conditions.
Float valve role
Control level of fuel in chamber
Throttle butterfly valve
Controls the amount of air passing through the throat
Pressure balance duct
Ensure that correct mixture ratio is maintained across a range of airspeeds and flight conditions
Increase in pressure in throat causes drop in fuel flow
Weak mixture
Diffuser
Ensure correct mixture ratio across whole speed range of the engine
Large addition of fuel leading excess rich mixture at high airflows
Slow Running Jet
Additional jet to cater for low power conditions
- places near butterfly to take advantage of strong pressure drop
Provide rich mixture at idle
Power Enrichment
Provide rich mixture needed to cool cylinder at high power settings
Accelerator Pump
Injects fuel directly into Venturi
Carb Icing most likely + symptoms
Dependent on humidity/ambient temp and throttle position
18/25 degrees + 30% humidity likely icing conditions
Cruise/descent power
Loss of RPM
Reduce Performance
Reduced inlet manifold pressure
Decreased exhaust gas temp
Rough running
Jammed throttle
Carb Heat advantages
Provides alternative source of air in event primary air intake becomes blocked
Prevents and removes ice in throat of carburettor
Carb heat disadvantages
Reduces engine power
Further reduce power when breaking down ice
Cause detonation at high power setting
Enrich mixture (hot air less dense)
Purpose of induction systems
Introduce the mixture into each cylinder
