Fuel Metering Flashcards
What are the air/fuel mixture ratios that support combustion?
8:1 - 17:1
What is the leanest air/fuel mixture?
17:1
What is the richest air/fuel mixture ratio?
8:1
What air/fuel mixture ratio is considered maximum power?
12:1
What is Stoichiometric?
The perfect air/fuel mixture in which both ingredients can be used up completely
What is the stoichiometric ratio?
15:1
What is the hottest air/fuel mixture?
Stoichiometric
What is the richest mixture ratio?
Idle mixture
(Because of poor air flow)
What is the SECOND richest mixture ratio?
Take off ratio
(Extra fuel is needed for cooling)
What is the leanest fuel/air mixture?
Cruise mixture
(Engine is running at reduced power & higher altitude)
What 2 reasons are why engines are shut down with the mixture control?
To prevent the un-burnt fuel from
washing away the oil film off the
cylinder wall
&
Safety (no accidental start ups)
What 3 instruments are used to monitor engine power?
Manifold Absolute Pressure (MAP) - airflow
Fuel Flow
Tachometer (RPM)
Where can manifold pressure be taken?
Anywhere after the throttle valve or before the intake valve
The manifold gauge measures pressure where?
In the inlet manifold which relates to the engine power
The fuel flow gauge measures what?
The amount of fuel delivered by the fuel system which relates to the engine power
What is the tachometer used to monitor?
Engine power and to ensure the engine is operated within certified limits
What air/fuel mixture burns the slowest?
Lean
Some aircraft use ________ ignition timing.
Staggered
What does a float carburetor do?
Provides a uniform air/fuel mixture as the airflow varies
Has an internal reservoir for fuel that maintains a constant level with a float/valve mechanism
What does the Venturi do?
Converts potential energy to kinetic energy or pressure to velocity
-Proportions the fuel/air mixture
-Decreases the pressure at the discharge nozzle
-Limits the airflow at full throttle
Where does the fuel level inside of a float bowl need to be adjusted to?
Slightly below the discharge nozzle outlet
Where is the discharge nozzle located?
In the Venturi
What is Air Bleed?
Aids in atomizing by increasing surface area of fuel.
Keeps a constant air/fuel ratio as air flow varies
What does the Metering Jet do?
Restricts maximum amount of fuel
What are the two types of mixture control?
Variable orifice
&
Back suction
How does a variable orifice work?
Restricts fuel leaving float bowl
How does back suction work?
Reduces float chamber pressure reducing fuel metering force
What is an economizer?
Power Enrichment System
Adds additional fuel at high power settings for cooling purposes
What is the purpose of the acceleration system?
Allows fuel to be fed from nozzle until flow can be generated
(Because fuel lags behind the airflow)
Can an A&P overhaul a pressure carburetor?
No, it is considered a major repair
What is the function of Chamber A in a pressure carb?
Impacts air pressure
What is the function of Chamber B in a pressure carb?
Venturi Pressure
What is the function of Chamber C in a pressure carb?
Metered fuel
What is the function of Chamber D in a pressure carb?
Unmetered fuel
What keeps a constant pressure inside of a pressure carburetor?
The discharge nozzle needle valve
