Module 5 Carburetors Flashcards
Main metering components
- Fuel regulator
- Main metering jet
- Throttle valve
Functions of the Fuel regulator ?
Responsible for metering the appropriate amount of fuel
Function of Main Metering jet?
calibrate orifice
Function of throttle valve ?
Determines airflow through carburetor
Primary purpose of carburetor is to:
Deliver the proper fuel/air ratio so it can combust
What is the function of the Venturi in the carburetor?
To create pressure differential required to deliver fuel
The pressure reduction created in the throat of a carburetor Venturi is due to ?
Velocity
Bernoulli’s principle
Explain Bernoulli’s principle ?
As velocity increase pressure and temp decrease
Main disadvantage of the carburetor
- Susceptible to icing
- Affect by maneuvers
- Incomplete vaporization of fuel
Why are float type carburetors prone to icing
The main discharge nozzle deliver fuel to the throat of the carburetor where the greatest temperature reduction is
Main factor contributing to carb icing?
Humidity
When applying carb heat the engine will?
Experience loss power and immediately run rough due to rich mixture
What is the most common method to prevent carb icing?
Pre heat the air before entering the carburetor by either Heat muff or engine compartment air
What does updraft it downdraft refer to :
Direction of the air flow
Main purpose of the throttle valve
Regulate the power output of the engine
On a float type carburetor, where is the throttle plate located?
After the main discharge nozzle and Venturi
What is the function of the float needle valve?
Controlled the amount of fuel stored in the float chamber
The function of the carburetor jet (fixed orifice) is to:
Meter fuel - control and limit WF (fuel flow) at full throttle
What is the function of the metering system ?
To supply fuel flow at all conditions above idle
What is the source and purpose of the main air bleed in float-type carb:
Atmospheric air add to emulsify the fuel, refusing the surface tension assuring with better vaporization.
Why is the idle system necessary in a carburetor?
At idle speeds the airflow through the Venturi is not sufficient to draw fuel out to the main discharge nozzle
Where does idle systems discharge fuel ?
Through small ports adjacent to the throttle valve
What is the function of the idle jet ?
Meters the fuel at idle speeds, and is an integral part of the emulation tube
The adjustment of the idle mixture affects ?
Idle power only
What is an indication of the idle mixture is to rich ?
RPM rise of 100, rough running with black smoke from the exhaust
How does the Manual mixture control work on the pressure carburetor?
Variable air bleed between the chamber A-B
How is the automatic mixture control (AMC) compensates for changes in air density?
Used brass bellows filled with helium to actuate a reverse tapered needle valve, to change the relationship between impact air and Venturi air.
As ambient pressure change the bellows expand and contracts, varying the size of the air bleed orifice between chamber A-B
How does the accelerator in pressure carburetor work ?
Increase the MAP on the diaphragm pressurized fuel in the primary chamber
What are the principle functions of the mixture control system?
- Prevent mixture becoming to rich at altitude
- To economize on fuel at Cruise
The variable orifice mixture controls mixture by?
A valve which controls the amount of fuel flow to discharge nozzle
The back suction mixture control, controls the amount of fuel to discharge nozzle by :
By position of the valve, controlling the differential pressure to the float chamber
Improper use of the carburetor mixture control would probably cause ?
Leaning to much causing damage to the engine due to overheat-detonation
Describe the difference between the idle mixture control and the manual mixture control ?
- Manual mix control operate from the flight deck and affect all power settings including idle
- Idle mixture control is set on the carburetor and effects idle mixture only
The purpose of a power enrichment/economizer is ?
Provide richer fuel/air mixture at higher power setting
A power enrichment system that increases fuel flow at higher RPM setting but allows for a leaner mixture cruise is sometimes refer to a?
The (Back suction) economizer system
Where is the fuel nozzle placed in a pressure carburetor ?
Downstream of the Venturi, therefore less likely to have carb-icing conditions
Differences between pressure carburetor and float type carburetor
The pressure carburetor supplies the fuel pressurized by a fuel pump
Most carb includes 5 systems:
- Main metering
- Idling
- Mixture control
- Accelerating
- Power enrichment or economizer
