Alex The Carburetor Flashcards
The Carburetor
The Carburetor - Once the air enters the induction system, it moves through a system of ducts and is introduced into the carburetor. The carburetor mixes the incoming air with fuel and delivers it to the combustion chamber.
Carburetor’s Function
Carburetor’s Function - The Carburetor mixes the incoming air with fuel and delivers it to the combustion chamber.
A float-type carburetor system is used
A float-type carburetor system is used on many light aircraft. When the air enters the carburetor it passes through a venturi. This increases its velocity and decreases its pressure. Fuel enters the carburetor from a float chamber where it is maintained at nearly constant level by a float device. The float chamber is vented to the outside so that pressure inside remains equal to the atmospheric pressure, even during climbs and descents. Since the discharge nozzle is located in an area of low pressure created by the venturi, the fuel is forced through the discharge nozzle by the higheratmosheric pressure in the float chamber.
In a float-type carburetor, fuel is drawn from
In a float-type carburetor, fuel is drawn from the float chamber past a mixture needle and into the venturi where it mixes with the incoming air.
AIR INLET - Air enters the carburetor through the air inlet.
VENTURI - The shape of the venturi creates an area of low pressure.
DISCHARGE NOZZLE - Fuel is forced through the discharge nozzle into the venturi by greater atmospheric pressure in the float chamber.
THROTTLE VALVE - The flow of the fuel-air mixture is controlled by the throttle valve. The throttle valve is adjusted from the cockpit by the throttle.
FUEL/AIR MIXTURE - The blend of fuel and air is routed to the combustion chamber to be burned.
AIR BLEED - The air bleed allows air to be mixed with the fuel being drawn out of the discharge nozzle to decrease fuel density and promote fuel vaporization.
FLOAT CHAMBER - Fuel level is maintained by a float-type device.
FUEL INLET - Fuel is received into the carburetor through the fuel inlet.
FUEL- FUEL
MIXTURE NEEDLE - The mixture needle contols fuel to the discharge nozzle,. Mixture needle position can be adjusted using the mixture control.
The operating principle of float type carburetors is based on the difference in pressue at the venturi throat and the air inlet.
The operating principle of float type carburetors is based on the difference in pressue at the venturi throat and the air inlet.
Carburetors are calibrated at
Carburetors are calibrated at sea level, and the correct fuel-to-air mixture ratio is established at that altitude with the mixture control set to FULL RICH position. However, as altitude increases, the density of air entering the carburetor decreases while the density of the fuel remain the same. This creates a progressively richer mixture which can result in engine roughness. The roughness normally is due to spark plug fouling from excessive carbon build up on the plugs. This occurs because the excessively rich mixture lowers the temperature inside the cylinder, inhibiting complete combustion of the fuel. This condition may occur during the pretakeoff runup at high-elevation airportsand during climbs or cruise flight at high altitudes. To maintain the correct fuel/air mixture , you must lean the mixture using the mixture control.
When you lean the mixture, you decrease the fuel flow to compensate for decreased air density. Leaning the mixture may eliminate engine roughness during runup at high-elevation airports.
When you lean the mixture, you decrease the fuel flow to compensate for decreased air density. Leaning the mixture may eliminate engine roughness during runup at high-elevation airports.
During a descent from high altitude, you must remember to
During a descent from high altitude, you must remember to enrich the mixture or it may become too lean. An overly lean mixture may result in hiigh engine temperatures which can cause excessive engine wear or even failure over a period of time. The best way to maintain the proper mixture is to monitor the engine temperature and enrichen the mixture as needed. Since the process of adjusting the mixture can vary from one airplane to another, it’s important that you refer to the pilot’s operatng handbook (POH) to determine the specific procedures for your airplane.
If you do not adjust the mixture control during descents from high to low altitudes, the fue/air mixture will be too lean.
If you do not adjust the mixture control during descents from high to low altitudes, the fue/air mixture will be too lean.
**One disadvantage of the float-type carburetor is **
**One disadvantage of the float-type carburetor is its icing tendency. Carburetor ice occurs due to the effect of fuel vaporization and decreasing air pressure in the venturi which causes a sharp temperature drop in the carburetor. If water vapor in the air condenses when the carburetor temperature is at or below freezing, ice may form on internal surfaces of the carburetor, including the trottle valve. **
**Carburetor ice occurs **
Carburetor ice occurs due to the effect of fuel vaporization and decreasing air pressure in the venturi which causes a sharp temperature drop in the carburetor. If water vapor in the air condenses when the carburetor temperature is at or below freezing, ice may form on internal surfaces of the carburetor, including the trottle valve.
**Carburetor ice reduces **
Carburetor ice reduces the size of the air passage to the engine. This restricts the flow of the fuel air mixture and reduces power. If enough ice builds up, the engine can cease to operate.
INTAKE AIR - Carburetor ice is most likely to occur when intake air temperature is below 21 degrees C (70 degrees F) and the relative humidity is above 80 %.
VENTURI - The reduced air pressure at the venturi throat creates a temperature decrease.
ICE - If conditions warrant, ice will generally form in the vicinity of the trottle valve.
FUEL/AIR MIXTURE - The vaporization of the fuel contributes to a temperature decrease in the carburetor.
Carburetor ice is more likely to occur when
Carburetor ice is more likely to occur when temperatures are below 21 degrees C (70 degrees F) and relative humidity is above 80%. However, due to the sudden cooling that takes place in the carburetor, icing can occur even with temperatures as high as 38 degrees C (100 degrees F) and humidity as low as 50%.
However, since not all carburetors are designed exactly the same, carburetor ice is possible under conditions not just mentioned above.
You should expect carburetor ice when temperatures are at or below 21 degrees C (70 degrees F) and relative humidity is high.
You should expect carburetor ice when temperatures are at or below 21 degrees C (70 degrees F) and relative humidity is high.
Carburetor Ice Indications
**Your first indication of carburetor icing in an airplane with a fixed-pitch propeller will be **
Carburetor Ice Indications
Your first indication of carburetor icing in an airplane with a fixed-pitch propeller will be a decrease in engine r.p.m., followed by engine roughness and possible fuel starvation.
In an airplane with a contant-speed propeller, the power changes are reflected by shifts in manifold pressure.
Although carburetor ice can occur during any phase of flight, it is particulary dangerous when you are using reduced power, such as a descent. Under the right conditions, carburetor ice could build unnoticed until you try to add power.
To combat the effects of carburetor ice, engines with a float-type carburetors employ a carburetor heat system which is designed to eliminate ice by routing air across a heat source before it enters the carburetor.
When you turn the carburetor heat ON, a valve cuts off air flow from the nomal air intake and allows heated air from an alternate source to enter the carburetor.
Carburetor heat is switched on
Carburetor heat control (incockpit) is turned on and a valve cuts off the air flow from the normal air intake
Air Intake turned off
Alternate Air source
is passed over heated Exhaust pipes from engine cylinderswhich goes to the muffler
Heated air is then directed to the carburetor
