Carbuterors
Aircraft Carburetors
You can contact us for parts of your aircraft and engine. You can also come straight to us for Repair and Overhaul of your carburetors Systems.

 

Below there is a lay out on the operation of the Carburetor.
Induction systems
The induction system brings air from outside to the inside of the engine, here the fuel is mixed with the air. And delivers the fuel / air mixture to the cylinder where combustion takes place. Outside air enters the induction system trough an intake port in the front of the cowling. This port usually contains an air filter that the entry of dust and other foreign matter inhibits. Because the filter may sometimes be clogged, an alternative source of air needs to be available. Usually, the alternative air comes from inside the engine compartment, where it bypasses a clogged air filter. Some alternative air sources function automatically, while for others are operated manually.

 

Two types of suction systems are often used in the engines of small aircraft:

 

1. Carburetor system, the fuel and air goes into the carburetor, where it mixes before this mixture enters the intake manifold.

 

2. The fuel injection system, so that the fuel and air are mixing just before they in each cylinder.
Carburetor Systems
Carburetors are classified as float or pressure type. Pressure carburetors are not usually found on small aircraft. The basic difference between a pressure and a float-type carburetor is that the pressure carburetor supplies the fuel that is pressurized by a fuel pump.

 

The fuel / air mixture is then drawn through the intake manifold into the combustion chambers, where it is ignited. The "float-type carburettor" gets its name from a float which rests on the fuel in the float chamber. A needle attached to the float opens and closes an opening at the bottom of the carburetor bowl. This ensures that the proper amount of fuel gets into the carburettor, depending on the position of the float, which is controlled by the fuel level in the float chamber. When the level of fuel is forced to increase the float needle valve closes the fuel opening and closes the fuel to the carburetor. The needle valve opens again when the engine requires extra fuel. The flow of the fuel / air mixture to the combustion chamber is controlled by the throttle valve, which is controlled by the throttle lever in the cockpit.
MIXTURE CONTROL
Carburetors are normally calibrated at sea level pressure, the correct fuel / air mixture ratio is determined by the mixture control to FULL RICH position. As altitude increases, the density of air decreases in the carburetor, while the density of the fuel remains the same. This creates a richer mixture, which can result in engine roughness, and a considerable loss of power. The roughness is normally caused by excessive carbon build-up on the spark plugs. Carbon build-up occurs because the mixture that is too rich lowers the temperature in the cylinder, preventing complete combustion of the fuel. This condition may occur during pre-takeoff run at high elevated airports and during climbs or cruise flight at high altitude. To maintain the correct fuel / air mixture, you must lean the mixture control. Leaned, the mixture reduces fuel flow, which compensates for the reduced air density at altitude. During a descent from high altitude, the opposite is true. The mixture is enriched, or it may be too poor. A too lean mixture causes detonation, which can result in rough engine operation, overheating and loss of power. The best way to maintain the correct mixture is to monitor the engine temperature and enrich the mixture if necessary. Proper control mix, and a reduced fuel consumption for fuel injection engines may be achieved by the use of an exhaust gas temperature gauge. As the process of adjusting the mixture by one plane to another, it is important to refer to the flight manual (AFM) or Pilot Operating Handbook (POH) to determine the specific procedures for a given airplane.

 

Two types of suction systems are often used in the engines of small aircraft:

 

1. carburetor system, the fuel and air goes into the carburetor, where it mixes before this mixture enters the intake manifold.

 

2. The fuel injection system, so that the fuel and air mixing just before they in each cylinder.
Carburetor Icing
A disadvantage of the float-type carburetor is icing. Carburetor ice occurs as a result of the effect of fuel evaporation and the decrease in the air pressure in the venturi, which causes a sharp decrease in the temperature in the carburetor. When water vapor in the air condenses when the carburetor temperature is at or below the freezing point of water on the internal surfaces of the carburetor, such as the throttle valve.

 

[The Figure shows that the formation of carburetor ice can reduce or block the fuel / air flow to the engine.]

 

The reduced air pressure, as well as the evaporation of the fuel, leads to the temperature reduction in the carburetor. Ice normally forms in the vicinity of the throttle valve and the venturi throat. This limits the flow of the fuel / air mixture and reduces power. If enough ice builds up, the engine can no longer work. Carburetor ice is most likely to occur at temperatures below 70 ° F (21 ° C) and when the relative humidity is above 80 percent. Because of the sudden cooling which takes place in the carburetor, ice can form even at temperatures of up to 100 ° F (38 ° C) and humidity as low as 50 percent prevented. This drop in temperature can be up to 60 to 70 ° F. Therefore, when there is an outdoor air temperature of 100 ° F and a temperature drop of 70 ° F. This causes an air temperature in the carburettor of 30 ° F.

 

The first indication of the carburetor icing in an airplane with a fixed propeller is a decrease in the engine speed, which may be followed by engine roughness. In a plane with a constant speed propeller, carburetor icing is usually indicated by a decrease in manifold pressure, but no reduction rpm. Propeller pitch is automatically adjusted to compensate for the loss of power. Thus, a constant r.p.m. is maintained. Although carburettor ice can occur during any phase of flight, it is particularly dangerous when using a reduced flow during a descent. Under certain circumstances, the carburetor can build ice unnoticed until you try to give it to power. To combat the effects of carburetor ice, float-type engines with carburetors use a carburetor heating system.

 

Carbutetor Heat
Carburetor heat is an anti-icing system that heats the air before it reaches the carburetor. Carburetor heat is intended to keep the fuel / air mixture above the freezing point in order to prevent the formation of ice in the carburetor. Carburetor heat can be used to melt ice that has already formed in the carburetor. The emphasis is on using carburetor heat as a preventive measure.

 

The carburetor heat should be checked during the engine run up. In the use of carburetor heat, following the recommendations of the manufacturer.

 

When conditions are conducive to carburetor icing during the flight, periodic checks should be done to detect his presence. If confirmed, the full carburetor heat is applied immediately, and it should be left in the ON position until you are sure all the ice has been removed. When ice is present, the application of a partial heat or leaving heat would worsen the situation in a sufficient time. In extreme cases of carburetor icing, even after the ice has been removed, full carburetor heat can be used to prevent further formation of ice. A carburetor temperature, if installed, is very useful in determining when to use carburetor heat.

 

When the throttle is closed during the flight, the engine quickly cools and the fuel evaporation is less complete than when the engine is warm. Also, in this state, the engine is more susceptible to carburetor icing. Therefore, if you suspect carburetor icing and anticipate closed throttle control, adjust the carburetor heat to the full ON position before closing the throttle, and leave it on during closed-throttle operation. The heat will assist in the vaporization of the fuel, and to help prevent the formation of the carburetor ice. Periodically, open the throttle smoothly for a few seconds to keep the engine warm, otherwise the carburetor heater can not generate enough heat to prevent icing.

 

The use of carburetor heat causes a power loss, sometimes up to 15 percent, because the heated air is less dense than the outside air that was in the engine. This enriches the mixture. When ice is present and carburetor heat is used in an airplane of fixed-pitch proppellor, there is a decrease in rpm, followed by a gradual increase in rpm when the ice melts. The RPM of the engine must also increase after the ice has been removed and carburator heat is OFF. If ice is not present and carburator heat is on, the r.p.m. decreases, then remains constant. When carburetor heat is used in a plane with a constant speed propeller and ice is present, a decrease in the inlet pressure will be noted, followed by a gradual increase. If carburetor icing is not present, the gradual increase in manifold pressure will not be clear until the carburetor heat is off. It is necessary that a pilot recognizes carburetor ice as it forms during the flight. These symptoms may be accompanied by vibrations of the engine. Once a power loss is noticed, action must be taken immediately to remove the ice already formed in the carburetor and prevent further icing. This is achieved by applying full carburetor heat, which will lead to a further reduction of the energy costs and possibly engine roughness as melted ice passes through the motor. These symptoms can last from 30 seconds to several minutes, depending on the severity of the icing. During this period, the pilot must resist the temptation to reduce carburator heat consumption. Carburetor heat must be returned in the full-cold position to normal flow.

 

Since the use of carburetor heat tends to reduce the output of the engine and also to increase the working temperature, carburetor heat should not be used at full power necessary (such as during take-off) or during normal engine operation, except for when carburator ice needs to be removed.
Carburetor Air Temperature Gauge
Some aircraft are equipped with a carburetor air temperature gauge, which is useful in detecting icing conditions. Typically, the face of the meter is calibrated in degrees Celsius (° C), with a yellow bow indicating the carburetor temperatures in which ice can form. This yellow bow typically varies between -15 ° C and + 5 ° C (5 ° F and 41 ° F). When the air temperature and the humidity of the air are such that the carburetor icing is unlikely, the motor can be operated with the indicator in the yellow range with no adverse effects. When the atmospheric conditions are conducive to carburetor icing, the indicator must be kept outside the yellow arc by the application of carburator heat.

 

Some meters have a red radial carburetor air temperature gauge, which is the maximum permissible carburetor inlet air temperature that is recommended by the manufacturer of the motor; Also, a green arc can be included to indicate the normal operating range.
Outside Air Temperature gauge
Most aircraft are also equipped with an outside air temperature (OAT) meter calibrated in both Celsius and Fahrenheit. It provides the outside or ambient temperature to calculate true airspeed, and is useful in detecting potential icing too. (Thanks to the FAA)

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