Carburetor-Definition, Main Parts, Working Principle, Function, PDF

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Carburetor Definition:

This is a device (Internal combustion engine) for mixing air with fuel in a system for the proper burn of fuel. In details like parts, function explained below:

Carburetor Main Parts or Construction:

The Main Parts of Carburetor is:

  1. Float Chamber
  2. Strainer
  3. Metering system
  4. Idling system
  5. Throttle valve
  6. Choke Valve

1. Float Chamber:

The float chamber serves as a storage tank of fuel for a continuous supply of fuel. It contains a float valve which maintains the level of fuel in the float chamber.

When the level of fuel decreases in float chamber the float moves downward, which open the fuel supply valve and allow the flow of fuel into the float chamber.

As the fuel level increases, the float moves upward which close and stop the fuel supply.

2. Strainer:

It is a device which is used to filter the fuel before entering into the float chamber.

It consists of a fine wire mesh which filters the fuel and removes dust and other suspended particles from it. If these particles not removed, can cause blockage of the nozzle.

3. Metering System:

The metering system controls the flow of fuel into the nozzle. It is responsible to form a correct mixture of air-fuel.

It consists of two main parts

  • 1. Metering orifice and
  • 2. Fuel discharge nozzle.

When the air passes through venturi, it generates a low-pressure field across the throat. Due to this pressure difference, fuel is discharged into the air stream.

The quantity of fuel is control by the metering orifice and discharge hole at the exit of the fuel discharge nozzle.

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4. Idling System:

The idling system consists of passage directly from the float chamber to the venturi tube.

It provides a rich mixture during idling and at low speed. It works during idling or when the throttle is open below 15%.

5. Throttle Valve:

It is a butterfly valve situated at the exit of the venturi tube. It controls the speed of the vehicle by providing a controlled amount of mixture.

Controls the quantity of air-fuel mixture. If the throttle is fully opened, then more mixture is drawn into the cylinder and thus gives high output.

6. Choke Valve:

It is the same as the throttle valve in construction but situated at the entrance of the venturi tube.

This is used to provide a very rich mixture during starting in the cold season.

This controls the quantity of airflow through the venturi tube. If the choke is fully open, a normal amount of airflow through venturi, which forms a normal mixture. But,

If the choke is partially closed, it results, low amount of airflow through venturi and a large amount of fuel flow through the discharge nozzle. It gives a rich mixture.

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Carburetor Working Principle / Diagram:


The Simple carburetor mainly consists of a

Float chamber,

Fuel discharge nozzle,

A metering orifice,

A venturi,

A throttle valve, and

A choke.

The Float and needle valve system maintains a constant level of gasoline in the float chamber.

If the amount of the fuel in the float chamber falls below the designed level, the float goes down, thereby opening the fuel supply valve and admitting fuel.

When the designed level has been reached, the float closes the fuel supply valve thus stoping additional fuel flow from the supply system.

The float chamber is vented either to the atmosphere or to the upstream side of the venturi.

During the suction stroke, the air is drawn through the venturi. Venturi is a tube of decreasing cross-section with a minimum area at the throat.

Venturi tube is also known as a choke tube and is so shaped that it offers minimum resistance to the airflow. As the air passes through the venturi the velocity increase reaching a maximum at the venturi throat.

Correspondingly, the pressure decreases reaching a minimum.

From the float chamber, the fuel is fed to a discharge jet, the tip of which is located in the throat of the venturi.

Because of the differential pressure between the float chamber and the throat of the venturi, known as carburetor depression, fuel is discharged into the air stream.

The fuel discharged is affected by the size of the discharge jet and it is chosen to give the required Air fuel ratio.

Carburetor Function:

The Main Function of the carburetor is:

  1. The main function of carburetors to mix air and gasoline and provides a high combustion mixture.
  2. It controls the engine speed.
  3. It also regulates the air-fuel ratio.
  4. Increase or decrease the amount of mixture according to the engine speed and load changing.

Carburetor Advantages:

The Main Advantages of the carburetor is:

  1. Carburetor parts are not as expensive as that of fuel injectors.
  2. With the use of a carburetor, you get more air and fuel mixture.
  3. In terms of a road test, carburetors have more power and precision.
  4. Carburetors are not restricted by the amount of gas pumped from the fuel tank which means that cylinders may pull more fuel through the carburetor that would lead to the denser mixture in the chamber and greater power as well.

Carburetor Disadvantages:

The Main Disadvantages of the carburetor is:

  1. At very low speed, the mixture supplied by a carburetor is so weak that, it will not ignite properly and for its enrichment, at such conditions, some arrangement in the carburetor is required.
  2. The working of a carburetor is affected by changes in atmospheric pressure.
  3. More fuels are consumed since carburetors are heavier than fuel injectors.
  4. More air emissions than fuel injectors.
  5. Maintenance costs of a carburetor are higher than the fuel injection system.

Carburetor Application:

  1. Used for Spark Engine.
  2. It used to control the speed of the vehicles.
  3. It converts the main fuel petrol into fine droplets and mixes with air to burn in smoothly and properly without any problem.

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Carburetor PDF:

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