Understanding Carburettor and Its Principle

Carburettors are used in different SI engines, especially for the combustible air-fuel mixture as a charge. A carburettor is one of the essential parts of an automobile engine, and in this article, we will talk about the definition, parts, and principles.

Definition of Carburettor

A carburettor is a device used in a combustible engine mainly for the mixture of air with fuel in a system to enhance the proper burning of fuel. It is also important to note that a carburettor is only used when a spark ignition occurs (generally with a sparking club).

Now, let us understand the different parts of a carburettor:

1. Throttle valve

One of the essential parts of a carburettor is a throttle valve. It mainly involves air and fuel mixture and is mainly supplied to the engine cylinder. When the driver presses the accelerator, it opens up the throttle valve.

2. Metering system

This system is mainly used for controlling the flow of fuel that is piped into the nozzle. It also plays a very important role in forming a proper mixture of air and fuel. It is mainly composed of two essential parts:

1. Metering orifice
2. Fuel discharge nozzle

A low-pressure field is generated across the throat when the air is passed through the venturi. Also, due to the pressure difference, the fuel gets discharged into air steam.

3. Strainer

This device is mainly used for filtering the fuel before it enters the float chamber. The strainer is mainly composed of a fine wire mesh that filters the fuel and removes dust and other suspended particles from it. So, if the particles are not removed, it leads to the blockage of the nozzle. 

4. The idling system

The idling system mainly consists of a passage between the float chamber to the venturi tube. It is responsible for providing a rich mixture during idling at low speed. It also works when the throttle is open at < 15%

5. Metering system

The metering system is mainly responsible for controlling fuel flow into the nozzle. It is also responsible for forming a correct mixture of air and fuel. It mainly consists of two parts:

1. The metering office
2. The fuel discharge nozzle

Hence, as the air is passed from the venturi, it generates a low-pressure field across the throat. Hence due to the pressure difference, the fuel gets discharged into the air stream.

The metering office and the discharge hole at the end of the fuel discharge nozzle control the fuel quantity.

6. Float chamber

The float chamber mainly works as a fuel storage tank for a continuous fuel supply. It mainly consists of a float valve used to maintain the fuel level in a float chamber. 

Hence, when the fuel level decreases, the float chamber moves downward, opening the fuel supply valve and allowing fuel flow in the float chamber.

Hence, when there is an increase in fuel level, the float moves upward, which closes and stops the supply of fuel.

7. The mixing chamber 

The mixture of air and fuel happens in the mixing chamber, which is eventually sent to the engine cylinder.

8. Transfer & idle port

Along with the main nozzle of the venturi portion of the carburettor, there are two other nozzles and ports mainly used to deliver fuel into the engine cylinder.

9. Choke valve

 A choke valve is a type of valve mainly used to control the mixture of air and fuel. The primary function of the choke valve is to control the quantity of air inside the mixing chamber mainly.

Generally, when there is a requirement for a proper mixture of air and fuel, this valve is operated; otherwise, it mainly stays in a semi-open condition. Also, due to snow, when the engine does not start in the winter season, this valve is used to get proper air and fuel supply.

Principle of Operation of Carburettor

A carburettor mainly works on the principle of Bernoulli. So, as and when the velocity increases, the pressure for the same will decrease. Mainly air and gasoline go to the combustion chamber of the engine, passing through the carburettor. 

The central principle and the working of a carburettor depend mainly upon the venturi tube, which is the central part of the carburettor. The pressure difference between the throat of the venturi and the float chamber is mainly responsible for the fuel and gasoline discharge in the air. 

The difference between the pressure mainly decides the mixing ratio for air and fuel that mainly controls the throttle valve.

Conclusion

A carburettor is a device for providing a mixture of air and fuel to a spark-ignition engine. Some common carburettor components include an idling jet, a liquid fuel storage chamber, an air-flow restriction (venturi-shaped), a choke,  the main jet, and an accelerator pump. This was all about the essential parts and understanding a simple carburettor. Hopefully, you have understood the carburettor and the principle behind it.