Carburetor Working Principle and Diagram

The vehicle can run because there is an engine in it, the car engine can generate power because there is a combustion process. The combustion process can generate expansion power from the gas that burn inside the combustion chamber.

Then this expansion power is used to make the vehicle's wheels spin.

The gas is not natural gas but a mixture of fresh air and oil such as gasoline or diesel fuel.

However, the two materials cannot mix themselves. To make it mixed it needs to be done by a component, called a carburetor.

Then how does the carburetor work? this is what we will discuss in detail today.

Carburetor Definition and Function

Carburetor is a component that are used to supply combustion material on gasoline engines. That means, the carburetor is only available on gasoline engines. While the diesel engine is not equipped with a carburetor.

The reason is, when the intake step is only fresh air is entered into the engine. So it doesn't need a carburetor to chalk the gas.

The function of carburetor is to mix the fresh air from outside with fuel in ideal ratio. This is called AFM (air fuel mixture), the AFM has ratio about 14 : 1. It mean, 14 air molecules and 1 fuel molecul. For understand the AFM, you need to learn about stoichiometric.

While in this article we just learn about carburator working principle, to understand how the carburator can mix the air and the fuel.

Working Principle of Carburetor

The carburetor working principle using pressure difference, as you know liquid or gas will always flow to areas with lower pressure.

The process that occurs in the carburetor is also the same, gasoline can enter the intake manifold because the pressure inside the intake manifold is smaller than in the gasoline storage chamber in the carburetor.

In general, there are three components in the carburetor. Namely;

  1. Venturi
  2. Fuel jet
  3. Gasoline storage room

Gasoline storage room, serves to accommodate gasoline shipments from tanks that are ready to be regularly suplied into the intake manifold. Here the pressure is made equal to atmospheric pressure because of that, there is usually ventilation.

Venturi is a part inside the carburetor that has smaller diameter than the intake manifold diameter, it mean inside the intake hose there are carburetor that has smaller diameter.

While the fuel jet is a hose that connects the gasoline storage room with the venturi chamber. Its function is only running gasoline, but the width or size of the pilot jet's diameter affects the fuel suply. The greater the diameter of the fuel jet, the greater the ratio of gasoline will be.

In it works, the gasoline will be served from fuel tank to gasoline storage room inside the carburetor. When the engine start, there will be an air flow inside the venturi. The flow make the pressure inside the venturi lower and the result the gasoline come out via fuel jet.

Now the question is, why is the pressure inside the venturi lower?

The differece of pressure occurs naturally. If you have ever read the principle of an aircraft wing, this might be the same. In Bernoulli's law, the pressure of a fluid such as air decreases when the air moves faster.

Just like we discussed above, the carburetor located in front of intake hose. And inside of carburetor there is venturi with smaller diameter than intake diameter. The smaller diameter, make the air flow faster. The faster air flowing, the higher pressure occurs.

It make the area inside of venturi have lower pressure than the other are inside the carburetor.

The pressure inside the venturi, is lower than the atmopheric pressure. While the gasoline inside the fuel chamber are equal with atmospheric pressure, it causes pressure difference. It makes the fuel automatically out to the venturi.

This pressure difference will also be greater if the air flow inside the intake get faster. So, when the engine run in high RPM, the airflow automatically increase and the pressure inside the venturi decreases, the reslut there will be bigger pressure difference that make more gasoline come out to venturi.

How does the carburetor regulate the volume of gasoline coming out?

To regulate the amount of gasoline that come out in specific RPM, it is set by making the diameter of the venturi and the fuel jet that fits. Both components have a vital role in AFM.

So, the amount of gasoline regulated by :

  • Engine RPM (it make difference pressure)
  • The diameter of venturi
  • The diameter of fuel jet

Type of carburetor

In general, there are only two types of carburetors, namely;

1. Fixed venturi type

The first type as the name implies, has a fixed venturi width. This carburetor is widely used in large capacity engines (above 1000 cc) as in cars and some are used also on motorcycle.

The fixed venturi type requires a throtle valve after the venturi to regulate the speed of air flow that passes through the venturi to regulate the engine RPM.

2. Variable venturi type

Is a type of carburetor with an adjustable venturi size. In contrast to the first type, the variable type venturi does not equip with a throtle valve. However to set the air flow speed, it carried out by the diameter of venturi that can be change.

When engine run in idle, the RPM is low. In this condition, the venturi is in smallest diameter. It make lower air flow. But, there is an additional part called a skep needle.

When the engine run in idle, then the width of the venturi is very small and the skep needle reduce the diameter of fuel jet, it’s due to of its tapered shape (larger base diameter). It will automatically reduce the fuel jet diameter, as a result the gasoline come out become litle.

When the engine run in high RPM, the width of the venturi gets bigger and the needle is lifted so that the fuel jet diameter increase. This will cause the air flow to get faster and more gasoline come out to the intake manifold.