Carburettor is the most important item in the fuel feed system of spark ignition engines. It is connected between the fuel filter and the induction manifold. It supplies the air-fuel mixture of varying proportions to suit the engine operating conditions. The fuel enters the float chamber of the carburetor. The air enters the horn of the carburetor. Mixing of the fuel and air takes place when both pass through the venturi in the mixing chamber of the carburetor. This air-fuel mixture then goes to the intake manifold.
The function of a carburetor–
The carburetor is a device for atomizing and vaporizing the fuel and mixing it with the air in varying proportions to suit the changing conditions of spark ignition engines. The air-fuel mixture so obtained from the carburetor is called the combustible mixture. The process of mixing the gasoline fuel with air to obtain the combustible mixture is called carburetion.
Hence, the terms vaporization and atomization should be understood clearly. Vaporization is the change of state of the fuel from liquid to vapor. Atomization is the mechanical breaking up of the liquid fuel into small particles (but not actually breaking up into atoms, as the name implies) so that every particle of the fuel is surrounded by air. In order to produce very quick vaporization of the liquid fuel, it is sprayed into the air passing through the carburetor. Spraying of the liquid turns it into many fine particles so that the vaporization occurs almost instantly.
The carburetor supplies the air-fuel mixture of varying proportions to suit the changing conditions of the engine. The mixture must be rich (have a higher percentage of fuel) for starting, acceleration, and high-speed operation. The mixtures should be lean (have a lower percentage of fuel) for operation at intermediate speed with a warm engine. The theoretically perfect mixture of air and gasoline contains 15 parts of air and 1 part of gasoline by weight. An ideal carburetor would pass the mixture of completely vaporized fuel and air in the proper proportion to the intake manifold and cylinder. But in present-day carburetors, the complete vaporization of fuel is not achieved, due to the heavy nature of the fuel and other limitations. The heated intake manifold and hot spots in the manifold vaporize part of atomized fuel. Even until the end of the compression stroke in the cylinder, the gasoline does not vaporize completely, although the heat and pressure during the compression stroke are applied to it.
Faq’s (Frequently asked question)
What is atomization in a carburetor?
Atomization is the process of breaking the fuel particles. The fuel jet compresses hydrogen and carbon into extremely small droplets. Fuel atomization helps the fuel to burn easily in the chamber.