CARBURETOR : PURPOSE AND WORKING !!

In case of S.I engine(Petrol Engine) the air and fuel are mixed into proper ratio before it enters into the combustion chamber.Also,the air is in gaseous form and fuel is in liquid form so the fuel has to be converted into gaseous form in order to mix them properly.This process of conversion of liquid fuel into gaseous form is known as vaporization.The fuel must be broken into small particles for proper mixing and the process of breaking fuel into small particles is known as atomization.

Carburetor is a device which atomizes,vaporizes and mixes air and fuel into proper ratio before it enters into the combustion chamber in case of S.I (Spark Ignition)engine.The process of preparation of air fuel mixture in S.I engine is called carburetion.

Working :

The carburetor works on Bernoulli's principle: the faster air moves, the lower its static pressure, and the higher its dynamic pressure. The throttle (accelerator) linkage does not directly control the flow of liquid fuel. Instead, it actuates carburetor mechanisms which meter the flow of air being pushed into the engine. The speed of this flow, and therefore its pressure, determines the amount of fuel drawn into the airstream.

1. Air flows into the top of the carburetor from the car's air intake.
2. When the engine is first started, the choke (blue) can be set so it almost blocks the top of the pipe to reduce the amount of air coming in (increasing the fuel content of the mixture entering the cylinders).
3. In the center of the tube, the air is forced through a narrow kink called a venturi. This makes it speed up and causes its pressure to drop.
4. The drop in air pressure creates suction on the fuel pipe (right), drawing in fuel (orange).
5. The throttle (green) is a valve that swivels to open or close the pipe. When the throttle is open, more air and fuel flows to the cylinders so the engine produces more power and the car goes faster.
6. The mixture of air and fuel flows down into the cylinders.
7. Fuel (orange) is supplied from a mini-fuel tank called the float-feed chamber.
8. As the fuel level falls, a float in the chamber falls and opens a valve at the top.
9. When the valve opens, more fuel flows in to replenish the chamber from the main gas tank. This makes the float rise and close the valve again.

Carburetors are not used in modern cars and bikes due to following limitations :

• At a 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.
• The working of carburetor is affected by changes of atmospheric pressure. 
• It gives the proper mixture at only one engine speed and load, therefore, suitable only for engines running at constant speed increase or decrease.
• More fuels are consumed since carburetors are heavier than fuel injectors.
• More air emissions than fuel injectors.
• Maintenance costs of carburetor is higher than with fuel injection system.

Carburetors are good for single cylinder engines but when it comes to multi-cylinder engines carburetors are not efficient.