Construction and Working , Diagram Of Simple Carburetor


Carburetor is a device used for atomizing and vapourizing the fuel and mixing it with the air in varying proportions to suit for changing the operating conditions of engines. The process of breaking up and mixing the fuel with the air is called carburetion. The term vapourization and atomization should be understood clearly. Vaporization is a change of state of the fuel from liquid to vapour whereas atomization is a mechanical breaking-up of the liquid into small particles so that every minute particle of the fuel is surrounded by the air.
The carburetor is supposed to supply the fuel air mixture in correct proportion under different conditions of temperature, speed and load on engine. Relatively rich mixture of air fuel ratio of 12:1 is required by the engine while accelerating or running at high speeds. A leaner mixture of air-fuel ratio of 16:1 is sufficient while running on levelled roads. For idling, a richer mixture of about 14:I is needed. Similarly, an extremely rich mixture having a ratio of 9:1 is required during cold starting.

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Simple Carburetor

The main components of a simple carburetor are float chamber, float, nozzle, venturi, throttle valve, inlet valve and metering jet. In the float chamber, a constant level of petrol is maintained by the float and a needle valve. The float chamber is ventilated to atmosphere. It is used to maintain the atmospheric pressure inside the chamber, The float which is normally a metallic hollow cylinder rises and closes the inlet valve as the fuel level in the float chamber a certain level.

The mixing chamber contains venturi, nozzle and throttle valve. The venturi tube is fitted with the inlet manifold. This tube has a narrow opening called venturi. A nozzle is provided just below the centre of this venturi. The nozzle keeps the same level of petrol as the level in the float chamber. The mixing chamber has two butterfly valves. One is to allow air into the mixing chamber known as choke valve. The other one b to allow air-fuel mixture to the engine known as throttle valve.

Simple Carburetor Diagram :

simple carburetor diagram
simple carburetor diagram


During suction stroke, vacuum is created inside the cylinder. It causes the pressure difference between cylinder and outside the carburetor. Due to this, the atmospheric air enters the carburetor. The air flows through venturi. The venturi increases the velocity of air and reduces the pressure. It produces the partial vacuum at the tip of the nozzle. Because of this vacuum, the fuel comes out from the nozzle in the form of fine spray. These fine fuel particles mix with the incoming air to form air-fuel mixture. Thus, it gives a homogeneous mixture of air-fuel to the engine.

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