Working Principle Of Carburetor

The carburetor is a device that provides the engine with a mixture of fuel and gas. The time it takes for an internal combustion engine to complete a four-stroke cycle is extremely short, and the time it takes for the fuel to burn is even shorter. Incomplete combustion of the fuel will result in fuel waste and even cause exhaust pollution and pipeline blockage. In order to ensure that the fuel burns fully, the fuel must be fully mixed with the air before ignition to increase the contact area between the fuel and the air so that the combustion is rapid, intense and complete. The carburetor is an effective tool for mixing fuel and air. 
Figure 1 is a schematic diagram of the structure of a carburetor for an engine. The amount of fuel in the fuel chamber is controlled by a float. According to the principle of fluid statics, the weight of the float is constant and the depth of immersion in the fuel is also constant. When the oil level reaches the height of the fuel injection port, the needle valve above the float just closes the fuel inlet and the fuel inlet stops supplying fuel. When the fuel level drops below the fuel injection port, the float also moves downward with the oil level, and the fuel inlet is opened again to continue supplying fuel until the oil level reaches the height of the fuel injection port again. The device for generating the fuel-gas mixture is a venturi tube with thick ends and thin middle. A nozzle connected to the fuel chamber is placed in the throat at the thinnest part. Since the fuel liquid level is at the same height as the nozzle, the fuel pressure at the nozzle is the atmospheric pressure. When the high-speed airflow flows in from the air inlet, the airflow velocity through the throat becomes larger. According to the Venturi effect, as the airflow velocity increases, the pressure will decrease. The air pressure at the throat is much lower than the atmospheric pressure. Under the action of the internal and external pressure difference, the fuel in the fuel pipe is quickly ejected and mixed with the air to form a mist-like mixture. When the pressure at the nozzle decreases, the amount of oil sucked out will increase accordingly. The amount of oil sucked out changes with the air flow rate, so the oil-gas ratio supplied by the carburetor to the engine can remain constant. The part that adjusts and controls the oil-gas ratio is the butterfly valve of the carburetor. The opening size of the butterfly valve can control the air flow to control the oil-gas ratio. Under normal circumstances, the mass ratio of oil to gas is about 1:13, and the volume ratio is about 1:9000. The throttle can control the total amount of mixed gas injected into the engine, thereby controlling the engine's output power. The throttle is installed in a venturi tube and is connected to the accelerator pedal externally. Modern carburetors also add some auxiliary equipment to reduce the release of hydrocarbon compounds, and can use computers to automatically control the oil-gas ratio and the amount of mixed gas supplied according to the engine's temperature, load and speed.