The simple carburetor(Simple Carburetor Working Principle) is the most important item in the fuel feed system of spark ignition engines. The carburetors are mainly used in the vehicle to feed the fuel and mix the air-fuel. Mixing of the air-fuel goes to the venturi chamber of the carburetor. Today in this article I will discuss the working principle of a simple carburetor.
Simple carburetor working principle–
A simple carburetor consists of a round cylinder with a constricted section, a fuel nozzle, a throttle valve, and a float chamber. The round cylinder is called the air horn and the constricted section is the venturi. The venturi and the float chamber are connected by the fuel nozzle. The throttle valve can be tilted to open or close the air horn. The construction and function of each part of the carburetor are as follows:
A venturi is a narrow space in the cylindrical air horn, through which the air passes. As the same amount of air must pass through every point in the air horn, its velocity will be greatest at the narrowest point. The more this area is reduced, the greater will be the velocity of air. The opening of the discharge jet is usually located just below the narrowest section of the venturi so that the suction is greatest.
The spray of gasoline from the nozzle and the air entering through the venturi are mixed together in the mixing chamber which is just below the discharge jet. In this chamber, the vaporization and atomization of the gasoline take place and it mixes with the air so that the combustible mixture is produced. This mixture passes through the intake manifold into the cylinder.
As the engine speed increases beyond a certain limit, suction also increases. Especially in simple plain-tube carburetors, the flow of fuel from the jet increases faster than the corresponding flow of air.
Thus, the mixture becomes richer. To maintain the correct air-fuel mixture at high speeds, some automatic compensating devices must be provided in the modem carburetors to maintain the desired mixture ratios at higher speeds. These devices act either to increase the air supply automatically as the suction above the jet increases or to increase the fuel supply automatically as the suction above the jet decreases. The compensating devices used in commercial carburetors are metering rods, air-bleed jets, economizers, compound jets, and auxiliary air valves. The type of compensating mechanism used determines the metering system of the carburetor.