 Hello students, myself Ganesh B. Aglawe working as an assistant professor in department of mechanical engineering, Valchin Institute of Technology, Solopur. Hello students, I am Ganesh B. Aglawe working as an assistant professor in department of mechanical engineering, Valchin Institute of Technology, Solopur. In this session, we will see the carburetor, learning outcome. At the end of this session, students will be able to design air-fuel ratio for the carburetor. You know the function of carburetor is to supply the required air-fuel ratio to the engine depending upon the engine condition. Carburetor is performing two tasks. First one, as we have seen, it is mixing the fuel in the air and it is mixing the fuel in the air. So, this homogeneous mixture is prepared by the carburetor. And second task, that is nothing but the function is the metering of the air-fuel mixture. So, the controlling and mixing is performed the carburetor. So, do you know the location of the carburetor? Yes. So, if this is the fuel tank, this is the fuel tank and this is the air filter, air filter. So, the mass of air, mass of the air is coming from the air filter. It enters in one device. At the same time, the fuel is also flowing with the rate m dot f towards this device. So, this device is nothing but carburetor, is carburetor. So, after filtration, air will flow through the venturi and this fuel gets injected in the venturi, venturi of the carburetor. So, it becomes the mixture of air and fuel. And if we will take its mass ratio, it is called air-fuel ratio. And this mixture goes to the engine through the intake manifold, through intake manifold, it enters into the engine. Now, depending upon the rider's requirement or the driver's demand, this engine will take air-fuel ratio. Here, for the reference, we will consider the stoichiometric air-fuel ratio. This is the stoichiometric air-fuel ratio, which is 15.2. And in this mixture, if we will go on increasing the mass of air, then its value will go to the 16, 17, 18, 19 and so on. On the reverse side, if I reduce it, if I reduce the mass of air, then I may get the air-fuel ratio as 14, 13, 12, 11, 10, 9. I stopped at 9 in the left-hand side and at 19 on right-hand side. So, if the air-fuel ratio is increasing, it is called lean range. And if it is decreasing, the mixture is called rich mixture. Now, practically, it is observed that the rich mixture less than 9 is too rich to burn. Whereas, on the lean mixture side, if we will supply the homogeneous mixture greater than 19, then that range is too lean to burn. So, this is the practical air-fuel ratio, range of air-fuel ratio. So, what is the conclusion from this figure? The air-fuel ratio supplied by the carburetor to the engine must be in the range of 9 to 19. So, that the engine will be in the running condition. There will be proper combustion in the rich mixture side and in the lean mixture side. So, this is the practical values of the air-fuel ratio. Here, this carburetor will work during the suction stroke. During the suction stroke, what is happening? There is opening of the inlet wall. This inlet wall gets open. So, your inlet wall is opening at this location and this is the crank angle. Crank shaft is rotating. It has rotated by 180 degree during suction stroke. The carburetor is going to supply this mixture during suction stroke. At this point, suppose point number b, your inlet wall closes. Then, as we know after the suction stroke, which is the next stroke, compression stroke. So, next is the compression stroke. Means what? The working of carburetor is during suction stroke. During this suction stroke, your carburetor works and it supplies the required mixture to this engine. Now, what is the stoichiometric air-fuel ratio? The stoichiometric air-fuel ratio means the minimum mass of air required to burn the fuel, to burn the fuel completely. So, there will be for complete combustion reaction, there will be two products only. First product is CO2. Second product will be H2O. Obviously, this will be in the gases form. So, this is all about the mixture requirement during the different stages of the engine. Now, which are the different stages of the engine? So, first stage is suppose acceleration. The acceleration stage of the engine will demand reach mixture. Whenever suppose you want to overtake, you want to increase the speed of the engine, then this carburetor should supply the reach mixture to the engine. Second stage of the engine is idling. Idling means your engine is running, but vehicle is not moving. So, the mass of fuel injected during the idling should be minimum enough to have to overcome the frictional power that I will explain over here now. Now, during idling once again, the engine will demand reach mixture. See here, if this is the indicated power, this is the frictional power, this is the brake power. During idling, the brake power is equal to 0, because engine is just running. To keep it in running condition, the indicated power should be equal to frictional power. So, to overcome the friction, the mass of fuel is to be injected, not more than that. Next stage of the engine is normal running. So, during normal running, the carburetor should supply the lean mixture. So, these are the different airfield ratios and the working of the carburetor we have seen over here, so that your engine will be always in running condition and it will satisfy the driver's requirements. It will satisfy the different stages, conditions of the engine. For further study, you can refer internal combustion engines by H N Gupta. Thank you.