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The air pollution is increasing at an alarming rate now a day mainly due to emissions coming out of automotive vehicles. The exhaust emissions gases are hazardous to human health. The increased number of vehicles on road will make the scenario even worse. In order to control the pollution level, the regulatory bodies are now implementing stringent emission norms. In India, the regulatory authorities has framed the transition of BS IV to BS VI emission norms in 2020 by skipping the BS V emission norms which makes the automotive industries to work on more advanced fuel management technologies. It is more tedious to control the tail pipe emissions beyond BS IV emission norms with the conventional carburetor system since it is operating on open loop system. It is evident that in order to meet the stringent emission norms we need to have a closed loop system which controls the Air Fuel Ratio (AFR) close to stoichiometric to increase the conversion efficiency of the catalytic converter.

In India, for two-wheeler application, carburettor is the preferred fuel supply system for majority of the market, owing to its simplicity and low cost. With the regulations becoming stringent, carburettor internal structure requires modification. One of the important parameters is the venturi shape, which controls the air-fuel mixture supply to the engine. Venturi shape plays an important role in deciding the transient performance characteristics. In this study, a CFD analysis has been carried out to predict the pressure and velocity at the venture of the carburettor. Four different cross sections namely, circular, oval, trapezoidal and double D venturi shapes were selected. The geometric model of the carburettor was created and mesh refinements were carried out in critical regions. At part open throttle, CFD prediction of airflow rate with Trapezoidal venturi shape was found higher when compared to other venturi shapes.