Numerical and Experimental Investigation on Carburettor Venturi Shape for a Two Wheeler 2013-01-2803

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. In actual vehicle trials, it was found that this venturi shape has a better acceleration time of 5% (0∼60 km) compared to circular shape. At wide open throttle, CFD predicted airflow rate with circular venturi shape was found better than other venturi shapes due to lesser restriction. In actual vehicle trials, this type of venturi cross section yielded 4% more power than the trapezoidal venturi carburetors. Finally it is concluded that oval shape is a good compromise for an optimum performance.