Theoretical and Experimental Investigation of Metering Characteristics of a Variable Venturi Mechanically Controlled Carburettor

The objective of the present work is to develop a mathematical model for predicting the metering characteristics of a variable venturi mechanically controlled two wheeler carburettors. Further the effect of carburettor operating parameters (viz. pilot jet size and main jet size) influencing the metering characteristics has also been studied.

The model is developed taking into account the type of venturi (circular or oval), jet needle restriction and needle jet projection inside the venturi. The compressible flow analysis gives the mass flow rate and the intake manifold vacuum, which acts as a driving force for the flow to take place. Based on the mass and energy conservation, the fuel flow rate through the pilot and main system is determined.

Experiments have been carried out to compare the predicted results with measurements so as to validate the model. The experiments were carried out at constant speed mode on a chassis dynamometer. Partial spacer rings were used to hold the throttle at required percentage throttle opening. The experiments were performed for a specific carburettor-engine combination.