Effect of Throttle Configuration on Wall Flow Behaviour of Fuel in a Carburetted Induction System

Abstract

The wall mass flow of fuel in the manifold of a carburetted induction system, known to have a significant effect on fuel maldistribution and air-fuel ratio excursion, is studied experimentally with a conventional and variable-area convergent/divergent throttling device. The thickness and velocity of the wall film is calculated using the measured wall mass flow. The effect of the stream velocity, throttle position and air—fuel ratio on wall mass flow and on the thickness and velocity of the film is reported. The wall mass flow decreases as the stream velocity increases and shows a tendency to stabilize at a velocity of about 100 m/s. It also decreases with smaller throttle openings and leaner mixtures. However, with the conventional throttle it shows a tendency to increase for throttle openings less than a quarter. The film thickness is found to be in the range of 0.014–0.025 mm. The effect of the experimental parameters on film thickness is similar to that on wall mass flow. The film velocity is in the range of 20–54 mm/s and is influenced by the air—fuel ratio and throttle position. Film velocity increases as the stream velocity increases for a film thickness larger than 0.1 mm. For a film thickness less than 0.1 mm, stream velocity is observed to have no effect on film velocity. The effect of the new throttling device in reducing wall mass flow is very significant in the near closed to part throttle conditions.