Theoretical and experimental study on the ultrasonic fuel injector valve.

This thesis describes a theoretical and experimental investigation of a novel ultrasonic fuel injector valve constructed from a tapered metal horn whose wide end is bonded to a quartz crystal. fuel enters sideways at the longitudinal antinode and passes along a central hole to a ball valve at the tip. When the crystal is driven by an oscillatory pulse, it excites longitudinal vibrations, bouncing the ball from its seat and releasing fuel. The ball motion without any liquid resistance has been studied theoretically through a computer program. Parameters such as the maximum gap between the ball and the seat, the frequency, amplitude and initial condition of the tip motion, and the time of impact have been studied, and compared with measurements of ball motion in a large vibrating model. The injector tip motion has been measured using a laser technique. The measurements have been made with and without fuel flow. The effects of the fuel supply pressure and pulse width on the tip motion have been studied. Using this data, the effect of the actual (non-ideal) motion of the tip on the behaviour of the ball was studied theoretically. A model of the valve was designed so that flow forces on the ball and the flow rates through the various passages could be measured. Using this data, the ball motion with fluid resistance was computed under various conditions. This in turn permitted the fluid flow from the injector valve to be predicted, Five scale models of new valve geometries were designed and installed on an improved test rig. By this means, the effect of valve geometry on flow force and the flow rates within the valve were studied. The behaviour of actual injector flow during flow pulses was studied using laser anemometry. The main findings of this investigation were as follows. The ball moves with a random frequency. An increase in the maximum gap between the ball and the seat caused, in general, a decrease in the frequency spectrum of the ball. Tip motion was found to build up in 5 ms to the steady state. Increasing the supply pressure caused a reduction in the amplitude of the tip motion. A decay of 1.5 ms in the tip motion was observed after switchi.ng off the injector. The effect of various geometrical changes in the design of the tip and its passageways on ball force and flow rates has been demonstrated. Ball motion bunt up in 1.5 -2 ms, and decayed in J ms. The liquid resistance was found to have a significant influence on the ball motion. The flow rate built up to the steady state in 2-J ms and decayed in 2 ms. The total flow was found to have linear characteristics after 1.5 -2 ms from switching on the injector. Of particular significance, it was predicted theoretically and measured experimentally that the flow rate was independent of supply pressures over 40 psi