Development and Evaluation of the Performance Characteristics of a Poly-Disperse Droplet Stream Generator

A specially designed generator has been developed to produce poly-disperse droplet streams: A liquid fuel (n-heptane) is metered to an ultrasonic atomizer to produce droplets, which are then carried and accelerated vertically upwards through a nozzle tube by carrier-air flow. Conditions of the streams at the nozzle exit are modulated by varying the length of nozzle tubes, the fuel and carrier-air flow rate. Optical measurement techniques such as direct photography method, schlieren photography and particle image velocimetry (PIV) are employed to characterize its performance characteristics.

Effects of the nozzle tube length, the carrier-air and fuel flow rate are investigated to evaluate the performance of the generator. Longer nozzle tubes provide a better flow guidance for the carrier-air, and tend to generate streams with less and smaller droplets due to the transporting losses. The increase of carrier-air flow is able to restrain the radial fluctuation of droplet velocities because of the overcoming of droplets inertia by increased outlet velocity. The fuel flow rate is determined by the request of fuel droplet concentration. As a result, in order to obtain uniform and stable streams, longer nozzle tubes and higher carrier-air flow rate are helpful.