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This paper reports the experimental study performed to understand the atomization characteristics of a miniaturized disc-type ultrasonic atomizer unit, which was developed for the purpose of fueling a two-wheeler engine. Ultrasonic atomizers are known to produce very fine droplets using high frequency vibrations. When a disc is made to vibrate at a very high frequency, with liquid above it, capillary waves are formed on the liquid surface, which become unstable, and eventually break up to form mist. The mist, thus formed, mostly contains liquid particles of less than 10 µm in size. Studies have been done earlier to use such a disc-type atomizer to fuel internal combustion engines, leveraging the advantage of small drop sizes produced by it. However, difficulties have been reported in packaging such fuel systems in small two-wheelers, where the space is constrained. Therefore, a new compact arrangement of fueling system using a disc-type ultrasonic atomizer is developed, for easy packaging of the fuel system in the intake path of the engine. While miniaturizing the fueling system, the need for maintaining a minimum liquid column above the disc had to be examined, which if not maintained could cause failure due to overheating of the disc. This reduction in the fuel level above the disc could possibly vary the liquid surface wave morphology and also its atomization characteristics. Thus, to understand the effect of small fuel levels or liquid films above the disc, visualization experiments were conducted, to study the near-disc liquid surface wave morphology and its break up process using backlit imaging technique. Initial experiments showed that having a thin liquid film above the disc produced multiple small crests and troughs on the liquid surface and also produced widespread breakup of drops and formation of fine mist. Most importantly a central tall plume usually seen when used a higher liquid column, was not seen with this compact system. This observation of absence of the central large plume ensures that this compact ultrasonic atomizer system, when used on the engine, is very unlikely to produce wall wetting. This study gives enough confidence for applying this compact ultrasonic atomizer on engine, with simplified packaging and less-complicated controls.
