Horn Geometry Effects on Atomization Characteristics of a Micro Nozzle Array Type Ultrasonic Fuel Injector

Effects of horn geometry on the atomization characteristics of an ultrasonic fuel injector using a micro nozzle array were investigated experimentally. Micro nozzles whose exit diameter d=3μm are mounted on a thin metal film. The number of the micro nozzles is from 2.0×104 to 1.2×105. Using an ultrasonic oscillator, gasoline is periodically pushed out from the micro nozzles at a frequency from 62 to 65 kHz. A disk type PZT is used as an ultrasonic oscillator, and the oscillation is amplified using a step-type horn. The input voltage to the PZT is varied from 0 to 200 V. To increase the fuel flow rate, the horn small end diameter Ds is increased from 10.5 to 25 mm, while the large end diameter is fixed at 30 mm. To prevent forming a liquid film on the micro nozzle array, gutters are machined on the small end of the horn. It is shown that the SMD (Sauter mean diameter) of the spray is almost uniform around 10 to 14μm, regardless of the horn small end diameter. The fuel flow rate increases, at the maximum, 2.8 times larger when compared to the original horn geometry.