Atomization characteristics of an ultrasonic fuel injector using a micro nozzle array were investigated experimentally. Micro nozzles whose exit diameter is d =3, 6 and 9μm are mounted on a thin metal film.The number of the micro nozzle is 2.0×104. Using an ultrasonic oscillator, gasoline is periodically pushed out from the micro nozzles at the frequency of 63.6kHz.A disk-type PZT is used as an ultrasonic oscillator, and the oscillation is amplified using a step-type horn.The input voltage is varied from 0 to 200 V.At the natural frequency, the oscillation amplitude of the horn is about 10μm.The droplet diameter and velocity are measured with a phase Doppler analyzer at 15 mm downstream from the micro nozzle array.For d=3μm, the Sauter mean diameter (SMD) is about 10μm, and the fuel flow rate is 0.023 cc/s. The SMD is much smaller when compared to conventional port fuel injectors.For d=6μm, the SMD is about 10 to 18μm, and the fuel flow rate is 0.055 cc/s.For d=9μm, the SMD is about 16 to 28μm, and the fuel flow rate is 0.41 cc/s.It is shown that, using the micro nozzle array, a uniform-diameter steady spray can be obtained without high-pressure fuel pump and nozzle type injectors.
