Abstract: In an ultrasonic oscillator which comprises an ultrasonic vibrator for driving an ultrasonic vibrator horn of an ultrasonic atomizer, a balanced circuit in which the ultrasonic vibrator is connected so that a balanced condition is established with respect to the damping capacity of the ultrasonic vibrator, and amplifier means for sending a signal to the balanced circuit and which includes a feedback circuit for positively feeding back the signal output from the balanced circuit, the feedback circuit is connected to means for adjusting the feedback quantity so that, when the ultrasonic oscillator starts the oscillation, the signal feedback quantity output from the balanced circuit is adjusted to make the gain of the amplifier means much greater than 1, and when the oscillator is in the steadily oscillating condition, the signal feedback quantity output from the balanced circuit is adjusted to broaden the allowable frequency band width of the ultrasonic vibrator.

Abstract: An apparatus for reforming fuel oil wherein ultrasonic waves are utilized. The apparatus comprises a closed vessel, a rotary collector formed in a cylindrical shape, an inlet conduit for supplying fuel oil to be reformed into the vessel, an outlet conduit for delivering reformed oil from the vessel, and a ultrasonic irradiating device. The rotary collector has a layered mesh structure of a fine mesh, preferably of mesh size between 2 .mu.m and 20 .mu.m, mounted thereon so that sludge contained in the fuel oil to be reformed is collected on the layered mesh structure. One end of a horn connected to the ultrasonic wave irradiating device faces the layered mesh structure forming a small gap therebetween so that the sludge collected on the layered mesh structure is dissociated by the ultrasonic waves.