Suppression of Combustion Instability in Rocket Motors Using Electrothermal Acoustics,

It was previously demonstrated that a conductive flame with a suitable arrangement of electrodes and coupling circuitry can transform an electrical signal into a high level acoustic output at audible and ultrasonic frequencies. Experimental evidence also indicated that complex effects involving the optical and electromagnetic spectrum took place concurrently. The objective of this research was to obtain a fundamental understanding of the observed phenomena to allow evaluation of potential applications in the fields of combustion instability, noise suppression, ultrasonic sound generation, communications and RF effects. Data on the acoustic, optical, electrical, and microwave scattering properties of a seeded oxygen-acetylene flame were obtained over the frequency range up to 150 kHz. A theoretical model was developed which correctly predicts the frequency dependent electrical impedance of the flame and the amplitude and directivity of the external sound field. Author