Flame radiation and acoustic intensity measurements in acoustically excited diffusion flames

This article describes results of an investigation of the mechanisms responsible for the driving of axial instabilities in solid propellant rocket motors. Specifically, the results of two different experimental methods for measuring the driving of axial acoustic fields by sidewall stabilized diffusion flames are compared. These methods utilize laser Doppler velocimetry (LDV) and CH flame radiation measurements, respectively. The results reveal that the interaction between the acoustic field and the flame produces a space-dependent, oscillatory normal velocity component in the flame region, and oscillatory reaction-and heat-release rates, which depend upon the excited acoustic field. The results suggest that the flame either drives or damps the acoustic fields, depending upon the amplitude and frequency of the excited acoustic wave. In addition, these studies show that the flame driving processes vary within the flame region. The results obtained from the flame radiation measurements are in excellent agreement with those obtained using the velocity measurements.