OH planar laser-induced fluorescence (PLIF) and particle image velocimetry have been used to study the frequency response of laminar C3H 8-air counterflow diffusion flames to assess the adequacy of the steady-flamelet models. Particle image velocimetry was used to determine the flame strain rate, while OH PLIF was used both to measure temperature at the flame front, using the two-line PLIF technique, and the reaction-zone width. Both measurements demonstrate that the frequency response of flames subjected to a time-varying flow field is diffusion-limited. At the 30-Hz and 50-Hz forcing frequencies, the maximum reaction-zone temperature and width were found to respond quasi-steadily. However, at higher forcing frequencies-i.e., 100 and 200 Hz-transient behavior is evident from the phase relationship between the imposed sinusoidal strain rate and the resulting peak temperature and reaction-zone width. The measured values of the OH-field widths were well fit by an offset sine function. In all cases when the oscillation amplitude is normalized by the cycle mean strain rate and plotted against the non-dimensional flow field frequency, the results collapse onto a single line having a steep negative slope.
|Original language||English (US)|
|Number of pages||13|
|Journal||Combustion and Flame|
|State||Published - Nov 2003|
Bibliographical noteFunding Information:
This work was supported by the Army Research Office, under ARO Grant DAAG55 to 98-1 to 0222 (Dr. David Mann, technical monitor), the Air Force Office of Scientific Research (Dr. Julian Tishkoff, technical monitor), and the Propulsion Directorate of the Air Force Research Laboratory, Wright-Patterson AFB.
- Diffusion flame
- Stokes parameter
- Transient flame
- Unsteady flame
ASJC Scopus subject areas
- Chemical Engineering(all)
- Fuel Technology
- Energy Engineering and Power Technology
- Physics and Astronomy(all)