PLIF measurements of combustion dynamics in a burner under forced oscillatory conditions

Abstract

-A technique has been devised which can provide insight into the local dynamic response of a flame to an acoustic field. In the experiments, a test chamber is acoustically excited by a pair of low frequency drivers. The response of the flame is visualized by planar laser-induced fluorescence (PLIF) of the hydroxyl (OH) radical, which is a good indicator for heat release in the flame. The resulting images are phase-locked and averaged to yield a qualitative picture of the fluctuation of the heat release. This is correlated with a pressure transducer near the flame, which allows stability to be evaluated using Rayleigh's criterion. Results indicate that the drive frequency and burner configuration have a pronounced effect on the response of the flame. Drive frequencies ranging from 22 Hz to 55 Hz are applied to the jet mixed burner, supplied with a premixed 50/50 mixture of methane and carbon dioxide at a Reynolds number of 20,000. The burner is operated in two configurations; with an aerodynamically stabilized flame, and with a flame stabilized by two protruding bluff-bodies. Results indicate that in general, the bluff-body stabilized flame is less sensitive to chamber acoustic excitation

Active control of combustors after twenty years' efforts

“…Building on early works [42,43], a program was initiated at Caltech to measure the frequency response of §ames at atmospheric pressure. There were two principal methods available at that time: (i) passively observed chemiluminescence and (ii) planar laser induced §uorescence (PLIF).…”

Effect of hydrogen addition and burner diameter on the stability and structure of lean, premixed flames

“…However, with the increase in technology and clarification of the limitations of chemiluminescence, 77 PLIF techniques are now prevalent in examinations of combustion instability in lean, premixed systems, including naturally unsteady systems and those in which the application of acoustic forcing is used to induce the formation of instability.…”

“…In addition to these two studies, PLIF has been used to investigate the dynamics and characteristics of both swirled-flame systems. 16,79,114,133,137,138,139,140 and non-swirled flame systems 77,118,141,142 .…”

“…In contrast to chemiluminescence imaging techniques, PLIF offers a better temporal resolution due to increased power of the signal and the resulting decreased amount of exposure time required for capturing the PLIF images. 77 In PLIF, the laser sheet localizes the data collected to the fluoresced plane, while in chemiluminescence techniques, the images collected are line-of-sight spatial averages, so PLIF also offers better spatial resolution than chemiluminescence. 83 Then, the increased temporal and spatial resolutions precipitate the use of PLIF (over chemiluminescence) in examinations involving internal flame structures.…”