Imaging of premixed flames in microgravity

A laser schlieren system which uses video recording and digital images analysis has been developed and applied successfully to microgravity combustion experiments performed in a drop-tower. The optical system and the experiment are installed within a small package which is subjected to free-fall. The images are recorded on video tape and are digitized and analyzed by a computer-controlled image processor. The experimental results include laminar and turbulent premixed conical flames in microgravity, normal positive gravity (upward), and reverse gravity (downward). The procedures to extract frequency information from the digitized images are described. Many gross features of the effects of gravity on premixed conical flames are found. Flames that ignite easily in normal gravity fail to ignite in microgravity. Buoyancy driven instabilities associated with an interface formed between the hot products and the cold surrounding air is the mechanism through which gravity influences premixed laminar and turbulent flames. In normal gravity, this causes the flame to flicker. In reverse gravity, -g, and microgravity, g, the interface is stable and flame flickering ceases. The flickering frequencies of +g flames vary with changing upstream boundary conditions. The absence of flame flickering in g suggest that g flames would be less sensitive to these changes.This work is supported by NASA Microgravity Sciences and Applications Divisions under contract No. C-32000-R through the U.S. Department of Energy Contract No. DE-AC03-76F00098. Technical support is provided by NASA Lewis Research Center. Project Scientist is Dr. Karen J. Weiland. The authors would like to acknowledge Dr. Liming Zhou for his contribution to early testing of the schlieren system, and to Mr. Gray Hubbard for writing the image analysis software