Experiments Concerning the Occurrence and Mechanism of High-Frequency Combustion Instability

Citation

Barker, Calvin LaRue (1958) Experiments Concerning the Occurrence and Mechanism of High-Frequency Combustion Instability. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/F39S-MP16. https://resolver.caltech.edu/CaltechETD:etd-10072004-092728

Abstract

The phenomenon of screeching combustion was examined experimentally with particular reference to the significance of the time lag proposed by Rogers and Marble. This investigation was conducted in a 1- x 4-inch rectangular cross-section water-cooled combustor in which was burned a premixed air - fuel mixture. This combustor contained a 70 % blockage solid V-wedge flameholder. Vortices were generated at the flameholder lips during smooth combustion by impinging a shock wave on the flamefront. These vortices were compared with those generated during screeching combustion and found to be similar to them in all major respects. Thus the common assumption that vortices are generated by the action of the oscillating velocity is a sound one. The fact that screech excitation occurs in the shear layers immediately downstream of the flameholders was demonstrated by injection of air into this region. Such injection was found to suppress the tendency of the combustor to screech. By comparison of observations of the screech limit with ignition time delay data obtained from bluff-body flameholding studies it was shown that the mechanism of screech excitation is indeed controlled by a characteristic time. A procedure, based on this result, was developed for determining in advance the behavior of the screech limit in a family of geometrically similar combustors under variations of fuel type and inlet temperature.

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