Thermal flow structure in a concentric-flows burner enhanced with a cap
Date Issued
2012
Date
2012
Author(s)
Ho, Tsai-Hsing
Abstract
The present study focused on the stabilizing mechanism of a cap combustor. According to our previous studies, premixing could be created between the central fuel jet and annual air flow in the cap. To understand the thermal flow pattern of the cap combustor, we studied the flow field by using photographic methods of Shadowgraph and Schlieren, Particle Image Velocimetry (PIV), and temperature measurement.
The results showed that the flame pattern of the cap combustor with changing of the relative velocities of fuel and air could be classified into four modes: jet-like flame, transition, premixed-like recirculated flame, and premixed-like jet flame. Flame in jet-like condition is characterized by rotated folding structure; recirculated flame around the cap surface began to develop in transition flame; premixed-like recirculated flame was formed by the fully developed recirculated flame and obvious central blue flame. The central blue flame was yielded due to the mixing of gas and air in the cap, and the interaction of central blue flame and recirculated flame could extend the range of flame stabilization; premixed-like jet flame was characterized by a central jet flame of mushroom shape without the recirculated flame, which revealed that the mixed gas in such flow condition could be ignited immediately after passing through the central exit of the cap. Flame then extinguished because of high speed of the input air.
From the results of flow visualization integrated with PIV analysis, we found the air-driven outer vortex structure was the important factor of changing flow patterns. The change of location of the center of outer vortex (forward stagnation point) would promote the development of recirculated flame in premixed-like recirculated flame, and provide another space for mixing.
Subjects
cap
concentric-flows burner
Particle Image Velocimetry (PIV)
flow visualization
Type
thesis
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