In this PhD project, the investigation of the stability of a laminar diffusion flame and the interaction of the flame with acoustic waves inside an acoustically excited cylindrical tube is presented. Interesting phenomena have been observed by studying both the infrasound and sound effect on the flame structure and dynamics.When a cylindrical tube burner is acoustically excited at one end, a standing wave will be produced along the tube burner. By applying a programming controlled signal from a signal generator, the loudspeaker generates acoustic waves with different frequencies and intensities to excite the flame, which can make the flame relatively stable or unstable, even blow out. Different methods in both frequency domain and time domain have been applied to analyze the flame stability affected by acoustic waves. Both infrasound and sound are tested in this research. Infrasound is the acoustic wave with a frequency too low to be heard by human ear covering sounds beneath the lowest limits of human hearing (20Hz) down to 0.001Hz. It is found that infrasound is able to take over buoyancy-driven flame flickering and make the flame flicker at the same frequency as the forcing infrasound. For some infrasound, half excited frequency has been detected clearly in the power spectrum of CH* chemiluminescence signals acquired by a photomultiplier. On the other hand, some higher frequency acoustic wave can have observable effect on flame flickering but the buoyancy-driven flickering is still the dominant oscillating mode; some other higher frequency acoustic wave can make the flame very stable, such as the acoustic wave at 140Hz. Image processing technique has shown that the influence of acoustic waves on the laminar diffusion flame varies spatially. It is also observed that a diffusion flame may oscillate at different frequency spatially. Taking the flame without acoustic excitation as an example, the inner most area of the flame oscillates at the typical flickering frequency, but the most outer areas of the flame oscillate at the second-harmonic of the typical flickering frequency. Finally, some control strategies are developed for the laboratory tube burner based on the gained physical insights in this research.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:539992 |
| Date | January 2011 |
| Creators | Guo, Huimin |
| Contributors | Zhang, Yang |
| Publisher | University of Manchester |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | https://www.research.manchester.ac.uk/portal/en/theses/flame-and-acoustic-waves-interactions-and-flame-control(d6306221-905e-425f-9144-d40453eabb7f).html |
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