Investigation on temperol-spatial dynamics and flame stabilization of stratified combustion
Date Issued
2014
Date
2014
Author(s)
Chen, Jing-Wei
Abstract
An experimental method of PIV and chemiluminescence coupled with POD was constructed to capture transient images for both flames and flows with procession of the reconstruction, and temporal/spatial dynamic characteristics on a stratified burner. The issues in this study include the effects of inflows on the combustion characteristics with its mechanisms of flame stabilization, and application of syngas combustion on V-shaped burner. The effects of inflows categorized with single, double and triple inflow mode were investigated for premixed methane flames, respectively. The increase of inflow number was found to enhance the peak value and broaden the higher level probability distribution function (PDF) for turbulence intensity, demonstrating that the presence of shear layer structure is the dominating factor. The mode 1 was found to be the dominant mode for all cases, but the energy-contained of low-rank mode was diverged to the high-rank mode. Both the horizontal and vertical oscillation was intensified with increase of inflow number; the presence of augmented oscillation and irregular vibration in turning point for high-rank mode was responsible for the fractalized structure. The effect of air co-flow on the single lean methane flame was investigated firstly. A variation of the position of co-flow injection shows that the inner one has no impact, whereas the outer one surpassing effective velocity ratios has a definite impact with flame configuration altered from a lift-off flame to a cone-like flame. This characteristic is similar with the presence of turning point the vertical oscillation because of a reversed flow with accumulated hot combustion products in the co-recirculation zone. It results in a lift-off flame propagating nearer the burner exit and demonstrats enhanced flame stabilization. Second, for stratified combustion of three premixed propane mixtures with velocity gradient, the operation region was expanded to phi = 0.5 with compressive vortex pair because of the enhanced preheating and mixing effects in the wake region. The compressive vortex pair structure effectively induces greater turbulent intensity to enhance the flame intensity, and thus achieves a salient performance of stabilization. Third, the flame intensity of the triple premixed propane flames with phi = 0.6－1.6 were found to correspond well with turbulence intensity in lean flames, but inversely in rich flames. With the mode 1 in POD analysis, the large scale vortex structures dominated in lean flames with low frequency, whereas the small stratified structures dominated in rich flames with high frequency. It indicates that the combustion characteristics influenced by the lean and rich flames were dominated by the change of diffusion-thermal instability. For the V-shaped burner the impinging region is capable of enhancing stabilization of rich propane flames due to benifits from the intense interaction between flame and recirculation. For the combustion characteristics with syngas addition the lean flammability of H2/C3H8/air is expanded to 0.38 and that of CO/C3H8/air is expanded to 0.50 with M type and hill type flame configurations. At phi = 0.6, the flame temperature of H2/C3H8/air with M-type flame is 1.37 times that of CO/C3H8/air with hill type flame, while the C3H8/air flame is extinguished; the CO emissions also change. The mechanisms of flame/flow interaction including alternation of flame structures, characteristics of recirculating flow, and chemical kinetics for impinging flames with H2 and CO addition were revealed.
Subjects
Stratified combustion
PIV
chemiluminescence
POD
temporal/spatial dynamics
co-flow
compressive vortex pair
diffusion-thermal instability
impinging flames
flame stabilization
Type
thesis
File(s)![Thumbnail Image]()
Loading...
Name
ntu-103-D00522026-1.pdf
Size
23.54 KB
Format
Adobe PDF
Checksum
(MD5):acb86590fb0f3ed201005fe6841ed706