<p> Lifted
non-premixed turbulent jet flames in the Transverse Instability Combustor (TIC)
have been analyzed using qualitative and quantitative methods. Lifted flames in
the TIC have been observed to stabilize about zero to five injector exit diameters
downstream of the dump plane into the chamber and exhibit pulsating, unsteady
burning. Anchored flames immediately begin reacting in the injector recess and
burn evenly in a uniform jet from the injector exit through the entire optically
accessible region. Statistically
significant, repeatable behavior lifted flames are observed. It is shown that the occurrence of lifted
flames is most likely for an injector configuration with close wall-spacing, second
greatest for a configuration with close middle-element spacing, and lowest for a
configuration with even element-spacing. For all configurations, of those
elements that have been observed to lift, the center element is most likely to
lift while the second element from the wall was likely. Flames at the wall elements
were never observed to lift. Evidence is shown to support that close injector element
spacing and stronger transverse pressure waves aid lateral heat transfer which
supports flame stability in the lifted position. It is hypothesized that the
stability of lifted flames is influenced by neighboring ignition sources, often
a neighboring anchored flame. It is also shown that instances of lifted flames
increase with the root-mean-squared magnitude of pressure fluctuation about its
mean (P’ RMS) up to a threshold, after which flames stabilize in the anchored recess
position.</p>
<p>Dynamic mode decomposition (DMD) and proper orthogonal decomposition (POD)
analyses of CH* chemiluminescence data is performed. It is found that lateral
ignition of the most upstream portion of lifted flames is dominated by the 1W
mode. Furthermore, it is shown that low-frequency high energy modes with spatial
layers resemble intensity-pulses, possibly attributable to ignition. These
modes are trademarks of CH* chemiluminescent intensity data of lifted flames.
It was also shown that the residence time in the chamber may be closely
associated with those low-frequency modes around 200 Hz. DMD and POD were
repeated for a downstream region on the center element, as well as a near-wall
element, highlighting differences between the lifted flame dynamics in all
three regions. </p>
<p>It is shown that lifted flames are best
characterized by their burning behavior and in rare cases may stabilize in the
recess, while still being “lifted”. Furthermore, it is shown that flame
position differentiation can extend into an initial period of highly stable combustor
operation. Dynamic mode decomposition is explored as potential method to understand
physical building blocks of proper orthogonal spatial layers. Non-visual indicators of lifted flames
within the high-frequency (HF) pressure signal are sought to seek a method that
allows for observation of lifted flames in optically inaccessible combustors, such
as those in industry. Some attributes of power-spectral diagrams and
cross-correlations of pressure signals are provided as potential indicators. </p>
| Identifer | oai:union.ndltd.org:purdue.edu/oai:figshare.com:article/8015393 |
| Date | 14 May 2019 |
| Creators | Aaron M Blacker (6613562) |
| Source Sets | Purdue University |
| Detected Language | English |
| Type | Text, Thesis |
| Rights | CC BY 4.0 |
| Relation | https://figshare.com/articles/Characterization_of_Lifted_Flame_Behavior_in_a_Multi-Element_Rocket_Combustor/8015393 |
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