Visualization of soot inception in turbulent pressurized flames by simultaneous measurement of laser-induced fluorescence of polycyclic aromatic hydrocarbons and laser-induced incandescence, and correlation to OH distributions
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Date
2015
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Journal ISSN
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Publisher
Springer
Abstract
Distributions of polycyclic aromatic hydrocarbons
(PAH) and their correlation with soot formation were
studied in ethylene–air swirl flames stabilized in a gas turbine
model combustor at increased pressure. The combustor
can be operated with secondary air injection to study
the influence of soot oxidation. We employed PAH laserinduced
fluorescence using UV excitation simultaneously
with IR-excited laser-induced incandescence to identify
soot. PAH signatures typically appear discontinuous unlike
OH, yet similar to soot but exhibit more uniform intensity
and larger size. The correlation of both diagnostics allowed
identification of a wide range of soot formation progress,
including isolated soot or PAH, as well as PAH transitioning
into soot. The occurrence of soot, PAH and OH
and their spatial variations are strongly dependent on the
properties of the flow field. In the bottom part of the inner
recirculation zone and for the reference case, a rich flame
with additional oxidation air, soot levels are relatively high,
while PAH intensities in this region are minimal. This correlates
well with high temperatures in this region published
recently, which are unfavorable for soot formation as the
precursors, PAH, decompose. Consequently, soot presence
here is attributed to transport. In contrast to OH and soot
distributions which change significantly upon addition of
secondary air downstream of the primary combustion zone,
PAH distributions for both cases look relatively similar.
This is attributed to a downstream consumption of PAH by different processes. Without oxidation air, PAH completely
transform into soot, while additional oxidation air leads to
their oxidation.