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Stabilization of a turbulent premixed flame by a plasma filament

Kong, Chengdong LU ; Li, Zhongshan LU ; Aldén, Marcus LU and Ehn, Andreas LU (2019) In Combustion and Flame 208. p.79-85
Abstract

The mechanism of stabilizing a turbulent premixed methane-air flame using warm filamentary plasma is investigated by using laser diagnostics. First, stabilization of a turbulent jet flame is demonstrated in a setup using a pin-to-pin plasma discharge. The coupled plasma-flame structures were visualized utilizing planar laser-induced fluorescence (PLIF) of formaldehyde (CH2O) and methylidyne radicals (CH), as well as laser Rayleigh scattering thermometry imaging. The results show that the plasma channel and the flame front are spatially separated by a layer of hot burning products attributed to the flame propagation from the plasma core. Because of this spatial separation, the impacts of plasma on combustion are primarily... (More)

The mechanism of stabilizing a turbulent premixed methane-air flame using warm filamentary plasma is investigated by using laser diagnostics. First, stabilization of a turbulent jet flame is demonstrated in a setup using a pin-to-pin plasma discharge. The coupled plasma-flame structures were visualized utilizing planar laser-induced fluorescence (PLIF) of formaldehyde (CH2O) and methylidyne radicals (CH), as well as laser Rayleigh scattering thermometry imaging. The results show that the plasma channel and the flame front are spatially separated by a layer of hot burning products attributed to the flame propagation from the plasma core. Because of this spatial separation, the impacts of plasma on combustion are primarily thermal since the energetic radical species (such as O, H), produced by the discharge, have short equilibration time and cannot spread far away from the discharge channel before reaching the equilibrium state. From this point of view, turbulence would be beneficial for promoting the transport of plasma-produced radicals and thus bridge the gap between the plasma and the flame front. The plasma is still able to stabilize the flame. Based upon the experimental results, a frequent ignition-flame propagation (FIFP) model is proposed to explain the flame stabilization process. For the contracted plasma filament, the local power density is high enough to initialize the flame kernel that propagates away from the plasma channel until extinction. The propagation process is, however, strongly affected by turbulence. Local extinction is highly probable and thus the flame front has to be close to the ignition source at strong turbulence. At such conditions, the stabilized flame can be regarded as a large number of flame pockets, repeating the three phases of ignition, propagation and extinction, which can be summarized as the FIFP model. It infers that the flame propagation phase is important for sustaining the flame to complete combustion. Hence, this phase should be extended, which is more probable to achieve if the plasma ignition pilot is located in a section of limited turbulence.

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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
Atmospheric-pressure discharge, Laser diagnostics, Plasma assisted combustion, Spatial separation, Turbulent flame stabilization
in
Combustion and Flame
volume
208
pages
7 pages
publisher
Elsevier
external identifiers
  • scopus:85068519882
ISSN
0010-2180
DOI
10.1016/j.combustflame.2019.07.002
language
English
LU publication?
yes
id
61286374-8be6-486a-9940-f3c68d03625e
date added to LUP
2019-07-16 08:56:38
date last changed
2019-08-14 04:41:47
@article{61286374-8be6-486a-9940-f3c68d03625e,
  abstract     = {<p>The mechanism of stabilizing a turbulent premixed methane-air flame using warm filamentary plasma is investigated by using laser diagnostics. First, stabilization of a turbulent jet flame is demonstrated in a setup using a pin-to-pin plasma discharge. The coupled plasma-flame structures were visualized utilizing planar laser-induced fluorescence (PLIF) of formaldehyde (CH<sub>2</sub>O) and methylidyne radicals (CH), as well as laser Rayleigh scattering thermometry imaging. The results show that the plasma channel and the flame front are spatially separated by a layer of hot burning products attributed to the flame propagation from the plasma core. Because of this spatial separation, the impacts of plasma on combustion are primarily thermal since the energetic radical species (such as O, H), produced by the discharge, have short equilibration time and cannot spread far away from the discharge channel before reaching the equilibrium state. From this point of view, turbulence would be beneficial for promoting the transport of plasma-produced radicals and thus bridge the gap between the plasma and the flame front. The plasma is still able to stabilize the flame. Based upon the experimental results, a frequent ignition-flame propagation (FIFP) model is proposed to explain the flame stabilization process. For the contracted plasma filament, the local power density is high enough to initialize the flame kernel that propagates away from the plasma channel until extinction. The propagation process is, however, strongly affected by turbulence. Local extinction is highly probable and thus the flame front has to be close to the ignition source at strong turbulence. At such conditions, the stabilized flame can be regarded as a large number of flame pockets, repeating the three phases of ignition, propagation and extinction, which can be summarized as the FIFP model. It infers that the flame propagation phase is important for sustaining the flame to complete combustion. Hence, this phase should be extended, which is more probable to achieve if the plasma ignition pilot is located in a section of limited turbulence.</p>},
  author       = {Kong, Chengdong and Li, Zhongshan and Aldén, Marcus and Ehn, Andreas},
  issn         = {0010-2180},
  keyword      = {Atmospheric-pressure discharge,Laser diagnostics,Plasma assisted combustion,Spatial separation,Turbulent flame stabilization},
  language     = {eng},
  month        = {10},
  pages        = {79--85},
  publisher    = {Elsevier},
  series       = {Combustion and Flame},
  title        = {Stabilization of a turbulent premixed flame by a plasma filament},
  url          = {http://dx.doi.org/10.1016/j.combustflame.2019.07.002},
  volume       = {208},
  year         = {2019},
}