Simultaneous 10-kHz PLIF and chemiluminescence imaging of OH radicals in a microwave plasma-enhanced flame

Stephen Hammack, Stanislav Kostka, Amy Lynch, Campbell Carter, Tonghun Lee

Research output: Contribution to journalArticlepeer-review


This paper examines the structure of microwave (MW)-enhanced flames through 10-kHz imaging. High repetition rate laser diagnostic methods are used to simultaneously record 2-D images of OH laser-induced fluorescence and chemiluminescence within an atmospheric plasma-enhanced flame. Collecting both OH planar laser-induced fluorescence and chemiluminescence allows for observation of OH radicals in the plane of the thin laser sheet as well as volume-integrated excited state emission. A tunable, MW waveguide plasma source - operating at 2.45 GHz and delivering 90-130 W to the flowfield - ignites and sustains a CH4/air flame, whereas laser-induced fluorescence and chemiluminescence are acquired at a sustained framing rate of 10 kHz, using two intensified CMOS cameras and a synchronized laser. Multiple geometries and flames (premixed and nonpremixed) are studied by adjusting gas flow compositions and the plasma applicator nozzle components. A stoichiometric premixed flame configuration produces a divergent flame with large-scale fluctuations and vortex shedding into ambient air and is capable of feedstock flow velocities >20 m/s for combustion-to-plasma power ratios >10:1. Another arrangement produces plasma along the initial mixing layer of a nonpremixed flame, yielding a thin cylindrical reaction zone of coincident chemiluminescence and fluorescence. Replacing the fuel with rich premixed gases produces a narrow conical flame anchored by the circular plasma discharge with a little flamefront fluctuation. The high-speed diagnostics capture OH signals in cinematic sequences, providing new understanding of the plasma-assisted flame holding mechanism and allowing for the tracking of individual flow feature development.

Original languageEnglish (US)
Article number6612636
Pages (from-to)3279-3286
Number of pages8
JournalIEEE Transactions on Plasma Science
Issue number12
StatePublished - Dec 2013
Externally publishedYes


  • Chemiluminescence
  • High repetition rate diagnostics
  • Laser diagnostics
  • Microwave plasma
  • Planar laserinduced fluorescence (PLIF)
  • Plasma-assisted combustion (PAC)

ASJC Scopus subject areas

  • Nuclear and High Energy Physics
  • Condensed Matter Physics


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