Visualizing CH* chemiluminescence in sooting flames

Abstract This investigation presents and validates a method to visualize CH* chemiluminescence in a sooting non-premixed flame. Excited-state CH radicals (A2Δ → X2Π, denoted CH*), upon relaxing, emit a photon in the visible portion of the electromagnetic spectrum, giving what is seen as a faint blue glow. Optical methods, especially those that rely on passive emission, provide a simple and non-intrusive means to characterize combustion; however, in the presence of hot solid particles – particularly soot – chemiluminescent emission can be obscured by blackbody radiation. This paper describes an image post-processing technique where flame emission is imaged through multiple filters near the CH* emission band in order to infer and filter the contribution of continuum radiation from soot in the CH* band. This information is then used to produce a soot-free image of CH* chemiluminescence.

[1]  Jerry Seitzman,et al.  CH∗ chemiluminescence modeling for combustion diagnostics , 2009 .

[2]  Yannis Hardalupas,et al.  Effect of fuel type on equivalence ratio measurements using chemiluminescence in premixed flames , 2010 .

[3]  Yuji Ikeda,et al.  Spatially resolved measurement of OH*, CH*, and C2* chemiluminescence in the reaction zone of laminar methane/air premixed flames , 2000 .

[4]  F. Lacas,et al.  Closed-loop equivalence ratio control of premixed combustors using spectrally resolved chemiluminescence measurements , 2002 .

[5]  V. Manta,et al.  Two-dimensional two-wavelength emission technique for soot diagnostics. , 2001, Applied optics.

[6]  C. Dasch,et al.  One-dimensional tomography: a comparison of Abel, onion-peeling, and filtered backprojection methods. , 1992, Applied optics.

[7]  Michael Frenklach,et al.  Reaction mechanism of soot formation in flames , 2002 .

[8]  Jerry Seitzman,et al.  Optical equivalence ratio sensors for gas turbine combustors , 2005 .

[9]  H. F. Calcote.  Mechanisms of soot nucleation in flames—A critical review , 1981 .

[10]  I. Glassman.  Sooting laminar diffusion flames: Effect of dilution, additives, pressure, and microgravity , 1998 .

[11]  J. Pastor,et al.  Measurements of OH* and CH* Chemiluminescence in Premixed Flames in a Constant Volume Combustion Bomb under Autoignition Conditions , 2011 .

[12]  A. Coppalle,et al.  Radiation properties of soot from premixed flat flame , 1987 .

[13]  Jay B. Jeffries,et al.  CH(A-X) and OH(A-X) optical emission in an axisymmetric laminar diffusion flame , 2000 .

[14]  Marshall B. Long,et al.  Experimental and computational study of CH, CH*, and OH* in an axisymmetric laminar diffusion flame , 1998 .

[15]  Jay B. Jeffries,et al.  Low pressure flame determinations of rate constants for OH(A) and CH(A) chemiluminescence , 2002 .

[16]  Marshall B. Long,et al.  Absolute light calibration using S-type thermocouples , 2013 .