Monochromatic Absorption of Luminous Flames

Abstract

A spectral absorption coefficient for soot in the visible range, whose first approximation given byis proposed in tenus of the Penndorf expansion of the Lorenz-Mie theory. Here A, m and D are the wavelength of radiation, the complex refractive index and the diameter of particles, respectively. The study provides a fundamental base for the experimental data hitherto correlated by the empirical relation KOlA"'" ;,,-1.39. NOMENCLATURE a, b A C C D f, i J k t m ñ ,Ñ Q fJ,f expansion coefficients nD' /4 [m'] cross section [m"] quantity defined by Eq. (10) diameter [m] soot volume fraction [m' particle/rrr'] complex unit "the imaginary part of' absorptive index summation index complex refractive index refractive index functions of nand k defined following Eqs. (5), (6), and by Eqs. (8), (9) particle number density [number of particles/m"] efficiency factor "the real part of' Greek symbols IX size parameter defined by Eq. (3d) K volumetric spectral coefficient [m-I ] A wavelength [m] Subscripts a absorption b blackbody e extinction 165 Downloaded by [University of California Santa Barbara] at 05:24 16 June 2016 166 A. SELAMET AND V. S. ARPACI

A Review of Terminology Used to Describe Soot Formation and Evolution under Combustion and Pyrolytic Conditions

“…In the visible and near-IR spectral regions, the emissivity of soot is approximately inversely proportional to the wavelength raised to the dispersion (or Ångström) exponent. [270][271][272] Incipient particles tend to absorb in the UV region of the spectrum but are nearly transparent in the visible and near-IR and are far from black or gray bodies. [9][10][11][12][13] As the particles mature, carbonize, and graphitize, their absorption cross sections and emissivity increase and broaden substantially.…”

“…Very few objects are true black or gray bodies, including soot, even when mature. In the visible and near-IR spectral regions, the emissivity of soot is approximately inversely proportional to the wavelength raised to the dispersion (or Ångström) exponent. − Incipient particles tend to absorb in the UV region of the spectrum but are nearly transparent in the visible and near-IR and are far from black or gray bodies. − As the particles mature, carbonize, and graphitize, their absorption cross sections and emissivity increase and broaden substantially. Mature soot particles absorb and emit at wavelengths in the UV, visible, and IR spectral regions, and their radiative emission is sometimes referred to as “quasi-black-body radiation” or “pseudo-black-body radiation”. ,,− …”