Infrared Mean Absorption Coefficients of Luminous Flames and Smoke

Hubbard, Gary L.; Tien, C. L.

doi:10.1115/1.3450788

Cited by 126 publications

(42 citation statements)

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“…For simplicity in presenting the role of radiative heat loss on the dynamics of flame ball formation, the results given in this section are based on calculations employing optically thin radiation with the Planck mean absorption/emission coefficients of Hubbard and Tien [20]. With respect to the scope of this work, the effects of reabsorption are mainly quantitative and do not affect the discussion of the underlying physical mechanisms.…”

Section: Phenomena and Concentration Limitsmentioning

confidence: 99%

“…Radiation heat loss is considered to be emitted only from H 2 O. Planck mean absorption/emission coefficients of Hubbard and Tien (H&T) [20], based on a wideband model, are compared with those of Ju et al [21], based on a statistical narrowband (SNB) model. For optically thick radiation, radiative transport including both emission and absorption is computed using the SNB model with exponential-tailed inverse line strength distribution [22].…”

Section: Problem Definitionmentioning

confidence: 99%

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A computational study of the transition from localized ignition to flame ball in lean hydrogen/air mixtures

Tse

Law

2000

Proceedings of the Combustion Institute

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A computational study has been conducted to determine the critical conditions for the transition from localized flame ignition and propagation to the establishment of a flame ball. Lean H 2 /air mixtures are investigated using a time-dependent, spherically symmetric code with detailed chemistry, transport, and radiation submodels. Results show that outwardly propagating spherical flames can be ignited for hydrogen mole fractions larger than ϳ3.5%. Furthermore, assuming optically thin radiative heat loss, flame balls X H 2 can be established from centrally ignited premixed spherical flames only within a narrow range of mixture compositions (i.e., ϳ3.5% Ͻ Ͻϳ6.5%). For ϳ6.5% Ͻ Ͻϳ11%, flames propagate until radiativeextinction, never evolving into flame balls, while for Ͼ ϳ11%, the expanding spherical flames develop X H 2 asymptotically into planar propagating flames. These findings corroborate the experimental result that the range of mixtures within which flame balls have been observed is much narrower than that predicted by previous one-dimensional instability analysis of the flame ball, where it was shown that steady flame balls exist for 3.5% Ͻ Ͻ 10.7%. The present simulation also shows that the dynamic transition from a X H 2 spherically propagating flame to the flame ball controls the range of mixtures for which flame balls can be reached, with radiative loss being both the requisite mechanism for and the limiting mechanism against the dynamic transformation. Additional calculations show that the size of the flame ball is noticeably enlarged when radiative reabsorption is incorporated.

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Section: Phenomena and Concentration Limitsmentioning

confidence: 99%

Section: Problem Definitionmentioning

confidence: 99%

A computational study of the transition from localized ignition to flame ball in lean hydrogen/air mixtures

Tse

Law

2000

Proceedings of the Combustion Institute

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“…For simplicity in presenting the role of radiative heat loss on the flame dynamics, the results given in this section are based on calculations employing optically thin radiation with the Planck mean absorption/ emission coefficients of Hubbard and Tien (1978), which also represents the most severe heat loss condition. With respect to the scope of this work, the effects of reabsorption have been found to be mainly quantitative (e.g., limited calculations revealed that reabsorption can shift the boundaries) and do not affect the discussion of the underlying physical mechanisms.…”

Section: Radiative Effects On Flammability Boundariesmentioning

confidence: 99%

“…Radiation heat loss is considered to be emitted only from H 2 O. Planck mean absorption/emission coefficients based on a wideband model are taken from Hubbard and Tien (1978).…”

Section: Problem Definitionmentioning

confidence: 99%

Dynamics of Flame Propagation From Localized Ignition in Rich Hydrogen/Air Mixtures: Effects of Elevated Pressure and Temperature

Tse

Zhao

2005

Combustion Science and Technology

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A computational study was conducted on expanding spherical premixed flames to investigate the dynamics of the stretch-affected, onedimensional, pulsating instability at elevated pressures and temperatures. Rich H 2 /air mixtures were investigated using a time-dependent, spherically symmetric code with detailed chemistry, transport, and radiation submodels. The study shows that the region of instability in the pressure versus equivalence ratio domain for outwardly propagating flames is significantly narrowed when compared with that for planar flames due to the presence of the local ignition limit despite stretchinduced pulsation modifying the other boundary. Moreover, a region of one oscillation ending in extinction (even under adiabatic conditions which are not present in planar flames) has been discovered. However, similar to planar flames, radiative loss in outwardly propagating spherical flames reduces the region of instability due to transient extinction. Interestingly, this limit lies next to and just below the concentration limit for ignition. For the same ignition/extinction reasons, the region of instability is expanded at elevated temperatures due to increased flammability. The calculations show that the dynamics of spherically expanding flames is significantly different than that for planar flames. As a result, the near-limit phenomenon is extremely geometry dependent, thereby having an impact on practical considerations of flammability and stability.

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“…It has been shown that CO 2 and H 2 0 emission is negligible compared with soot emission (3) which is characterized by fv' the fraction of the flame volume occupied by solid carbon particles (4). While much progress has been made in developing procedures for calculating flame radiation (5,6), it is not possible to predict fv in fires because the soot formation and destruction mechanisms have not been quantified (7). It is therefore necessary to measure ~ situ flame carbon particles.…”

Section: Introductionmentioning

confidence: 99%

Soot generation within radiating diffusion flames

Pagni

Okoh

1985

Symposium (International) on Combustion

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C 7 H 16 and (C S H 8 0 2 )n] in free, radiating, boundary layer, diffusion flames are represented analytically. Approximate particle concentrations and size distributions, determined with previously reported optical techniques, are used. These sizes, r -30 nm, indicate the particles are in the free molecular flow regime, Kn -10, so that the thermal boundary layer thickness around the particle approaches zero and the particle temperature is locked to the local gas temperature. Based on this coupling and the experimental -soot fv -1 ppm, the optically thin approximation is valid for incorporating soot radiation in the gas boundary layer equations. The pertinent fields, i.e. tpmperature, velocity and species, are reported. Thermophoretic forces are included in particle trajectory calculations. The local soot mass flow rates within the boundary layer are derived and net soot mass generation rates are obtained for these well characterized laminar flames. An Arrenhius expression appears to suffice to describe the temperature dependence of the soot growth rate over a 400 0 K temperature range, 19S0 < T < 23S0K. Toluene has Ea = 108 kcal/mole while all the other fuels examined have Ea = 86 kcal/mole, very close to H3C -C6HS and C-C bond energies, respectively. Consistent with the goal of fire radiation prediction, calculated temperatures and velocities were used to obtain these empirical energies. Temperature and velocity measurements are in progress. Future work will include mixed flow boundary layer systems where control over the free stream oxygen mass fraction in a combustion tunnel configuration provides greater flame stability and a wider temperature range.

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Infrared Mean Absorption Coefficients of Luminous Flames and Smoke

Cited by 126 publications

References 0 publications

A computational study of the transition from localized ignition to flame ball in lean hydrogen/air mixtures

A computational study of the transition from localized ignition to flame ball in lean hydrogen/air mixtures

Dynamics of Flame Propagation From Localized Ignition in Rich Hydrogen/Air Mixtures: Effects of Elevated Pressure and Temperature

Soot generation within radiating diffusion flames

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