Hydroxyl concentrations in rich hydrogen-air flames held on porous burners

Kaskan, W.E.

doi:10.1016/0010-2180(58)90044-0

Cited by 121 publications

(17 citation statements)

References 7 publications

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“…Since OH has been shown to exist in superequilibrium concentrations close to the flame front [22] and under the fuel lean conditions in flow reactor studies [23], it can be assumed that superequilibrium OH concentrations exist in our flames. In fact, in a recent study in a laminar methane-air flame [24], the experimental peak concentration was found to be at least twice as large as the estimated full equilibrium values over a range of equivalence ratios.…”

Section: Methodsmentioning

confidence: 99%

The Role Of Soot Particle Formation On The Production Of Carbon Monoxide In Fires

Puri¹,

Santoro²

1991

Fire Safety Science - Proceedings of the Third International Sy

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A systematic study of the effects of soot formation on the production of carbon monoxide (CO) in laminar diffusion flames has been conducted. Increased amounts of soot have been observed to result in larger concentrations of CO in the higher regions of the flames. Comparisons of CO state relationships as a function of local equivalence ratio show distinct effects as the local soot volume fraction is varied. Fuel rich regions exhibit lower CO mole fractions as soot concentration increases, whereas higher CO mole fractions are observed under fuel lean conditions. Radiative quenching and competition between soot and CO for OH are examined. Competition for OH is a plausible mechanism that can be responsible for the high CO emissions from fires. Radiative quenching does not seem to playa significant role in fuel rich regions but can be important under fuel lean conditions.

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Section: Methodsmentioning

confidence: 99%

The Role Of Soot Particle Formation On The Production Of Carbon Monoxide In Fires

Puri¹,

Santoro²

1991

Fire Safety Science - Proceedings of the Third International Sy

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“…A 0.5 m Ebert Jarrell-Ash monochromator was used with a conventional A.C. phase-sensitive detection method. Absolute calculations of concentration were made in a manner similar to that used by Kaskan (1958). Transition probability atmosphere.…”

Section: Methodsmentioning

confidence: 99%

The Structure of a Reaction-Broadened Diffusion Flame

Melvin¹,

Moss²,

Clarke

1971

Combustion Science and Technology

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Results of an experimental investigation of the structure of flat diffusion flames on a Parker-Wolfhard burner are compared with theoretical predictions of perturbation solutions which incorporate realistic schemes for the chemical kinetics. Measurements of hydroxyl radical concentrations show that the flames are reaction-broadened for temperatures below 1950OK, while at higher temperatures reaction zone structure is of equilibriumbroadened type. Experiment also shows that, close to extinction, there is significant convective transfer of material from one stream to the other at the flame base. It is suggested that the consequent disruption of mixing in, or shielding of, the reaction zone makes extinction a progressive process. Complementary studies of spherical and counter flow diffusion flames suggest that the former geometry is preferable in future studies designed to test hypotheses about the role of kinetics in diffusion flame extinction.Despite the practical importance of laminar diffusion flames, they have received relatively little attention in comparison with premixed flames, which have been studied extensively. Part of this neglect has been due to the lack of an adeq uate treatment of diffusion flame structure. In the main, this lack can be ascribed to the two-dimensional nature of most steady diffusion flames. Since premixed flames can often be made quasi-unidimensional, solution of the appropriate conservation equations is a relatively much more simple problem. As a result, many of the studies of diffusion flames which appear in the literature are concerned not with structure but with ancillary problems e.g. carbon formation. Burke and Schumann (1928) produced the first simple treatment of diffusion flame structure for a single reaction of infinite rate. This model was modified in an empirical way by Barr (1949) but Fendell (1965) Chung and Blankenship (1966 and Clarke (1967a, b) interpreted the original BurkeSchumann flame sheet model as a singular perturbation problem. The model was extended by the method of matched asymptotic expansions for sets of reactions in chemical equilibrium by Clarke (1968) and for systems not in that chemical state also by Clarke (1969). The burner configuration dealt with was an idealisation of the two-dimensional Parker-Wolfhard burner and the conservation equations were simplified by use of the Oseen approximation. Clarke and Moss (1970) have recently applied a similar analysis to the 3 one-dimensional spherical diffusion flame (for which the Oseen approximation is now unnecessary) and have tentatively interpreted a breakdown in the analysis for reaction-broadened hydrogen-oxygen flames as a possible kinetically-controlled extinction condition operating in the region of 1500 OK. The work on hydrogen-oxygen flames also leads to prediction of hydroxyl radical concentrations in the reaction zones of these flames. There appears to be no relevant experimental information on extinction conditions or on hydroxyl radical concentrations for such diffusion flames in which the rea...

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“…These observations were confirmed by measurements of HNO emission. It was concluded that k,,,,, is not greater than 5 x 10" cm6 mole-' s-I at 293 OK. Table IX compares the present results and the shock tube data with the flame studies (18)(19)(20), assuming that all the abundant species in hydrogen-air flames give similar values of Ic,,,. This assunlption seems reasonable in view of the value of k,,,,, found here and because the only extensive data on temperature coefficients of a recombination reaction (iodine atoms) for a wide range of third bodies (45,46) show that the rate constailts for different third bodies become more similar as the temperature is raised.…”

Section: Surface Reactionsmentioning

confidence: 75%

“…In the flame studies (18)(19)(20), the rate constants fit between the room temperature and shock tube results on the basis of a T-' temperature dependence if the assumption is made that H,O is less than an order of magnitude more efficient than -H, as third body (see, for example, Dixon-Lewis, Sutton, and Williams (18)). …”

Section: Introductionmentioning

confidence: 99%

Homogeneous rate of recombination of hydrogen atoms

Larkin¹

1968

Can. J. Chem.

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The rate of decay of hydrogen atoms has been measured in a conventional type of discharge-flow system at temperatures between 190-350 OK. The recombination fitted the equation where Ic, is the first order surface rate constant. No three-body recombination for M = H was observed at the low levels of dissociation (2-5 %) employed. When the flow gases contained traces of water vapor and (or) oxygen as impurities, the homogeneous rate constants (k,,,) had a small positive activation energy which was due to the influence of a surface reaction between hydrogen atoms and the impurities.In the absence of impurities, true homogeneous rate constants were obtained. A value of k,,,, = 4.6 + 0.5 x 1015 cm6 mole-' s-' was found at 291 OK. The temperature variation was approximately T-'1' over the range 19G350 OK.

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Hydroxyl concentrations in rich hydrogen-air flames held on porous burners

Cited by 121 publications

References 7 publications

The Role Of Soot Particle Formation On The Production Of Carbon Monoxide In Fires

The Role Of Soot Particle Formation On The Production Of Carbon Monoxide In Fires

The Structure of a Reaction-Broadened Diffusion Flame

Homogeneous rate of recombination of hydrogen atoms

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