Hydrogen-diffusion air flame

E. Gutheil and F.A. Williams, A Numerical and Asymptotic Investigation of Structures of Hydrogen-Air Diffusion Flames at Pressures and Temperatures of High Speed Combustion, 23th Symp. (Int.) Comb. (1990) pp. 513-521. 

Ma, A.S.C., Sun, R.L.T. and Spalding, D.B. (1982), Application of ESCIMO to the turbulent hydrogen-air diffusion flame, 19th Combustion Symposium, Haifa. 

J. P. Gore, S.-M. Jeng, and G. M. Faeth, Spectral and Total Radiation Properties of Turbulent Hydrogen/Air Diffusion Flames, ASME Journal of Heat Transfer, 110, pp. 173-181,1987. 

The FID consists of a small hydrogen-air diffusion flame burning at the end of a jet, to which the eluted components from the column are directed with carrier gas... 

Gicquel, O., Darabiha, N., Thevenin, D. Laminar piemixed hydrogen/air counterflow flame simulations using flame prolongation of ILDM with differential diffusion. Proc. Combust. Inst. 28, 1901-1908 (2000)... 

Boundaries and Parameters of Hydrogen Stationary Diffusion Flames in Air... 

The formation of carbon black in a candle flame was the subject of a series of lectures in the 1860s by Michael Faraday at the Royal Institution in London (23). Faraday described the nature of the diffusion flame, the products of combustion, the decomposition of the paraffin wax to form hydrogen and carbon, the luminosity of the flame because of incandescent carbon particles, and the destmctive oxidation of the carbon by the air surrounding the flame. Since Faraday s time, many theories have been proposed to account for carbon formation in a diffusion flame, but controversy still exists regarding the mechanism (24). 

Miller, J.A. and Kee, R.J., Chemical nonequilibrium effects in hydrogen-air laminar jet diffusion flames, /. Phys. Chem., 81, 2534,1977. 

A number of theoretical (5), (19-23). experimental (24-28) and computational (2), (23), (29-32). studies of premixed flames in a stagnation point flow have appeared recently in the literature. In many of these papers it was found that the Lewis number of the deficient reactant played an important role in the behavior of the flames near extinction. In particular, in the absence of downstream heat loss, it was shown that extinction of strained premixed laminar flames can be accomplished via one of the following two mechanisms. If the Lewis number (the ratio of the thermal diffusivity to the mass diffusivity) of the deficient reactant is greater than a critical value, Lee > 1 then extinction can be achieved by flame stretch alone. In such flames (e.g., rich methane-air and lean propane-air flames) extinction occurs at a finite distance from the plane of symmetry. However, if the Lewis number of the deficient reactant is less than this value (e.g., lean hydrogen-air and lean methane-air flames), then extinction occurs from a combination of flame stretch and incomplete chemical reaction. Based upon these results we anticipate that the Lewis number of hydrogen will play an important role in the extinction process. 

The variation of flame speed with equivalence ratio follows the variation with temperature. Since flame temperatures for hydrocarbon-air systems peak slightly on the fuel-rich side of stoichiometric (as discussed in Chapter 1), so do the flame speeds. In the case of hydrogen-air systems, the maximum SL falls well on the fuel-rich side of stoichiometric, since excess hydrogen increases the thermal diffusivity substantially. Hydrogen gas with a maximum value of 325 cm/s has the highest flame speed in air of any other fuel. 

There has been interest in the low radiative background, low quenching argon-hydrogen diffusion flame. The temperature of this flame is too low to prevent severe chemical interferences and therefore the argon-separated air-acetylene flame has been most widely used. The hot nitrous oxide-acetylene flame (argon separated) has been used where atomization requirements make it essential. In all cases, circular flames, sometimes with mirrors around them, offer the preferred geometry. 

Fig. 17.7 Structure of a hydrogen-air, opposed-flow diffusion flame.

G. Dixon-Lewis and M. Missaghi. Structure and Extinction Limits of Counterflow Diffusion Flames of Hydrogen-Nitrogen Mixtures in Air. Proc. Combust. Inst., 22 1461-1470,1988. 

In lean hydrogen mixtures the flame temperature in diffusive combustion is higher than in normal propagation and so, in a wide region of concentrations (from 4 to 9% H2 in a mixture of hydrogen with air), normal propagation is impossible, only diffusive combustion is possible. Our point of view is in accord with the observed properties of flame propagation in this concentration interval. 

The vapor can be atomized in inert gas-hydrogen diffusion flames, in narrow-bore quartz tubes electrically heated or heated over an air-acetylene flame, and in plasmas. Additionally, the atomizer can act as a vapor preconcentration medium just before atomizing. This is what happens in graphite furnace atomizers (in situ trapping) or on silver or gold wires for direct amalgamation of mercury. 

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