Turbulent Reactive Flows pp 10-32 | Cite as

# Finite Chemical Kinetics Effects in a Subsonic Turbulent Hydrogen Flame

## Abstract

Departures from chemical equilibrium appear in nonpremixed turbulent flames at very high mixing rates, as shown by dimensional analysis based on Damköhler number (characteristic time of mixing over characteristic time of chemical reaction). This paper presents an experimental study that shows departures from chemical equilibrium in a hydrogen-air flame, which is often erroneously considered to have an infinitely fast chemical rate and therefore to be at chemical equilibrium.

These departures from chemical equilibrium are measured with nonintrusive laser diagnostics. Instantaneous and spatially resolved measurements of major combustion species (H_{2}, O_{2}, H_{2}O, and N_{2}), density, and temperature are performed by means of Raman and Rayleigh scattering in a turbulent jet flame with a fuel of 22 mole percent argon in hydrogen. From these measurements we infer the local fuel mixture fraction *f*. Departures from chemical equilibrium are manifested by the comparison between the measured temperature and the equilibrium temperature deduced from the value of *f*.

We vary the Damköhler number by adjusting either the aerodynamic conditions or the chemical rate. In the first case, a range of Reynolds numbers is explored: Re=8,500, Re=17,000, and Re=20,000, using the same fuel. The experimental results show a dramatic effect of the Reynolds number on the extent of departure from the limit of chemical equilibrium. Differences between the measured temperature and the inferred equilibrium temperature are as large as 450K as the flame approaches blow-off conditions. In the second case, we hold the aerodynamic conditions constant, and alter the chemical reaction rate by diluting the fuel with increasing amounts of nitrogen. These last experiments also show a difference between measured temperature and the inferred equilibrium temperature. Consequently, departures from the limit of chemical equilibrium are achieved through increasing the rate of mixing or by decreasing the rate of chemical reaction.

## Keywords

Chemical Equilibrium Mixture Fraction Damkohler Number Combustion Institute Total Number Density## Preview

Unable to display preview. Download preview PDF.

## References

- [1]Bilger, R. W., “Turbulent Jet Diffusion Flames”, Prog. Energ. Combust. Sciences, 1 87–109, 1976CrossRefGoogle Scholar
- [2]Mitchell, R. E., “Chemical Element Diffusion Factors for Use in the Conserved Scalar Approach to Diffusion Flame Modeling”, Western States Section/The Combustion Institute, Fall Meeting, 1980.Google Scholar
- [3]Libby, P. A. and Williams, F. A., “Fundamentals Aspects”, in
*Turbulent Reacting Flows*, (P. A. Libly and F. A. Williams, Eds.), Springer-Verlag, New York, 1980.Google Scholar - [4]Jones, W. P. and Whitelaw, J. H., “Modeling and Measurements in Turbulent Combustion”,
*Twentieth Symposium (International) on Combustion*, Pittsburg, The Combustion Institute, pp 233–249, 1984.Google Scholar - [4]Dibble, R. W., Kollman, W., and Schefer, R. W., “Conserved Scalar Fluxes Measured in a Turbulent Nonpremixed Flame by Combined Laser Doppler Velocimetry and Laser Raman Scattering”, Comb, and Flame 55:3, pp 307–321, 1984.CrossRefGoogle Scholar
- [6]Starner, S. H. and Dilger, R. W. (1983). “Differential Diffusion Effects on Measurements in Turbulent Diffusion Flames by the Mie Scattering Technique”,
*Flames, Lasers, and Reactive Systems*(Bowen, J.R. et al Eds.), Prog, in Astronautics and Aeronautics, Vol. 88, American Institute of Aeronautics and Astronautics, New York, p. 81.Google Scholar - [7]Mungal, M. C, Dimotakis, P. E., and Broadwell, J. E., “Turbulent Mixing and Combustion in a Reacting Shear Layer”,
*A1AA J*. 22, pp 797–800, 1984.Google Scholar - [8]Wall, T. F., Duong, H.T., Stewart, I. M., and Truelove, J. S., “Radiative Heat Transfer in Furnaces: Flame and Surface Models of the IFRF Ml- and M2-Trials”,
*Nineteenth Symposium (International) on Combustion*, The Combustion Institute, pp 537–547, 1982.Google Scholar - [9]Bilger, R. W., “Molecular Transport Effects in Turbulent Diffusion Flames at Moderate Reynolds Numbers”,
*AIAA J*. 20:962, 1982.ADSMATHCrossRefGoogle Scholar - [10]Bilger, R. W., and Dibble, R. W., “Differential Molecular Diffusion Effects in Turbulent Mixing”, Combustion Science Technology, Vol.28, pp 161–172, 1982.ADSCrossRefGoogle Scholar
- [11]Liew, S. K.,Bray, K. N. C, and Moss, J. B., “A Stretched Laminar Flamelet Model of Nonpremixed Combustion”, Comb. Flame 51, 199, 1984.CrossRefGoogle Scholar
- [12]Bilger, R. W., “Turbulent Flows with Nonpremixed Reactants,”
*Turbulent Reacting Flows*, (P.A. Libby and F.A. Williams,Eds.), Springer-Verlag, New York, pp. 65–113, 1980.Google Scholar - [13]Janicka, J. and Kollmann, W., “A Two-Variables Formalism for the Treatment of Chemical Reactions in Turbulent H
_{2}-Air Diffusion Flames”,*Seventeenth Symposium (International) on Combustion*, The Combustion Institute, pp. 421–430, 1979.Google Scholar - [14]Pope, S., “Monte Carlo Calculations of Premixed Turbulent Flames”,
*Eighteenth Symposium (International) on Combustion*, The Combustion Institute, pp 1001–1010, 1981.Google Scholar - [15]Eickhof, H, “Turbulent Hydrocarbon Jet Flames”, Prog. Energ. Combust. Sciences, 8 159, 1982.CrossRefGoogle Scholar
- [16]Peters, N., and Donnerhack, S., “Structure and Sirniliraty of Nitric Oxide Production in Turbulent Diffusion Flames”,
*Eighteenth Symposium (International) on Combustion*, The Combustion Institute, pp 33–42, 1981.Google Scholar - [17]Janicka, J. and Peters, N., “Prediction of Turbulent Jet Diffusion Flame Lift-OfT Using a PDF Transport Equation”,
*Nineteenth Symposium (International) on Combustion*, The Combustion Institute, pp 367–374, 1982.Google Scholar - [18]Peters, N., “Laminar Diffusion Flamelet Models in a Nonpremixed Combustion” Prog. Energy Combust. Sci., 10 p.319, 1984.CrossRefGoogle Scholar
- [19]Williams, F. A., “Combustion Theory”, Second Ed., Benjamin/Cummings, Menlo Park, CA, 1985.Google Scholar
- [20]Strehlow, R., “Combustion Fundamentals”, McGraw-Hill, 1984.Google Scholar
- [21]Eckbreth, A. C, “Recent Advances in Laser Diagnostics for Temperature and Species Concentration in Combustion”,
*Eighteenth Symposium (International) on Combustion*, The Combustion Institute, pp 1471–1488, 1981.Google Scholar - [22]Rahn, L. A., Mattern, P. L., and Farrow, R. L. (1981), “A Comparison of Coherent and Spontaneous Raman Combustion Diagnostics”,
*Eighteenth Symposium (International) on Combustion*, The Combustion Institute pp 1533–1542, 1981.Google Scholar - 23.Dibble, R. W., Schefer, R. W., Chen, J. Y., Hartmann, V., and Kollmann, W., “Velocity and Density Measurements in a Turbulent Nonpremixed Flame with Comparison to a Numerical Model” presented to the Spring Meeting of the Western States Section of the Combustion Institute, Banff, Cananda, 28–30 April 1986. to be submitted to Comb, and Flame.Google Scholar
- [24]Dibble, R. W., Magre, P., Schefer, R. W., Chen, J. Y., Hartmann, V., and Kollmann, W., “Simultaneous Mixture Fraction and Velocity Measurements in a Turbulent Nonpremixed Flame”, paper A1AA 86–1666, AIAA/SAE/ASME 22nd Joint Propulsion Conference, Huntsville, AL, 16–18 June 1986, to be submitted to Comb. Science and Tech.Google Scholar
- [25]Dibble, R. W., and Hollenbach, R. E., “Laser Rayleigh Thermometry in Turbulent Flames”,
*Eighteenth Symposium (International) on Combustion*, The Combustion Institute, pp 1489–1499, 1981.Google Scholar - [26]Drake, M. C, Bilger, R. W. and Starner, S. H.,“Raman Measurements and Conserved Scalar Modeling in Turbulent Diffusion Flames”,
*Nineteenth Symposium (International) on Combustion*, The Combustion Institute, 1983, pp. 459–467.Google Scholar - [27]Masri, A., Dibble, R. W., and Bilger, R. W., “Simultaneous Concentration Measurements in Nonpremixed Flame of Methane”, to be submitted to Combustion and Flame, 1987.Google Scholar
- [28]Hinze, J. O., “Turbulence”, 2nd Edition, McGraw-Hill, 1975.Google Scholar
- [29]Everett, K. W., and Robins, A. G., “The Development and Structure of Turbulent Plane Jets”, JFM 88, pp 563–583, 1978.ADSCrossRefGoogle Scholar
- [30]Glarborg, P., and Kee, R. J., Sandia Report available from NTIS as SAND86-8209.Google Scholar
- [31]Drake, M. C,
*Twenty First Symposium (International) on Combustion*, 1986.Google Scholar - [32]Northam, G. B., and Anderson, G. Y., paper AIAA86-0159, AIAA 24th Aerospace Sciences Meeting, Reno, 6–9 Jan. 1986.Google Scholar
- [33]Peters, N.,
*Twenty First Symposium (International) on Combustion*, 1986.Google Scholar - [34]Mungal, M. G., and Frieler, C. E., GALCIT Report FM85-01, 1985. Submitted to Combustion and Flame.Google Scholar