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Stability of lifted laminar round gas-jet flame

Published online by Cambridge University Press:  21 April 2006

Ö. Savas  and
S. R. Gollahalli
Ö. Savas
Affiliation:
School of Aerospace, Mechanical and Nuclear Engineering, The University of Oklahoma, Norman, Oklahoma 73019, USA
S. R. Gollahalli
Affiliation:
School of Aerospace, Mechanical and Nuclear Engineering, The University of Oklahoma, Norman, Oklahoma 73019, USA
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Abstract

The exact solution of the concentration field of jet fluid in a round laminar jet is presented. This analytical solution, which assumes constant kinematic viscosity and molecular diffusivity, establishes the dependence of the concentration field on the Schmidt number. This solution and a kinematic argument are used to calculate the shape of the lifted flame front in a round laminar jet. The observed shape of the lifted laminar propane flame front is compared with the prediction of this formulation. A spatial-stability criterion of the flame is developed and applied to examine the stability of the lifted flame in the flow field of the round laminar jet. The laminar flame blowout height and the corresponding Reynolds number are calculated from the stability criterion. The predictions agree well with the experimental values. The flame blowout Reynolds number of laminar fuel jets of pure fuels discharging from round pipes with fully developed laminar flow is shown to be directly proportional to the pipe diameter. At blowout the fuel concentration in the vicinity of the flame is found to attain a constant value which lies between the lean flammability limit and the fuel concentration at which the laminar flame speed is maximum. This stability criterion is generalized to laminar gas-jet flames of different fuels using three experimentally determined parameters describing their flame speed–concentration characteristics. The general form can account for dilution of fuel jets with inert gases. That flames can be lifted and blown out while they are still laminar is also demonstrated experimentally.

Type
Research Article
Information
Journal of Fluid Mechanics , Volume 165 , April 1986 , pp. 297 - 318
Copyright
© 1986 Cambridge University Press

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