Lewis Number Effects in Premixed Turbulent Combustion and Highly Perturbed Laminar Flames

Abstract

Various perturbed laminar flames are numerically simulated by reducing combustion chemistry to a single reaction. The following flame configurations are addressed: expanding spherical, cylindrical, and symmetrical planar flames; converging spherical flame; expanding cylindrical and symmetrical planar flames affected by external steady or time-dependent strain rate; steady strained cylindrical and symmetrical planar flames. The results (1) show that a simple linear relation between the local consumption velocity and flame stretch rate is valid only for weakly perturbed laminar flames; (2) highlight the importance of transient effects; and (3) show that, in the case of a small Lewis number, the highest local combustion rate is reached in the expanding spherical flame ignited by the hot pocket of the critical radius. This highest local combustion rate is successfully used to describe the extensive Karpov's experimental data base on turbulent burning velocities for mixtures characterized by substantially different values of the Lewis number. Discussion of Karpov's experimental data showing the drastic effect of the Lewis number on turbulent burning velocity implies the important role played by highly perturbed flamelets in premixed turbulent combustion.

Keywords:

• Premixed turbulent combustion
• Lewis number
• flame perturbations

Additional information

Notes on contributors

A. N. LIPATNIKOV

e-mail: [email protected]