Effect of the Lewis number on the flame propagation mechanism

1992 ◽  
Vol 28 (6) ◽  
pp. 614-619 ◽  
Author(s):  
G. A. Zulinyan ◽  
G. M. Makhviladze ◽  
V. I. Melikhov
Keyword(s):  
Flame Propagation ◽  
Lewis Number ◽  
Propagation Mechanism

scholarly journals Effects of Lewis Number on the Evolution of Curvature in Spherically Expanding Turbulent Premixed Flames

Fluids ◽  
2019 ◽  
Vol 4 (1) ◽  
pp. 12 ◽  
Author(s):  
Ahmad Alqallaf ◽  
Markus Klein ◽  
Nilanjan Chakraborty
Keyword(s):  
Transport Equation ◽  
Burning Rate ◽  
Flame Propagation ◽  
Premixed Flames ◽  
Lewis Number ◽  
Flame Surface ◽  
Turbulent Premixed Flames ◽  
Diffusive Instability ◽  
Negatively Curved ◽  
Positively Curved

The effects of Lewis number on the physical mechanisms pertinent to the curvature evolution have been investigated using three-dimensional Direct Numerical Simulation (DNS) of spherically expanding turbulent premixed flames with characteristic Lewis number of L e = 0.8 , 1.0 and 1.2. It has been found that the overall burning rate and the extent of flame wrinkling increase with decreasing Lewis number L e , and this tendency is particularly prevalent for the sub-unity Lewis number (e.g., L e = 0.8 ) case due to the occurrence of the thermo-diffusive instability. Accordingly, the L e = 0.8 case has been found to exhibit higher probability of finding saddle topologies with large magnitude negative curvatures in comparison to the corresponding L e = 1.0 and 1.2 cases. It has been found that the terms in the curvature transport equation due to normal strain rate gradients and curl of vorticity arising from both fluid flow and flame normal propagation play pivotal roles in the curvature evolution in all cases considered here. The net contribution of the source/sink terms of the curvature transport equation tends to increase the concavity and convexity of the flame surface in the negatively and positively curved locations, respectively for the L e = 0.8 case. This along with the occurrence of high and low temperature (and burning rate) values at the positively and negatively curved zones, respectively acts to augment positive and negative curved wrinkles induced by turbulence in the L e = 0.8 case, which is indicative of thermo-diffusive instability. By contrast, flame propagation effects tend to weakly promote the concavity of the negatively curved cusps, and act to decrease the convexity of the highly positively curved bulges in the L e = 1.0 and 1.2 cases, which are eventually smoothed out due to high and low values of displacement speed S d at negatively and positively curved locations, respectively. Thus, flame propagation tends to smoothen the flame surface in the L e = 1.0 and 1.2 cases.

Non-uniqueness for flame propagation when the Lewis number is less than 1

1995 ◽  
Vol 6 (4) ◽  
pp. 287-306 ◽  
Author(s):  
Alexis Bonnet
Keyword(s):  
Activation Energy ◽  
Flame Propagation ◽  
Chemical Reaction ◽  
Sufficient Conditions ◽  
Lewis Number ◽  
Heat Diffusion ◽  
High Activation ◽  
High Activation Energy ◽  
One Step ◽  
Species Diffusion

We discuss the question of uniqueness of planar flames for a simple one-step chemical reaction. We show that when the Lewis number is less than unity (i.e. species diffusion is larger than heat diffusion) uniqueness cannot be generally assumed. An example with three flames, two of them being stable, is exhibited. Other related questions, such as sufficient conditions for uniqueness to hold and high activation energy limits, are discussed.

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