Microgravity Observation on Flame Propagation Behavior of Quiescent Combustible Mixture at Low Lewis Number

2003 ◽  
Vol 2003.40 (0) ◽  
pp. 65-66
Author(s):  
Naoto Sugawara ◽  
Takahiro Oyama ◽  
Shunsuke Yamana ◽  
Satoshi Okajima
Keyword(s):  
Flame Propagation ◽  
Lewis Number ◽  
Combustible Mixture ◽  
Propagation Behavior

scholarly journals Irregular Flame Propagation Behavior of Combustible Mixtures at Low Lewis Number

2002 ◽  
Vol 2002 (0) ◽  
pp. 81-82
Author(s):  
Shunsuke Yamana ◽  
Takahiro Oyama ◽  
Naohito Sugawara ◽  
Satoshi Okajima
Keyword(s):  
Flame Propagation ◽  
Lewis Number ◽  
Propagation Behavior ◽  
Combustible Mixtures

The theory of flame phenomena with a chain reaction

1956 ◽  
Vol 249 (957) ◽  
pp. 1-25 ◽  
Keyword(s):  
Reaction Zone ◽  
Flame Propagation ◽  
Reaction Rate ◽  
Laminar Flame ◽  
Combustible Mixture ◽  
Flame Speed ◽  
Spontaneous Ignition ◽  
Chain Reaction ◽  
Hydrazine Decomposition ◽  
A Chain

For single-step reactions there is a unique relation between reaction rate and reactedness for a given combustible mixture at a specified pressure and initial temperature. This paper examines whether the relation is still unique when chain reactions are present, by considering three types of flame—spontaneous ignition, laminar-flame propagation, and the homogeneous steady-flow reaction zone—with a chain-reaction scheme proposed by Adams & Stocks for the decomposition of hydrazine. It is found that the relation is not unique but that similarities exist between the relation for laminar-flame propagation and the relation for the homogeneous reaction zone. Incidentally, a general method of calculating laminar-flame speeds with reaction schemes of arbitrary complexity is presented. When applied to the hydrazine decomposition flame the predictions of the theory are in fair agreement with experimental results. In particular, the variation of flame speed with temperature is correctly predicted. It is shown that the use of the Karman-Penner 'steady-state assumption' would lead to an overestimate of the flame speed. Consideration of the changes which would result if the chain reaction should branch shows that there would once again tend to be a unique reaction rate versus reactedness relation, and that the laminar-flame speed would be increased by a factor of about three for the hottest flame considered but by larger factors for cooler flames.

Validation of an Ignition and Flame Propagation Model for Multiphase Flows

2011 ◽  
Author(s):  
J. M. Boyde ◽  
P. Le Clercq ◽  
M. Di Domenico ◽  
M. Rachner ◽  
G. C. Gebel ◽  
...  
Keyword(s):  
Boundary Conditions ◽  
Flame Propagation ◽  
Multiphase Flows ◽  
Numerical Models ◽  
Turbulent Flame ◽  
Propagation Model ◽  
Test Case ◽  
Turbulent Flame Speed ◽  
Propagation Behavior ◽  
Ignition Characteristics

This paper presents a numerical investigation of a generic lab scale combustor with focus on the ignition characteristics. The test case has been examined thoroughly in a comprehensive measurement campaign to provide a detailed set of boundary conditions and a profound data base of results. The experimental setup comprises five parallel-aligned mono-disperse droplet chains which are ignited, using a focused laser beam. One aspect of the experimental study is the ignitability with respect to the imposed boundary conditions. The second covers the growth and the propagation of the flame after the establishment of an initial kernel. The outcome of the numerical simulations is compared to the experimental results which allows an in-depth assessment of the employed numerical models. The chemistry and, thus, the flame propagation behavior is captured by a turbulent flame speed closure approach with an adaptation to render the model suitable to multiphase flows. For the dispersed phase a Lagrangian particle tracking scheme is employed in combination with a continuous thermodynamics fuel model for the evaporation. The overall good agreement demonstrates the capability of a multiphase flow CFD solver in the field of ignition modeling.

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.

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