A Numerical Simulation to the Influence of Unsteady Strain Flow on Twin Premixed Flames

2019 ◽  
Vol 11 (3) ◽  
Author(s):  
Faisal Al-Malki
Keyword(s):  
Numerical Simulation ◽  
Finite Elements ◽  
Strain Rate ◽  
Premixed Flames ◽  
Lewis Number ◽  
Critical Value ◽  
The Other ◽  
Constant Density ◽  
Nonmonotonic Dependence

The aim of this paper was to examine the response of twin premixed flames formed in a counterflow configuration to the presence of an unsteady straining flow. We began by describing the problem mathematically using the thermodiffusive model with constant density and then adopted a finite elements approach to solve the problem numerically. The study has shown that the role of flow on flame propagation is determined by three main parameters, namely, flow amplitude A, strain rate ε, and fuel Lewis number LeF. For LeF ≥ 1, the flow is seen to promote flame extinction, while LeF < 1 the flow clearly enhances the flame reactivity. Qualitatively, it has been shown that for LeF = 1, there exists a critical value of A (that varies with ε) below which the reactivity decreases monotonically with A. For small LeF < 1, on the other hand, the reactivity was seen to increase with A. For LeF > 1, however, a nonmonotonic dependence, especially for small ε, is predicted.

Multiplicity of Premixed Flames Under the Effect of Heat Loss

2017 ◽  
Vol 9 (3) ◽  
Author(s):  
Eman Al-Sarairah ◽  
Chaouki Ghenai ◽  
Ahmed Hachicha
Keyword(s):  
Strain Rate ◽  
Heat Loss ◽  
Combustion Wave ◽  
Premixed Flames ◽  
Lewis Number ◽  
The Other ◽  
Premixed Flame ◽  
Two Dimensional ◽  
Combustion Waves ◽  
Loss Parameter

We investigate numerically the effect of heat loss and strain rate on the premixed flame edges encountered in a two-dimensional counterflow configuration for Lewis number higher than one. Under nonadiabatic conditions, multiple flame edges and multiple propagation speeds (positive and negative) are discussed. Different regions of multiple propagation speeds have been revealed ranging from two to four, depending on the value of the heat loss parameter and Damkohler number, which is inversely proportional to the strain rate. A combustion wave is modeled by connecting a strongly burning flame on one side of the burner to a weakly burning flame on the other side. These combustion waves are changing with increasing Dam number into flame edges with the fact that the strongly burning flame is the dominant.

The Combined Effects of Heat Loss and Reversibility on the Propagation of Planar Premixed Counterflow Flames

2018 ◽  
Vol 10 (6) ◽  
Author(s):  
Faisal Al-Malki
Keyword(s):  
Activation Energy ◽  
Finite Elements ◽  
Strain Rate ◽  
Heat Loss ◽  
Constant Density ◽  
Combined Effects ◽  
Stability Of Solutions ◽  
Counterflow Flames ◽  
The Stability ◽  
The Impact

Abstract We study in this paper the combined effect of heat loss and reversibility on the propagation of planar flames formed within the counterflow configuration. The problem has been formulated first using the thermodiffusive model with constant density and then solved numerically using finite elements. The impact of four main parameters, namely the reversibility r, the heat loss κ, the strain rate ε, and the activation energy β, on the propagation of planar flames has been discussed in details. The study has shown that planar flames under reversible conditions behave qualitatively similar to those observed for irreversible reactions, which agree with the asymptotic findings. In the presence of heat loss, the problem exhibits multiplicity of solutions whose number and stability were found to vary according to the strain rate ε. In addition, the study has predicted the existence of a certain value of the reversibility parameter r beyond which the impact of reversibility becomes negligible. Finally, we have examined the stability of the solutions and determined the domain of stability of solutions and their multiplicity for this problem.

scholarly journals STRUCTURE OF A FLAME FRONT PROPAGATING AGAINST THE FLOW NEAR A COLD WALL

2002 ◽  
Vol 12 (11) ◽  
pp. 2547-2555 ◽  
Author(s):  
VADIM N. KURDYUMOV ◽  
AMABLE LIÑÁN
Keyword(s):  
Flame Front ◽  
Velocity Gradient ◽  
Front Propagation ◽  
Lewis Number ◽  
Critical Value ◽  
Constant Density ◽  
Density Approximation ◽  
Cold Wall ◽  
Low Velocity ◽  
Velocity Region

The flashback or propagation of premixed flames against the flow of a reacting mixture, along the low velocity region near a cold wall, is investigated numerically. The analysis, carried out using the constant density approximation for an Arrhenius overall reaction, accounts for the effects of the Lewis number of the limiting reactant. Flame front propagation and flashback are only possible for values of the near wall velocity gradient below a critical value. The flame propagation becomes chaotic for small values of the Lewis number.

The Role of Grain Size on Deformation of 316H Austenitic Stainless Steel

2012 ◽  
Vol 525-526 ◽  
pp. 201-204
Author(s):  
S. Mahalingam ◽  
Peter E.J. Flewitt ◽  
A. Shterenlikht
Keyword(s):  
Grain Size ◽  
Stainless Steel ◽  
Austenitic Stainless Steel ◽  
Strain Rate ◽  
High Purity ◽  
Constant Strain Rate ◽  
The Other ◽  
Point Bend ◽  
Different Grain Size

The polycrystalline high purity 316H austenitic stainless steel has been thermo-mechanically treated to produce material with two layers of grain size, one of coarser and the other of finer grains. Small three point bend specimens containing a notch positioned in either the coarser or finer layer have been tested at a constant strain rate and a temperature of -196°C. The results are discussed with respect to the effect of grain size on the underlying deformation between the two layers of different grain size.

scholarly journals Local Strain Rate and Curvature Dependences of Scalar Dissipation Rate Transport in Turbulent Premixed Flames: A Direct Numerical Simulation Analysis

2014 ◽  
Vol 2014 ◽  
pp. 1-29 ◽  
Author(s):  
Y. Gao ◽  
N. Chakraborty ◽  
N. Swaminathan
Keyword(s):  
Numerical Simulation ◽  
Direct Numerical Simulation ◽  
Strain Rate ◽  
Dissipation Rate ◽  
Premixed Flames ◽  
Scalar Dissipation ◽  
Scalar Dissipation Rate ◽  
Turbulent Premixed Flames ◽  
The Mean ◽  
Turbulent Premixed

The statistical behaviours of the instantaneous scalar dissipation rateNcof reaction progress variablecin turbulent premixed flames have been analysed based on three-dimensional direct numerical simulation data of freely propagating statistically planar flame and V-flame configurations with different turbulent Reynolds numberRet. The statistical behaviours ofNcand different terms of its transport equation for planar and V-flames are found to be qualitatively similar. The mean contribution of the density-variation termT1is positive, whereas the molecular dissipation term(-D2)acts as a leading order sink. The mean contribution of the strain rate termT2is predominantly negative for the cases considered here. The mean reaction rate contributionT3is positive (negative) towards the unburned (burned) gas side of the flame, whereas the mean contribution of the diffusivity gradient term(D)assumes negative (positive) values towards the unburned (burned) gas side. The local statistical behaviours ofNc,T1,T2,T3,(-D2), andf(D)have been analysed in terms of their marginal probability density functions (pdfs) and their joint pdfs with local tangential strain rateaTand curvaturekm. Detailed physical explanations have been provided for the observed behaviour.

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