scholarly journals An apparatus-independent extinction strain rate in counterflow flames

2019 ◽  
Vol 37 (2) ◽  
pp. 1979-1987 ◽  
Author(s):  
Alan E. Long ◽  
Hugo Burbano ◽  
Raymond L. Speth ◽  
Ashkan Movaghar ◽  
Fokion N. Egolfopoulos ◽  
...  
Keyword(s):  
Strain Rate ◽  
Counterflow Flames ◽  
Extinction Strain Rate

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.

Investigation of unsteady premixed micro/macro counterflow flames for lean to rich methane/air mixture

2020 ◽  
pp. 1-15
Author(s):  
Ali Edalati-nejad ◽  
Sayyed Aboozar Fanaee ◽  
Maryam Ghodrat ◽  
Javad Khadem
Keyword(s):  
Strain Rate ◽  
Flame Structure ◽  
Time Dependent ◽  
Stability Parameters ◽  
Steady State Condition ◽  
Counterflow Flame ◽  
Time Period ◽  
Counterflow Flames ◽  
The Impact ◽  
Time Dependent Analysis

Abstract In the current work, an unsteady analysis of methane/air premixed counterflow flame is carried out for different flame conditions and stability parameters considering different strain rate values. The results are presented at unsteady and final steady conditions and the impact of time-dependent regimes and variations in equivalence ratio, from lean flame to rich one are analysed. The governing equations including continuity, momentum, energy, and species are numerically solved with a coupled of simple and Piso algorithm. It is also found that when the strain rate value is 1000s-1, for flame stability, the hydraulic distance of the microchannel must be at least 0.05mm. Increasing the strain rate results in decreasing the time of stabilizing temperature distribution with a faster quasi-steady equilibrium. The necessity of time dependent analysis is to comprehend the variations in main factors of flame structure before reaching the finalized steady state condition. Therefore, by designing an intermittent automatic valve, if the flow stops in time period of 0.0025s and starts again, the formation of NO2 and CO2 will be reduced about 50% and 9%, respectively, in a case with a=100s-1.

Dynamics of Premixed H2/CH4 Flames Under Near-Blowoff Conditions

2009 ◽  
Author(s):  
Qingguo Zhang ◽  
Santosh J. Shanbhogue ◽  
Tim Lieuwen
Keyword(s):  
Strain Rate ◽  
Temporal Dynamics ◽  
Complex Dynamics ◽  
Vortex Breakdown ◽  
Local Strain ◽  
Mie Scattering ◽  
Flame Stabilization ◽  
Local Extinction ◽  
Extinction Events ◽  
Extinction Strain Rate

Swirling flows are widely used in industrial burners and gas turbine combustors for flame stabilization. Several prior studies have shown that these flames exhibit complex dynamics under near-blowoff conditions, associated with local flamelet extinction and alteration in the vortex breakdown flow structure. These extinction events are apparently due to the local strain rate irregularly oscillating above and below the extinction strain rate values near the attachment point. In this work, global, temporally resolved and detailed spatial measurements were obtained of hydrogen/methane flames. Supporting calculations of extinction strain rates were also performed using detailed kinetics. It is shown that flames become unsteady (or local extinctions happen) at a nearly constant extinction strain rate for different hydrogen/methane mixtures. Based upon analysis of these results, it is suggested that classic Damkohler number correlations of blowoff are, in fact, correlations for the onset of local-extinction events, not blowoff itself. Corresponding Mie scattering imaging of near-blowoff flames also was used to characterize the spatio-temporal dynamics of holes along the flame that are associated with local extinction.

scholarly journals Strain rate and pressure effects on multi-branched counterflow flames

2020 ◽  
Vol 221 ◽  
pp. 256-269 ◽  
Author(s):  
Claudia-F. López-Cámara ◽  
Albert Jordà Juanós ◽  
William A. Sirignano
Keyword(s):  
Strain Rate ◽  
Pressure Effects ◽  
Counterflow Flames

scholarly journals Strain rate and fuel composition dependence of chemiluminescent species profiles in non-premixed counterflow flames: comparison with model results

2012 ◽  
Vol 107 (3) ◽  
pp. 561-569 ◽  
Author(s):  
B. Prabasena ◽  
M. Röder ◽  
T. Kathrotia ◽  
U. Riedel ◽  
T. Dreier ◽  
...  
Keyword(s):  
Strain Rate ◽  
Composition Dependence ◽  
Fuel Composition ◽  
Counterflow Flames

Impact of Equivalence Ratio on the Macrostructure of Premixed Swirling CH4/Air and CH4/O2/CO2 Flames

2015 ◽  
Author(s):  
Hirotatsu Watanabe ◽  
Santosh J. Shanbhogue ◽  
Ahmed F. Ghoniem
Keyword(s):  
Strain Rate ◽  
Shear Layer ◽  
Equivalence Ratio ◽  
Burning Velocity ◽  
Flame Temperature ◽  
Flame Stabilization ◽  
Sudden Expansion ◽  
Strain Rates ◽  
Cross Point ◽  
Extinction Strain Rate

Premixed CH4/O2/CO2 flames (oxy-flames) and CH4/air flames (air-flames) were experimentally studied in a swirl-stabilized combustor. For comparing oxy and air flames, the same equivalence ratio and adiabatic flame temperature were used. CO2 dilution was adjusted to attain the same adiabatic temperature for the oxy-flame and the corresponding air-flame while keeping the equivalence ratio and Reynolds number (=20,000) the same. For high equivalence ratios, we observed flames stabilized along the inner and outer shear layers of the swirling flow and sudden expansion, respectively, in both flames. However, one notable difference between the two flames appears as the equivalence ratio reaches 0.60. At this point, the outer shear layer flame disappears in the air-flame while it persists in the oxy-flame, despite the lower burning velocity of the oxy-flame. Prior PIV measurements (Ref. 9) showed that the strains along the outer shear layer are higher than along the inner shear layer. Therefore, the extinction strain rates in both flames were calculated using a counter-flow premixed twin flame configuration. Calculations at the equivalence ratio of 0.60 show that the extinction strain rate is higher in the oxy than in the air flame, which help explain why it persists on the outer shear layer with higher strain rate. It is likely that extinction strain rates contribute to the oxy-flame stabilization when air flame extinguish in the outer shear layer. However, the trend reverses at higher equivalence ratio, and the cross point of the extinction strain rate appears at equivalence ratio of 0.64.

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