Stability of the normal flame front

1971 ◽  
Vol 4 (3) ◽  
pp. 202-207 ◽  
Author(s):  
L. A. Gussak ◽  
E. N. Sprintsina ◽  
K. I. Shchelkin
Keyword(s):  
Flame Front ◽  
Normal Flame

Mechanism of detonation formation as a result of free flame propagation in unconfined space

2019 ◽  
Vol 489 (5) ◽  
pp. 461-464
Author(s):  
A. D. Kiverin ◽  
I. S. Yakovenko ◽  
V. E. Fortov
Keyword(s):  
Shock Waves ◽  
Flame Front ◽  
Flame Propagation ◽  
Linear Stage ◽  
Local Formation ◽  
Stage Of Development ◽  
Detonation Transition

The problem of the detonation formation as a result of unconfined flame propagation is solved numerically. The mechanism of detonation formation is distinguished. It is related to the local formation of shock waves du- ring the linear stage of development of flame front perturbations formed on the surface of the expanding flame front. General criteria of the establishment of the conditions for the detonation transition via the proposed mechanism are formulated.

Shifting of the flame front in a small-scale commercial downdraft gasifier by water injection and exhaust gas recirculation

Fuel ◽  
2021 ◽  
Vol 303 ◽  
pp. 121297
Author(s):  
A. Zachl ◽  
M. Buchmayr ◽  
J. Gruber ◽  
A. Anca-Couce ◽  
R. Scharler ◽  
...  
Keyword(s):  
Flame Front ◽  
Water Injection ◽  
Exhaust Gas Recirculation ◽  
Small Scale ◽  
Exhaust Gas ◽  
Downdraft Gasifier ◽  
Gas Recirculation

scholarly journals Combustion and Flame Front Morphology Characterization of H2–CO Syngas Blends in Constant Volume Combustion Bombs

2021 ◽  
Vol 35 (4) ◽  
pp. 3497-3511
Author(s):  
M. Reyes ◽  
F.V. Tinaut ◽  
B. Giménez ◽  
A. Camaño
Keyword(s):  
Flame Front ◽  
Constant Volume ◽  
Constant Volume Combustion ◽  
Morphology Characterization

scholarly journals Simplified Flame Models and Prediction of the Thermal Radiation Emitted by a Flame Front in an Outdoor Fire

2010 ◽  
Vol 182 (10) ◽  
pp. 1457-1477 ◽  
Author(s):  
Jean-Louis Rossi ◽  
Khaled Chetehouna ◽  
Anthony Collin ◽  
Basiliu Moretti ◽  
Jacques-Henri Balbi
Keyword(s):  
Thermal Radiation ◽  
Flame Front

Effects of the Equivalence Ratio and Reynolds Number on Turbulence and Flame Front Interactions by Direct Numerical Simulation

2016 ◽  
Vol 30 (8) ◽  
pp. 6727-6737 ◽  
Author(s):  
Cong Xu ◽  
Zhihua Wang ◽  
Wubin Weng ◽  
Kaidi Wan ◽  
Ronald Whiddon ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
Reynolds Number ◽  
Direct Numerical Simulation ◽  
Flame Front ◽  
Equivalence Ratio

The Effect of Lewis Number on Instantaneous Flamelet Speed and Position Statistics in Counter-Flow Flames With Increasing Turbulence

2017 ◽  
Author(s):  
Sean D. Salusbury ◽  
Ehsan Abbasi-Atibeh ◽  
Jeffrey M. Bergthorson
Keyword(s):  
Flame Front ◽  
Turbulence Intensity ◽  
High Speed ◽  
Rayleigh Scattering ◽  
Turbulent Flame ◽  
Lewis Number ◽  
Turbulent Flames ◽  
Flame Speed ◽  
Laminar Flames ◽  
Counter Flow

Differential diffusion effects in premixed combustion are studied in a counter-flow flame experiment for fuel-lean flames of three fuels with different Lewis numbers: methane, propane, and hydrogen. Previous studies of stretched laminar flames show that a maximum reference flame speed is observed for mixtures with Le ≳ 1 at lower flame-stretch values than at extinction, while the reference flame speed for Le ≪ 1 increases until extinction occurs when the flame is constrained by the stagnation point. In this work, counter-flow flame experiments are performed for these same mixtures, building upon the laminar results by using variable high-blockage turbulence-generating plates to generate turbulence intensities from the near-laminar u′/SLo=1 to the maximum u′/SLo achievable for each mixture, on the order of u′/SLo=10. Local, instantaneous reference flamelet speeds within the turbulent flame are extracted from high-speed PIV measurements. Instantaneous flame front positions are measured by Rayleigh scattering. The probability-density functions (PDFs) of instantaneous reference flamelet speeds for the Le ≳ 1 mixtures illustrate that the flamelet speeds are increasing with increasing turbulence intensity. However, at the highest turbulence intensities measured in these experiments, the probability seems to drop off at a velocity that matches experimentally-measured maximum reference flame speeds in previous work. In contrast, in the Le ≪ 1 turbulent flames, the most-probable instantaneous reference flamelet speed increases with increasing turbulence intensity and can, significantly, exceed the maximum reference flame speed measured in counter-flow laminar flames at extinction, with the PDF remaining near symmetric for the highest turbulence intensities. These results are reinforced by instantaneous flame position measurements. Flame-front location PDFs show the most probable flame location is linked both to the bulk flow velocity and to the instantaneous velocity PDFs. Furthermore, hydrogen flame-location PDFs are recognizably skewed upstream as u′/SLo increases, indicating a tendency for the Le ≪ 1 flame brush to propagate farther into the unburned reactants against a steepening average velocity gradient.

Flame Characteristics and Turbulent Flame Speeds of Turbulent, High-Pressure, Lean Premixed Methane/Air Flames

2005 ◽  
Author(s):  
P. Griebel ◽  
R. Bombach ◽  
A. Inauen ◽  
R. Scha¨ren ◽  
S. Schenker ◽  
...  
Keyword(s):  
Flame Front ◽  
Gas Turbines ◽  
Equivalence Ratio ◽  
Turbulent Flame ◽  
Flame Speed ◽  
Operating Conditions ◽  
Turbulent Flame Speed ◽  
Front Position ◽  
Preheating Temperature ◽  
Lean Premixed

The present experimental study focuses on flame characteristics and turbulent flame speeds of lean premixed flames typical for stationary gas turbines. Measurements were performed in a generic combustor at a preheating temperature of 673 K, pressures up to 14.4 bars (absolute), a bulk velocity of 40 m/s, and an equivalence ratio in the range of 0.43–0.56. Turbulence intensities and integral length scales were measured in an isothermal flow field with Particle Image Velocimetry (PIV). The turbulence intensity (u′) and the integral length scale (LT) at the combustor inlet were varied using turbulence grids with different blockage ratios and different hole diameters. The position, shape, and fluctuation of the flame front were characterized by a statistical analysis of Planar Laser Induced Fluorescence images of the OH radical (OH-PLIF). Turbulent flame speeds were calculated and their dependence on operating conditions (p, φ) and turbulence quantities (u′, LT) are discussed and compared to correlations from literature. No influence of pressure on the most probable flame front position or on the turbulent flame speed was observed. As expected, the equivalence ratio had a strong influence on the most probable flame front position, the spatial flame front fluctuation, and the turbulent flame speed. Decreasing the equivalence ratio results in a shift of the flame front position farther downstream due to the lower fuel concentration and the lower adiabatic flame temperature and subsequently lower turbulent flame speed. Flames operated at leaner equivalence ratios show a broader spatial fluctuation as the lean blow-out limit is approached and therefore are more susceptible to flow disturbances. In addition, because of a lower turbulent flame speed these flames stabilize farther downstream in a region with higher velocity fluctuations. This increases the fluctuation of the flame front. Flames with higher turbulence quantities (u′, LT) in the vicinity of the combustor inlet exhibited a shorter length and a higher calculated flame speed. An enhanced turbulent heat and mass transport from the recirculation zone to the flame root location due to an intensified mixing which might increase the preheating temperature or the radical concentration is believed to be the reason for that.

Metastability for a generalized Burgers equation with applications to propagating flame fronts

1999 ◽  
Vol 10 (1) ◽  
pp. 27-53 ◽  
Author(s):  
X. SUN ◽  
M. J. WARD
Keyword(s):  
Flame Front ◽  
Principal Eigenvalue ◽  
Vertical Channel ◽  
Front Propagation ◽  
Slow Motion ◽  
Diffusion Limit ◽  
Asymptotic Results ◽  
Small Diffusion ◽  
Generalized Burgers Equation ◽  
Exponentially Small

In the small diffusion limit ε→0, metastable dynamics is studied for the generalized Burgers problemformula hereHere u=u(x, t) and f(u) is smooth, convex, and satisfies f(0)=f′(0)=0. The choice f(u)=u2/2 has been shown previously to arise in connection with the physical problem of upward flame-front propagation in a vertical channel in a particular parameter regime. In this context, the shape y=y(x, t) of the flame-front interface satisfies u=−yx. For this problem, it is shown that the principal eigenvalue associated with the linearization around an equilibrium solution corresponding to a parabolic-shaped flame-front interface is exponentially small. This exponentially small eigenvalue then leads to a metastable behaviour for the time- dependent problem. This behaviour is studied quantitatively by deriving an asymptotic ordinary differential equation characterizing the slow motion of the tip location of a parabolic-shaped interface. Similar metastability results are obtained for more general f(u). These asymptotic results are shown to compare very favourably with full numerical computations.

Flame front disturbance induced by a weak pressure wave

1994 ◽  
Vol 25 (1) ◽  
pp. 1415-1422 ◽  
Author(s):  
Ritsu Dobashi ◽  
Toshisuke Hirano ◽  
Takashi Tsuruda
Keyword(s):  
Flame Front ◽  
Pressure Wave
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