Influence of Transverse Slot Jet on Premixed Flame Acceleration

An experimental study has been carried out to investigate the flame acceleration in closed pipe. A horizontal steel pipe, with 2 m long and 0.1 m diameter, giving L/D ratio of 20 was used in this project. For test with 90 degree bends, the bend has a radius of 0.1 m and added a further 1 m to the length of the pipe (based on the centerline length of the segment). Ignition was affected at one end of the vessel while the other end was closed. Natural gas/oxygen mixtures were studied with equivalence ratio, Ф ranges from 0.5 to 1.8. It was demonstrated that bending pipe gave three times higher in overpressure (5.5 bars) compared to 2.0 bars of straight pipe. It is also shown that the flame speed is 63 m s-1, greater by factor of ~ 3 for explosion in bending pipe in comparison with straight pipe (23 m s-1). This is due to bending acting similar to obstacles. This mechanism could induce and create more turbulence, initiating the combustion of unburned pocket at the corner region, causing high mass burning rate and hence, increasing the flame speed.

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Acceleration of Premixed Flames in Obstructed Pipes with Both Extremes Open

Energies ◽

10.3390/en13164094 ◽

2020 ◽

Vol 13 (16) ◽

pp. 4094

Author(s):

Abdulafeez Adebiyi ◽

Olatunde Abidakun ◽

V’yacheslav Akkerman

Keyword(s):

Flame Propagation ◽

Premixed Flame ◽

Critical Parameters ◽

Reacting Flow ◽

Computational Simulations ◽

Chemical Parameters ◽

Flow Equations ◽

Flame Acceleration ◽

Logistic Regression Algorithm ◽

Steady Propagation

Premixed flame propagation in obstructed channels with both extremes open is studied by means of computational simulations of the reacting flow equations with a fully-compressible hydrodynamics, transport properties (heat conduction, diffusion and viscosity) and an Arrhenius chemical kinetics. The aim of this paper is to distinguish and scrutinize various regimes of flame propagation in this configuration depending on the geometrical and thermal-chemical parameters. The parametric study includes various channel widths, blockage ratios, and thermal expansion ratios. It is found that the interplay of these three critical parameters determines a regime of flame propagation. Specifically, either a flame propagates quasi-steady, without acceleration, or it experiences three consecutive distinctive phases (quasi-steady propagation, acceleration and saturation). This study is mainly focused on the flame acceleration regime. The accelerating phase is exponential in nature, which correlates well with the theoretical prediction from the literature. The accelerating trend also qualitatively resembles that from semi-open channels, but acceleration is substantially weaker when both extremes are open. Likewise, the identified regime of quasi-steady propagation fits the regime of flame oscillations, found for the low Reynolds number flames. In addition, the machine learning logistic regression algorithm is employed to characterize and differentiate the parametric domains of accelerating and non-accelerating flames.

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Analysis of Gaseous and Gaseous-Dusty, Premixed Flame Propagation in Obstructed Passages with Tightly Placed Obstacles

Fluids ◽

10.3390/fluids5030115 ◽

2020 ◽

Vol 5 (3) ◽

pp. 115

Author(s):

Furkan Kodakoglu ◽

Sinan Demir ◽

Damir Valiev ◽

V’yacheslav Akkerman

Keyword(s):

Flame Propagation ◽

Premixed Flame ◽

Dust Particles ◽

Blockage Ratio ◽

Two Dimensional ◽

Analytical Formulation ◽

Flame Acceleration ◽

Explosive Materials ◽

Run Up ◽

The Impact

A recent predictive scenario of premixed flame propagation in unobstructed passages is extended to account for obstructions that can be encountered in facilities dealing with explosive materials such as in coalmines. Specifically, the theory of globally-spherical, self-accelerating premixed expanding flames and that of flame acceleration in obstructed conduits are combined to form a new analytical formulation. The coalmining configuration is imitated by two-dimensional and cylindrical passages of high aspect ratio, with a comb-shaped array of tightly placed obstacles attached to the walls. It is assumed that the spacing between the obstacles is much less or, at least, does not exceed the obstacle height. The passage has one extreme open end such that a flame is ignited at a closed end and propagates to an exit. The key stages of the flame evolution such as the velocity of the flame front and the run-up distance are scrutinized for variety of the flame and mining parameters. Starting with gaseous methane-air and propane-air flames, the analysis is subsequently extended to gaseous-dusty environments. Specifically, the coal (combustible, i.e., facilitating the fire) and inert (such as sand, moderating the process) dust and their combinations are considered, and the impact of the size and concentration of the dust particles on flame acceleration is quantified. Overall, the influence of both the obstacles and the combustion instability on the fire scenario is substantial, and it gets stronger with the blockage ratio.

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Analysis of “Finger” Flame Acceleration as a Stage of a Methane-Air-Dust Fire in a Coal Mine

ASME 2015 Power Conference ◽

10.1115/power2015-49240 ◽

2015 ◽

Author(s):

Sinan Demir ◽

V’yacheslav Akkerman ◽

Ali S. Rangwala ◽

Vitaly Bychkov

Keyword(s):

Coal Mine ◽

Premixed Flame ◽

Gas Explosion ◽

Flame Acceleration ◽

Micro Channels ◽

Order Of Magnitude ◽

Inert Dust ◽

Flame Shape ◽

Air Explosion ◽

Dust Distribution

To reveal the inner mechanism of gas explosion, the entire scenario of premixed flame front evolution within an accidental fire is prescribed. Specifically, “finger” flame shape, which is one of the key stages of flame evolution, is scrutinized with the situation of a methane-air explosion. A transition from a globally-spherical front to a finger-shaped one occurs when a flame starts approaching the passage walls. While this acceleration is extremely strong, it stops as soon as the flame touches the passage wall. This mechanism is Reynolds-independent; being equally relevant to micro-channels and giant tunnels. The flame speed increases by an order of magnitude during this stage. To implement dusty environments, Seshadri formulation for the planar flame [Combustion and Flame 89 (1992) 333] is employed with a non-uniform distribution of inert dust gradients, specifically, linear, parabolic and hyperbolic spatial dust distribution gradients are incorporated into the “finger” flame shape. This study systematically investigates how the noncombustible dust distributions affect fire evolution, the flame shape, and propagation velocity.

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