Ignition phenomenology and criteria associated with hotspots embedded in a reactive material

Brindley, J.; Griffiths, J. F.; McIntosh, Andy C.

doi:10.1016/s0009-2509(00)00429-2

Cited by 20 publications

(44 citation statements)

References 12 publications

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“…We shall always use the value p = 1000 W m −2 , which gives a combustion wave in all cases considered. Note that in previous work concentrating solely on reaction and diffusion, [5,8], it was found that the critical power was unique for both the slab and cylindrically symmetric geometries. In contrast, for a spherically symmetric geometry it was found that for small-radii hotspots three distinct critical powers exist, p 1 < p 2 < p 3 .…”

Section: Pseudo-homogeneous Results: Ph Modelmentioning

confidence: 85%

“…In low-exothermicity materials a significant degree of reactant consumption takes place before any critical temperature is reached, [5][6][7][8][9], and, in contrast to the high-exothermicity case, the realization of a critical (so-called ignition) temperature is not a guarantee of a combustion wave. It is natural therefore to re-define 'ignition' for low-exothermicity materials to mean that a self-sustained combustion wave is formed, i.e., that the wave continues to the boundary, even if the hotspot heating is switched off after it has formed.…”

Section: Pseudo-homogeneous Results: Ph Modelmentioning

confidence: 99%

“…Clearly, the hotspot heating at x = 0 generates a self-propagating combustion wave that leads to complete depletion of the reactant. Waves of this type have been discussed at length in [5][6][7][8][9], as mentioned earlier.…”

Section: Pseudo-homogeneous Results: Ph Modelmentioning

confidence: 99%

“…For a constant hotspot heat-flux, ignition criteria associated with low-exothermicity solids have been obtained numerically in [5][6][7][8][9] for the finite slab, cylinder and sphere. In contrast to high-exothermicity solids, the calculations reveal that: (i) a substantial degree of reactant consumption occurs before the onset of ignition; (ii) ignition typically occurs away from the hotspot boundary, within the virgin solid; (iii) reactant consumption can prevent the formation of a combustion wave.…”

Section: Introductionmentioning

confidence: 99%

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Gas-phase and heat-exchange effects on the ignition of high- and low-exothermicity porous solids subject to constant heating

Shah

Brindley

McIntosh³

et al. 2006

J Eng Math

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This article investigates the ignition of low-exothermicity reactive porous solids exposed to a maintained source of heat (hotspot), without oxygen limitation. The gas flow within the solid, particularly in response to pressure gradients (Darcy's law), is accounted for. Numerical experiments related to the ignition of low-exothermicity porous materials are presented. Gas and solid products of reaction are included. The first stage of the paper examines the (pseudo-homogeneous) assumption of a single temperature for both phases, amounting to an infinite rate of heat exchange between the two. Isolating the effect of gas production and flow in this manner, the effect of each on the ignition time is studied. In such cases, ignition is conveniently defined by the birth of a self-sustained combustion wave. It is found that gas production decreases the ignition time, compared to equivalent systems in which the gas-dynamic problem is effectively neglected. The reason for this is quite simple; the smaller heat capacity of the gas allows the overall temperature to attain a higher value in a similar time, and so speeds up the ignition process. Next, numerical results using a two-temperature (heterogeneous) model, allowing for local heat exchange between the phases, are presented. The pseudo-homogeneous results are recovered in the limit of infinite heat exchange. For a finite value of heat exchange, the ignition time is lower when compared to the single-temperature limit, decreasing as the rate of heat exchange decreases. However, the decrease is only mild, of the order of a few percent, indicating that the pseudo-homogeneous model is in fact a rather good approximation, at least for a constant heat-exchange rate. The relationships between the ignition time and a number of physico-chemical parameters of the system are also investigated.

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Section: Pseudo-homogeneous Results: Ph Modelmentioning

confidence: 85%

Section: Pseudo-homogeneous Results: Ph Modelmentioning

confidence: 99%

Section: Pseudo-homogeneous Results: Ph Modelmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Gas-phase and heat-exchange effects on the ignition of high- and low-exothermicity porous solids subject to constant heating

Shah

Brindley

McIntosh³

et al. 2006

J Eng Math

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“…Recent works, reported by Brindley et al [1][2][3], have studied the effect of a constant source of heat on a reactive solid X, where the reaction was assumed to be of the form X → product.…”

Section: Introductionmentioning

confidence: 99%

The effect of oxygen starvation on ignition phenomena in a reactive solid containing a hot-spot

Shah

McIntosh

Brindley

et al. 2003

Combustion Theory and Modelling

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(2003) 'The effect of oxygen starvation on ignition phenomena in a reactive solid containing a hot-spot', Combustion Theory and Modelling, 7: 3, 509 -523 To link to this Article: DOI: 10.1088/1364-7830/7/3/304 URL: http://dx.doi.org/10.1088/1364-7830/7/3/304Full terms and conditions of use: http://www.informaworld.com/terms-and-conditions-of-access.pdf This article may be used for research, teaching and private study purposes. Any substantial or systematic reproduction, re-distribution, re-selling, loan or sub-licensing, systematic supply or distribution in any form to anyone is expressly forbidden.The publisher does not give any warranty express or implied or make any representation that the contents will be complete or accurate or up to date. The accuracy of any instructions, formulae and drug doses should be independently verified with primary sources. The publisher shall not be liable for any loss, actions, claims, proceedings, demand or costs or damages whatsoever or howsoever caused arising directly or indirectly in connection with or arising out of the use of this material. AbstractIn this paper, we explore the effect of oxygen supply on the conditions necessary to sustain a self-propagating front from a spherical source of heat embedded in a much larger volume of solid. The ignition characteristics for a spherical hot-spot are investigated, where the reaction is limited by oxygen, that is, reactant + oxygen → product. It is found that over a wide range of realistic oxygen supply levels, constant heating of the solid by the hot-spot results in a self-propagating combustion front above a certain critical hot-spot power; this is clearly an important issue for industries in which hazard prevention is important. The ignition event leading to the formation of this combustion wave involves an extremely sensitive balance between the heat generated by the chemical reaction and the depletion of the reactant. As a result, for small hot-spot radii and infinite oxygen supply, not only is there a critical power above which a self-sustained combustion front is initiated there also exists a power beyond which no front is formed, before a second higher critical power is found. The plot of critical power against hot-spot radius thus takes on a Z-shape appearance. The corresponding shape for the oxygen-limited reaction is qualitatively the same when the ratio of solid thermal diffusion to oxygen mass diffusion (N ) is small and we establish critical conditions for the initiation of a self-sustained combustion front in that case. As N gets larger, while still below unity, we show that the Z-shape flattens out. At still larger values of N , the supercritical behaviour becomes increasingly difficult to define and is supplanted by burning that depends more uniformly on power. In other words, the transition from slow burning to complete combustion seen at small values of N for some critical power disappears. Even higher values of N lead to less solid burning at fixed values of power.

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Compression and Shear Experimental Study of PBX Explosive

Chen

Yuan

Chen

et al. 2018

Propellants Explo Pyrotec

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Generate compress-shear loading on Polymer Bonded Explosive (PBX) specimens. The research was carried out to determine the pressure and macroscopic temperature variation occurring in the specimen by using a pressure sensor and a thermocouple. High-speed photography was used to reveal the macroscopic ignition phenomena. X-ray diffraction (XRD) was used to study the material composition of raw and recovered specimens. The results of the experiments described here clearly show that specimens underwent crush, melt and ignition from impact to reaction. At the same time, the relative content of aluminium decreased. Compared to the direct impact results from split Hopkinson compression-shear bar tests, the drop-weight loading pulse is longer, so PBX specimens ignite more easily.

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Ignition phenomenology and criteria associated with hotspots embedded in a reactive material

Cited by 20 publications

References 12 publications

Gas-phase and heat-exchange effects on the ignition of high- and low-exothermicity porous solids subject to constant heating

Gas-phase and heat-exchange effects on the ignition of high- and low-exothermicity porous solids subject to constant heating

The effect of oxygen starvation on ignition phenomena in a reactive solid containing a hot-spot

Compression and Shear Experimental Study of PBX Explosive

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