A few fundamental aspects about ignition and flame propagation in dust clouds

Proust, Christophe

doi:10.1016/j.jlp.2005.06.035

Cited by 125 publications

(48 citation statements)

References 40 publications

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“…that the propagation flame is mainly conducted by conduction within the 20L sphere. However, it should be reminded that it is experimentally [17] and theoretically [20,3] expected that the flame propagation within nanodust cloud is probably mainly conducted by radiation.…”

Section: Intrinsic Oxide Contentmentioning

confidence: 99%

Ignition and explosion of nanopowders: something new under the dust

Dufaud

Vignes

Henry

et al. 2011

J. Phys.: Conf. Ser.

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Abstract. This work deals with the study of ignition and explosion characteristics of nanoparticles. It has been carried out on various powders: zinc, aluminum, carbon blacks… Specific behaviours have been highlighted during the first phase of this project (Nanosafe 2). For instance, it has been demonstrated that there mainly exists two combustion regimes that are either kinetically controlled, for small size particles, or diffusion controlled, for large size particles (generally with diameters greater than 1 or 2 µm). It has been found that as the particle size decreases, minimum ignition temperature and minimum ignition energy decrease (even lower than 1 mJ), indicating higher potential inflammation and explosion risks for metallic nanopowders. Moreover, the presence of agglomerates in the nanopowders could modify their reactivity. Thus, the explosion severity of Al powders tends to increase as the specific surface area decreases, before reaching a peak for 1 µm particle size. These results are essential for industries producing or handling nanopowders in order to propose/design new and proper prevention and protection means. Nevertheless, the validity of the classical characterization tools with regard to nanopowders should be discussed. For example, the experimental laminar flame velocity of Al dusts has been compared to a theoretical one, determined by Huang's model, which assumes that the propagation of the flame is run mainly by conduction. It has shown a good agreement. However, under certain conditions, the Al flame propagation is expected to be mainly conducted by radiation. Two hypotheses can then be made. On the one hand, it can be assumed that the 20 L sphere probably disturbs the flame propagation and thermal mechanisms by absorbing radiation (wall quenching effect). On the other hand, it has been observed, thanks to the use of a high speed camera that the preheating zone is smaller for some nanopowders than for micro-particles (figure below). It could notably be explained by the fact that the flame radiation is absorbed by the cloud of unburnt Al nanopowders. Several other factors may have an impact on the explosion severity. If these points are correctly addressed, it will be possible to get more reliable ignition and explosion characteristics.

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Section: Intrinsic Oxide Contentmentioning

confidence: 99%

Ignition and explosion of nanopowders: something new under the dust

Dufaud

Vignes

Henry

et al. 2011

J. Phys.: Conf. Ser.

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“…For a typical mean dust density ρ d ≡ Nm p = 0.1-0.3 kg/m 3 , the corresponding radiation absorption length is L a = 1/κ ≈ (ρ p /2ρ d )d p ≈ 10 cm, where ρ p = 1 kg/cm 3 and d p = 10 μm. If particles are accumulated in optically thick clusters, with the particle number density within clusters n cl much larger than N , the effective radiation absorption length can be roughly estimated as L eff = 1/σ cl N cl , where σ cl is the cluster cross section and N cl is the mean number density of clusters.…”

Section: Mean-field Equation For Radiation Transfermentioning

confidence: 99%

Mechanism of unconfined dust explosions: Turbulent clustering and radiation-induced ignition

2017

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It is known that unconfined dust explosions typically start off with a relatively weak primary flame followed by a severe secondary explosion. We show that clustering of dust particles in a temperature stratified turbulent flow ahead of the primary flame may give rise to a significant increase in the radiation penetration length. These particle clusters, even far ahead of the flame, are sufficiently exposed and heated by the radiation from the flame to become ignition kernels capable to ignite a large volume of fuel-air mixtures. This efficiently increases the total flame surface area and the effective combustion speed, defined as the rate of reactant consumption of a given volume. We show that this mechanism explains the high rate of combustion and overpressures required to account for the observed level of damage in unconfined dust explosions, e.g., at the 2005 Buncefield vapor-cloud explosion. The effect of the strong increase of radiation transparency due to turbulent clustering of particles goes beyond the state of the art of the application to dust explosions and has many implications in atmospheric physics and astrophysics.

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“…So if these parameters are introduced in Eqs. (4), (6), and (7), the following equations can be rewritten as…”

Section: Dimensionless System Of Governing Equationsmentioning

confidence: 99%

“…The interaction of Lewis number with different transient effects, such as fluctuating reactant concentrations, fluctuating reactant temperatures, and variable partial premixing, was considered in this research. Proust [6][7] measured the laminar burning velocities and maximum flame temperatures for combustible dust-air mixtures such as starch dust-air mixtures, lycopodium-air mixtures and sulphur flour-air mixtures.…”

Section: Introductionmentioning

confidence: 99%

Investigation over the recirculation influence on the combustion of micro organic dust particles

Bidabadi

Fanaee

Rahbari

2010

Appl. Math. Mech.-Engl. Ed.

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This paper investigates the role of recirculation and non-unity Lewis number on the combustion of organic dust particles. Since recirculation effect is more noticeable in micro-combustors, it is necessary to propose a modeling approach of this phenomenon to better simulate the performance of micro-combustors. In this research, in order to model the combustion of organic dust particles, it is assumed that the dust particles vaporize first to yield a known chemical structure which is oxidized in the gas phase, and the chemical structure of this gaseous fuel is assumed methane. To study the flame structure and solve the governing equations, it is considered that the flame structure consists of three zones titled the preheat-vaporization zone, the narrow reaction zone and finally the post flame zone. The recirculation phenomenon is evaluated by entering the exhausted heat from the post flame zone into the preheat zone. The solution is based on the following approach. First, the governing equations in each zone are nondimensionalized. Then the needed boundary and matching conditions are applied in each zone. After that, these equations and the required boundary and matching conditions are simultaneously solved with the analytical model. Consequently, the remarkable effects of recirculation and nonunity Lewis number on the combustion characteristics of the organic dust particles such as burning velocity and temperature profiles for different particle radii are obtained. The results show reasonable agreement with published experimental data.

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A few fundamental aspects about ignition and flame propagation in dust clouds

Cited by 125 publications

References 40 publications

Ignition and explosion of nanopowders: something new under the dust

Ignition and explosion of nanopowders: something new under the dust

Mechanism of unconfined dust explosions: Turbulent clustering and radiation-induced ignition

Investigation over the recirculation influence on the combustion of micro organic dust particles

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