double séminaire : Augustin Guibaud &Guillaume Legros

Mardi 14 mai 2019 à 11h00, amphi 3, Centrale Marseille

Flame Spread in Microgravity : How to reduce the risk of fire on a journey to Mars.

Augustin Guibaud

Sorbonne Université, CNRS, UMR 7190, Institut d'Alembert, Paris, France

Should manned deep space exploration missions happen in the near future, many safety issues must be solved. As astronauts will be confi ned for a long duration in an environment with limited resources, there is a crucial need to prevent any damage to the structure by an accidental event such as a re. This requires the careful development of material and procedures to minimize the risk of a re. As a result, fundamental understanding of the heat and mass transfer processes that drive ignition and  flame spread in microgravity is required to reduce a lengthy and costly systematic characterization of material flammability in microgravity. In order to run experiments in this unusual environment, a combustion chamber has been developed at Sorbonne Université by a team of scientists and engineers [1]. It allows the investigations on  flames spreading over polyethylene coated wires on Novespace A310 ZeroG parabolic flights. The chamber enables the control of the pressure, oxygen concentration and the velocity of the  flow rate surrounding the samples.

In this talk, I will describe the experimental setup, and show how a series of optical tools has been designed to evaluate the impact of these flow parameters on flame spread properties in microgravity. Basic image processing leads to the determination of flame existence domain; as well as flame spread rate, flame topology and smoke point in the case of propagation. A more sophisticated new methodology was specially developed to map soot volume fraction, temperature and radiative heat feedback using a broadband compact setup that fi ts strict compacity requirements [3]. 

I will then describe a numerical model currently under development. Using detailed experimental fields as points of comparison, this numerical model is validated and provides access to information that are not experimentally accessible.
I will finally share some key results of the flight campaigns, and illustrate how it can upgrade fire safety in a spacecraft.

[1] J.M. Citerne, H Dutilleul, K Kizawa, M Nagachi, O Fujita, M. Kikuchi, G. Jomaas,S. Rouvreau, J.L. Torero, G. Legros, Fire safety in space / Investigating flame spread interaction over wires, Acta Astr., 126 500-509 (2016).
[2] G. Legros, J.L.Torero, Phenomenological model of soot production inside a non-buoyant laminar diffusion flame, Proc. Combust. Inst. 35 (2015).
[3] A. Guibaud, J.M. Citerne, J.M. Orlach, O. Fujita, J.L. Consalvi, J.L. Torero, G. Legros, Broadband modulated absorption/emission technique to probe sooting flames: Implementation, validation, and limitations, Proc. Combust. Inst., 37 1540-7489 (2018).

Control of soot production : What about playing with magnetic fields?

Guillaume Legros

Sorbonne Université, CNRS, UMR 7190, Institut d'Alembert, Paris, France

Soot particles represent a major combustion hazard. From Aristotle, who recognized candle smoke as a serious threat to pregnant women, up to latest studies that evidenced the dramatic effects that soot inhalation can induce, the public awareness of this issue has grown to such a point that todays public policies clearly integrate dedicated legislations. Thus, control of soot particles release and impact has to be a priority in the fields of reacting  flows.

Standard strategies of soot production control involve post-treatment methods, such as fi lters and/or catalysts. However, using in situ strategies looks like an increasingly promising method. Examples are the design of new fuels [1], addition of exhaust gases to the combustion process [2], or combustion control by electric fields. Interestingly, none of these strategies utilises magnetic fields. We will examine recent investigations [3] assessing the influence of a magnetic perturbation on soot production and release by flames.

[1] D.D. Das, J.C.S. John, C.S. McEnally, S. Kim, L.D. Pfe erle, Measuring and predicting sooting tendencies of oxygenates, alkanes, alkenes, cycloalkanes, and aromatics on a uni ed scale, Comb. Flame, 190 349-364 (2018).
[2] M. Kashif, J. Bonnety, A. Matynia, P. Da Costa, G. Legros, Sooting propensities of some gasoline surrogate fuels: Combined effects of fuel blending and air vitiation, Comb. Flame, 161 1840-1847 (2015) .
[3] A. Jocher, H. Pitsch, T. Gomez, J. Bonnety, G. Legros, Combustion instability mitigation by magnetic fields, Phys. Rev. E, 95 063113 (2017).