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Some Recent Applications of Laser Tomography in Combustion

L. Boyer
Department de Combustion, LA. 72 du C.N.R.S., Universite' de Provence, Centre St. Jerome, 13397 Marseille Cedex 13, France

G. Searby
Department de Combustion, LA. 72 du C.N.R.S., Universite' de Provence, Centre St. Jerome, 13397 Marseille Cedex 13, France

J. Quinard
Department de Combustion, LA. 72 du C.N.R.S., Universite' de Provence, Centre St. Jerome, 13397 Marseille Cedex 13, France

Resumo

Laser Tomography is a technique that has been developed to give access to quantitative measurements of the dynamical properties of flame fronts. This technique, which will be briefly described, provides a means of obtaining an instantaneous measurement of the position and velocity of a flame front.
A propagating flame front in a premixed gaseous mixture may be considered, as a first approximation, to be the surface of a hydrodynamic and a thermal discontinuity. An aerosol of oil droplets one micron in diameter are injected uniformly into the unburnt mixture. These droplets are vaporised and burnt when they cross the front. A sheet of laser light illuminating the combustion zone is made visible by the presence of the aerosol in the unburnt mixture but remains invisible in the transparent burnt gases. The frontier between the bright and dark regions of the sheet of light thus provides the visualisation of a cut through the flame front.
The following applications will be presented :

  1. Stabilisation of the average position of an unattached flame by active control of the gas flow.
  2. Experimental study of the interaction between combustion and turbulent flow with emphasis on the retro-action of a flame front on the flow of the unburnt gases.
  3. Experimental study of the initial propagation of a spherical flame ignited by a spark.
  4. Swept laser tomography, which provides a quasi-instantaneous cartography of a flame front, and its application to the onset of propagation instabilities.

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