Etude de la combustion de gaz de synthèse issus d'un processus de ...

Bibliographic revision
The burning velocity of a flame is affected by flame radiation, and hence by flame
temperature, by local gas properties such as viscosity, thermal conductivity and
diffusion coefficient, and by the imposed variables of pressure, temperature, air-fuel
ratio and heat of reaction of mole of mixture. However, although its theoretical definition
is straightforward, its practical measurement undoubtedly is not, and there is a
considerable discrepancy between the results obtained by the various methods. One of
the main problems in measuring the normal burning velocity is that a plane flame front
can be observed only under very special condition. In nearly all-practical cases, the
flame front is either curved or is not normal to the direction of velocity of the gas
stream. Broadly speaking there are two types of measurements for burning velocity;
one uses flames travelling through stagnant mixtures, whereas the other employs
flames that are held stationary in space by a counter flow of fresh mixture.
tel-00623090, version 1 - 13 Sep 2011
The following will describe briefly some of the different techniques for measuring the
laminar burning velocity for non-stationary flames. Emphasis will be given to
propagating flames at constant volume and constant pressure since they are
extensively used.
In these methods of measurements, the flame moves through the initially quiescent
mixtures. The subsequent spread of such a flame is determined by the nature of the
bounding surface between the mixture and its surroundings. These types of bounding
surface have been used: rigid cylindrical tube, either closed at both ends or open at
one end or both ends; soap bubble solution or thin elastic membranes; and rigid
spherical vessels.
Burning velocity measurement can be made by direct measurement of flame
propagation. This requires locating the position of the flame front at two (or more)
known times. Rapid visualization is required, and it is necessary to know the flame front
geometry and the flow constraints, and often the density change across the flame front.
The followings are the measurement techniques, which have been used for measuring
the laminar burning velocity with non-stationary flames.
2.5.2.1 Tube method
This is one of the earliest methods and was first used by Mallard and LeChatelier,
(1883) in which the mixture is ignited at the open end of a tube and the flame front is
photographed as propagating toward the closed end. The expression for the burning
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