Untitled - Aerobib - Universidad Politécnica de Madrid

6.1. INTRODUCTION 133
papers presented at the two International Colloquia sponsored by this organization in
1954 and 1956. The work by von Kármán [10] is a complete review of the state of
knowledge on this problem up to 1956.
At the same time that this theory which considers the flame as a wave propagating
through a continuous medium was developed, other theories have attempted to
emphasize only partial aspects of the phenomenon. From them the most representative
is the one proposed by Tanford and Pease on the diffusion of radicals from the hot
boundary [11]. It has also been objected that flames cannot be treated by the methods
of the Mechanics of Continua. This objection has originated such theories as the
one proposed by van Tiggelen [12], who applies a method analogous to that used by
Semenov in studying chain reactions.
At present, however, it seems clearly established and widely accepted that the
correct method which should be applied to this problem is the one expanded in the following
paragraphs, and that its difficulty reduces to the use of the adequate chemical
kinetic scheme for each case; the knowledge of the corresponding physico-chemical
constants and of the transport coefficients of the mixtures; and finally to the obtaining
of satisfactory methods of solution of the difficult mathematical problem of the
integration of the flame equations.
In addition to this progress of theory, a substantial improvement has been
achieved in the field of experimental techniques to measure the propagation velocity
of the flame. An increasing number of data is now available on the influence of
several parameters such as the composition, pressure, initial temperature of the mixture,
etc., on the flame propagation velocity. As a bibliography for the study of these
techniques, their limitations and applicability we recommend the works by Jost [13],
Gaydon and Wolfhard [14] and specially the one of Ref. [15]. Linnet [16] has published
a review on these methods, in which he classifies the experimental techniques
most commonly used into the following five groups:
1) Method of the bunsen burner (Gouy and Michelson). The most universal, of
which a great number of variations are used.
2) Method of the tube (Coward-Hartwell, Gerstein, etc). Not considered reliable
enough.
3) Method of the spherical flame in a constant volume bomb (Fick, Lewis-von
Elbe). Not frequently used and difficult to observe.
4) Method of the soap film or spherical flame at constant pressure. Not frequently
used and limited to mixtures which are not sensitive to the influence of water
vapor.