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

Chapter 2
2.5.3 Burning velocity empirical correlations
tel-00623090, version 1 - 13 Sep 2011
The simultaneous change in the pressure and temperature of the unburned mixture
during a closed vessel explosion makes it necessary to rely on correlations which take
these effects into account. While correlations for the laminar flame thickness are
scarce, many have been proposed to describe the behavior of the laminar burning
velocity. Because of their simplicity and the minimal computational burden they impose,
this section is restricted to correlations which express the laminar burning velocity in
terms of properties of the unburned mixture only (i.e. S u = f(T,P,φ)). These relationships
may be classified as follows:
- Equations that separately describe the influence of pressure and temperature
on the laminar burning velocity for a given equivalence ratio.
- Correlations describing the simultaneous influence of pressure and temperature
on the burning velocity for a given equivalence ratio.
- Correlations describing the simultaneous influence of pressure, temperature
and equivalence ratio.
The first group of correlations, when applied to closed vessel explosions, has the
disadvantage that not all combinations of pressure and temperature, as these occur in
the course of the combustion process, are covered. Clearly, correlations are needed
which describe the simultaneous influence of pressure and temperature on the burning
velocity. In the second group, this combined influence of pressure and temperature on
burning velocity is covered for a given equivalence ratio. In the third group of
correlations, in addition to describing the simultaneous effect of pressure and
temperature on the burning velocity, also include the influence of equivalence ratio.
Clearly, this latter group of correlations are more robust an practical and so it will be
described and used in this work.
Sharma et al. (1981) proposed, for methane-air mixtures, a system of equations for
predicting the laminar burning velocity (in cm.s -1 ) for pressures from 1 to 8 atm,
temperatures from 300 to 600 K, and equivalence ratios from 0.8 to 1.2:
1.68
⎧
⎪CT
( / T0
) φ if φ ≤ 1
Su
= ⎨
⎪
1.68 φ
⎩CT
( / T0
) if φ > 1
1287 1196 360
C =− + − + −
φ φ φ
10
418 15 log
2 3
φ
P
(2.87)
Iijima and Takeno (1986) proposed a correlation which expresses the laminar burning
velocity, S u (P, T), at an arbitrary pressure and temperature, in terms of the laminar
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