Chemical-kinetic prediction of critical parameters in gaseous detonations Page: 12 of 26
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13b
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Computed values of A for stoichoimetric fuel-air mixtures are also
shown in Fig. 3. For these mixtures, only the results for CJ-L-air fall
along a straight line. The most surprising behavior is that of stoichiometric
H2~air, which has multiple values of PQ for a range of dc between 9 and
13 cm. Computed results for the other mixtures are also somewhat curved, with
methane once again being an exception with the curvature in the opposite
direction. However, none of the hydrocarbon-air mixtures show the
multiple-valued behavior displayed by H2~air.
The computed results for H2-air are caused by the gradual growth in
importance of the recombination reaction H + 02 + M = H02 + M with
increasing pressure. In this way the behavior is reminiscent of the second
explosion limit for Ho-02 described by Lewis and von Elbe [14]. The rate
of this reaction is pressure-dependent, and as the post-shock unreacted gas
pressure increases it eventually begins to compete with the principal chain
branching reaction H + 02 = 0 + OH. When this occurs the overall rate of
fuel consumption actually decreases as Pq increases, due to the reduced
chain branching rate, so the induction length grows larger. Further increases
in PQ reverse this trend and A again decreases with increasing P .' This
second reversal occurs because the greater density and species concentrations
provide more rapid rates of the key bimolecular reactions which overcome the
inhibiting effect of the recombination reaction. In particular,, the H02
thus formed is rapidly consumed by the sequence of reactions
ho2 + ho2 = h2o2 + o2
H2°2 + M " 0H + 0H + M
making this effectively a chain propagation path.
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Westbrook, C.K. & Urtiew, P.A. Chemical-kinetic prediction of critical parameters in gaseous detonations, article, January 12, 1982; [Livermore,] California. (https://digital.library.unt.edu/ark:/67531/metadc1072235/m1/12/: accessed April 25, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.