Premixed hydrogenoxygen flames. Part I: Flame structure near the flammability limits
1993; Elsevier BV; Volume: 93; Issue: 4 Linguagem: Inglês
10.1016/0010-2180(93)90140-x
ISSN1556-2921
Autores Tópico(s)Gas Dynamics and Kinetic Theory
ResumoA numerical investigation of flammability limits and structure of adiabatic planar flames in premixed hydrogenoxygen gases is carried out with a detailed chemistry and using a pseudo-stationary code. The well-known kinetic mechanism responsible for the second limit of explosion results from a competition between chain branching and chain breaking reactions, concerning mainly the H radical. In the flame propagation problem, this mechanism defines a cross over flame temperature. The corresponding critical values of the equivalence ratio indicates a change in the chemical kinetic regime sustaining the flame propagation. The one-dimensional laminar flame structure and the burning velocity are studied by direct numerical simulations close to these limits. When they are approached, the flame velocity decreases to very small values (∼ mm/s) and the global activation energy increases. These pure kinetic mechanisms, which are studied here, are essential for explaining the phenomena which are observed at the flammability limits. Reduced schemes describing these effects have been also identified. The hydrogen rich flame is found to be well represented by a reduced scheme of two steps involving one radical H, while the lean flame requires a reduced scheme of three steps involving two radicals H and OH.
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