Isothermal chain-branching, reaction exothermicity, and transport interactions in the stability of methane/air mixtures
- Univ. of Massachusetts, Amherst, MA (United States). Dept. of Chemical Engineering
The influence of reaction exothermicity and transport of species on the bifurcation behavior of CH{sub 4}/air mixtures is studied in a continuous stirred tank reactor with numerical bifurcation techniques, using the 177-reaction/31-species Gas Research Institute mechanism, version 1.2. Ignition points are analyzed through various sensitivity analyses, quasi-steady-state analysis, and numerical experiments. Principal component analysis is also applied at ignition to derive a reduced 28-reaction mechanism capable of accurately predicting ignition temperature as a function of pressure at intermediate to high pressures. Results show that isothermal chain-branching chemistry can drive complex instabilities, with up to five multiple solutions and Hopf bifurcations. However, thermal feedback (reaction exothermicity) promotes ignition and considerably extends the range of multiplicity with respect to pressure, residence time, and inlet CH{sub 4} concentration. Reaction exothermicity eliminates a turning-back behavior and results in a monotonic pressure-temperature ignition diagram. This ignition pressure-temperature stability diagram considerably shifts with residence time, especially at low pressures. It is shown that this shift in ignition temperature is mainly due to transport of CH{sub 2}O at high pressures and transport of CH{sub 3} radicals at low pressures. Sensitivity analyses with respect to heats of reactions and reaction preexponentials reveal a strong coupling between kinetic and thermal interactions in controlling ignition. Qualitative comparison with experiments is also performed, and results are briefly contrasted to H{sub 2}/air ignition.
- OSTI ID:
- 619650
- Journal Information:
- Combustion and Flame, Vol. 114, Issue 1-2; Other Information: PBD: Jul 1998
- Country of Publication:
- United States
- Language:
- English
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