Computational fluid dynamics （CFD） combined with detailed chemical kinetics was employed to model the filtration combustion of a mixture of methane/air in a packed bed of uniform 3 mm diameter alumina spherical particles. The standard k-ε turbulence model and a methane oxidation mechanism with 23 species and 39 elemental reactions were used. Various equivalence ratios （1.47, 1.88, 2.12 and 2.35） were studied. The numerical results showed good agreement with the experimental data. For ultra-rich mixtures, the combustion temperature exceeds the adiabatic value by hundreds of centigrade degrees. Syngas （hydrogen and carbon monoxide） can be obtained up to a mole fraction of 23%. The numerical results also showed that the combination of CFD with detailed chemical kinetics gives good performance for modeling the pseudo-homogeneous flames of methane in porous media.
This paper presents an experimental study on the emission characteristics and combustion instabilities of oxy-fuel combustions in a swirl-stabilized combustor. Different oxygen concentrations (Xoxy=25%～45%, where Xoxy is oxygen concentra- tion by volume), equivalence ratios (φ=0.75～1.15) and combustion powers (CP=1.08～2.02 kW) were investigated in the oxy-fuel (CH4/CO2/O2) combustions, and reference cases (Xoxy=25%～35%, CH4/N2/O2 flames) were covered. The results show that the oxygen concentration in the oxidant stream significantly affects the combustion delay in the oxy-fuel flames, and the equivalence ratio has a slight effect, whereas the combustion power shows no impact. The temperature levels of the oxy-fuel flames inside the combustion chamber are much higher (up to 38.7%) than those of the reference cases. Carbon monoxide was vastly produced when Xoxy>35% or φ>0.95 in the oxy-fuel flames, while no nitric oxide was found in the exhaust gases because no N2 participates in the combustion process. The combustion instability of the oxy-fuel combustion is very different from those of the reference cases with similar oxygen content. Oxy-fuel combustions excite strong oscillations in all cases studied Xoxy=25%～45%. However, no pressure fluctuations were detected in the reference cases when Xoxy>28.6% accomplished by heavily sooting flames which were not found in the oxy-fuel combustions. Spectrum analysis shows that the frequency of dynamic pressure oscillations exhibits randomness in the range of 50～250 Hz, therefore resulting in a very small resultant amplitude. Temporal oscillations are very strong with amplitudes larger than 200 Pa, even short time fast Fourier transform (FFT) analysis (0.08 s) shows that the pressure amplitude can be larger than 40 Pa.
