Exhaust Gas Analysis in a Catalytic Combustion System With a Methane Mixture

Exhaust gas from the catalytic combustion of methane mixture was analyzed experimentally. A palladium catalyst supported on a cordierite honeycomb was used. The methane/air mixture, which was pre-heated to 530K, was introduced into the catalyst. Combustion states were investigated under various conditions of the equivalence ratio. In the case of lean mixture, homogeneous surface reaction in the catalyst was observed, and combustion reaction was completed within the catalyst. However, in the case of rich mixture, a thermal combustion flame appeared after the catalyst with the homogeneous surface reaction. In order to investigate exhaust gas composition, exhaust gas was sampled by a quartz probe, and was analyzed by a FTIR. Furthermore, low level NO in the exhaust gas was detected by a LIF method. In order to obtain the NO concentration from the NO fluorescence, temperature dependency of the fluorescence was obtained by using a NO/N₂ mixture. NO concentration in a exhaust gas just after the catalyst was highest when the equivalence ratio was 0.3. When the thermal combustion flame appeared after the catalyst, CO and CH₄ were detected just after the catalyst. These concentrations decreased around the thermal combustion flame. This result suggests that unburnt CH₄ and CO which was produced by a partial combustion in the catalyst were converted in a gas phase reaction. In this case, although NO was hardly detected just after the catalyst, it was detected around the thermal flame.