Investigation of Intermediate Products in Post-Catalytic Combustion Using an Ion Probe

The combustion phenomena of vaporizing spray in a catalyst and a post-catalyst flame were studied experimentally. This study is a part of the development of a catalytic combustor for a ceramic gas turbine engine. A palladium catalyst supported on the cordierite honeycomb monolith was used as a combustion catalyst. A premixture of air and kerosene vapor was introduced into the catalyst. The parabolic shaped flame, called a thermal combustion flame, which was supported on the catalyst, was formed even when the equivalence ratio of the mixture was less than stoichiometry. Intermediate products in the exhaust gas after the catalyst honeycomb were investigated using an ion probe. When the thermal flame appeared, ions were detected in the exhaust gas between the honeycomb and the flame. It was indicated that some reactive species were included in the exhaust gas. Even when the thermal flame did not appear, the ions were slightly detected in the exhaust gas. The concentration of the ions rapidly decreased a slight distance away from the honeycomb surface and increased in front of the thermal flame. When the equivalence ratio was increased, the ion concentration at the honeycomb surface increased. Furthermore, in order to investigate the effect of the mixing behavior of the vaporized fuel on post-catalytic combustion, the length of the mixing tube was changed. When the mixing of fuel was insufficient, the thermal flame appeared at a lower equivalence ratio than the more homogeneous mixing condition. However, regardless of the mixing length and equivalence ratios, the concentration of ions near the honeycomb surface was almost constantly at the onset conditions of the thermal combustion flames.