A ceramic honeycomb is applied to a 1-kW class compact tubular-type fuel reformer based on non-catalytic partial oxidation (POX) of methanol. Liquid methanol was used due to its easy handling characteristics. It is confirmed that POX in a super-rich condition can be sustained within the reactor. In most conditions, the reaction was stabilized near the outlet surface of the ceramic honeycomb where the maximum temperature is observed. The maximum temperature reaches approximately the adiabatic flame temperature, therefore, the ceramic honeycomb works as an adiabatic layer and a reaction stabilizer which can sustain the reaction at a certain location. The location of the reaction varies with regard to the thermal load conditions. Stable and high conversion rate was obtained when the reaction is stabilized on the outlet surface of the ceramic honeycomb. This robust feature of reaction stabilization is a significant characteristic of the ceramic honeycomb. The reaction characteristic and its effect on the reforming performance are investigated in this study using detailed measurements of temperature distributions and gas components.

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A compact tubular-type fuel reformer was fabricated and operated under fuel-rich combustion conditions of methanol, focusing on the partial oxidation reaction (POR). Ceramic honeycomb strainer blocks were inserted in the reactor. In the authors’ previous study, Case-1 of only one honeycomb block insertion showed that the reaction region formed in the downstream of the block. This block worked as a reaction stabilizer. The other condition, Case-2, was operated with the secondary honeycomb block inserted in the downstream of the reaction region in addition to the first block. This geometrical structure sandwiched the reaction region between the two blocks, and the thermal energy possessed by the exhaust gas could be regenerated to the reaction region by radiation exchange between these two blocks, which resulted in enhancing the preheating of the premixed gas. By this effect, the methanol-conversion and hydrogen-production in Case-2 were enhanced by about 10% compared to Case-1. In the present study, the reaction characteristics of the fuel reformer were investigated in detail, by detecting the location of the reaction region. Detailed temperature profiles in the streamwise direction were measured with traversable thermocouples, and positive ion current distributions corresponding to the reaction region were measured with a Langmuir probe. It was confirmed by the both measurements that there exists a reaction region right after the first honeycomb block which accompanies with sharp temperature gradients. The estimated thickness of the reaction region, however, was as wide as several millimeters to a centimeter, which is believed to be a ‘mild reaction’ stabilized by the first honeycomb block. In Case-2, the high-temperature region became broader compared to Case-1, which indicates that the enhancement of preheating of premixed gas was achieved by the heat regenerated from the secondary honeycomb block.

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