Abstract
High-temperature air combustion is promising solution for the reduction of NOx emission. For downsizing the combustion system, we used a catalytic combustion for generating the highly preheated oxidizer with low oxygen concentration. In this combustion system, high-temperature air combustion was performed by a fuel jet flame in the high-temperature section right after the catalytic combustion. The temperature and oxygen concentration of the oxidizer depended on the equivalence ratio and the inlet velocity of the mixture flowing into the catalyst. In addition, the uniform and the non-uniform catalytic combustion were observed with the conditions. The lifted turbulent flame was observed on the fuel jet and the lifted height decreased with decreasing the gas velocity and increasing equivalence ratio of the oxidizer, and also with increasing the fuel jet velocity. The fact that the reduction of NOx emission was correlated with the lifted height of the flame implies that the turbulent mixing of the fuel jet and the oxidizer has a significant influence on NOx emission. Furthermore, NOx emissions were really reduced under uniform catalytic combustion conditions, whereas NOx emissions under some non-uniform catalytic combustion conditions were comparable to or higher than that without the catalytic combustion system. This is probably because the oxygen concentration of the oxidizer was not low enough under the non-uniform catalytic combustion conditions. Consequently, an appropriate management of catalytic combustion is necessary for low NOx combustion.
