Combustion characteristics of the lean premixed mixture in a catalytically stabilized combustor

Abstract

This work aims to investigate combustion characteristics of the lean premixed mixture ina catalytically stabilized combustor through the experiment and the numerical simulation. The catalytically stabilized combustor has been known to have an advantage that it can combust the ultra lean mixture stably. The catalytically stabilized combustor consists of a catalyst bed and a thermal combustor. In this study, characteristics of both the catalyst bed and the thermal combusor were examined. Three kinds of catalyst beds - Pd, Pt and Pd/Pt catalyst - were tested to evaluate how the catalyst bed affects the surface reaction and the gas reaction. Results showed that the surface ignition temperature decreased as the fuel-air ratio increased, and it increased as the mixture velocity was raised. In the case of the CAT-1 consisting of Pd catalyst, the temperature of the catalyst bed was kept constant irrespective of the inlet temperature of the mixture when its temperature became 700-800℃.This is attributed to the phase change of Pd catalyst. Pd catalyst changed from the very active PdO to the non-active metal Pd when its temperature increases over 750℃. As a test result about effects of catalyst beds on the flame ignition, the CAT-3 consisting of Pd/Pt catalyst was revealed to have the lowest flame ignition temperature. The CAT-1 of Pd catalyst and the CAT-2 of Pt catalyst had nearly the same flame ignition temperature. Catalyst bed temperatures of CAT-1 and CAT-2 became over 1000 ℃, the maximum allowable temperature of Pd and Pt catalysts, soon after the flame ignites. However, the overheating of the catalyst bed of CAT-3 occurred when the inlet temperature increased further by 105 ℃ after the flame ignites. These results imply that CAT-3 is most favorable for the catalytically stabilized combustor. NOx emissions from the catalytically stabilized combustor increased as the inlet temperature of the mixture and the fuel-air ratio increased. It is attributed to the fact that...