NOx Emission Characteristics of a Catalytic Combustor Under High-Temperature Conditions

Abstract

A catalytic combustor concept with short catalyst segments and a thermal reactor is investigated with regard to NO, production of this concept under high-temperature conditions. The maximum combustor exit temperature was more than 1800 K with catalyst temperatures below 1300 K. For combustion of iso-octane, NO emissions of 4 ppm (day. 15% 02) at a flame temperature of 1800 K were measured. No significant influence of catalyst length, reference velocity and overall residence time on NO" emissions was observed.Additionally, the test combustor was fuelled with commercial diesel and kerosene (Jet-A). In this case, NO emissions were noticeable higher due to fuel-bound nitrogen. The emissions measured were for diesel, 12 ppm, and for kerosene, 7 ppm, (each dry, 15% 02), again at a flame temperature of 1800 K. To evaluate the conversion ratio of fuel-bound nitrogen to NO,, isooctane was doped with various amounts of ammonia and metyhlamine. The conversion rates were 70 to 90%, with a slight tendency to lower values (50%) for nitrogen mass fractions above 0.1%.Considering the NO emission level of actual premix burners, the lower emission value of the presented catalytic combustor results from a perfect premixed plug-flow combustion system incorporating a catalyst herein and not from a specific advantage of the principle of catalytic combustion itself. Again similar to a premix-combustor are the NO emission characteristics in the case of lean combustion of nitrogen bound fuels, which yield very high conversion rates.