Experimental demonstration of in-situ cracked premixed swirl NH3-air flames

Abstract

This study investigates the in-situ thermo-catalytic cracking of ammonia (NH₃) and the combustion characteristics of the resulting cracked flame. A swirl-stabilized burner equipped with a novel multi-pass heat exchanger and a catalytic tube was employed to analyse NH₃ cracking and combustion. Five catalysts were evaluated, including three developed in-house‑ruthenium (Ru) and cobalt (Co) electroplated on stainless steel wire mesh, and Ru nanoparticles loaded onto sodium zeolite along with two commercially available alumina-based Ni and Ru pellets. The performance of thermal cracking is then compared to thermo-catalytic cracking. The cracking efficiency decreased inversely with NH₃ flow rate, from 70 % to 17 % at 773-813 K and 100 % to 60 % at 893–932 K, with Ru-based catalysts outperforming thermal cracking by 20 % at 35 SLPM of NH₃. At 773–813 K, both electroplated Ru and RuCo stainless steel mesh configurations performed similarly, indicating that catalyst contact time can be further optimised. The stability and emissions of the cracked flames were assessed at air flow rates of 100–200 SLPM. The cracking efficiencies of 54–58 %, 61–62 %, and 58–65 % were observed at 798–825 K, 836–857 K, and 878–901 K for cracker flow rates of 15, 20, and 25 SLPM respectively. Emissions analysis revealed increasing N₂O levels with higher air flow and NO peaks at an equivalence ratio between 0.74 and 0.83. Flame instabilities under lean conditions led to NH₃ slip. These findings highlight the need for catalyst optimisation to enhance NH₃ cracking efficiency, improve flame stability, and reduce emissions, advancing sustainable combustion technologies.