Numerical investigation of blended hydrogen/ammonia combustion in a bluff-body and swirl stabilized micro combustor for micropower applications

Micro combustion offers a promising pathway for powering small-scale devices, yet achieving stable flame propagation at this scale remains challenging. Ammonia, a carbon-free fuel, has emerged as a potential candidate, but its intrinsic combustion characteristics pose challenges. Blending ammonia with hydrogen enhances its combustion properties. This study investigates the performance of a hydrogen/ammonia micro combustor, stabilized by both a bluff-body and swirling flows, under various flow parameters and bluff-body configurations. Key findings indicate that increasing the inlet mass flow rate and ammonia-to-hydrogen ratio enhances thermal efficiency and exhaust gas temperatures, albeit at the cost of decreased radiation efficiency. Furthermore, increasing the equivalence ratio diminishes thermal efficiency and reduces emissions, while oxygen enrichment significantly boosts combustion and radiation efficiencies, as well as mean outer wall temperatures, despite a decrease in thermal efficiency. Additionally, the size and half-angle of the bluff-body emerge as critical factors affecting combustion and thermal efficiencies. Larger bluff-bodies enhance combustion and radiation efficiencies, leading to more uniform wall temperatures. On the other hand, emissions decrease with increasing bluff-body size but increase with greater half-angles. These insights hold substantial implications for the design and optimization of micro combustion-based power generators, particularly in the pursuit of minimizing carbon emissions.