Effect analysis on thermal performance enhancement and NOx emissions reduction in hydrogen/ammonia-powered micro-combustors with porous media based on multi-field synergy theory

Micro-combustors utilizing carbon-free hydrogen/ammonia blends represent critical technologies for decarbonizing portable renewable energy devices. In this work, three-dimensional numerical simulations were firstly employed to evaluate the effect of ammonia blended ratio(χ) across three combustor configurations: without porous medium (C-R), fully filled with porous medium (C-F), and partially filled with an innovative annular porous medium (C-P). Results indicate that increasing χ shifts flames downstream improves outer wall temperature uniformity and reduces NOx emissions. Critically, at χ = 90 %, the combustor C-P demonstrates substantial performance gains compared to reference combustor C-R: a 69.8 K increase in mean outer wall temperature, 25.9 % higher radiation efficiency and 44.7 % lower NOx emissions. Leveraging combustor C-P's superiority, field synergy analysis was uniquely applied to optimize its key parameters, revealing maximum radiation efficiency at porosity of 0.8 and minimal NOx emissions at inner diameter (non-porous zone) of 0.9 mm. This work establishes two key innovations: 1)an annular porous medium design specifically tailored for high ammonia blends; 2)using field synergy theory to elucidate fundamental mechanisms governing multi-field interactions in porous media. The optimized combustor C-P delivers exceptional thermal-radiative performance with concurrently reduced NOx emissions under high-χ conditions. These advancements were useful for realizing high-performance, low-emission micro-power generation essential for next-generation portable renewable energy applications.