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Stability, Reactive Structures, and Emissions of Cracked Ammonia and NH3-H2 Mixtures in a Semi-Industrial Furnace under MILD Conditions

par Rahmani, Ebrahim ;Cid Rodríguez, Natalia ;Kamal, Muhammad Mustafa ;Coussement, Axel ;Parente, Alessandro ;Lubrano Lavadera, Marco
Référence 15th European Conference on Industrial Furnaces and Boilers
Publication Publié, 2026-04-07

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Résumé :

Ammonia (NH3) is a carbon-free fuel with strong potential for decarbonizing high-temperature energy systems. However, its practical application is challenged by poor reactivity, low flame stability, and high NOₓ emissions. A common strategy to overcome these limitations is enriching NH3 with hydrogen (H2), which improves stability but often makes NOₓ formation worse. Alternatively, cracked NH3, consisting mainly of H2 and N2, has been proposed as a self-contained route to enhance reactivity while avoiding external H2 supply. However, both these strategies, similar to other combustion-intensity enhancement approaches for NH3, tend to increase NOₓ emissions, but these can be effectively mitigated in regimes such as Moderate or Intense Low-Oxygen Dilution (MILD) combustion. This study investigates the combustion behavior of pure, partially cracked, and fully cracked NH3 and compares it with blended NH₃-H₂ mixtures under MILD conditions in a semi-industrial reverse-flow furnace at stochiometric conditions. The experiments were conducted at constant thermal input and furnace temperature to enable a direct comparison between cracked NH3 and NH3-H2 mixtures at matched inlet NH3 fractions. The results indicate that cracked NH3 systematically yields lower NOₓ emissions and NH3 slip than NH3-H2 mixtures. MILD operation leads to low NOₓ emissions and distributed reaction zones but high NH3 slip, whereas decreasing inlet NH3 fraction promotes more localized flame structures and modifies emission behavior. For both fuel strategies, NO emissions exhibit a non-monotonic dependence on the inlet NH₃ fraction, peaking at 20% NH₃ fraction, while NO2 dominates total NOₓ at high NH3 fractions (≥60%) and decreases progressively with increasing H2 content.