Résumé : Ammonia/hydrogen-fueled combustion represents a very promising solution for the futureenergy scenario. This study aims to shed light and understand the behavior of ammonia/hydrogen blends under flameless conditions. A first-of-its-kind experimental campaignwas conducted to test fuel flexibility for different ammonia/hydrogen blends in a flamelessburner, varying the air injector and the equivalence ratio. NO emissions increaseddrastically after injecting a small amount of NH3 in pure hydrogen (10% by volume). Anoptimum trade-off between NOx emission and ammonia slip was found when workingsufficiently close to stoichiometric conditions (ϕ=0.95). In general, a larger air injector(ID25) reduces the emissions, especially at ϕ=0.8. A well-stirred reactor network withexhaust recirculation was developed exchanging information with computational fluiddynamics (CFD) simulations, to model chemistry in diluted conditions. Such a simplifiedsystemwas then used in two ways: 1) to explain the experimental trends of NOx emissionsvarying the ammonia molar fraction within the fuel blend and 2) to perform an uncertaintyquantification study. A sensitivity study coupled with latin hypercube sampling (LHS) wasused to evaluate the impact of kinetic uncertainties on NOx prediction in a well-stirredreactor network model. The influence of the identified uncertainties was then tested inmore complex numerical models, such as Reynolds-averaged Navier–Stokes (RANS)simulations of the furnace. The major over-predictions of existing kinetic scheme was thenalleviated significantly, confirming the crucial role of detailed kinetic mechanisms foraccurate predictive simulations of NH3/H2 mixtures in flameless regime.