Experimental and numerical investigation of non-premixed ammonia flames stabilized on a heated slot burner

n this study, non-premixed laminar ammonia/air flames are investigated using a custom-designed heated
slot burner developed at KIT. This innovative setup enables investigations into ammonia decomposition and
pollutant formation processes through in-situ diagnostics, numerical simulations, and global performance
analyses, providing a unique dataset. Experiments are conducted at three oven temperatures (T = 1073 K,
1123 K, and 1173 K) and two thermal loads (0.2 and 0.6 kW) at a global equivalence ratio of 𝛷 = 1.
Inlet temperatures, as well as qualitative insights into NH*, NH$_2$*, and OH* along the flame are obtained
using thermocouples and emission spectroscopy. To assess global combustion characteristics, gas analyzers
measure exhaust species, including NO, NO$_2$, N$_2$O, NH$_3$, and O$_2$. The experimental setup is reconstructed
in two dimensions for numerical simulations using an in-house OpenFOAM solver. Flame and emission
characteristics are investigated for different operating conditions and chemical mechanisms. While experiments
and simulations agree well regarding flame length, flame stability, and chemiluminescence profiles, some
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deviations in exhaust gas emissions remain. These are attributed to experimental uncertainty from the
assumption of flow symmetry, boundary conditions, and uncertainty due to the choice of chemical reaction
mechanism at elevated temperatures. Emissions are strongly influenced by oven temperature and flow velocity,
with lowest NH$_3$, N$_2$O, and NO$_x$ levels observed at high oven temperatures. The non-premixed configuration
achieves NO$_x$ emissions down to 335 ppmv at 𝛷 = 1, significantly below values from premixed combustion,
which typically exceed several thousand ppmv. Pathway analysis reveals that the investigated reaction
mechanisms predict routes with different relative contributions to NO production, but provide similar trends
for NO consumption. The results highlight the suitability of the platform for systematic ammonia combustion
studies and the potential of non-premixed strategies for NO$_x$ mitigation