Measurements of flame temperatures and burning velocities of laminar NH 3 / N 2 / H 2 –air flames in a slot burner using 2D Rayleigh thermometry

Abstract Ammonia ( NH 3 ) has emerged as a carbon-free fuel with great potential for long-term and easily transportable energy storage, offering a means to address the intermittency and geographical limitations of renewable energy sources. However, its low chemical reactivity requires flame enhancement strategies such as partial cracking, fuel blending, preheating, or plasma activation. Although these approaches improve ignition and stability, they can also influence NO formation, highlighting the need for a detailed understanding of flame structure, temperature distribution, and intermediate species. In this study, laminar premixed flames are stabilized on a slot burner over a range of equivalence ratios and fuel compositions. Flame enhancement is achieved using NH 3 / N 2 / H 2 mixtures that mimic partially cracked ammonia. Single-shot two-dimensional Rayleigh scattering thermometry at 266 nm is employed to measure the flame temperature fields, benefiting from enhanced Rayleigh scattering cross sections at this wavelength. The Rayleigh scattering cross section of NH 3 relative to N 2 is determined experimentally to enable accurate temperature calculation. The resulting 2D temperature maps are used to identify flame fronts, from which temperature profiles along the flame-normal direction are extracted to evaluate the thermal flame thickness. The reconstructed flame cone provides the mean flame surface area and local laminar burning speeds. Experimental results obtained for various mixtures and equivalence ratios are compared with one-dimensional flame simulations and data reported in the literature.