(513dr) The Influence of Ammonia-Blending on Flame Properties and Soot Formation in Co-Flow Methane Flames

There is renewed interest in ammonia (NH₃) as a carbon-free combustion fuel since it has the potential to be made renewably and yields N₂ and H₂O upon complete combustion. Because of narrow stability limits for the efficient burning of ammonia (NH₃), strategies for enhancing the stability of NH₃ combustion processes have been pursued, such as through co-firing with hydrocarbons. In this case soot formation becomes possible, and the influence of NH₃ on soot becomes relevant. Furthermore, few studies have numerically and experimentally analyzed the ability of chemical mechanisms to capture flame characteristics in atmospheric nonpremixed NH₃-CH₄ systems with large ratios of NH₃. In order to close these knowledge gaps, the influence of NH₃ on flame characteristics and soot formation were experimentally and computationally analyzed. To judge the suitability of various chemical mechanisms in capturing flame characteristics in NH₃-CH₄ blends, experimental targets including centerline temperatures and lift-off/flame heights were compared to values obtained from 2D simulations employing different chemical mechanisms. The most suitable mechanism was used to predict species and soot concentrations, which were compared to experimentally measured values. The results show that a nitrogen-chemistry mechanism developed by Glarborg et al. captures NH₃ flame characteristics better than the GRI mechanism developed for natural-gas combustion. NH₃ was also found to have strong chemical influence on suppressing soot formation, although the simulations were unable to capture the magnitude in soot reduction. Soot-relevant chemical pathway influenced by fuel-nitrogen and future areas of study are discussed.