RICH AMMONIA FLAME SHAPES AND NO RELAXATION: FACILITY DEVELOPMENT AND CHARACTERIZATION

Abstract

Ammonia (NH3) is a carbon-free fuel and hydrogen carrier; however, the presence of fuel-bound nitrogen has the potential to produce substantial nitrous oxide (NOx) emissions. Staged combustion, starting with a rich fuel reaction/decomposition zone, has the potential for low NO levels but can also lead to very significant NO levels if not designed correctly. This staged strategy takes advantage of the fact that equilibrium NO emissions from rich NH3 combustion are quite low. However, significant NO levels are still produced in rich flames and require a specific relaxation time, which can be quite long, to drop down to equilibrium levels. Thus, a key design attribute for ammonia combustors is sufficient residence time for NO relaxation. Given an overall combustor length, the NO relaxation zone is a direct function of the rich flame length, which can be quite long. Moreover, the flame length is a strong function of the flame stabilization location, e.g., the flame length in an annular swirling flow can easily vary by a factor of two depending upon the flame stabilization location. Moreover, swirl flames exhibit very long "tornado" configurations in certain conditions. For these reasons, even under conditions where the flame is stabilized, its configuration will dramatically influence the amount of time for the NO relaxation process. This paper introduces a test rig to explore flame configurations and post-flame NO relaxation for ammonia combustion. The rig features a modular swirler, a long primary stage, and a traversing emissions probe. The paper presents images of flame configurations over a range of conditions and maps different bifurcations in flame configuration.