Numerical Study of Buoyancy and Flame Characteristics of Ammonia-Air Flames

Abstract There is growing interest in ammonia, NH3, as a zero-carbon fuel for use in transportation as part of broader decarbonization efforts. Ammonia has several advantages as an alternative fuel, including an existing global infrastructure and the ability to be stored as a liquid at room temperature and moderate pressures, thereby increasing its volumetric energy density relative to hydrogen. However, ammonia has a very slow flame speed and can be challenging to ignite. There are growing efforts to develop numerical models of ammonia combustion. However, difficulties still remain to match experimental validation data. The low flame speeds of ammonia flames result in significant buoyancy effects, but buoyancy is neglected in standard modeling and analysis approaches. The buoyancy also affects the flame shape, and therefore can affect the flame speed derived from constant volume combustion chamber (CVCC) experiments. This study examines how well different computational fluid dynamics (CFD) modeling setups are able to capture the effects of buoyancy on ammonia flames, and the sensitivity of flame speeds derived from the CVCC simulations to post-processing and simulation parameters.