Composition stratification in ammonia-hydrogen flames

Hydrogen fuel provides a potential path forward for carbon-free combustion, but can be challenging to store and transport. Recent work has focused on using ammonia as an energy vector that can be cracked on-the-fly to produce hydrogen as needed. Transient variation in the cracking of ammonia introduces fluctuations in the ammonia-hydrogen mixture downstream. In this study, the effect of temporal and spatial heterogeneity of partially cracked ammonia-hydrogen-air mixtures on the flame structure is studied. Direct Numerical Simulations are employed to study laminar and turbulent flames with spatially and temporally varying inlet conditions mimicking partial cracking. In particular, the inlet fuel composition is varied by changing the local ratio of ammonia to hydrogen. The amplitude and lengthscale of these variations are selected relative to the flame thickness. The response of flame properties, such as the local flame speed, is analyzed based on the extent of cracking.