Schematic Lean Hydrogen Combustion Modeling

The schematics compare combustion modeling for lean hydrocarbon (C_xH_y) and lean hydrogen flames across fidelity levels from DNS to LES and URANS, focusing on the impacts of differential diffusion in hydrogen flames (Le<1), absent in hydrocarbons (Le≈1).

In lean hydrogen flames, differential diffusion leads to regions with positively curved flames (towards the unburned mixture) showing local enrichment and super-adiabatic temperatures, and negatively curved regions exhibiting the opposite trends. This imbalance drives thermo-diffusive instabilities, enhancing flame speed and promoting local de-mixing into lean and rich zones. Hydrocarbon flames, with Le≈1, show no such differential diffusion effects.

The schematic highlights these phenomena, fully resolved in DNS, partially modeled in LES, and simplified in URANS, emphasizing the complexities of turbulent lean hydrogen combustion modeling.