Combustion characteristics and emissions of nitrogen oxides (NO, NO₂, N₂O) from spherically expanding laminar flames of ammonia–hydrogen blends

While ammonia (NH₃) and hydrogen (H₂) are promising carbon-free fuels, there are significant challenges presented by their combustion properties. Blending them can help mitigate some of these issues; however, the fundamental behaviors of these blends need to be well understood. A constant volume combustion chamber (CVCC) is used to study the emissions of nitrogen oxides (NO, NO₂, N₂O), laminar burning velocity (LBV), and intrinsic instabilities for H₂-NH₃ blends across a wide range of equivalence ratios (Φ = 0.5 to 1.5) and volume fractions of H₂ in the blends (0% to 50%). Measurements of LBV are consistent with existing data where available. The largest NO_x and N₂O emissions are found at lean conditions and decrease significantly for rich mixtures. NO_x emissions tend to increase with H₂ fractions in fuel for lean mixtures. Intrinsic instabilities are more prominent at lean conditions and heavily influenced by the amount of H₂ in the blend.