Effect of Hydrogen-Enriched Syngas and Nitrogen Dilution on Ammonia Deflagration Characteristics at Moderate Pressure

This research investigates the impact of syngas, hydrogen-enriched syngas (H/C ratio), and nitrogen (N₂) diluent on the combustion characteristics of NH₃/air mixtures in a constant volume vessel. Pressure peak (p _max), combustion duration time (t _c), maximum rate of pressure rise (dp/dt)_max, and laminar burning velocity (S _L) were obtained at an initial pressure p ₀ = 3 bar, a temperature T = 300 K, and at various equivalence ratios ϕ = 0.8-1.3. The results indicate that increasing the syngas proportion and/or H/C ratio could enhance p _max, (dp/dt)_max, S _L, and shorten t _c. The reverse is true for the dilution of N₂ to the NH₃/syngas mixtures. The maximum value of S _L of NH₃/syngas/air mixture is nearly at ϕ = 1.1 for all cases in which S _L varies from 7.5 to 22 cm/s, increasing by 1.25 to 3.7-fold as compared to its values of NH₃ flame. Using Mei-Mech, the sensitive analysis shows the most dominant reactions for S _L of the stoichiometric NH₃/syngas/air mixtures, including (R1): H + O₂ = O + OH, (R15): H + O₂ (+M) = HO₂ (+M), (R76): NH₂ + NH = N₂H₃, and (R94): NH₂ + NH = N₂H₂ + H, where R1 and R15 exhibit the highest positive and negative sensitivity coefficients, respectively. Notably, in the case of H/C ratio effect, the net reaction rate of (R3): H₂ + OH = H₂O + H significantly increases, whereas it is less or negligible for the remaining reactions.