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 (<i>p</i> _max), combustion duration time (<i>t</i> _c), maximum rate of pressure rise (d<i>p</i>/d<i>t</i>)_max, and laminar burning velocity (<i>S</i> _L) were obtained at an initial pressure <i>p</i> ₀ = 3 bar, a temperature <i>T</i> = 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 <i>p</i> _max, (d<i>p</i>/d<i>t</i>)_max, <i>S</i> _L, and shorten <i>t</i> _c. The reverse is true for the dilution of N₂ to the NH₃/syngas mixtures. The maximum value of <i>S</i> _L of NH₃/syngas/air mixture is nearly at ϕ = 1.1 for all cases in which <i>S</i> _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 <i>S</i> _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.