Flame Structure of Ammonia/Hydrogen/Oxygen/Argon Mixtures at High Pressure

Abstract
The search of alternative fuels is one of the most important issues. Hydrogen is the most attractive one since its combustion products include only water. However, due to its specific properties wide implementation of hydrogen is not possible. There is an idea to use chemical carriers of hydrogen, for example, ammonia. The addition of hydrogen, which is the product of ammonia cracking, can improve the combustion characteristics of ammonia. The work presents experimental data on the structure of NH₃/H₂/O₂/Ar flames at 4 atm. Equivalence ratio values were 0.8, 1.0 and 1.2, NH₃/H₂ ratio – 1/1. Flame structure was measured with molecular beam mass spectrometry with soft electron impact ionization. In the experiments, flames were stabilized on the flat burner. Temperature profiles were measured with thin S-type thermocouples. Numerical simulations were performed with PREMIX code from CHEMKIN package. The comparison of the experimental and numerical data enabled to reveal the mechanism of NH₃/H₂ oxidation showing the best predictive capability. Experimental and numerical data showed that the nitrogen-containing species which are present in the post-flame zone are N₂ and NO whereas concentration of N₂O and NO₂ is negligible. It was revealed that in terms of NO reduction slightly rich conditions are more effective. In addition, the effect of equivalence ratio on the peak concentration of NO, N₂O and NO₂ was analyzed. Rich conditions appeared to be more effective to reduce peak concentrations of NO, N₂O and NO₂.

Keywords
ammonia, hydrogen, flame structure, mass-spectrometry
УДК 536.461

Flame Structure of Ammonia/Hydrogen/Oxygen/Argon Mixtures at High Pressure