Ammonia oxidation in an arc-heated flow reactor

Abstract

The over-all kinetics of the gas-phase oxidation of ammonia has been investigated in anarc-heated flow reactor, over a temperature range of 1106°–1377°K. The fuel equivalence ratio ranged from 0.53 to 4.97, with the reactor operated at atmospheric pressure. Ammonia and oxygen were added to an argon stream heated by a DC plasma torch, and the reaction zone was distributed through a zirconia reactor duct. Concentration profiles through the distributed reaction zone were obtained with a water-cooled stainless-steel sampling probe, with mass-spectrometric gas analysis. Temperature profiles were obtained with a ceramic coated W-5% Re/W-26% Re thermocouple. Reaction-rate constant and reaction orders for the over-all reaction were determined by a multiple linear regression analysis. The ammonia oxidation process was found experimentally to proceed according to the expression -d[NH3]/dt=k[NH3]0.86±.08[O2]1.04±.13, k=4.9×1014exp[-(39,031±5,500)]/RT (cc0.9/mole0.9sec). These over-all kinetic results are in general agreement with other reacting flow and shock-tube studies, but differ from earlier studies in static reactors. Further results of the present study indicate that nitrogen and water vapor were the major stable product species under the conditions investigated. In particular, no NO, NO2, or N2O were detected in the reaction zone by the mass spectrometer. In fuel-rich mixtures, decomposition of the unreacted ammonia was not detected. The profiles indicated that wall reaction was not important in contributing to the rate process in the core of the flow.