A PYROLYSIS MECHANISM FOR AMMONIA

The mechanism of NH3 pyrolysis was investigated over a wide range of conditions behind reflected shock waves. Quantitative time‐history measurements of the species NH and NH2 were made using narrow‐linewidth laser absorption. These records were used to establish an improved model mechanism for ammonia pyrolysis. The risetime and peak concentrations of NH and NH2 in this experimental database have also been summarized graphically. Rate coefficients for several reactions which influence the NH and NH2 profiles were fitted in the temperature range 2200 K to 2800 K. The reaction and the corresponding best fit rate coefficients are as follows: (Formula Presented.) with a rate coefficient of 4.0 × 1013 exp(−3650/RT) cm3 mol−1 s−1, (Formula Presented.) with a rate coefficient of 1.5 × 1015T−0.5 cm3 mol−1 s−1 and (Formula Presented.) with a rate coefficient of 5.0 × 1013 exp(−10000/RT) cm3 mol−1 s−1. The uncertainty in rate coefficient magnitude in each case is estimated to be ±50%. The temperature dependences of these rate coefficients are based on previous estimates. The experimental data from four earlier measurements of the dissociation reaction (Formula Presented.) were reanalyzed in light of recent data for the rate of NH3 + H → NH21 + H2, and an improved rate coefficient of 2.2 × 1016 exp(−93470/RT) cm3 mol−1 s−1 in the temperature range 1740 to 3300 K was obtained. The uncertainty in the rate coefficient magnitude is estimated to be ± 15%. Copyright © 1990 John Wiley & Sons, Inc.