Book Description

The results of an investigation of the decomposition kinetics of nitric oxide at high temperatures are presented. Mixtures of nitric oxide, molecular hydrogen, and inert gas (either argon or krypton) were heated by incident shock waves in a shock tube. The subsequent chemical reaction was monitored by using two high-speed infrared detectors to measure infrared emission from the 5.3-micron fundamental vibration-rotation band of NO and the 6.3-micron v2-band of water vapor. Each detection system was calibrated to determine the response to NO and to H2O, which permits the calculation of NO and H2O concentrations from the measured emission records. Post-shock temperatures ranged from 2400 K to 4200 K. The pressure behind the incident shock was between 0.25 and 0.62 atm in all tests. The nominal initial NO:H2 ratios of the test gases were 1:2, 1:1, and 2:1 with the inert diluent making up approximately 90% of the test gas for all experiments. A seventeen-reaction kinetic model of the reacting flow was used to calculate theoretical NO and H2O concentration histories. Kinetic calculations indicate the rate-limiting reaction for NO decomposition for the experimental conditions of this study is the reaciton of NO with atomic hydrogen, (1) NO + H [right arrow] N + OH. The chemical rate constant for reaction (1), k1, was determined for each experiment by optimizing the agreement between calculated and measured emission records for NO and H2O. A thorough sensitivity analysis confirmed that calculated NO and H2O records are more sensitive to small changes in K1 than to variations in the rate constants of the other sixteen reactions within the uncertainty limits of each. The rate constant for the reaction NO + N [right arrow] N + OH which best fits the data from 21 shock-tube experiments was found to be k1 = 2.22 x 1014 − 0.08 exp( -50.5/RT) cm3/mole-sec in the temperature range 2400 - 4200 K. These data provide useful information for modelling the decomposition of NO at high temperatures.