The unimportance of the reaction H2 + N2O ⇆ H2O + N2: A shock-tube study using H2O time histories and ignition delay times

The hydrogen-nitrous oxide (H-2-N2O) system is of paramount importance in safety considerations for nuclear waste management and semiconductor manufacturing. For less-dilute H-2-N2O mixtures, a reaction of key importance in determining ignition delay times is the direct reaction between H-2 and N2O to give H2O and N-2, although this reaction has received only one direct investigation in the work of Kosarev et al. (2007). To examine the importance of the title reaction, new H2O time histories were obtained using a laser absorption technique at 1.39 pm in a mixture of 0.222% N2O/1.778% H-2/Ar between 1414 and 1811 K near 1.2 atm. Additionally, the ignition delay time measurements of Kosarev et al. (2007) were repeated using endwall emission and pressure diagnostics. The new datasets show excellent agreement with the predictions of a recent mechanism when the title reaction is reduced by a factor of 30 relative to the work of Kosarev et al. Furthermore, the accurate mechanism predictions of H-2-N2O ignition delay time data available in the literature (other than those of Kosarev et al.) were not degraded when the proposed value of k(1) = 7.0 x 10(13)exp(-16, 356/T) was used (k(1) in cm(3) mole(-1) s(-1), Tin K). This expression for k(1) should be viewed as an upper limit on the rate for the title reaction and should make the title reaction negligibly important in future NOx modeling efforts; the true value of k(1) is likely even lower than this expression. A factor of 2 uncertainty is assigned to this expression for k(1). Finally, it is recommended that the data of Kosarev et al. (2007) be neglected in future mechanism validations as these data appear to be inaccurate, in part due to non-ideal pressure rise effects and choice of emission diagnostic. (C) 2018 The Combustion Institute. Published by Elsevier Inc. All rights reserved.