Shock tube studies of the N 2O/CH 4/CO/Ar and N 2O/C 2H 6/CO/Ar systems

Abstract

Reflected shock waves were used to heat N 2O/C 2H 6/CO/Ar and N 2O/CH 4/CO/Ar mixtures to temperatures of 1875–2855 K at total concentrations of 5 × 10 18 cm −3. Oxygen atom production was monitored via the flame band emission at 450 nm, and CO 2 production was observed at 4.27 μm. These data were then compared to the results of numerical integration of the rate equations, using rate constant and mechanistic information obtained in earlier studies of H 2 and CH 2O oxidation under similar conditions. For the C 2H 6 mixture, it was possible to achieve good agreement between these calculations and the observed data using only one additional reaction O+CH 3→CH 2O+OH The calculations were insensitive to the precise value of the rate constant used, but the results are consistent with recent high temperature literature values. For the CH 4 mixture, the best agreement was achieved using a recent high temperature value for O+CH 4→CH 3+OH The data indicated that this reaction has a markedly non-Arrhenius rate constant; use of a value based upon low temperature data gives results inconsistent with those observed. The CH 4 system was insensitive to any other methane reaction rate constant. There was some experimental evidence to suggest an unsuspected complexity in methyl radical decay channels at the lowest temperatures observed. The mechanism/rate constant combination used here was then applied to the analysis of literature data for CH 3 oxidation by O 2. This analysis was designed to obtain a value for the rate constant of CH 3+O 2→CH 2O+OH Results indicated that the most recent high temperature studies yield values consistent with the present analysis.