A chemical kinetics model for the fast ignition of syngas at lower temperatures and higher pressures
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From a recent set of shock-tube and flow reactor experiments (Petersen et al., 2007) it was shown that current, detailed CO/H 2 oxidation kinetics mechanisms over-predict by more than two orders of magnitude the ignition delay time of CO/H 2 mixtures at elevated pressure (20 atm) and temperatures below 1000 K. The current study shows that no reasonable changes to the gas-phase rate coefficients of any reactions in the current mechanisms result in significant improvement between model predictions and experimental measurements at these conditions. Pre-ignition pressure increases much larger than could be attributed to boundary layer effects have been measured in recent shock-tube data and are shown to accelerate the onset of the main ignition event. These pressure increases are likely due to earlier-than-expected deflagration and subsequent compression of the bulk gas mixture within the test region. The addition of the hydrogen peroxide formation reaction H 2 +O 2 +M=H 2 O 2 +M (R1) with a small rate coefficient provides excellent agreement between the models and both flow reactor and shock-tube data at high pressures and low temperatures, without disturbing the good agreement between models and data at all other temperatures and pressures. Including this reaction in the mechanisms may represent pressure-dependent catalytic wall reactions, which is discussed herein. The resulting, early accumulation of H 2 O 2 may help to explain the early reactivity in the shock-tube experiments. Good agreement with measurements from 640 to 940 K and 5 to 30 atm is achieved using an effective gas-phase three-body rate coefficient of k1=210 9 exp(-1500/T, K) cm 6 /mol 2 -s.
