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N. Chaumeix; S. Pichon; ; C.E. Paillard

The first part of the present work is to validate a detailed kinetic mechanism for the oxidation ofhydrogen ? methane ? air mixtures in a detonation waves. A series of experiments on auto-ignitiondelay times have been performed by shock tube technique coupled with emission spectrometry for H2 /CH4 / O2 mixtures highly diluted in argon. The CH4/H2 ratio was varied from 0 to 4 and theequivalence ratio from 0.4 up to 1. The temperature range was from 1250 K to 2000 K and thepressure behind reflected shock waves was between 0.15 and 1.6 MPa. A correlation was proposedbetween temperature (K), concentration of chemical species (mol m-3) and ignition delay times. Theexperimental auto-ignition delay times were compared to the modelled ones using four differentmechanisms from the literature: GRI [22], Marinov et al. [23], Hughes et al. [24], Konnov [25]. Alarge discrepancy was generally found between the different models. The Konnov?s model thatpredicted auto-ignition delay times close to the measured ones has been selected to calculate theignition delay time in the detonation waves. The second part of the study concerned the experimentaldetermination of the detonation properties, namely the detonation velocity and the cell size. The effectof the initial composition, hydrogen to methane ratio and the amount of oxygen in the mixture, as wellas the initial pressure on the detonation velocity and on the cell size were investigated. The ratio ofmethane / (methane + hydrogen) varied between 0 and 0.6 for 2 different equivalence ratio (0.75 and1) while the initial pressure was fixed to 10 kPa. A correlation was established between thecharacteristic cell size and the ignition delay time behind the leading shock of the detonation. It wasclearly showed that methane has an important inhibitor effect on the detonation of these combustiblemixtures.

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