Experimental and modeling study of 1-hexene oxidation behind reflected shock waves.

Abstract: The auto-ignition delay times ? _i of 1-C₆H₁₂/O₂/Ar mixtures have been measured between 1270 and 1700K using shock tube technique for 3 equivalence ratios (? =0.5, 1, and 1.5) at a pressure of about 0.2MPa. At higher temperatures (>1400K), the logarithm of ? _i varies linearly as a function of the temperature inverse for a given value of equivalence ratio. The apparent activation energy, E _a, is approximately equal to 230kJmol^?1. At lower temperature (<1400K), E _a strongly decreases and becomes equal to about 120kJmol^?1 around 1300K. A correlation between ? _i , reactant concentrations, and temperature behind reflected shock waves was proposed for each temperature range. These correlations give an estimation of ? _i with an accuracy better than 12%. A detailed chemical mechanism of the 1-hexene oxidation has been developed with the “EXGAS” program. The agreement between computed and measured values of ? _i was correct at high temperatures (>1400K). The major channels of the chemical species fluxes have been discussed: at low temperatures, 1-hexene is mainly consumed by retro-ene reaction to give propene and, in a smaller ratio, by unimolecular decomposition to give allyl and 1-propyl radicals. At high temperature, unimolecular decomposition becomes more important than retro-ene reaction. The change in E _a below 1400K is not explained by the model. The auto-ignition delay times of 1-hexene have been compared to those of other unsaturated hydrocarbons. For stoichiometric mixtures diluted by 99mol% of argon at a pressure of 200kPa, the shortest delays were obtained for 1-octene while the longest delays were obtained for propene. With iso-butene and ethylene, the delay times are closer to 1-hexene in the low temperature side and to propene in the high temperature one. [Copyright &y& Elsevier]