Measuring the ignition delay time for hydrogen-oxygen mixtures behind the front of an incident shock wave

The delay time τ has been measured for the formation of the ^·OH radical in igniting hydrogenoxygen mixtures diluted with argon (79–97%). The experiments have been carried out under incident shock wave conditions at temperatures of 900–3000 K, pressures of 0.5–2.5 atm, and H₂/O₂ ratios of 0.2–20. The dependence of τ on the pressure P _s of the stoichiometric part of the combustible mixture (2H₂-O₂) has been investigated for different mixture compositions. Under the above conditions, τ depends practically linearly on 1/P _s at P _s = 0.02−0.1 atm, irrespective of the mixture composition. This allows the measured τ data to be converted to one quantity, τP _s. The temperature dependence of τP _s in the P _s range from 0.02 to 0.1 atm is Arrhenius-like. For the hydrogen-rich mixtures (H₂/O₂ = 2–20), this dependence appears as τP _s= 0.057 + 0.0256exp(7470/T) μs atm; for the lean mixtures (H₂/O₂ = 0.125–1), τP _s = 0.021 + 0.0069exp(7470/T) μs atm. The length of the shock-heated gas plug in the incident shock wave poses limitations on the ignition delay time measurements at T < 900 K.