Abstract
An IR laser absorption diagnostic has been further developed for accurate and sensitive timeβresolved measurements of ethylene in shock tube kinetic experiments. The diagnostic utilizes the P14 line of a tunable CO~2~ gas laser at 10.532 ΞΌm (the (0 0 1) β (1 0 0) vibrational band) and achieves improved signalβtoβnoise ratio by using IR photovoltaic detectors and accurate identification of the P14 line via an MIR wavemeter. Ethylene absorption cross sections were measured over 643β1959 K and 0.3β18.6 atm behind both incident and reflected shock waves, showing evident exponential decay with temperature. Very weak pressure dependence was observed over the pressure range of 1.2β18.6 atm. By measuring ethylene decomposition time histories at highβtemperature conditions (1519β1895 K, 2.0β2.8 atm) behind reflected shocks, the rate coefficient of the dominant elementary reaction C~2~H~4~ + M β C~2~H~2~ + H~2~ + M was determined to be k~1~ = (2.6 Β± 0.5) Γ 10^16^exp(β34,130/T, K) cm^3^ mol^β1^ s^β1^ with low data scatter. Ethylene concentration time histories were also measured during the oxidation of 0.5% C~2~H~4~/O~2~/Ar mixtures varying in equivalence ratio from 0.25 to 2. Initial reflected shock conditions ranged from 1267 to 1440 K and 2.95 to 3.45 atm. The measured time histories were compared to the modeled predictions of four ethylene oxidation mechanisms, showing excellent agreement with the Ranzi et al. mechanism (updated in 2011). This diagnostic scheme provides a promising tool for the study and validation of detailed hydrocarbon pyrolysis and oxidation mechanisms of fuel surrogates and realistic fuels. Β© 2012 Wiley Periodicals, Inc. Int J Chem Kinet 44: 423β432, 2012