IR laser absorption diagnostic for C₂H₄ in shock tube kinetics studies

Abstract

An IR laser absorption diagnostic has been further developed for accurate and sensitive time-resolved measurements of ethylene in shock tube kinetic experiments. The diagnostic utilizes the P14 line of a tunable CO 2 gas laser at 10.532 μm (the (0 0 1) → (1 0 0) vibrational band) and achieves improved signal-to-noise ratio by using IR photovoltaic detectors and accurate identification of the P14 line via an MIR wavemeter. Ethylene absorption cross sections were measured over 643-1959 K and 0.3-18.6 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 1.2-18.6 atm. By measuring ethylene decomposition time histories at high-temperature conditions (1519-1895 K, 2.0-2.8 atm) behind reflected shocks, the rate coefficient of the dominant elementary reaction C 2 H 4 + M → C 2 H 2 + H 2 + M was determined to be k 1 = (2.6 ± 0.5) × 10 16 exp(−34,130/T , K) cm 3 mol −1 s −1 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. C 2012 Wiley Periodicals, Inc. Int J Chem

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“…However, we consider this to be implausible. Firstly, there is a ~100 % difference between the green and violet curves at t = 150 μs, which could not have been caused by a mere 13 K (or 0.97 %) change in temperature, from 1339 to 1352 K. Secondly, evidence from multiple sources [11,23,25,[32][33][34] describing the pyrolysis of various stable hydrocarbon molecules predisposes the existence of monotonic-only behaviour with time, in contrast to what is otherwise seen in the two traces of Fig. 8.…”

Shock tube measurements of 3-pentanone pyrolysis and oxidation

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Shock tube and modeling study of 2,7-dimethyloctane pyrolysis and oxidation

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