Oxidation and Pyrolysis of Ethylene in Shock Waves

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Abstract
The oxidation of C2H4 has been studied in a shock tube by monitoring the infrared emissions from CO and CO2 and the visible emission from CH*. The characteristics of this oxidation closely resemble oxidations of C2H2 and C2H2+H2. The induction periods and exponential time constants for the early phase of CO formation are the same for all three oxidations over the temperature range 1500°—2300°K and lead to a common activation energy of 17±1 kcal/mole. Above 1800°K, the C2H4–O2 reaction, in its early stages, consists mainly of the pyrolysis of C2H4, and the concurrent oxidation of pyrolysis products, C2H2 and H2. Later in the reaction, and more prominently so at lower temperatures, the reaction changes in character to a slower direct oxidation of C2H4. The relative rates of CO and CO2 production in both C2H4–O2 and C2H2–O2 reactions are reported as a function of temperature. The pyrolysis of C2H4 has also been studied in the shock tube by an infrared technique and its rates determined between 1950° and 2250°K. The results are in good agreement with previous work and give an activation energy of 52 kcal/mole for the reaction. The oxidation results would indicate that C2H4, above 1800°K, decomposes mainly by a molecular rather than a radical mechanism.

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