VUV ABSORPTION DIAGNOSTIC FOR SHOCK-TUBE KINETICS STUDIES OF C2H4

A sensitive and quantitative absorption diagnostic has been developed for measurement of C2H4 in shock tube kinetics experiments. This diagn ostic has been calibrated from 300 to 2571 K at 1.2 atm in shock tube experiments, resulting in an absorption coefficient at 174.4 nm of k(a bs) = 3.11 x 10(5)/T[K]-51.0 cm-1 atm-1. The absorption coefficient fo r C2H2 at this wavelength was also measured over the same temperature and pressure range. Kinetics experiments were performed to measure the rate of ethylene decomposition at reflected shock conditions of 1600- 2300 K at 1.2 atm, with mixtures of 189-444 ppm C2H4 in argon. Sensiti vity analysis based on a comprehensive hydrocarbon mechanism confirmed that the rate of ethylene decomposition was significantly affected by the rate of only one reaction: C2H4 + M --> C2H2 + H-2 + M. The rate coefficient for this reaction near the low-pressure limit was determin ed to be k = 9.17 x 10(16) exp(-37780/T) cm3 . mol-1 . s-1 +/- 20% ove r the entire temperature range, in good agreement with past measuremen ts.