A shock tube study of ignition delay in the combustion of ethylene

Ethylene combustion was investigated behind reflected shock waves. The experimental conditions covered a temperature range of 1000–1650 K, at pressures of 2, 10 and 18 atm, equivalence ratios of 3 and 1, for several mixture compositions using argon as the diluent (93%, 96% and 98% (vol)). In all experiments, dwell times were kept in the range of 7.55–7.85 ms by using a suitable argon–helium mixture as the driver gas. Ignition delay times were determined from the onset of visible broadband emission observed at the end plate of the shock tube. In selected experiments ignition delay times were also determined by simultaneous measurement of chemiluminescence emissions of CH* and OH*. In relatively concentrated ethylene/oxygen mixtures with 93% argon (vol), the results show an indiscernible difference between ignition delay times over the ranges of pressure and equivalence ratio tested. In more dilute mixtures (with 98% and 96% argon), longer ignition delay times were observed and there was a noticeable variation of delay times as a function of pressure; with an increase in pressure having the effect of shortening the delay time and an increase in the apparent activation energy. Modeling results using USC Mech II (Wang et al., 2007 [31]) based kinetic model, SERDP PAH model 0.1, developed by Wang and Colket, show good agreement with experiments under stoichiometric and fuel-rich conditions at low pressures. At high pressures for fuel-rich mixtures, optimized version of USC Mech II model (Wang et al., 2009 [36]) had to be used to produce good agreement between calculated ignition delay times and the experimental results. The results of this study are consistent with literature data. The present work extends the existing ethylene ignition delay experimental data set to high pressure and fuel-rich domain, the conditions that are critical for soot and polycyclic aromatic hydrocarbons (PAHs) formation.