An experimental and modeling study of ethylene–air combustion over a wide temperature range

Abstract

Ethylene is an important intermediate during oxidation and pyrolysis process of higher hydrocarbons, and also serves as a fuel under practical engines. An experimental and modeling study is performed to investigate the combustion chemistry of ethylene–air mixtures under a wide range of conditions. The shock tube experiments are conducted at pressures of 1, 4, 10 and 19 atm with equivalence ratios of 0.5, 1.0 and 2.0 to determine the ignition delay times by measuring the emission signal of excited methylidyne (CH*). The ignition data under 10 and 19 atm both span a wide temperature range varying from a low temperature of 721 K to a high temperature of 1320 K. No typical negative-temperature-coefficient is observed, but the ignition at low temperatures is much shorter than the extrapolation at high temperatures. Simulations are performed and compared to the experiments using contemporary core models with consideration of a linear pressure rise of 3% /ms, but no simulation could predict the ignition trend under low-to-intermediate temperatures. Therefore, a detailed model of ethylene oxidation is proposed based on AramcoMech2.0 in the present work.The modeling behavior at high temperatures is improved by revision of addition reaction between ethylene and oxygen atom (C2H4+Ӧ). The modeling behavior at the region of low-to-intermediate temperatures is improved by detailed updating of β-hydroxyethyl oxidation (PĊ2H4OH+O2). The effect of reactions at the potential energy surface of C2H4+HȮ2 and Ċ2H5+O2 is determined, and the second oxygen addition (Ċ2H4OOH+O2) is added into current model. The present model is extensively validated by ignition delay times, concentration profiles of stable species in jet-stirred reactors and laminar flame speed under various test conditions. Sensitivity analyses are carried out to identify the dominant reactions during the auto-ignition process and laminar premixed flame propagation. Additional simulations are performed to investigate the effect of model modifications on predictions of ethane and ethanol oxidation. The present model slightly promotes the low-temperature ignition of both ethane and ethanol, and its prediction on the concentration profiles of some stable species is also improved. The proposed model of ethylene oxidation can be used as a cornerstone to develop models of larger hydrocarbon fuels.