In order to investigate the ignition characteristic of ethylene combustion at low-to-medium temperature, contem-porary detailed kinetic mechanisms for ethylene combustion, including AramcoMech_1.3 mechanism, Creck mechanism, Glarborg's mechanism, San Diego (UCSD) mechanism and Wang's mechanism, were used to simulate ignition delay times of ethylene combustion by Chemkin Pro software reflected shock tube model and closed homogeneous reactor under the as-sumption of constant-volume, homogeneous and adiabatic conditions. Simulated ignition delay times of ethylene combustion using these mechanisms disagree with the experimental data from literatures at low-to-medium temperature.
Sensitivity analysis was carried out to identify the controlling steps of C₂H₄ ignition at 800~1300 K. The sensitivity of ig-nition delay time was calculated by the formula Sensitivity=[τ_ign(2k_i)-τ_ign(k_i)]/τ_ign(k_i)×100%. Here τ_ign(k_i) is ignition delay time based on the original combustion mechanism, τ_ign(2k_i) is ignition delay time simulated using this mechanism in which the rate constant of reaction i is doubled through multiplying the pre-exponential factor of reaction i by 2. It was demonstrated that C₂H₃+O₂=CH₂CHO+O(R1), C₂H₃+O₂=CH₂O+HCO(R2) have great sensitivity to the ignition of C₂H₄ over a wide temperature range, while those reactions involved HO₂ (including H₂-O₂ and C₂H₄+HO₂ system) are important for C₂H₄ ignition process at low temperature.
By modifying these rate constants of R1 and R2 with more accurate calculated results and adding C₂H₃+O₂=C₂H₃OO reaction and those reactions involved C₂H₄+HO₂ system, one revised mechanism (UCSD-R2) was obtained. UCSD-R2 mechanism can produce better agreement with recent ethylene ignition delay time experimental data from literatures at low-to-medium temperature compared with UCSD mechanism.
When UCSD-R2 mechanism was adopted to simulate the ignition delay time of ethylene combustion, the first stage ignition delay time at low temperature (800~950 K) and negative temperature coefficient at medium temperature (950~1100 K) were found. They were explained by using sensitivity analysis and rate-of-production analysis. The method of rate-of-production analysis can be employed to calculate the contribution of each reaction to the production and consumption of every species or to calculate total rate-of-production of every species, by Chemkin Pro software closed homogeneous reactor under the assumption of constant-volume, homogeneous and adiabatic conditions. It was demonstrated that C₂H₄+HO₂ system can shorten the ignition delay time obviously, the production and consumption of HO₂ radical play a significant role for first stage ignition of C₂H₄ at low temperature, the consumption of C₂H₃ radical results in the negative temperature coefficient at medium temperature.

Key words: ethylene, low-to-medium temperature, ignition delay time, first stage ignition, negative temperature coefficient, mechanism