Measurement and Chemical Kinetics Modeling of Shock-Induced Ignition of Ethanol-Air Mixtures

A detailed kinetics model for the thermal oxidation of ethanol air mixtures at intermediate temperatures and high pressures is proposed and validated against ignition delay times measured in a shock tube under stoichiometric conditions at 10, 30, and 50 bar and for lean mixtures (phi = 0.3) at 30 bar in the 650-1220 K temperature range. The measurements showed a typical decrease of the ignition delay at low temperatures and a reduced sensitivity to pressure for higher pressures. All data were scaled to 30 bar by a multiple linear regression, yielding tau = tau(30)(p/30)(-0.88). A temperature dependence of tau/(p/bar)(-0.88) = 10(-3.21) exp(139 kJ/mol/RT) mu s was derived for the stoichiometric mixture. The chemical kinetics model was built upon sub-mechanisms for ethanol (Marinov, N. M. Int. J. Chem. Kinet. 1999, 31, 183-220) and C-3 oxidation (Konnov, A. A. Combust. Flame 2009, 156, 2093-2105). Additional key reactions obtained from computational chemistry were included. The model was validated in the 650-1600 K temperature range at stoichiometric composition for 10, 30, and 50 bar, at an equivalence ratio phi = 0.3 for 30 bar, and in the 1200-1600 K range at 0.25 <= phi <= 2.0 in the 2.0-4.6 bar pressure range by comparing the predictions against these measurements and models of Dunphy and Simmie(Dunphy, M. P.; Simmie, J. M. J. Chem. Soc., Faraday Trans. 1991, 87, 1691-1696). Sensitivity coefficients for temperature and OH, H2O2, and C2H5OH concentrations were determined using a time-dependent homogeneous reactor assumption at 800, 950, and 1100 K. The sensitivity analysis identified a set of important reactions involving hydrogenatom abstraction from the ethanol molecule by the hydroperoxy radical (HO2), giving CH3CHOH, acetaldehyde, and H2O2. For higher pressures, the model presents good agreement with the temperature dependence. At lower pressures, the model overpredicts the value of the apparent ignition delay activation energy obtained from the measurements by 34%. Overall, the model predicts well the global trend of ignition delay times on pressure.