Comparative High Temperature Shock Tube Ignition of C1−C4 Primary Alcohols

The high temperature ignition of C1−C4 primary alcohols, methanol, ethanol, n -propanol, and n -butanol, is studied behind reflected shock waves. The experiments are carried out at pressures of 2, 10, and 12 atm with argon/oxygen ratios of 10, 15, and 20 under lean, ϕ = 0.5, stoichiometric, ϕ = 1, and rich, ϕ = 2, conditions between 1070 and 1760 K. It is observed that the ignition delay time data for ethanol, n -propanol, and n -butanol collapse under conditions of constant equivalence ratio, pressure, and dilution. The ignition delay times of methanol are comparable with the other alcohols but show a slightly lower activation energy than the other fuels. The observed collapse of the ignition delay times for the four alcohols under lean-to-stoichiometric conditions is comparable with recent observations by Veloo et al. (Veloo, P. S.; Wang, Y. L.; Egolfopoulos, F. N.; Westbrook, C. K. Combust. Flame 2010, 157, 1989−2004) that over a range of equivalence ratios less than one, methanol, ethanol, and n -butanol have similar laminar flame speeds. Measured ignition delay times for selected conditions are compared to simulated delay times using their corresponding chemical kinetic models developed in previous studies: methanol by Li et al. (Li, J.; Zhao, Z.; Kazakov, A.; Chaos, M.; Dryer, F.; Scire, J. Int. J. Chem. Kinet. 2007, 39, 109−136), ethanol by Marinov (Marinov, N. Int. J. Chem. Kinet. 1999, 31, 183−220), n -propanol by Johnson et al. (Johnson, M. V.; Goldsborough, S. S.; Serinyel, Z.; O’Toole, P.; Larkin, E.; Malley, G.; Curran, H. J. Energy Fuels 2009, 23, 5886−5898), and n -butanol by Sarathy et al. (Sarathy, S. M.; Thomson, M. J.; Togbé, C.; Dagaut, P.; Halter, F.; Mounaim-Rousselle, C. Combust. Flame 2009, 156, 852−864). The agreement of the various mechanisms with experiment is reasonable; however, the lower temperature ignition delay times for n -propanol and n -butanol tend to be longer than measured. The closest agreement between experiment and model predictions is observed for ethanol with the Marinov mechanism. Ignition delay time correlations for the alcohols are obtained by linear regression of the experimental data. This correlation method is also applied to the chemical kinetic mechanisms to obtain simplified expressions for their ignition delay times that allow a general assessment of their performance relative to experiment. Although sensitivity and reaction pathway analyses indicate similar modeling approaches for the four alcohols, the models do not capture the quantitative similarity observed in the experiment. These results will be useful in the process of developing a generalized chemical kinetic model for C1−C4 primary alcohol combustion as well as reduced models for combustion engineering.

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