(178k) Mechanism Development for Combustion of Morpholine

With the emergence of biofuels, oxygen- and nitrogen-containing fuels are becoming of new interest in combustion science. The fuel additive morpholine (1-oxa-4-aza-cyclohexane) is appropriate to study relevant combustion chemistry features because in one molecule, it mixes structural features of cycloalkanes, ethers, and amines.

Our collaboration at the Advanced Light Source of Lawrence Berkeley National Laboratory has measured spatial profiles of mole fraction in a premixed flat flame under low-pressure, fuel-rich (phi=1.3) conditions [1]. We were able to identify a large number of radical and stable species in the flame. Based on mechanistic insights from experiments and modeling of cyclohexane flames [2], we proposed probable reaction paths that should occur in a mechanism for morpholine combustion.

Gaussian 03 [3], ideal-gas thermochemistry from a rigid-rotor/harmonic-oscillator representation, transition-state theory, Bimolecular Quantum-RRK reaction theory [4], and the PREMIX/CHEMKIN flat-flame codes [5,6] were used to develop a morpholine model quantitatively. The Complete Basis Set method CBS-QB3 was employed to obtain thermochemical and kinetics parameters for key species and reactions in the mechanism. For many reactions, rate constants are adapted from cyclohexane kinetics, corrected for heat of reaction and reaction path degeneracy. When compared to our experimental data provided, we find good correlation between the experimental species profiles and our predictions.

Acknowledgments. This work is supported by the Division of Chemical Sciences, Geosciences, and Biosciences, the Office of Basic Energy Sciences, the U. S. Department of Energy, in part under grants DE-FG02-91ER14192 (P.R.W.) and DE-FG02-01ER15180 (T.A.C.). Sandia is a multi-program laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the National Nuclear Security Administration under contract DE-AC04-94-AL85000. The Advanced Light Source is supported by the Director, Office of Science, Office of Basic Energy Sciences, Materials Sciences Division, of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231 at Lawrence Berkeley National Laboratory. Support is also provided by the Deutsche Forschungsgemeinschaft under contract Ko 1363/18-3 (A.L., P.O., U.S., K.K.-H).

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