Laminar Burning Velocity and Development of a Chemical Kinetic Model for Small Oxygenated Fuels

Abstract: The thesis work was performed with the aim of increasing knowledge and understanding of the combustion of oxygenated fuels and intermediates. This was accomplished in two steps: experimental measurements of the laminar burning velocity to expand current databases and development of a reaction mechanism.
In the first part of the project, the laminar burning velocity of oxygenated fuels and intermediates was measured using the heat flux method. Emphasis was placed on extending the experimental database for fuels and intermediates with limited or scattered experimental data. The laminar burning velocities of acetaldehyde and methyl formate were investigated experimentally and were compared with kinetic mechanisms from the literature.
In addition, temperature dependence of the laminar burning velocity, expressed as SL=SL0(T/T0)α, was investigated both numerically and experimentally. It was found that a kinetic mechanism can overpredict the experimental laminar burning velocity yet still display good agreement with the experimentally determined temperature dependence. To investigate the temperature dependence further a sensitivity analysis of the α coefficient was performed. The sensitivity analysis provided a different view of the chemistry involved compared to the sensitivity of the laminar burning velocity.
In the second part of the project, a contemporary detailed kinetic mechanism for the combustion of small oxygenated fuels and intermediates was developed. The mechanism was developed with the version 0.6 of the Konnov mechanism as a starting point. Reactions involved in the combustion of formaldehyde, methanol and acetic acid were reviewed and the most reliable rate constants were selected. The new kinetic mechanism was validated against experimental data from the literature covering a wide range of conditions including shock tube and flow reactors as well as burner stabilized and freely propagating flames.
The sub mechanism for methanol and formaldehyde successfully reproduced experimental data from shock tube pyrolysis and flow reactor oxidation. The mechanism was in closer agreement with experimental data concerning the laminar burning velocity of methanol than version 0.6 of the Konnov mechanism was. Validation of the mechanism for acetic acid combustion included laminar burning velocities, measured here for the very first time by use of the heat flux method. The calculated velocities were about 3 cm/s higher than the experimental results. Further validation of the kinetic mechanism was achieved by simulating species profiles of burner stabilized acetic acid flames. While major species were reproduced successfully, minor species were either under-or-over predicted. Sensitivity analysis showed ketene to play an important role in the acetic acid combustion.
The results of this project provide the scientific community with experimental data potentially useful for model validation as well as a new kinetic mechanism for small oxygenated fuels and intermediates.