Influence of Pyrolysis Gas Composition and Reaction Kinetics on Leaf-Scale Fires

ABSTRACT

The impact of pyrolysis gas composition and the underlying reaction kinetics on the burning characteristics of a leaf was computationally investigated. The computational configuration resembled a previous experimental setup where vertically oriented manzanita (Arctostaphylos glandulosa) leaves were burned. Different compositions and reaction kinetics for the pyrolysis gas released during the leaf thermal decomposition were examined. The most detailed composition included $\mathrm{C}{\mathrm{H}}_4$, $\mathrm{C}\mathrm{O}$, $\mathrm{C}{\mathrm{O}}_2$, and ${\mathrm{H}}_2$, which was suggested by the previous experimental study of pyrolysis products of different plant species. The least involved compositions only included either $\mathrm{C}{\mathrm{H}}_4$ or $\mathrm{C}\mathrm{O}$. In all considered compositions, in addition to pyrolysis gas, the release of the heavy gas, i.e. tar, was accounted for. Tar breakdown was represented by a single-step reaction with the light gases above and soot as the products where the stoichiometric coefficients were determined by an optimization technique for consistency with the measurements for the tar molecule. The burning simulation results agreed best with the previous experimental data when a mixture of $\mathrm{C}{\mathrm{H}}_4$, $\mathrm{C}\mathrm{O}$, $\mathrm{C}{\mathrm{O}}_2$ was used. The least agreement was noted when pyrolysis gas was represented by only $\mathrm{C}{\mathrm{H}}_4$. Inclusion of tar breakdown reaction appreciably increased the overall heat release due to combustion of its products above the leaf.

KEYWORDS:

• Pyrolysis
• reaction kinetics
• combustion
• tar
• live fuel

Acknowledgments

The authors acknowledge Thomas H. Fletcher of BYU for providing the tar molecule formula measured by his research group and suggesting to include soot as a product in the tar breakdown reaction. This work was supported by DOD/EPA/DOE Strategic Environmental Research and Development Program project RC-2640 administered by the USDA Forest Service PSW Research Station through cooperative agreement JV-11272167-025 with UAH. High performance computing resources and technical support provided by the Alabama Supercomputer Authority are appreciated.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by the DOD/EPA/DOE Strategic Environmental Research and Development Program [RC-2640]; USDA Forest Service PSW Research Station [JV-11272167-025].