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Convex Speciation

Overlapping spectra of species formed during propane pyrolysis
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The development of accurate kinetic models to describe emerging energy systems requires the accurate determination of species' time histories and their underlying reaction rates.

Reacting systems involving large species with similar structures are notoriously challenging to study optically, because the absorbance at a single wavelength is the summation of overlapping spectra of multiple species. Convex speciation, a technique developed in the Hanson Group, overcomes this challenge by using multiple laser measurements, convex-optimization techniques, and a comprehensive absorption cross-section library to isolate the contributions of each species.

By considering all measured signals together as a system of equations, convex speciation solves for the mole fraction of each absorber and employs various additional constraints (e.g., carbon and hydrogen accounting, measurements weighted by their uncertainty) to improve accuracy. The technique has revealed new insight into how fuels such as natural gas and jet fuel react [1–4] and has unlocked new opportunities to study previously inaccessible chemical reactions.

Pyrolysis of 2% propane in Argon
Nine-wavelength convex speciation applied to the pyrolysis of propane resolves the seven major species present and enables a comprehensive understanding of the hydrocarbon-decomposition process [1].

To learn more, check out some of our publications:

[1] S. J. Cassady, R. Choudhary, V. Boddapati, N. H. Pinkowski, D. F. Davidson, and R. K. Hanson, "The pyrolysis of propane," International Journal of Chemical Kinetics, Vol. 52(11) (2020) pp. 725–738. DOI: 10.1002/kin.21395

[2] S. J. Cassady, R. Choudhary, N. H. Pinkowski, J. Shao, D. F. Davidson, and R. K. Hanson, "The thermal decomposition of ethane," Fuel, Vol. 268 (2020) 117409. DOI: 10.1016/j.fuel.2020.117409

[3] N. H. Pinkowski, Y. Wang, S. J. Cassady, D. F. Davidson, and R. K. Hanson, "A streamlined approach to hybrid-chemistry modeling for a low cetane-number alternative jet fuel," Combustion and Flame, Vol. 208 (2019) pp. 15–26. DOI: 10.1016/j.combustflame.2019.06.024

[4] N. H. Pinkowski, S. J. Cassady, D. F. Davidson, and R. K. Hanson, "Multi-wavelength speciation of high-temperature 1-butene pyrolysis," Fuel, Vol. 244 (2019) pp. 269-281. DOI: 10.1016/j.fuel.2019.01.154