Measurement of the Average Molecular Weight of Gaseous Pyrolyzates Produced by Combustible SolidsF

Published

March 16, 2025

Author(s)

Ryan Greene, Alec Tripi, Isaac Leventon, Kevin McGrattan

Abstract

In order to predict fire phenomena such as flame structure, stability, and growth, computational fire models require an accurate description of the gaseous volatiles released by combustible solids during pyrolysis. The difficulty in this characterization is that the majority of materials release a mixture of dozens of gaseous species. Rather than identifying and quantifying each individual molecule, modelers often use an effective molecule to represent the average of the mixture. In this work, an experimental method was developed to identify the molecular formula of this average molecule. An organic elemental analyzer was used to determine average composition, while a heated, non-stirred pressure vessel was used to determine molecular weight. The average molecular formula was produced by the combination of these experimental results. The experimental apparatus were calibrated separately, and a series of validation tests using known composition and molecular weight species were performed. Validation tests found accurate elemental compositions within an average of 1.19\%, while the molecular weights of known volatiles were found within an average of 1.13\%. Poly(methyl methacrylate), PMMA, and polyoxymethylene, POM, which are known to pyrolyze primarily to their monomers, were carried through the entire experimental procedure. The molecular formulas of each pyrolyzate were found to match their monomer within 3.99\% and 27.33\% respectively. Ongoing work aims to refine this methodology and extend its application to a broader range of materials, contributing to the development of more accurate fire dynamics simulations.

Proceedings Title

U.S National Combustion Meeting

Conference Dates

March 16-19, 2025

Conference Location

Boston, MA, US

Pub Type

Conferences

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Keywords

Fire Modeling, Gas Analysis, Material Flammability, Pyrolysis

Citation

Greene, R. , Tripi, A. , Leventon, I. and McGrattan, K. (2025), Measurement of the Average Molecular Weight of Gaseous Pyrolyzates Produced by Combustible SolidsF, U.S National Combustion Meeting, Boston, MA, US, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=959393 (Accessed May 6, 2026)

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