Reduced Gravity Combustion of Thermoplastic Spheres

Published

January 1, 2000

Author(s)

Jiann C. Yang, Anthony P. Hamins, Michelle K. Donnelly

Abstract

A series of low-gravity experiments were conducted to investigate the combustion of supported thermoplastic polymer spheres under varying ambient conditions. The three types of thermoplastics investigated were polymethyl methacrylate (PMMA), polypropylene (PP), and polystyrene (PS). The low-gravity environment was achieved by performing the experiments aboard the NASA DC-9 and the KC-135 Reduced Gravity Aircraft. Spheres with diameters ranging from 2 mm to 6.35 mm were tested yielding Grashof numbers calculated to be less than 0.1. The polymer sphere was supported using a 75mum-diameter Al/Cr/Fe alloy wire. The total initial pressure varied from 0.05 MPa to 0.15 MPa whereas the ambient oxygen concentration varied from 19% to 30% (by volume). The ignition system consisted of a pair of retractable energized coils. Two CCD cameras recorded the burning histories of the spheres. The video sequences revealed a number of dynamic events including bubbling, and sputtering as well as soot shell formation and break-up during combustion of the spheres at reduced gravity. The ejection of combusting material from the burning spheres represents a fire hazard that must be considered at reduced gravity. The ejection was found to be sensitive to polymer type, but independent of oxygen concentration and pressure. The average value of the ejection frequency was found to be 3 Hz, 5 Hz, and 5 Hz for PMMA, PS, and PP, respectively. The velocities of the ejected material were estimated by tracking the material in two consecutive video frames. For the PP spheres, Va = 2.3 (+ 1.2) cm/s (with 60 events observed). The ejected material appeared to decelerate at an average rate of = 40 cm/s2, and traverse an average distance of only 8 mm before burning to completion. The Va for PS and PMMA was not determined because the ejected material was never observed to exist beyond the visible flame of the parent sphere.

Citation

Combustion and Flame

Volume

120

Issue

No. 1/2

Pub Type

Journals

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Keywords

combustion, thermoplastics, fire safety, polymers, polymethyl methacrylate, polypropylene, polystyrene, reduced gravity, spheres

Citation

Yang, J. , Hamins, A. and Donnelly, M. (2000), Reduced Gravity Combustion of Thermoplastic Spheres, Combustion and Flame, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=909870 (Accessed May 4, 2024)