Pyrolysis Smoke Generated Under Low-Gravity Conditions

Abstract

A series of smoke experiments were carried out in the Microgravity Science Glovebox on the International Space Station (ISS) Facility to assess the impact of low-gravity conditions on the properties of the smoke aerosol. The smokes were generated by heating five different materials commonly used in space vehicles. This study focuses on the effects of flow and heating temperature for low-gravity conditions on the pyrolysis rate, the smoke plume structure, the smoke yield, the average particle size, and particle structure. Low-gravity conditions allowed a unique opportunity to study the smoke plume for zero external flow without the complication of buoyancy. The diameter of average mass increased on average by a factor of 1.9 and the morphology of the smoke changed from agglomerate with flow to spherical at no flow for one material. The no flow case is an important scenario in spacecraft where smoke could be generated by the overheating of electronic components in confined spaces. From electron microcopy of samples returned to earth, it was found that the smoke can form an agglomerate shape as well as a spherical shape, which had previously been the assumed shape. A possible explanation for the shape of the smoke generated by each material is presented.

Smoke Characterization and Feasibility of the Moment Method for Spacecraft Fire Detection

“…Summaries are given on the morphology of all five materials tested, and details on the pyrolysis and formation are in the companion article (Mulholland et al 2015). Kapton particles are the smallest of the five materials tested and are rarely agglomerated.…”

“…A specific set of test points were run in low gravity with no flow through the SAME smoke generation duct, which resulted in significantly larger spherical particles. Details of these tests are outlined in the companion article (Mulholland et al 2015).…”

“…After a period of aging, the remaining smoke was measured. Additional information on the sample heating sequence and temperatures is given in the companion article (Mulholland et al 2015).…”

“…The purpose of this article is two-fold: (1) Report the pyrolysis smoke characteristics of common spacecraft materials to inform future fire detector design, and (2) evaluate the feasibility and limitations of using combined moments for measuring smoke aerosol size distribution parameters in low gravity, particularly the validity of the lognormal assumption. A companion article (Mulholland et al 2015) discusses other aspects of the SAME smoke, such as pyrolysis rate, smoke plume structure, yield, and particle structure.…”

“…While some studies have shown that the DustTrak TM response is not proportional to mass (Moosm€ uller et al 2001;Maricq 2013), after applying calibration factors, the DustTrak TM was found to correlate with the mass concentration. The calibration factors with uncertainty are given in the companion article by Mulholland et al (2015). Some smoke could be sent to an autonomously operated thermal precipitator in which smoke particles are deposited on transmission electron microscope (TEM) grids.…”