Forced forward smoldering experiments in microgravity

Abstract

Results from two forward forced-flow smolder tests on polyurethane foam using air as oxidizer conducted aboard the NASA Space Shuttle (STS-105 and STS-108 missions) are presented in this work. The two tests provide the only presently available forward smolder data in microgravity. A complimentary series of ground-based tests were also conducted to determine, by comparison with the microgravity data, the effect of gravity on the forward smolder propagation. The objective of the study is to provide a better understanding of the controlling mechanisms of smolder for the purpose of control and prevention, both in normaland microgravity. The data consists of temperature histories from thermocouples placed at various axial locations along the fuel sample centerline, and of permeability histories obtained from ultrasonic transducer pairs also located at various axial positions in the fuel sample. A comparison of t he tests conducted in normal-and microgravity indicates that smolder propagation velocities are higher in microgravity than in normal gravity, and that there is a greater tendency for a transition to flame in microgravity than in normal gravity. This is due primarily to the reduced heat losses in the microgravity environment, leading to increased char oxidation. This observation is confirmed through a simplified one-dimensional model of the forward smolder propagation. This finding has important implications from the point of view of fire safety in a space-based environment, since smolder can often occur in the forward mode and potentially lead to a smolder-initiated fire.

Radiant Ignition of Polyurethane Foam: The Effect of Sample Size

“…Previous work on smouldering ignition of polyurethane (PU) foam has focused on the effects of flow through the porous fuel [1][2][3], enhanced or reduced oxygen concentration [4] and the heat flux and exposure time [5]. In this work we present the * Correspondence should be addressed to: Guillermo Rein, E-mail: g.rein@imperial.ac.uk effect of sample size on the ignition and spread of smouldering under atmospheric oxygen concentrations and natural flow conditions.…”

“…Using typical experimental data for smouldering PU foam with forced oxidizer flow (d ¼ 0:04 m; Q sml ¼ 5880 kJ/kg-O 2 ; U loss ¼ 14 W m À1 K À1 ; T sml ¼ 450 C and T 0 = 20°C) [1,2], a minimum sample size on the order of 160 mm is found to be required to sustain smouldering propagation [8]. Equation 1 is only valid for forced flow through the PU foam; however, the scenarios of most importance in fire safety occur under natural flow conditions.…”

“…Ignition is governed by the balance between heat flux applied to the surface, heat losses and fuel kinetics [6,8], while the self-sustained propagation is governed primarily by the oxygen supply to, and heat losses from the reaction front [8][9][10]. The heat losses are a function of surface area of the front, and the heat released from the reaction depends on the volume of the reaction front; therefore, smouldering combustion is sensitive to the size of the sample [1,2,8]. This work aims to experimentally identify the effect of size on the ignition and subsequent propagation of smouldering and flaming in PU foam over a wide range of heat fluxes using three sample sizes.…”

Numerical examination of two-dimensional smolder structure in polyurethane foam

“…The experiments simulated here [6] involve the forward propagation of a smolder wave through a polyurethane foam cylinder 12 cm in diameter and 14 cm in length. The experiments were conducted in microgravity on the NASA Space Shuttle (mission STS-108).…”

Space experimental studies of microgravity fluid science in China

“…Since the smoldering reaction is very weak and the flow velocity inside the solid fuel is relatively low, the buoyancy-induced flow can strongly influence the processes of smoldering combustion initiation, propagation and transition to flaming. Conducted on board NASA's space shuttles, previous microgravity smoldering combustion experiments [66][67][68] were focused on the smolder configurations of pure opposed flow (i.e. the reaction front propagates opposing the oxidizer flow) or forward flow (i.e.…”