Smolder ignition of polyurethane foam: effect of oxygen concentration

Abstract

Experiments have been conducted to study the ignition of both forward and opposed smolder of a high void fraction, flexible, polyurethane foam in a forced oxidizer flow. Tests are conducted in a small scale, vertically oriented, combustion chamber with supporting instrumentation. An electrically heated Nichrome wire heater placed between two porous ceramic disks, one of which is in complete contact with the foam surface, is used to supply the necessary power to ignite and sustain a smolder reaction. The gaseous oxidizer, metered via mass flow controllers, is forced through the foam and heater. A constant power is applied to the igniter for a given period of time and the resulting smolder is monitored to determine if smolder is sustained without the assistance of the heater, in which case smolder ignition is considered achieved. Reaction zone temperature and smolder propagation velocities are obtained from the temperature histories of thermocouples embedded at predetermined positions in the foam with junctions placed along the fuel centerline. Tests are conducted with oxygen mass fractions ranging from 0.109 to 1.0 at a velocity of 0.1 mm/s during the ignition period, and 0.7 or 3.0 mm/s during the self-sustained propagation period. The results show a well defined smolder ignition regime primarily determined by two parameters: igniter heat flux, and the time the igniter is powered. These two parameters determine a minimum igniter/foam temperature, and a minimum depth of smolder propagation (char), which are conditions required for ignition to occur. The former is needed to establish a strong smolder reaction, and the latter to reduce heat losses from the incipient smolder reaction to the surrounding environment. The ignition regime is shifted to shorter times for a given igniter heat flux with increasing oxygen mass fraction. A model based on concepts similar to those developed to describe the ignition of solid fuels has been developed that describes well the experimental ignition results.3

Organic liquid mobility induced by smoldering remediation

“…Once TC1 reached its peak temperature and began to decline, the heater was turned off and only the air supply remained on. The consistent and repetitive temperature-time slopes, the crossing of successive curves, and the consistency of the peak temperatures (564 ± 12 °C), are all indicative of a self-sustaining smoldering process [12]. The velocity of the leading edge of the smoldering front is steady in time (0.41 ± 0.04 cm/min).…”

“…Intentional smoldering of organic liquid/sand mixtures as a treatment method is a relatively new concept [6]. To ignite a smoldering reaction in these mixtures, a short and localized heat source is applied, followed by air injection [12].…”

The Effect of Buoyancy on Opposed Smoldering

“…4c) once the reaction progresses beyond the area where it is influenced by the igniter. In upward opposed-propagation, the smolder front does not self-propagate, most likely as a result of the opposition of the forced flow and the buoyant flow (Walther et al 2000).…”

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.…”