Experimental Evaluation of Flame Radiative Feedback: Methodology and Application to Opposed Flame Spread Over Coated Wires in Microgravity

Abstract

The objective of this work is to quantify for the first time soot-related radiative heat transfer in opposed flow flame spread in microgravity. This article presents experimental results obtained in parabolic flight facilities. A flame is established over a solid cylindrical polyethylene coated metallic wire and spreads at a steady rate, in low velocity flow conditions allowed by the absence of buoyancy. Implementing the Broadband Modulated Absorption/Emission (B-MAE) technique, the two-dimensional fields of soot volume fraction and temperature are obtained for the first time in flame spread configuration over an insulated wire in microgravity. The consistency of the results is assessed by comparing results from independent experimental runs. From these fields, radiative losses attributed to soot in the flame are computed at each location. This map of radiative losses together with the profile of the wire surface are then used as inputs to a novel experimental approach that enables the assessment of soot radiative heat feedback to the wire. Results are extracted from a specific case of a flame propagating over a polyethylene coated Nickel-Chrome (NiCr) wire at nominal pressure. The oxidizer, composed of 19% oxygen and 81% nitrogen in volume is blown at opposed flow parallel to the wire at a velocity of 200 mm.s −1. This new approach provides the first detailed quantitative measurements which are required to check the relevance

The impact of radiative heat transfer in combustion processes and its modeling – with a focus on turbulent flames

“…The role of RHT on the opposed flow spreading behavior of non-buoyant diffusion flames over thin electrical wires coated by low-density polyethylene was investigated recently through experiments, theory and numerical computations [12], [219]. Measurements were performed in parabolic flights and flame spread rate, pyrolysis rate, stand-off distance, soot volume fraction, and soot temperature were experimentally determined based on optical diagnostics that capture the flame spread in parabolic flights.…”

Can a spreading flame over electric wire insulation in concurrent flow achieve steady propagation in microgravity?

“…As a result the camera not only captured the direct flame emission, but also the image with a backlight, which was used to visualize the behavior of molten insulation and the soot distribution in the flame. Also, further research to measure the soot volume fraction and temperature using this camera is ongoing [26]. The pressure inside the chamber was always set to 1 atmosphere using a Rapid Control Valve (This valve allows exhaust flow rates up to 1800 NL/min).…”

Introduction to Special Issue on Spacecraft Fire Safety

“…Unique space fire experiments have been conducted in the International Space Station [5,6], unmanned spacecraft [7], and a satellite [8] to understand the long-term micro-gravity combustion and fire phenomena. The fire dynamics small and thin fuels are also explored through ground-based microgravity experiments using drop towers [9] and parabolic flights [10][11][12][13][14]. In addition, combustion and fire experiments under reduced pressures [15][16][17] and a narrow channel [18] are applied to lower the influence of buoyancy and simulate low-gravity environments on Earth.…”

“…Thus, microgravity also provides an ideal environment for fundamental combustion research [4]. Unique phenomena for flame spread in microgravity over thin paper [9], thick plastic plates [7,10,18], cylindrical rods [8,17], spherical fuels [5] and electrical wires of different thicknesses [11,12,14,20] are observed, and the influence of airflow speed, direction, and oxygen concentration on flame stability are investigated.…”

“…The role of radiation heat transfer becomes more important for the near-limit flame phenomena in microgravity, where flame radiation and surface reradiation dominate the heat loss from the fuel. Important progress has been made in the quantification of the radiation profile and its effects on flame spread via experimental measurements [6,14] and computational simulations [6,19]. For the design of firefighting strategies in spacecraft, special fire-suppression technologies are required.…”