Application of RF frequency-division multiplexing for multiple species measurements in large pool fires

Researchers at Sandia have been experimentally and numerically investigating large-scale pool fires for several years, because of the risk that these fires pose to critical engineered systems during transport accident scenarios. Due to the difficulty of fielding optical measurement techniques in this turbulent, optically thick, high-temperature environment, experimental measurements in large fire research have traditionally been limited to thermocouples, heat-flux gauges, and bidirectional velocity probes. Recently, Sandia developed and successfully implemented an insulated, water-cooled fiber optic probe (see Figure 1) that utilized a combined HeNe-laser-absorption and a 2-coIor emission technique to determine soot volume fraction distributions and soot temperatures over a 2-cm sampling distance in a 6-meter diameter JP-8 pool fire [1]. With the collection and analysis of soot property data, attention has turned to the measurement of gas-phase species concentrations (together with soot properties), in order to evaluate mixing phenomena, gas-phase radiation interactions, and soot formation and oxidation chemistry in these large fires.