Publications

A joint temperature/soot laser-based optical diagnostic was developed for the determination of the joint temperature/soot probability density function (PDF) for hydrocarbon-fueled meter-scale turbulent pool fires. This Laboratory Directed Research and Development (LDRD) effort was in support of the Advanced Simulation and Computing (ASC) program which seeks to produce computational models for the simulation of fire environments for risk assessment and analysis. The development of this laser-based optical diagnostic is motivated by the need for highly-resolved spatio-temporal information for which traditional diagnostic probes, such as thermocouples, are ill-suited. The in-flame gas temperature is determined from the shape of the nitrogen Coherent Anti-Stokes Raman Scattering (CARS) signature and the soot volume fraction is extracted from the intensity of the Laser-Induced Incandescence (LII) image of the CARS probed region. The current state of the diagnostic will be discussed including the uncertainty and physical limits of the measurements as well as the future applications of this probe.

We present a dual-pump coherent anti-Stokes Raman scattering (CARS) instrument, which has been constructed for the probing of temperature fluctuations in turbulent pool fires of meter-scale. The measurements were performed at the Fire Laboratory for Accreditation of Models and Experiments (FLAME) facility at Sandia National Laboratories, which provides a canonical fire plume in quiescent wind conditions, with well-characterized boundary conditions and access for modern laser-diagnostic probes. The details of the dual-pump CARS experimental facility for the fire-science application are presented, and single-laser-shot CARS spectra containing information from in-fire N2, O2, H2, and CO2 are provided. Single-shot temperatures are obtained from spectral fitting of the Raman Q-branch signature of N2, from which histograms that estimate the pdf of the enthalpy-averaged temperature fluctuations at the center of the fire plume are presented. Results from two different sooting fire experiments reveal excellent test-to-test repeatability of the fire plume provided by FLAME, as well as the CARS-measured temperatures. The accuracy and precision of the CARS temperatures is assessed from measurements in furnace-heated air, where the temperature can be accurately determined by a thermocouple. At temperatures in excess of 500 K, the furnace results show that the CARS measurements are accurate to within 2-3% and precise to within ±3-5% of the measured absolute temperature. © 2009 The Combustion Institute. Published by Elsevier Inc. All rights reserved.