Jill Marie Suo-Anttila

Measurement of visible and near-IR optical properties of soot produced from laminar flames

This study describes the measurements of the dimensionless extinction constant, K e , of soot in the visible and IR spectrum using the National Institute of Standards and Technology Large Agglomerate Optics Facility. Soot was produced using a 11 mm i.d. laminar diffusion flame burner fueled with acetylene and ethene. Light extinction measurements were performed using light sources at 543.5, 632.8, 856, 1314, and 1565 nm. The mean values of present measurements of K e range from 7.95 to 10.0. These unique experiments provide accurate values of K e to be used for measurements of soot concentration and temperature in the IR spectrum. These measurements represent the first fuel-specific data available in the near-IR spectrum. The measured K e values for all wavelengths are significantly larger than values calculated using reported values of the refractive index and the Rayleigh theory. Transmission electron microscopy and optical microscopy analyses were used to analyze soot morphology and aerosol properties to estimate the influences of beam shielding and light scattering on the observed variations of K e .

Measurement of Soot Morphology, Chemistry, and Optical Properties in the Visible and Near-Infrared Spectrum in the Flame Zone and Overfire Region of Large JP-8 Pool Fires

Abstract The dimensionless extinction coefficient, K e , was measured for soot produced in 2 m JP-8 pool fires. Light extinction and gravimetric sampling measurements were performed simultaneously at 635 and 1310 nm wavelengths at three heights in the flame zone and in the overfire region. Measured average K e values of 8.4 ± 1.2 at 635 nm and 8.7 ± 1.1 at 1310 nm in the overfire region agree well with values from 8–10 recently reported for different fuels and flame conditions. The overfire K e values are also relatively independent of wavelength, in agreement with recent findings for JP-8 soot in smaller flames. K e was nearly constant at 635 nm for all sampling locations in the large fires. However, at 1310 nm, the overfire K e was higher than in the flame zone. Chemical analysis of physically sampled soot shows variations in carbon-to-hydrogen (C/H) ratio and polycyclic aromatic hydrocarbon (PAH) concentration that may account for the smaller K e values measured in the flame zone. Rayleigh–Debye–Gans theory of scattering for polydisperse fractal aggregate (RDG-PFA) was applied to measured aggregate fractal dimensions and found to under-predict the extinction coefficient by 17–30% at 635 nm using commonly accepted refractive indices of soot, and agreed well with the experiments using the more recently published refractive index of 1.99–0.89i. This study represents the first measurements of soot chemistry, morphology, and optical properties in the flame zone of large, fully-turbulent pool fires, and emphasizes the importance of accurate measurements of optical properties both in the flame zone and overfire regions for models of radiative transport and interpretation of laser-based diagnostics of soot volume fraction and temperature.

Thermal Measurements from a Series of Tests with a Large Cylindrical Calorimeter on the Leeward Edge of a JP-8 Pool Fire in Cross-Flow

As part of the full scale fuel fire experimental program, a series of JP-8 pool fire experiments with a large cylindrical calorimeter (3.66 m diameter), representing a C-141 aircraft fuselage, at the lee end of the fuel pool were performed at Naval Air Warfare Center, Weapons Division (NAWCWPNS). The series was designed to support Weapon System Safety Assessment (WSSA) needs by addressing the case of a transport aircraft subjected to a large fuel fire. The data collected from this mock series will allow for characterization of the fire environment via a survivable test fixture. This characterization will provide important background information for a future test series utilizing the same fuel pool with an actual C-141 aircraft in place of the cylindrical calorimeter.

The Effects of Wind on Fire Environments Containing Large Cylinders

An experimental investigation of the fire phenomenology associated with the presence of a large (3.66 m diameter), fuselage-sized cylindrical calorimeter engulfed in a large (18.9 m diameter) JP-8 pool fire subjected to various winds was performed. These measurements and analyses are of particular interest since few studies to date provide measured heat flux distributions under wind conditions for a case where the fire and object are of comparable size. A comparison of the fire environments resulting from the presence of the cylinder combined with the influence of different wind conditions is presented. The location of the continuous flame zone and the magnitude and distribution of the heat fluxes on the engulfed cylinder changed dramatically with the variation in wind speed. The high wind speed (10.9 m/s) conditions resulted in a twofold increase in the incident heat flux (up to 300 kW/m2 on the leeward side) to the surface of the object relative to heat fluxes typical of large hydrocarbon fires without engulfed objects. These results emphasize the need to consider the interaction of wind and large objects when estimating the incident heat fluxes on an engulfed object.

Validation of Heat Transfer Thermal Decomposition and Container Pressurization of Polyurethane Foam.

Polymer foam encapsulants provide mechanical, electrical, and thermal isolation in engineered systems. In fire environments, gas pressure from thermal decomposition of polymers can cause mechanical failure of sealed systems. In this work, a detailed uncertainty quantification study of PMDI-based polyurethane foam is presented to assess the validity of the computational model. Both experimental measurement uncertainty and model prediction uncertainty are examined and compared. Both the mean value method and Latin hypercube sampling approach are used to propagate the uncertainty through the model. In addition to comparing computational and experimental results, the importance of each input parameter on the simulation result is also investigated. These results show that further development in the physics model of the foam and appropriate associated material testing are necessary to improve model accuracy.

Numerical predictions and experimental results of a dry bay fire environment.

The primary objective of the Safety and Survivability of Aircraft Initiative is to improve the safety and survivability of systems by using validated computational models to predict the hazard posed by a fire. To meet this need, computational model predictions and experimental data have been obtained to provide insight into the thermal environment inside an aircraft dry bay. The calculations were performed using the Vulcan fire code, and the experiments were completed using a specially designed full-scale fixture. The focus of this report is to present comparisons of the Vulcan results with experimental data for a selected test scenario and to assess the capability of the Vulcan fire field model to accurately predict dry bay fire scenarios. Also included is an assessment of the sensitivity of the fire model predictions to boundary condition distribution and grid resolution. To facilitate the comparison with experimental results, a brief description of the dry bay fire test fixture and a detailed specification of the geometry and boundary conditions are included. Overall, the Vulcan fire field model has shown the capability to predict the thermal hazard posed by a sustained pool fire within a dry bay compartment of an aircraft; although, more extensive experimental data and rigorous comparison are required for model validation.

Towards Characterization of Soot Morphology, Composition, and Optical Properties From Large Pool Fires

The thermal hazard posed by large hydrocarbon fires is dominated by the radiative emission from high temperature soot. Since the optical and morphological properties of soot are not well known, especially in the infrared, efforts to characterize these properties are underway. Measurements of optical properties and morphology in large fires are important in heat transfer calculations, interpretation of laser-based diagnostics, and to build revised soot property models for fire field models. This research utilizes extractive measurement diagnostics to characterize soot morphology, composition, and optical properties in pool fires. The fires of interest are realistic in size, and considerably larger than recent studies, from transitionally turbulent to fully turbulent JP-8 pool fires. For measurement of the extinction coefficient, soot extracted from the flame zone is transported to a transmission cell where measurements are made using both visible and infrared lasers. Soot morphological properties are obtained by analysis via transmission electron microscopy of soot samples obtained thermophoretically within the flame zone, overfire region, and in the transmission cell. Soot composition, including carbon-to-hydrogen ration and PAH concentration, is obtained by analysis of soot collected on filters. In addition to providing insight into optical properties, soot samples obtained allow researchers to determine that the soot morphology is not affected by the transport to the transmission cell. This paper describes the diagnostics and presents some preliminary data for soot morphology, composition, and optical properties measurements within the flame zone of pool fires.Copyright