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Combustion Fire Processes Laboratory

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Research

Experiments to Measure Smoldering Behavior in Simulated Wildland Fuels

Researchers:
Jeanette Cobian-Iñiguez, Carlos Fernandez-Pello

Accelerated tree mortality in the Sierra Nevada has led to the rapid accumulation of large downed fuels on the forest floor. The presence of these fuels represents a shift in surface fuel layer composition; from thin fuels such as grasses and debris which burn in the flaming regime, to large downed trees with a high risk of burning in the smoldering regime. Smoldering fires are characterized by lower temperatures, heat release and spread rates than flaming fires and produce greater concentrations of gas and particulate emissions. The latter suggests that smoldering fires are highly pollutant wildfires.  In addition, because smoldering fires require lower temperatures to ignite, transition from smoldering to flaming is often considered a shortcut to flaming ignition. Although smolder propagation rate has been measured for natural fuels, primarily wood, little is known quantitatively of the smolder burn rate, temperature and emissions characteristics particularly under the influence of wind. To fill this void, we aim to quantify the rate of smoldering burn rate and smoldering to flaming transition. Although our focus is on the Sierra Nevada, results can be applicable to similar ecosystems enduring heightened tree mortality. Experiments to study smoldering behavior are conducted in a bench scale wind tunnel where fuel beds were simulated using wooden cribs. We examine smoldering burning rate and smoldering to flaming behavior under various crib configurations and wind velocities. Crib permeability is varied by changing stick distance and thickness.  Burning rate is calculated from measurements of mass loss rate, smoldering to flaming transition was diagnosed in the initial state of the study through visual diagnostic obtained from experiment video. Measurement of emissions including CO, CO2 and NOx are taken with the goal of obtaining emission rate and calculating yields of fire products.

Different stages of the experimental procedure

Temperature Measurement of Glowing Firebrands

Published in Fire Technology:https://doi.org/10.1007/s10694-018-0810-3
Pre-print available on ResearchGate:
Link
Researchers:
James L Urban, Michela Vicariotto, Derek Dunn-Rankin, Carlos Fernandez-Pello

In this project we measured the temperature of glowing firebrands in various air-flows (1-4 m/s) using Color Pyrometry and Infra-Red (IR) photography. The results show that the emissivity of the firebrand surface changes as it burns and the char is reduced to ash, which is then shed intermittently throughout the burning. This makes IR camera measurements more difficult as the emissivity must be dynamically compensated for.

Comparison between Infra-Red & Color Pyrometry

Comparison of firebrand surface temperature measurements at different times though out a test. It is observed that the effective emissivity of the firebrand changes with time.

Time evolution of a Firebrand

Time evolution of a sample test including image, temperature image, and temperature distribution of firebrand surface

Temperature & Motion Tracking of Metal Sparks

Summary of research Published in Fire Technology: (accepted – DOI link will be added when online)

Researchers:
Yudong Liu, James L Urban, Chuanlong Xu, Carlos Fernandez-Pello

In this project we measured the temperature, motion (position & velocity), and size of moving metal sparks and hot particles. The goal is to better understand the danger that such sparks can pose in terms of their ability to start a fire. Here sparks were produced using an abrasive cutting steel cutting rebar. These measurements were done using streak tracing velocimetry, color pyrometry, and image processing.

Temperature History Results (no velocity measurement)

  • Single spark reacts with air and heats up, bursts and then cools
  • Spark bursts into spark fragments which each quickly heat then cool

Temperature & Velocity Results

Image of Spark Spray and spark temperature-velocity distributions from various locations from the source marked on the image.

It can be seen that the sparks start off well concentrated in terms of both temperature and velocity, but as they travel farther they eventual separate into two peaks: one with high temperatures and velocities and another with low temperatures and velocities.

Material Ignition and Suppression Test (MIST) in Space Exploration Atmospheres – NASA Funding

Researchers:
Andy Rodriguez, Maria Thomsen Solis, Carlos Fernandez-Pello

Fire safety is a concern in space travel, particularly with the current plans of increasing the length of the manned space missions (e.g. missions to Mars), and of using spacecraft atmospheres different than in Earth, such as microgravity, low-velocity gas flows, low pressure and elevated oxygen concentration.

The focus of this research is to understand how these new environmental conditions could affect the fire behavior. In this research, a small-scale wind tunnel is used to conduct flame spread experiments over a cylindrical polymer, polymethyl methacrylate (PMMA) also known as Acrylite, of several dimensions. We measure changes on forced flow velocity, oxygen concentration, ambient pressure, and external radiation. Furthermore, several sets of experiments have been conducted on board of the International Space Station (ISS) allowing us to study also the effect of gravity.

Additionally, the research done for this project is funded by NASA and is done in support of the Burning and Suppression of Solids – II project (BASS-II). This project examines the burning and extinction characteristics of different fuel samples burning in microgravity. The BASS-II experiment will guide strategies for materials flammability screening for use in spacecraft as well as provide valuable data on solid fuel burning behavior in microgravity. This unique data can be used later for validation of numerical models used in the design of fire detection and suppressions system on earth and on space.

http://coe2cfp.wpengine.com/wp-content/uploads/2018/01/videos.mp4

 

A summary presentation of the current projects can be downloaded at the following link Spacecraft_Fire_Research

Wire Combustion with External Radiation – NASA/JAXA Funding

Researchers:
Lauren Gagnon, Carlos Fernandez-Pello

Electrical wires with flammable polymer insulation and metal core are responsible for fire accidents in space exploration missions, because of poor contact, short circuiting, external heating, and ground fault, electrical wires and harnesses are easy to ignite. As a support for “International Standard of Space Fire Safety”, the focus of this research is to understand the changes in flammability of electrical wires under external radiation in the environment expected in space-based facilities. Experiments are first designed and conducted in normal gravity to measure the limiting oxygen concentration (LOC) and flame spread rate for different wire core conditions and insulation materials. The melting and dripping (see video) of the wire insulation are also investigated. Meanwhile, the numerical simulations of wire combustion are conducted to predict potential wire fires in the conditions expected in microgravity and Space Exploration Atmospheres (SEA).

This work is a part of “Flammability Limits at Reduced-g Experiment” (FLARE) project which aims to (1) develop a methodology to correlate material flammability limits in normal and microgravity, and (2) allow quantitative estimation of material flammability limit in microgravity based on the flammability data obtained on the ground. The project involves an international team including JAXA, NASA, ESA and universities in Japan, USA and France.

A summary presentation of the current projects can be downloaded at the following link Spacecraft_Fire_Research

Material Testing and Selection in Support of the Saffire Experiments – NASA Funding

Researchers:
Maria Thomsen Solis, Carlos Fernandez-Pello

In practical applications a given material can be exposed to a wide range of scenarios and its flammability can change depending of the ambient conditions at which is exposed. Therefore, a material that is expected to be fire resistant can present different behaviors under different conditions. The focus of this research is to understand how these environmental conditions affect the flame spread behavior. In this research, a small-scale wind tunnel is used to conduct flame spread experiments over thin fire-resistant fabric samples or thermoplastics under a varied range of ambient pressures, oxygen concentrations, forced flow and an external radiant heat flux.

 

During each experiment, videos are recorded and then post processed to obtain flame spread measurements and develop Flame/No-flame spread boundaries. Such boundaries allow understanding the shifts in the flammability of a material as it is exposed to varying environmental conditions. Ambient conditions may change depending on location, application, etc., as well as during emergencies. Studying the flammability of materials over a wide range of ambient conditions presents a better picture of the flammability behavior expected in both, standard and non-standard situations.

Additionally, the research done for this project is funded by NASA and is done in support of the Spacecraft Fire Experiment also known as Saffire. This project is focused on two main objectives: the understanding of flame spread and growth of a fire in microgravity, and the investigation of low-g flammability limits to determine if NASA’s material selection standards are appropriate screening methods for low gravity flammability. The Saffire experiments (I, II, and III) intentionally light a large-scale fire inside an empty Cygnus resupply vehicle after it leaves the International Space Station (ISS) and before it re-enters Earth’s atmosphere. Instruments measure flame growth, oxygen use and more, improving understanding of fire growth in microgravity and safeguarding future space missions.

A summary presentation of the current projects can be downloaded at the following link Spacecraft_Fire_Research

Spot Ignition of Natural Fuels

Fires can be started when smoldering debris from fires, embers/firebrands or hot metal particles from welding or clashing powerlines land on natural fuels.  Our laboratory has studied this ignition process through ignition experiments and modelling.  The embedded video was made by the NSF to showcase our research.

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