A. James Clark School of Engineering
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The collections in this community comprise faculty research works, as well as graduate theses and dissertations.
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Item COMPARISON OF IGNITION AND COMBUSTION CHARACTERISTICS OF PRESSURE TREATED WOOD AND TREX EXPOSED TO THERMALLY CHARACTERIZED GLOWING FIREBRAND PILES(2023) Lauterbach, Alec; Stoliarov, Stanislov I; Fire Protection Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)In recent decades, the intensity of wildfires worldwide has escalated, leading to a rise in the destruction of structures and loss of lives within the Wildland-Urban Interface (WUI). Firebrands are small fragments of ignited vegetation or structural material that are carried by the plume of a wildfire, traveling in advance of the main fire front. Firebrand exposure has been recognized as the primary mechanism for the propagation of wildfires as well as a source of ignition of structural elements. However, this complex ignition process of structural elements in the WUI has yet to be fully understood. The ignition and combustion characteristics of a thermoplastic-wood composite (Trex) and Pressure Treated Wood (PTW), two frequently used WUI decking materials, when exposed to glowing firebrand piles were studied using a bench scale wind tunnel. An inert insulation material, ii Kaowool PM, was also used as a deposition substrate to quantify the heat feedback and combustion characteristics of solely the firebrand pile. Firebrand pile densities of 0.16 g cm-2 and 0.06 g cm-2 were deposited on each substrate in rectangular 10 cm x 5 cm orientations and exposed to air flow velocities of 0.9 m s-1, 1.4 m s-1, 2.4 m s-1, and 2.7 m s-1. Infrared camera measurements were used to determine the back surface temperatures of Kaowool PM tests. Using DSLR cameras, surface ignitions of the decking material in front of the firebrand pile (preleading zone ignition events), ignitions on top of the firebrand pile (pile ignition events), and surface ignitions of the decking material behind the firebrand pile (downstream ignition events) were visually quantified via their probability of ignition, time to ignition, and burn duration at each testing condition. A gas analyzer was used to compare combustion characteristics of Trex, PTW, and Kaowool PM tests through heat release rate (HRR) and modified combustion efficiency (MCE). Peak back surface temperatures of the firebrand pile were found to increase with increased air flow up to 2.4 m s-1, and then plateau. The same trend was observed for the ignition probabilities of preleading zone and pile ignition events. The probability of downstream ignition events increased with increasing air flow velocity. Peak HRR increased with increasing air flow velocity. Trex exhibited significantly less smoldering combustion than PTW yet was prone to more intense flaming combustion. When the rectangular 5 cm x 10 cm firebrand pile (10 cm edge facing the airflow), of which the majority of tests were conducted on, was rotated 90 degrees so that the 5 cm edge faced the airflow, the result was a significant decrease in the probability of ignition for both Trex and PTW, along with notable reductions in their HRR and MCE profiles.Item A Study Of Intermittent Convective Heating Effects On Fine Fuel Ignition(2019) Benny, Lana; Gollner, Michael J.; Fire Protection Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Recent studies have suggested the potential importance of intermittent convective heating on the ignition of fine fuels during wildland fire spread. In this study, a novel pulsed-gas line burner similar to a Rubens' tube, driven by acoustic oscillations, is used to re-create the pulsations observed in wildland fires in a controlled environment. After acoustically stimulating a long tube with perforations at the top, creating a pulsed linear flame, thin fuels with different densities and diameters are quickly placed in the center of the flame. The temperature of these fuels is measured using an infrared camera, distinguishing the temperature at which the fuel starts to pyrolyze. As expected, smaller-diameter fuels ignite faster when exposed to flames; however, they also are least affected by intermittent heating. Larger-diameter fuels are more dramatically affected by intermittent heating frequencies, in large part due to cooling effects between pulses and the larger thermal mass of the fuels. The results are discussed and compared with a simple numerical model incorporating measured velocities and temperatures present in the burner and their effect on a thermally-thin fuel element over time.Item Critical Ignition Conditions of Structural Materials by Cylindrical Firebrands(2019) Salehizadeh, Hamed; Gollner, Michael J; Fire Protection Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Smoldering firebrands (embers) are a major cause of ignition and eventual structural damage during wildfires at the wildland-urban interface (WUI). These small pieces of wood can loft several kilometers ahead of the main flame front and ignitespot fires directly on structural elements such as decks. In this research, dense structural materials such as wood and engineered wood will be studied with a focus on capturing the critical thermal conditions necessary for ignition. Unique to this study will be a configuration where whole piles of firebrands are placed on the recipient material, emulating observations from WUI fires. In order to design appropriate fire safety standards at the WUI and, someday, to model the propagation of these fires, the conditions leading to ignition of common WUI materials by piles of lofted firebrands must be quantified. Firebrands were modeled using small cylindrical wooden dowels which were ignited and placed in a small-scale wind tunnel. Two tests were performed for each loading condition of firebrands, one studying ignition of wooden structural elements such as decking and marine-grade plywood and another measuring temperatures and heat fluxes over an inert piece of ceramic insulation. A single-point water-cooled heat flux gauge was used for time-resolved measurements of heat flux at the center of the inert setup surrounded by thin-skin calorimeters and K-type thermocouples which allowed for a spatial characterization of heating. The wind speed was the main quantity of interest changed during the test to determine the effects of wind speed on the heat flux released from the glowing dowels to recipient fuels. The results showed a drastic increase in heating from piles of firebrands vs. individual brands. The piles also produced higher heat fluxes under increasing winds. This is due, for the most part, to higher surface temperatures resulting from increased surface oxidation under higher wind speeds. Both smoldering and flaming ignition of wood was found to be similarly dependent on wind speed. Larger piles also produced higher peak heat fluxes at the center of the pile, highlighting the role of re-radiation within the pile influencing heat fluxes to recipient fuels. Critical heat flux and firebrand loading conditions required to achieve smoldering and flaming ignition of structural materialsused in the WUI are determined by comparing tests with inert and flammable fuels. These critical conditions can be used to model the propagation of WUI fires over structural elements to design appropriate fire safety standards at the WUI. A non-dimensional relationship incorporating fuel type, geometry, and ambient conditions is also proposed to describe the results.Item Characterizing Cigarette Lighter Flames to Reduce Unwanted Ignition(2004-09-14) Williamson, Justin Wade; Marshall, Andre W; Quintiere, James G; Trouve, Arnaud; Fire Protection Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This investigation provides detailed measurements and analysis for improved understanding of ignition from the 'small' flames produced by cigarette lighters. This research program is motivated by the need to improve the fire safety of cigarette lighters in response to the juvenile firesetter problem. A novel cigarette lighter concept for improved ignition safety has been developed, characterized, and compared with conventional lighters. Diagnostics were performed to measure laminar near-field plume behavior and turbulent far-field behavior in these small-scale (75W) flames. Plume diagnostics include centerline temperature, heat flux to a horizontal flat plate, and ignition of filter paper. Data was scaled and compared to plume theory and measurements. Other practical cigarette lighter performance related properties were also noted, such as lighter surface temperatures and cigarette ignition effectiveness.