Publications

@article{Hariharan2021CNF,

title = {Comparison of Particulate Emissions from Liquid-Fueled Pool Fires and Fire Whirls at Dierent Length Scales},

author = {Sriram Bharath Hariharan, Hamed Farmahini Farahani, Ali S.Rangwala, Joseph L. Dowling, Elaine S. O, Michael J. Gollner},

url = {https://escholarship.org/content/qt5g22t2pb/qt5g22t2pb_noSplash_b91b18b1b2cb87f247b1b4e1e930078d.pdf?t=qq3u8i

},

doi = {10.1016/j.combustflame.2020.12.033},

year  = {2021},

date = {2021-05-01},

journal = {Combustion and Flame},

volume = {227},

pages = {483-496},

abstract = {In-situ burning (ISB) is one of the most effective means of removing oil spilled over open water. While current ISB practices can eliminate a large fraction of the spilled oil, they still result in significant airborne emissions of particulate matter. ISBs are classified as large, free-buoyant pool fires, from which black smoke consisting of particulate matter (PM, soot) emanates as a plume. An experimental investigation of soot emissions from pool fires (PF) and fire whirls (FW) was conducted using liquid hydrocarbon fuels, n-heptane and Alaska North Slope (ANS) crude oil, in fuel pools 

 cm in diameter. Burning attributes such as burning rate, fuel-consumption efficiency, and emissions of PM, unburned hydrocarbons, carbon dioxide, and oxygen consumption were measured. For both fuels and all pool diameters, compared to PFs, FWs consumed fuel at a higher rate, had lower post-combustion residual mass and PM emission rates. Collectively, these resulted in consistently lower PM emission factors (EF) for FWs at all scales. For FWs, EF decreased linearly with a nondimensional quantity defined as the ratio of inverse Rossby number to nondimensional heat-release rate. These results show that the addition of ambient circulation to free-burning PFs to form FWs can increase burning efficiency, reducing both burning duration and EF across length scales. The reduction in EF with increasing influence of circulation is attributed to a feedback loop of higher temperatures, heat feedback, burning rate and air-entrainment velocity, which in turn contributes to maintaining the structure of a FW. Boilover was observed for fires formed with ANS crude oil at the 70 cm scale, although the overall EF was not affected significantly. This investigation presents a foundation to evaluate the detailed mechanisms further, such that appropriate configurations can be developed help minimize the environmental impact of ISBs.},

keywords = {crude oil, Fire whirl, in situ burning},

pubstate = {published},

tppubtype = {article}

}

@article{hadi2021,

title = {A Methodology for Experimental Quantification of Firebrand Generation from WUI Fuels},

author = {Mohammadhadi Hajilou, Steven Hu, Thomas Roche, Priya Garg & Michael J. Gollner},

url = {http://link.springer.com/article/10.1007/s10694-021-01119-9

},

doi = {10.1007/s10694-021-01119-9},

year  = {2021},

date = {2021-04-22},

journal = {Fire Technology},

keywords = {firebrand},

pubstate = {published},

tppubtype = {article}

}

@article{salehizadehfirebrand2021,

title = {Critical Ignition Conditions of Wood by Cylindrical Firebrands},

author = {Hamed Salehizadeh, Raquel S. P. Hakes and Michael J. Gollner},

url = {https://www.frontiersin.org/articles/10.3389/fmech.2021.630324/full?&utm_source=Email_to_authors_&utm_medium=Email&utm_content=T1_11.5e1_author&utm_campaign=Email_publication&field=&journalName=Frontiers_in_Mechanical_Engineering&id=630324},

doi = {10.3389/fmech.2021.630324},

year  = {2021},

date = {2021-03-16},

journal = {Frontiers in Mechanical Engineering},

volume = {16},

abstract = {This study investigated the thermal conditions preceding ignition of three dense woody fuels often found on structures by firebrands, a major cause of home ignition during wildland-urban interface (WUI) fires. Piles of smoldering cylindrical firebrands, fabricated from wooden dowels, were deposited either on a flat inert surface instrumented with temperature and heat flux sensors or on a target fuel (marine-grade plywood, oriented-strand board, or cedar shingles) to investigate critical conditions at ignition. The former provided thermal data to characterize the time before and at ignition, while the latter provided smoldering and flaming ignition times. Tests were conducted in a small-scale wind tunnel. Larger firebrand piles produced higher temperatures at the center of the pile, thought to be due to re-radiation within the pile. Ignition was found to be dependent on target fuel density; flaming ignition was additionally found to be dependent on wind speed. Higher wind speeds increased the rate of oxidation and led to higher temperatures and heat fluxes measured on the test surface. The heat flux at ignition was determined by combining results of inert and ignition tests, showing that ignition occurred while transient heating from the firebrand pile was increasing. Ultimately, critical ignition conditions from firebrand pile exposure are needed to design appropriate fire safety standards and WUI fire modeling.},

keywords = {WUI},

pubstate = {published},

tppubtype = {article}

}

@article{hariharan2020PRL,

title = {Effects of circulation and buoyancy on the transition from a fire whirl to a blue whirl},

author = {Sriram Bharath Hariharan, Yu Hu, Michael J. Gollner, and Elaine S. Oran},

url = {http://firelab.berkeley.edu/wp-content/uploads/2021/01/2020-PhysRevFluids.5.103201-effects-of-circulation-and-buouyancy-on-the-transition-from-a-fire-whirl-to-a-blue-whirl_PREPRINT.pdf},

doi = {10.1103/PhysRevFluids.5.103201},

year  = {2020},

date = {2020-10-14},

journal = {Physical Review Fluids},

volume = {5},

number = {103201},

abstract = {The relative influence of circulation and buoyancy on fire whirls (FWs), blue whirls (BWs), and the transition between these regimes of a whirling flame is investigated using a combination of experimental data and scaling analyses. FWs are whirling, turbulent, cylindrical yellow (sooting) flame structures that form naturally in fires and are here created in laboratory experiments. In contrast, a BW is a laminar, blue flame (nonsooting) with an inverted conical shape. Measurements of the circulation and heat-release rate are combined with measurements of the flame geometry, defined by the flame width and the height, to provide characteristic length scales for these whirling-flame regimes. Using these, a nondimensional circulation (Γ∗f) and a heat-release rate (˙Q∗f) were defined and shown to correspond to azimuthal and axial (buoyancy driven) momenta, respectively. The ratio  R∗=Γ∗f/˙Q∗f, a quantity analogous to the swirl number used to characterize swirling jets, was evaluated for FWs and BWs. For FWs, R∗<1, so that axial momentum is greater than azimuthal momentum and the flame is dominated by buoyant momentum. For BWs, R∗>1, so that the flame is circulation dominated. This is argued to be consistent with vortex breakdown being an important part of the transition of FWs to BWs. This work presents a basis for predicting when a BW will form and remain a stable regime.

},

keywords = {Blue whirl, Burning rate, Fire whirl},

pubstate = {published},

tppubtype = {article}

}

@article{hakes2020proci,

title = {Stability of laminar flames on upper and lower inclined fuel surfaces},

author = {R.S.P. Hakes, W. Coenen, A.L. Sánchez, M.J. Gollner, F.A. Williams},

url = {https://doi.org/10.1016/j.proci.2020.06.302},

doi = {10.1016/j.proci.2020.06.302},

year  = {2020},

date = {2020-09-01},

journal = {Proceedings of the Combustion Institute},

abstract = {Experiments have found substantial morphological differences between buoyancy-driven flames developing on the upper and lower surfaces of inclined burning plates. These differences cannot be explained on the basis of existing analytical solutions of steady semi-infinite flames, which provide identical descriptions for the top and bottom configurations. To investigate the potential role of flame instabilities in the experimentally observed flow differences, a temporal linear stability analysis is performed here. The problem is formulated in the limit of infinitely fast reaction, taking into account the non-unity Lewis number of the fuel vapor. The stability analysis incorporates non-parallel effects of the base flow and considers separately spanwise traveling waves and Görtler-like streamwise vortices. The solution to the stability eigenvalue problem determines the downstream location at which the flow becomes unstable, characterized by a critical value of the relevant Grashof number, whose value varies with the plate inclination angle. The results for the flame formed on the underside of the fuel surface indicate that instabilities emerge farther downstream than they do for a flame developing over the top of the fuel surface, in agreement with experimental observations. Increased buoyancy-induced vorticity production is reasoned to be responsible for the augmented instability tendency of topside flames.

},

keywords = {buoyancy driven instability, inclined flame, laminar reacting flow},

pubstate = {forthcoming},

tppubtype = {article}

}

@article{Tao2020,

title = {Effect of firebrand size and geometry on heating from a smoldering pile under wind},

author = {Zhenxiang Tao, Bryce Bathras, Byoungchul Kwon, Ben Biallas, Michael Gollner, Rui Yang},

doi = {https://doi.org/10.1016/j.firesaf.2020.103031},

year  = {2020},

date = {2020-05-07},

journal = {Fire Safety Journal},

abstract = {Smoldering firebrands can be lofted over long distances, easily igniting spot fires. This poses a threat to structures in the wildland-urban interface (WUI), where wildland fires spread into and within communities. This study investigates the influence of firebrand size and makeup on heating from a pile to a recipient surface in a small-scale wind tunnel. Two sizes of fluted birch wooden pins and wooden discs, one size of cylindrical birch dowels, two lengths of eucalyptus sticks, and pine bark flakes were used to simulate firebrands; all with 4 g of smoldering brands deposited. The porosity of the different firebrand piles, the heat flux to an inert test surface, spatial measurements of surface temperature, and videos of the experiments were recorded and analyzed. It was found that the realistic fuels, i.e. pine bark and eucalyptus sticks, could achieve higher peak heat fluxes than artificial birch fuels at higher wind speeds …

},

keywords = {firebrand},

pubstate = {forthcoming},

tppubtype = {article}

}

@article{Ren2020,

title = {Temperature measurement of a turbulent buoyant ethylene diffusion flame using a dual-thermocouple technique},

author = {Xingyu Ren, Dong Zeng, Yi Wang, Gang Xiong, Gaurav Agarwal, Michael Gollner

},

url = {https://doi.org/10.1016/j.firesaf.2020.103061},

doi = {10.1016/j.firesaf.2020.103061},

year  = {2020},

date = {2020-05-07},

journal = {Fire Safety Journal},

abstract = {High-frequency temperature measurements were carefully conducted for a 15 kW buoyant turbulent ethylene diffusion flame over a 15.2 cm diameter gas burner with air co-flow. A dual-thermocouple probe, consisting of two fine-wire thermocouples with 25 μm and 50 μm wire diameters, was used to determine a compensated turbulent gas temperature. A sensitivity analysis shows that temperatures resolved using this dual-thermocouple technique are less sensitive to changes in thermocouple bead size, therefore, uncertainty is greatly reduced even when soot deposition on the thermocouple bead occurs in sooty flames. Mean and root-mean square (rms) fluctuations of gas temperature were recorded in a two-dimensional plane across the flame centerline. The mean gas temperature monotonically decreases away from the flame centerline at most flame heights, except for 1 diameter above the burner, where a …

},

keywords = {temperature},

pubstate = {forthcoming},

tppubtype = {article}

}

@article{MANZELLO2020100801,

title = {Role of firebrand combustion in large outdoor fire spread},

author = {Samuel L Manzello and Sayaka Suzuki and Michael J Gollner and Carlos A Fernandez-Pello},

url = {http://www.sciencedirect.com/science/article/pii/S0360128519300942},

doi = {https://doi.org/10.1016/j.pecs.2019.100801},

issn = {0360-1285},

year  = {2020},

date = {2020-01-01},

journal = {Progress in Energy and Combustion Science},

volume = {76},

pages = {100801},

abstract = {Large outdoor fires are an increasing danger to the built environment. Wildfires that spread into communities, labeled as Wildland-Urban Interface (WUI) fires, are an example of large outdoor fires. Other examples of large outdoor fires are urban fires including those that may occur after earthquakes as well as in informal settlements. When vegetation and structures burn in large outdoor fires, pieces of burning material, known as firebrands, are generated, become lofted, and may be carried by the wind. This results in showers of wind-driven firebrands that may land ahead of the fire front, igniting vegetation and structures, and spreading the fire very fast. Post-fire disaster studies indicate that firebrand showers are a significant factor in the fire spread of multiple large outdoor fires. The present paper provides a comprehensive literature summary on the role of firebrand mechanisms on large outdoor fire spread. Experiments, models, and simulations related to firebrand generation, lofting, burning, transport, deposition, and ignition of materials are reviewed. Japan, a country that has been greatly influenced by ignition induced by firebrands that have resulted in severe large outdoor fires, is also highlighted here as most of this knowledge remains not available in the English language literature. The paper closes with a summary of the key research needs on this globally important problem.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Zhao2019,

title = {Lateral Flame Spread over PMMA Under Forced Air Flow},

author = {Kun Zhao and Michael J Gollner and Qiong Liu and Junhui Gong and Lizhong Yang},

url = {https://doi.org/10.1007/s10694-019-00904-x http://link.springer.com/10.1007/s10694-019-00904-x},

doi = {10.1007/s10694-019-00904-x},

issn = {0015-2684},

year  = {2019},

date = {2019-09-01},

journal = {Fire Technology},

publisher = {Springer US},

abstract = {In wildland and other flame spread scenarios a spreading fire front often forms an elliptical shape, incorporating both forward and lateral spread. While lateral flame spread is much slower than forward rates of spread, it still contributes to the growth of the overall fire front. In this work, a small-scale experiment is performed to investigate the mechanisms causing this lateral spread in a simple, small-scale configuration. PMMA strips with thicknesses ranging from 1 mm to 3.1 mm and widths of 5 cm and 10 cm were ignited under forced flow in a laminar wind tunnel. Unlike traditional concurrent or opposed flame spread experiments, flames were allowed to progress from one side of the sample to the other, perpendicular to the wind direction. An infrared camera was used to track the progression of the pyrolysis front by estimating the surface temperature of the PMMA. The flame spread rate, depth of the burning region, thermal diffusion length, and radiant heat flux were determined and analyzed. Based on a theory of heat and mass transfer for a laminar diffusion flame, a thermal heat transfer model was developed for the preheating region to predict the lateral flame spread rate. Results show that the thermal diffusion length decreases with wind velocity, ranging from 4.5 mm to 3 mm. Convection dominates the flame-spread rate, accounting for more than 80% of the total heat flux. The theoretical flame spread rate agrees well with experimental data from all but the thinnest samples tested, overpredicting the lateral flame spread rate for 1 mm thick samples. The resulting model for lateral flame spread under concurrent flow works for forced-flow dominated flame spread over thermally-thin fuels and helps provide physical insight into the problem, aiding in future development of two-dimensional, elliptical fire spread models.},

keywords = {Diffusion flame, Forced flow, Heat transfer, Lateral flame spread, PMMA},

pubstate = {published},

tppubtype = {article}

}

@article{Hakes2019,

title = {Thermal characterization of firebrand piles},

author = {Raquel S P Hakes and Hamed Salehizadeh and Matthew J Weston-Dawkes and Michael J Gollner},

url = {https://linkinghub.elsevier.com/retrieve/pii/S0379711218302698},

doi = {10.1016/j.firesaf.2018.10.002},

issn = {03797112},

year  = {2019},

date = {2019-03-01},

journal = {Fire Safety Journal},

volume = {104},

pages = {34--42},

publisher = {Elsevier Ltd},

abstract = {The cause of the majority of structure losses in wildland-urban interface fires is ignition via firebrands, small pieces of burning material generated from burning vegetation and structures. To understand the mechanism of these losses, small-scale experiments designed to capture heating from firebrand piles and to describe the process of ignition were conducted using laboratory-fabricated cylindrical wooden firebrands. Two heat flux measurement methods were compared, and the influences of firebrand diameter, pile mass, and wind on heating from firebrand piles were explored. Diameter had little effect on heating, pile mass a moderate effect, and wind a large effect. Peak heat fluxes showed distinct differences between heat fluxes produced by firebrand piles as opposed to individual firebrands, which have been studied exclusively on the small-scale in the past. Above a critical mass, piles did not produce higher heat fluxes; however, they heated fuels for an increasingly longer duration and over a larger area. Water-cooled heat flux gauges provided reliable heat flux measurements for large firebrand piles and an array of thin-skin calorimeters indicated significant spatial variation in heat flux. A recipient fuel transitioned from smoldering to flaming under an adequate wind speed soon after a firebrand pile was deposited on its surface.},

keywords = {burning embers, firebrands, wildfire, wildland-urban interface},

pubstate = {published},

tppubtype = {article}

}

@article{May2019,

title = {An examination of fuel moisture, energy release and emissions during laboratory burning of live wildland fuels},

author = {Nathaniel May and Evan Ellicott and Michael Gollner},

doi = {10.1071/WF18084},

issn = {10498001},

year  = {2019},

date = {2019-01-01},

journal = {International Journal of Wildland Fire},

volume = {28},

number = {3},

pages = {187--197},

abstract = {A series of small-scale laboratory fires were conducted to study the relationship between fuel type, moisture content, energy released and emissions during the combustion process of live wildland fuels. The experimental design sought to understand the effects that varying moisture content of different fire-promoting plant species had on the release of total energy, gaseous emissions (CO, CO2), particulate matter less than 2.5µm in diameter (PM2.5) and fire radiative energy (FRE). Instantaneous FRE, or fire radiative power (FRP), is an important parameter used in remote sensing to relate the emitted energy to the biomass fuel consumption. Currently, remote sensing techniques rely on empirically based linear relationships between emitted FRE and biomass consumed. However, this relationship is based on the assumption that all fuels emit the same amount of energy per unit mass, regardless of fuel conditions (type, moisture, packing, orientation, etc.). In this study, we revisited these assumptions under the influence of moisture content for species that are adapted to fire, containing volatile oils. Results show that, in terms of the total energy released, this assumption holds fairly well regardless of fuel type and moisture content. However, FRE was found to be slightly dependent on the fuel type and very dependent on the moisture content of the fuel. Most of this variation was attributed to changes in the behaviour of the combustion process for different fuels, similarly observed in emissions measurements. These results highlight a need to further examine the role of fuel moisture and combustion state when determining emissions from remotely sensed measurements.},

keywords = {fire radiative energy, moisture content, pyrophytic, remote sensing},

pubstate = {published},

tppubtype = {article}

}

@article{Hariharan2019,

title = {Thermal structure of the blue whirl},

author = {Sriram Bharath Hariharan and Evan T Sluder and Michael J Gollner and Elaine S Oran},

url = {https://linkinghub.elsevier.com/retrieve/pii/S1540748918301160},

doi = {10.1016/j.proci.2018.05.115},

issn = {15407489},

year  = {2019},

date = {2019-01-01},

journal = {Proceedings of the Combustion Institute},

volume = {37},

number = {3},

pages = {4285--4293},

abstract = {textcopyright 2018 Elsevier Ltd. The blue whirl is a recently discovered regime of the fire whirl that burns without any visible soot, even while burning liquid fuels directly. This flame evolves naturally from a traditional fire whirl in a fixed-frame self-entraining fire whirl experimental setup. Here, detailed thermal measurements of the flame structure performed using thermocouples and thin-filament pyrometry are presented. Thermocouple measurements reveal a peak temperature of ~2000 K, and 2-D temperature distributions from pyrometry measurements suggest that most of the combustion occurs in the relatively small, visibly bright, blue vortex ring. Different liquid hydrocarbon fuels such as heptane, iso-octane and cyclohexane consistently formed the blue whirl with similar thermal structures, indicating that blue whirl formation is independent of fuel type, and also that the transition from a fire whirl to a blue whirl may be influenced by vortex breakdown.},

keywords = {Blue whirl, Fire whirl, Soot},

pubstate = {published},

tppubtype = {article}

}

@article{Caton-Kerr2019,

title = {Firebrand Generation From Thermally-Degraded Cylindrical Wooden Dowels},

author = {Sara E Caton-Kerr and Ali Tohidi and Michael J Gollner},

doi = {10.3389/fmech.2019.00032},

issn = {2297-3079},

year  = {2019},

date = {2019-01-01},

journal = {Frontiers in Mechanical Engineering},

volume = {5},

number = {June},

pages = {1--12},

keywords = {dimensional analysis, firebrand, thermal-degradation, wildfire, wildland, wildland-urban interface},

pubstate = {published},

tppubtype = {article}

}

@article{Hariharan2019a,

title = {The blue whirl: Boundary layer effects, temperature and OH* measurements},

author = {Sriram Bharath Hariharan and Paul M Anderson and Huahua Xiao and Michael J Gollner and Elaine S Oran},

url = {https://doi.org/10.1016/j.combustflame.2019.02.018},

doi = {10.1016/j.combustflame.2019.02.018},

issn = {15562921},

year  = {2019},

date = {2019-01-01},

journal = {Combustion and Flame},

volume = {203},

pages = {352--361},

publisher = {Elsevier Inc.},

abstract = {The blue whirl is a small flame with an inverted conical shape, first observed as it developed from fire whirls formed using liquid fuels burning on a water surface. Here, it is shown that the water surface is not critical for a transition from a fire whirl to a blue whirl, but that the surface over which the whirl is formed must be flat without any obstructions to the incoming flow. This observation highlights the importance of the radial boundary layer formed at the base of the whirl. The transition therefore also occurs over a flat metal plate, over which temperature maps of blue whirls are obtained using thin-filament pyrometry. Visualization of the reaction front, by imaging spontaneous OH* chemiluminescence, shows that a significant fraction of the combustion occurs in the small, visibly bright, blue ring. The temperature maps are consistent with the burning structure seen with chemiluminescence, and they are qualitatively similar for blue whirls formed over both water and metal plates. High frame-rate images of the transition process show the presence of a recirculation zone within the flame. Together, these observations distinguish the blue whirl as a flame structure unique from the fire whirl and present a basis for understanding the physical processes which control blue whirl formation and its structure.},

keywords = {Blue whirl, Chemiluminescence, Fire whirl, Vortex breakdown},

pubstate = {published},

tppubtype = {article}

}

@article{Tang2019,

title = {An Experimental Study of Intermittent Heating Frequencies From Wind-Driven Flames},

author = {Wei Tang and Mark Finney and Sara McAllister and Michael Gollner},

doi = {10.3389/fmech.2019.00034},

issn = {2297-3079},

year  = {2019},

date = {2019-01-01},

journal = {Frontiers in Mechanical Engineering},

volume = {5},

number = {June},

pages = {1--9},

abstract = {An experimental study was conducted to understand the intermittent heating behavior downstream of a gaseous line burner under forced flow conditions. While previous studies have addressed time-averaged properties, here measurements of the flame location and intermittent heat flux profile help to give a time-dependent picture of downstream heating from the flame, useful for understanding wind-driven flame spread. Two frequencies are extracted from experiments, the maximum flame forward pulsation frequency in the direction of the wind, which helps describe the motion of the flame, and the local flame-fuel contact frequency in the flame region, which is useful in calculating the actual heat flux that can be received by the unburnt fuel via direct flame contact. The forward pulsation frequency is obtained through video analysis using a variable interval time average (VITA) method. Scaling analysis indicates that the flame forward pulsation frequency varies as a power-law function of the Froude number and fire heat-release rate, . For the local flame-fuel contact frequency, it is found that the non-dimensional flame-fuel contact frequency remains approximately constant before the local Rix reaches 1, e.g., attached flames. When Rixtextgreater1, decreases with local as Rix flames lift up. A piece-wise function was proposed to predict the local flame-fuel contact frequency including the two Rix scenarios. Information from this study helps to shed light on the intermittent behavior of flames under wind, which may be a critical factor in explaining the mechanisms of forward flame spread in wildland and other similar wind-driven fires.},

keywords = {flame contact, Flame spread, pulsation frequency, wildfire, wind-driven},

pubstate = {published},

tppubtype = {article}

}

@article{Hu2019,

title = {Conditions for formation of the blue whirl},

author = {Yu Hu and Sriram Bharath Hariharan and Haiying Qi and Michael J Gollner and Elaine S Oran},

doi = {10.1016/j.combustflame.2019.03.043},

issn = {15562921},

year  = {2019},

date = {2019-01-01},

journal = {Combustion and Flame},

volume = {205},

pages = {147--153},

abstract = {This paper presents a laboratory study of the relation between blue whirls and fire whirls in terms of circulation (swirl) and energy-release rate. The blue whirl is a small, completely blue, soot-free flame that was originally seen when it evolved from more traditional fire whirls burning liquid hydrocarbons on water. The experimental apparatus consists of two offset quartz half-cylinders suspended over a water surface, with fuel injected onto the water surface from below. The flow circulation is calculated using the diameter of the enclosure and hot-wire velocity measurements made at the inlet gap between the half-cylinders. The heat-release rate was varied by adjusting the volumetric supply rate of liquid n-heptane, and is calculated assuming complete combustion. Results show that stable blue whirls form in a narrow range of circulation and energy-release rate close to a previously cited extinction limit. A scaling law derived from the data, based on the length scale of the enclosure, shows that the transition to a blue whirl depends on the gap size between the half-cylinders of the enclosure.},

keywords = {Blue whirl, Fire whirl, Scaling},

pubstate = {published},

tppubtype = {article}

}

@article{JU20191,

title = {Downstream radiative and convective heating from methane and propane fires with cross wind},

author = {Xiaoyu Ju and Michael J Gollner and Yiren Wang and Wei Tang and Kun Zhao and Xingyu Ren and Lizhong Yang},

url = {http://www.sciencedirect.com/science/article/pii/S0010218019300951},

doi = {https://doi.org/10.1016/j.combustflame.2019.03.001},

issn = {0010-2180},

year  = {2019},

date = {2019-01-01},

journal = {Combustion and Flame},

volume = {204},

pages = {1 - 12},

abstract = {Experiments were conducted to elucidate the radiative and convective heating occurring downstream of wind-driven fires produced by a gaseous burner. These flames model, at reduced scale, some of the dynamics observed in wind-driven fire spread through wildlands, buildings, mines or tunnels. Methane and propane were used to create fires ranging from 5 to 25 kW with ambient velocities ranging from 0.6 to 2.2 m/s. The total and incident radiative heat flux to a nearly-adiabatic downstream surface were measured by a water-cooled total heat flux gauge and a radiometer, respectively. The interaction between the buoyancy induced by the flame and momentum from the free stream was represented by a mixed-convection parameter, ξ=Grx2/Rex1n, where n = 3/2, 2 or 5/2. ξ was evaluated with two length scales in order to capture effects of both the boundary layer development length (x1) and heated distance downstream of the burner (x2). Results showed that the propane flame (high luminosity) exhibited slightly higher radiative heat fluxes than methane flames (low luminosity) under the same external conditions, while the convective heat flux followed an opposite trend. The downstream local radiative heat flux was quantified using a dimensionless flame thickness δx*, which showed a good relationship with ξ for n = 5/2 but not 3/2 or 2. The local convective heat transfer coefficient was expressed in the form of a local Nusselt number, Nux2Rex1−1/2, and correlated well as a piecewise function with ξ for n = 5/2. It was found that both δx* and Nux2Rex1−1/2 have a turning point at ξ ≈ 0.005, which was visually shown to denote the location where transition between an attachment and plume-like flame occurs. By separately describing both radiative and convective downstream heating, the mechanisms controlling heating which drives flame spread in wind-driven fires can be further understood.},

keywords = {Cross wind, Downstream heating, Flame attachment, Flame spread},

pubstate = {published},

tppubtype = {article}

}

@article{MCNAMEE2019102889,

title = {IAFSS agenda 2030 for a fire safe world},

author = {Margaret McNamee and Brian Meacham and Patrick van Hees and Luke Bisby and W K Chow and Alexis Coppalle and Ritsu Dobashi and Bogdan Dlugogorski and Rita Fahy and Charles Fleischmann and Jason Floyd and Edwin R Galea and Michael Gollner and Tuula Hakkarainen and Anthony Hamins and Longhua Hu and Peter Johnson and Björn Karlsson and Bart Merci and Yoshifuni Ohmiya and Guillermo Rein and Arnaud Trouvé and Yi Wang and Beth Weckman},

url = {http://www.sciencedirect.com/science/article/pii/S0379711219303509},

doi = {https://doi.org/10.1016/j.firesaf.2019.102889},

issn = {0379-7112},

year  = {2019},

date = {2019-01-01},

journal = {Fire Safety Journal},

volume = {110},

pages = {102889},

abstract = {The International Association of Fire Safety Science (IAFSS) is comprised of members from some 40 countries. This paper presents the Association's thinking, developed by the Management Committee, concerning pressing research needs for the coming 10 years presented as the IAFSS Agenda 2030 for a Fire Safe World. The research needs are couched in terms of two broad Societal Grand Challenges: (1) climate change, resiliency and sustainability and (2) population growth, urbanization and globalization. The two Societal Grand Challenges include significant fire safety components, that lead both individually and collectively to the need for a number of fire safety and engineering research activities and actions. The IAFSS has identified a list of areas of research and actions in response to these challenges. The list is not exhaustive, and actions within actions could be defined, but this paper does not attempt to cover all future needs.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Zhao2018,

title = {Experimental and theoretical study on downward flame spread over uninhibited PMMA slabs under different pressure environments},

author = {K Zhao and X Zhou and X Liu and W Tang and M Gollner and F Peng and L Yang},

doi = {10.1016/j.applthermaleng.2018.02.059},

issn = {13594311},

year  = {2018},

date = {2018-01-01},

journal = {Applied Thermal Engineering},

volume = {136},

abstract = {textcopyright 2018 Elsevier Ltd This paper presents an experimental and theoretical study of side-edge effects on downward flame spread over two parallel polymethyl methacrylate (PMMA) slabs under different pressure environments. Identical experiments of downward flame spread over thin PMMA slabs with side-edges unrestrained were conducted at different altitudes in Hefei (102 kPa), Geermu (73.2 kPa) and Lhasa (66.3 kPa). Experimental results show that the flame spread rate is controlled by ignition along the side-edge, rather than at the center of the samples, for experiments with both single and two parallel slabs. Based on these results, a thermal model is developed which describes flame spread along the edge and quantitatively agrees with experimental results. In the parallel-slab case, convective heating appears to influence the spread rate only when the separation distance is very small, with radiative heating playing a more important role as separation distance increases. The angle of the pyrolysis front, formed between the faster side-edge spread and slower center-region spread, hardly changes with pressure, but changes significantly with separation distance, due to differing modes of heat transfer between the side-edge and center region. In addition, variations of flame height with pressure and separation distance are reasonably interpreted from diffusion flame theory.},

keywords = {Ambient pressure, Downward flame spread, Heat transfer, Parallel-slab, Side-edge effects},

pubstate = {published},

tppubtype = {article}

}

@article{Miller2018,

title = {Boundary layer instabilities in mixed convection and diffusion flames with an unheated starting length},

author = {Colin H Miller and Wei Tang and Evan Sluder and Mark A Finney and Sara S McAllister and Jason M Forthofer and Michael J Gollner},

url = {https://doi.org/10.1016/j.ijheatmasstransfer.2017.11.040},

doi = {10.1016/j.ijheatmasstransfer.2017.11.040},

issn = {00179310},

year  = {2018},

date = {2018-01-01},

journal = {International Journal of Heat and Mass Transfer},

volume = {118},

pages = {1243--1256},

publisher = {Elsevier Ltd},

abstract = {The following study examines the role of streaklike coherent structures in mixed convection via a horizontal heated boundary layer possessing an unheated starting length. The three-dimensionality of flows in this configuration, which is regularly encountered in practical scenarios, has been experimentally probed using non-invasive detection methods. Experiments were conducted in a wind tunnel at the Missoula Fire Sciences Lab, and the wind speed was varied from 0.70 to 2.47 m/s. The buoyant source was varied significantly by either manipulating the surface temperature of a downstream hot plate or employing a diffusion flame. Streaks were visualized in the flow by means of infrared imaging or high speed video, and a novel detection algorithm was developed to quantify important properties and to spatially track these structures over time. Lognormal distributions of spacing were observed initially, and gradual deviations from this fit indicated a deviation from streaklike behavior. The onset of streaks was determined to be controlled by the pre-existing disturbances populating the incoming boundary layer. Further downstream, buoyant forces dominated the growth and deformation of these structures, whose length scale increased significantly. The width of structures was observed to asymptote to a stable value downstream, and this was determined to be a consequence of the finite distance over which heating was applied.},

keywords = {Boundary layer, Coherent structures, Flame, Instability, Laminar, Mixed convection, Streaks},

pubstate = {published},

tppubtype = {article}

}

@article{Miller2018a,

title = {Boundary layer instabilities in mixed convection and diffusion flames with an unheated starting length},

author = {C H Miller and W Tang and E Sluder and M A Finney and S S McAllister and J M Forthofer and M J Gollner},

doi = {10.1016/j.ijheatmasstransfer.2017.11.040},

issn = {00179310},

year  = {2018},

date = {2018-01-01},

journal = {International Journal of Heat and Mass Transfer},

volume = {118},

abstract = {textcopyright 2017 The following study examines the role of streaklike coherent structures in mixed convection via a horizontal heated boundary layer possessing an unheated starting length. The three-dimensionality of flows in this configuration, which is regularly encountered in practical scenarios, has been experimentally probed using non-invasive detection methods. Experiments were conducted in a wind tunnel at the Missoula Fire Sciences Lab, and the wind speed was varied from 0.70 to 2.47 m/s. The buoyant source was varied significantly by either manipulating the surface temperature of a downstream hot plate or employing a diffusion flame. Streaks were visualized in the flow by means of infrared imaging or high speed video, and a novel detection algorithm was developed to quantify important properties and to spatially track these structures over time. Lognormal distributions of spacing were observed initially, and gradual deviations from this fit indicated a deviation from streaklike behavior. The onset of streaks was determined to be controlled by the pre-existing disturbances populating the incoming boundary layer. Further downstream, buoyant forces dominated the growth and deformation of these structures, whose length scale increased significantly. The width of structures was observed to asymptote to a stable value downstream, and this was determined to be a consequence of the finite distance over which heating was applied.},

keywords = {Boundary layer, Coherent structures, Flame, Instability, Laminar, Mixed convection, Streaks},

pubstate = {published},

tppubtype = {article}

}

@article{Jiang2018,

title = {Flame spread and burning rates through vertical arrays of wooden dowels},

author = {Lin Jiang and Zhao Zhao and Wei Tang and Colin Miller and Jin Hua Sun and Michael J Gollner},

doi = {10.1016/j.proci.2018.09.008},

issn = {15407489},

year  = {2018},

date = {2018-01-01},

journal = {Proceedings of the Combustion Institute},

volume = {000},

pages = {1--8},

publisher = {Elsevier Inc.},

abstract = {Fuel loads in real-world fire scenarios often feature discrete elements, discontinuities, or inhomogeneities; however, most models for flame spread only assume a continuous, homogeneous fuel. Because discrete fuels represent a realistic scenario not yet well-modeled, it is of interest to find simple methods to model fire growth first in simple, laboratory-scale configurations. A detailed experimental and theoretical study was therefore performed to investigate the controlling mechanisms of flame spread through arrays of wooden dowels, with dowel spacings of 0.75, 0.875, and 1.5 cm. Flames were found to spread vertically for all spacings; however, for the 1.5 cm spacing, the gap was too large for horizontal flame spread to occur. A radiation-controlled model for horizontal flame spread was developed that predicted the horizontal flame spread rate through various arrays of dowels. Combined with an existing convection-based model for vertical flame spread, both horizontal and vertical flame spread was modeled to predict the number of burning wooden dowels as a function of time. Using models for the burning rate of wooden dowels and boundary-layer theory, a global burning rate model was developed that provided reasonable agreement with experimental results.},

keywords = {Flame spread, Heat transfer, Mass loss rate, Wooden dowel},

pubstate = {published},

tppubtype = {article}

}

@article{Manzello2018,

title = {Summary of workshop large outdoor fires and the built environment},

author = {Samuel L Manzello and Raphaele Blanchi and Michael J Gollner and Daniel Gorham and Sara McAllister and Elsa Pastor and Eul{à}lia Planas and Pedro Reszka and Sayaka Suzuki},

url = {https://doi.org/10.1016/j.firesaf.2018.07.002},

doi = {10.1016/j.firesaf.2018.07.002},

issn = {03797112},

year  = {2018},

date = {2018-01-01},

journal = {Fire Safety Journal},

volume = {100},

number = {December 2017},

pages = {76--92},

publisher = {Elsevier Ltd},

abstract = {Large outdoor fires present a risk to the built environment. Wildfires that spread into communities, referred to as Wildland-Urban Interface (WUI) fires, have destroyed communities throughout the world, and are an emerging problem in fire safety science. Other examples are large urban fires including those that have occurred after earthquakes. Research into large outdoor fires, and how to potentially mitigate the loss of structures in such fires, lags other areas of fire safety science research. At the same time, common characteristics between fire spread in WUI fires and urban fires have not been fully exploited. In this paper, an overview of the large outdoor fire risk to the built environment from each region is presented. Critical research needs for this problem in the context of fire safety science are provided. The present paper seeks to develop the foundation for an international research needs roadmap to reduce the risk of large outdoor fires to the built environment.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Tohidi2018,

title = {Fire Whirls},

author = {Ali Tohidi and Michael J Gollner and Huahua Xiao},

doi = {10.1146/annurev-fluid-122316-045209},

issn = {0066-4189},

year  = {2018},

date = {2018-01-01},

journal = {Annual Review of Fluid Mechanics},

volume = {50},

number = {1},

pages = {187--213},

abstract = {Fire whirls present a powerful intensification of combustion, long studied in the fire research community because of the dangers they present during large urban and wildland fires. However, their destructive power has hidden many features of their formation, growth, and propagation. Therefore, most of what is known about fire whirls comes from scale modeling experiments in the laboratory. Both the methods of formation, which are dominated by wind and geometry, and the inner structure of the whirl, including velocity and temperature fields, have been studied at this scale. Quasi-steady fire whirls directly over a fuel source form the bulk of current experimental knowledge, although many other cases exist in nature. The structure of fire whirls has yet to be reliably measured at large scales; however, scaling laws have been relatively successful in modeling the conditions for formation from small to large scales. This review surveys the state of knowledge concerning the fluid dynamics of fire whirls, including the conditions for their formation, their structure, and the mechanisms that control their unique state. We highlight recent discoveries and survey potential avenues for future research, including using the properties of fire whirls for efficient remediation and energy generation.},

keywords = {Combustion, Fire whirl, tornado, vortex, Vortex breakdown},

pubstate = {published},

tppubtype = {article}

}

@article{BROWN20181,

title = {Proceedings of the first workshop organized by the IAFSS Working Group on Measurement and Computation of Fire Phenomena (MaCFP)},

url = {http://www.sciencedirect.com/science/article/pii/S0379711218301814},

doi = {https://doi.org/10.1016/j.firesaf.2018.08.009},

issn = {0379-7112},

year  = {2018},

date = {2018-01-01},

journal = {Fire Safety Journal},

volume = {101},

pages = {1 - 17},

abstract = {This paper provides a report of the discussions held at the first workshop on Measurement and Computation of Fire Phenomena (MaCFP) on June 10–11 2017. The first MaCFP workshop was both a technical meeting for the gas phase subgroup and a planning meeting for the condensed phase subgroup. The gas phase subgroup reported on a first suite of experimental-computational comparisons corresponding to an initial list of target experiments. The initial list of target experiments identifies a series of benchmark configurations with databases deemed suitable for validation of fire models based on a Computational Fluid Dynamics approach. The simulations presented at the first MaCFP workshop feature fine grid resolution at the millimeter- or centimeter-scale: these simulations allow an evaluation of the performance of fire models under high-resolution conditions in which the impact of numerical errors is reduced and many of the discrepancies between experimental data and computational results may be attributed to modeling errors. The experimental-computational comparisons are archived on the MaCFP repository [1]. Furthermore, the condensed phase subgroup presented a review of the main issues associated with measurements and modeling of pyrolysis phenomena. Overall, the first workshop provided an illustration of the potential of MaCFP in providing a response to the general need for greater levels of integration and coordination in fire research, and specifically to the particular needs of model validation.},

keywords = {Buoyant plumes, Fire modeling, Flame extinction, Large eddy simulation, Pool fires, Pyrolysis modeling, Wall fires},

pubstate = {published},

tppubtype = {article}

}

@article{Caton2016a,

title = {Review of Pathways for Building Fire Spread in the Wildland Urban Interface Part I: Exposure Conditions},

author = {Sara E Caton and Raquel S P Hakes and Daniel J Gorham and Aixi Zhou and Michael J Gollner},

url = {http://link.springer.com/10.1007/s10694-016-0589-z},

doi = {10.1007/s10694-016-0589-z},

issn = {0015-2684},

year  = {2017},

date = {2017-03-01},

journal = {Fire Technology},

volume = {53},

number = {2},

pages = {429--473},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Tang2017,

title = {An experimental study on the intermittent extension of flames in wind-driven fires},

author = {W Tang and D J Gorham and M A Finney and S Mcallister and J Cohen and J Forthofer and M J Gollner},

doi = {10.1016/j.firesaf.2017.03.030},

issn = {03797112},

year  = {2017},

date = {2017-01-01},

journal = {Fire Safety Journal},

volume = {91},

abstract = {textcopyright 2017 Elsevier Ltd Experiments were conducted to study the intermittent extension of flames from wind-driven line fires using stationary burners. These fires are thought to share similar features with propagating wildland fires, where forward pulsations of flame have been observed to quickly ignite material far ahead of the mean flame front. However, stationary burners offer the ability to study the movement of the flame and its heating processes in greater detail than a spreading fire. In these stationary experiments, propane gas was used as a fuel with different burner sizes, 25–30 cm wide and 5–25 cm long in the direction of the flow. A specially-built wind tunnel was used to provide a well-characterized laminar flow for the experimental area. The free-stream flow velocity, measured by a hot-wire anemometer, ranged in the experiments from 0.2 to 2.7 m/s. The shape of the flame was measured using a high-speed video camera mounted perpendicular to the apparatus. A method was developed to track the extension of the flame close to the surface, simulating flame contact with unburnt fuel downstream of the fire. This extension length was then measured frame by frame and frequencies of flame presence/absence determined as a function of downstream distance. The location of maximum pulsation frequency, x max , for each burner/wind configuration, was obtained using a level-crossing approach (essentially the variable-interval time-average (VITA) method). Further study indicates that x max can be well estimated using mean flame properties. Probability distributions describing the location of the flame over time also showed that, the probability the flame extends far beyond the mean flame front is sensitive to increasing ambient winds and fire size.},

keywords = {Flame extension, Forward pulsation, Intermittent heating, Wind-driven fires},

pubstate = {published},

tppubtype = {article}

}

@article{Jiang2017,

title = {Sample width and thickness effects on horizontal flame spread over a thin PMMA surface},

author = {L Jiang and C H Miller and M J Gollner and J -H Sun},

doi = {10.1016/j.proci.2016.06.157},

issn = {15407489},

year  = {2017},

date = {2017-01-01},

journal = {Proceedings of the Combustion Institute},

volume = {36},

number = {2},

abstract = {textcopyright 2016 Elsevier Ltd. In previous studies, it was found that there exists a minimum flame spread rate under a certain range of sample widths for steady burning horizontal flame spread. While this was hypothesized to occur due to a transition between convectively-dominated to radiation-dominated flame spread, no measurements were performed to quantify this process. This paper presents a detailed experimental study investigating sample width and thickness effects on steady horizontal flame spread, including detailed measurements of the components of radiation, convection, and conduction. Water-cooled heat flux gauges, R-type micro-thermocouples traversed through the gas phase, and K-type thermocouples embedded in the solid phase were all used to deduce these heat transfer components. Results show that convective heat transfer decreases with increasing sample width as the shape of the flame front is on average farther from the fuel surface, while radiation increases as the view factor from the fire to unignited fuel increases with larger sample size. Conduction measured within the fuel sample is, as expected, confirmed to be negligible. Comparing a combination of these components, the total heat flux first decreases as the competition between radiation and convection changes, followed by steadily increasing heat fluxes as the width of the sample increases. Heat feedback also influences the sample pyrolysis rate, so there was a coupled response following this trend. The apparent dip followed by an increase in total heat flux can now explain why a period of minimum flame spread rate exists. Modification of an existing theory also matches experimental results very closely. Finally, a dimensionless heat-release rate for different sample configurations is used to scale the dimensionless flame heights with a power-law correlation having exponents 0.39 for Q∗ textgreater 1 and 0.6 for Q∗ textless 1, closely resembling the 2/5 and 2/3 predicted by Zukoski's model.},

keywords = {Convection, Horizontal flame spread, Radiation, Thickness, Width},

pubstate = {published},

tppubtype = {article}

}

@article{Tang2017a,

title = {Local flame attachment and heat fluxes in wind-driven line fires},

author = {W Tang and C H Miller and M J Gollner},

doi = {10.1016/j.proci.2016.06.064},

issn = {15407489},

year  = {2017},

date = {2017-01-01},

journal = {Proceedings of the Combustion Institute},

volume = {36},

number = {2},

abstract = {textcopyright 2016 by The Combustion Institute. Published by Elsevier Inc. A detailed experimental investigation of turbulent diffusion flames under forced flow was conducted to study local heat fluxes to a nearly adiabatic surface downstream of a gaseous line burner. A variety of ambient wind velocities and fuel flow rates were employed to study different fire scenarios modeling the dynamics of wind-driven fire spread as found in wildland, mine or tunnel fires. The downstream heat flux distribution was correlated as a piecewise function with the Richardson number in two regimes, the first with higher heat fluxes, where the flame remained attached the downstream surface (attached region) and the second with a steeper decay of heat fluxes (plume region). Analysis of the heat flux distribution revealed that local heat fluxes roughly reach a maximum where the Richardson number equaled unity. This was thought to be a good marker of the regime where the flame detaches from the surface, e.g. where buoyancy from the flame overcomes inertial forces from the oncoming flow. This observation was further corroborated by analysis of side-view images of the flame, which showed the attachment location was linearly correlated with the location where the Richardson number equaled unity. The results from this study suggest that local heat flux values reach a maximum at the transition between a momentum-dominated (attached, wind-driven) to buoyancy-dominated (plume or fire) regime in forced flow scenarios. The results have interesting implications to the problem of flame attachment, which is known to accelerate fire spread in both inclined and wind-driven fire scenarios.},

keywords = {Concurrent spread, Flame attachment, Heat flux, Wildland fire, Wind-driven flame spread},

pubstate = {published},

tppubtype = {article}

}

@article{Miller2017,

title = {Investigating coherent streaks in wildfires via heated plates in crosswind},

author = {C Miller and M A Finney and S McAllister and E Sluder and M J Gollner},

doi = {10.1016/j.firesaf.2017.03.035},

issn = {03797112},

year  = {2017},

date = {2017-01-01},

journal = {Fire Safety Journal},

volume = {91},

abstract = {textcopyright 2017 Elsevier Ltd Streaklike coherent structures are consistently observed in boundary layer flames, but their role in modifying heat and mass transfer remains unknown. In the following experiment, a non-reactive thermal plume was employed to study analogous streaks in an environment where the local source of buoyancy could be directly modified. A horizontal hot plate was exposed to crossflow, and infrared thermography was successfully employed to capture thermal traces of streaks on the surface. Post-processing of surface temperature data enabled the quantification of important properties of streaks, such as location, spacing, width, and strength. The distribution of streak spacing was found to have a lognormal distribution. Mean streak spacing and width increased with downstream distance, indicating the amplification and aggregation of coherent structures. Streak spacing decreased when either the hot plate temperature increased from 150 °C to 300 °C or the wind speed increased from 0.5 to 1.2 m/s. Streaks were seen to modify the spanwise distribution of heat transfer to the surface, most notably when the hot plate temperature was increased from 150 °C to 300 °C.},

keywords = {Boundary layer, Coherent structure, Flame spread, Heat transfer, Infrared, Streak, Thermography, Wildfires},

pubstate = {published},

tppubtype = {article}

}

@article{Singh2017,

title = {Steady and transient pyrolysis of a non-charring solid fuel under forced flow},

author = {A V Singh and M J Gollner},

doi = {10.1016/j.proci.2016.07.043},

issn = {15407489},

year  = {2017},

date = {2017-01-01},

journal = {Proceedings of the Combustion Institute},

volume = {36},

number = {2},

abstract = {textcopyright 2016 by The Combustion Institute. Published by Elsevier Inc. In previous work, the Reynolds analogy was used to develop a theoretical expression that allowed for the estimation of local mass burning rates in steady laminar boundary layer diffusion flames established over liquid and solid fuels. This technique was used to elucidate the mechanisms responsible for pyrolysis of both solid and liquid fuels in forced and free convective environments. These previous studies, however, focused on steady results that occur early in the combustion process, before regression of the fuel surface begins to influence results. In this work, a thorough experimental investigation of steady and transient pyrolysis of clear cast Poly Methyl Methacrylate (PMMA) is presented using both local pyrolysis rates and heat feedback to the condensed fuel surface measured at different streamwise locations in a bench-scale wind tunnel. A functional form of the Nusselt number is derived that can be readily used to identify these steady and transient regimes of PMMA burning in the form of local convective heat transfer coefficients. At early times ( textless 150 s), a steady burning regime is identified where heat feedback properties are constant and the gas phase can be assumed to be in a steady state. At later times, a transient burning regime dominated by solid-phase effects occurs. Heat feedback from the flame and hence local mass loss rates measured at later times are transient in nature and do not correspond well with the steady state theoretical solution. Investigation under different forced-flow wind conditions reveals this transient phenomena most likely occurs due to both deformation of the surface of PMMA and solid-phase conduction into the fuel, which eventually influences the gas phase. The results presented will be useful for future modeling of transient solid-phase combustion, especially as it is applied to studies of flame spread.},

keywords = {Local heat fluxes, Local pyrolysis rate, Nusselt number, PMMA, Reynolds analogy},

pubstate = {published},

tppubtype = {article}

}

@article{Hariharan2017,

title = {The Structure of the Blue Whirl},

author = {S B Hariharan and Y Hu and H Xiao and M J Gollner and Elaine S Oran},

url = {http://meetings.aps.org/link/BAPS.2017.DFD.D35.3},

doi = {10.1016/j.proci.2018.05.115},

issn = {1540-7489},

year  = {2017},

date = {2017-01-01},

journal = {70th Annual Meeting of the APS Division of Fluid Dynamics},

volume = {000},

pages = {1--9},

abstract = {Recent experiments have led to the discovery of the blue whirl, a small, stable regime of the fire whirl that burns typically sooty liquid hydrocarbons without producing soot. The physical structure consists of three regions -- the blue cone, the vortex rim and the purple haze. The physical nature of the flame was further investigated through digital imaging techniques, which suggest that the transition (from the fire whirl to the blue whirl) and shape of the flame may be influenced by vortex breakdown. The flame was found to develop over a variety of surfaces, which indicates that the formation of the blue whirl is strongly influenced by the flow structure over the incoming boundary layer. The thermal structure was investigated using micro-thermocouples, thin-filament pyrometry and OH* spectroscopy. These revealed a peak temperature around 2000 K, and that most of the combustion occurs in the relatively small, visibly bright vortex rim. The results of these investigations provide a platform to develop a theory on the structure of the blue whirl, a deeper understanding of which may affirm potential for applications in the energy industry. *This work was supported by an NSF EAGER award and Minta Martin Endowment Funds in the Department of Aerospace Engineering at the University of Maryland.},

keywords = {Blue whirl, Fire whirl, Soot},

pubstate = {published},

tppubtype = {article}

}

@article{Hall2017,

title = {A Survey of Transient Fire Load on Passenger Ferry Vessels},

author = {Brian M Hall and Michael J Gollner},

doi = {10.1007/s10694-016-0629-8},

issn = {15728099},

year  = {2017},

date = {2017-01-01},

journal = {Fire Technology},

volume = {53},

number = {3},

pages = {1471--1478},

publisher = {Springer US},

abstract = {Aluminum ferries in the United States are unique in that they have policy requirements limiting the weight of luggage carried per fixed passenger seat, which is accomplished by controlling the weight of baggage per passenger, but no means to enforce this requirement. A survey of passenger ferry vessels was performed to determine the type of baggage loading present in these passenger compartments. The type, carriage rate, and weight were recorded to determine the transient fire load as well as the average weight of luggage brought on board. The average baggage weight for the commuter vs. non-commuter ferries surveyed in this study were found to be 2.8 and 3.7 kg per person, respectively. These numbers are in close agreement with the average weight per person calculated for carriage on trains. Survey data indicates that the current average baggage weight of 3.7 kg exceeds that allowed by Coast Guard policy for 93% of vessels, with the remaining 7% falling within the policy requirements due to unusually low seat density in the main passenger compartment. This highlights a potential pitfall in current regulatory standards that may present a mismatch for performance and prescriptive based requirements. As few baggage surveys have been conducted on commuter vessels, this data which includes both number and weight distributions per baggage type may also be useful for transient fire load calculations in the future.},

keywords = {Aluminum, Baggage, Ferry, Fire load, Transient},

pubstate = {published},

tppubtype = {article}

}

@article{caton2017review,

title = {Review of pathways for building fire spread in the wildland urban interface part I: exposure conditions},

author = {Sara E Caton and Raquel SP Hakes and Daniel J Gorham and Aixi Zhou and Michael J Gollner},

year  = {2017},

date = {2017-01-01},

journal = {Fire technology},

volume = {53},

number = {2},

pages = {429--473},

publisher = {Springer},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{hakes2017review,

title = {A review of pathways for building fire spread in the wildland urban interface part II: response of components and systems and mitigation strategies in the United States},

author = {Raquel SP Hakes and Sara E Caton and Daniel J Gorham and Michael J Gollner},

year  = {2017},

date = {2017-01-01},

journal = {Fire technology},

volume = {53},

number = {2},

pages = {475--515},

publisher = {Springer},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{ZHANG2017758,

title = {Evaluation of a data-driven wildland fire spread forecast model with spatially-distributed parameter estimation in simulations of the FireFlux I field-scale experiment},

author = {Cong Zhang and Mélanie Rochoux and Wei Tang and Michael Gollner and Jean-Baptiste Filippi and Arnaud Trouvé},

url = {http://www.sciencedirect.com/science/article/pii/S0379711217301005},

doi = {https://doi.org/10.1016/j.firesaf.2017.03.057},

issn = {0379-7112},

year  = {2017},

date = {2017-01-01},

journal = {Fire Safety Journal},

volume = {91},

pages = {758 - 767},

abstract = {The general objective of this research is to develop a prototype data-driven wildland fire spread simulator, called FIREFLY, using an ensemble-based data assimilation approach with the objective to forecast the location and speed of the fire. The specific focus of the present study is on evaluating the new features of FIREFLY at field scale in a controlled grassland fire experiment known as FireFlux I. FIREFLY features the following components: an Eulerian front-tracking solver that treats the fire as a propagating front and uses Rothermel's model for the rate of spread (ROS); a series of observations of the fire front position (based here on high-resolution fireline data previously generated by validated numerical simulations); and a data assimilation algorithm based on an ensemble Kalman filter configured in a parameter estimation mode to address model bias and uncertainties in the input data to the ROS model. In this work, FIREFLY is modified to allow for an estimation of spatially-distributed surface wind speed and direction. To generate a reliable ensemble and ensure an accurate correction, the ensemble Kalman filter requires sampling truncated probability density functions as well as localizing, i.e., dynamically selecting the areas where the wind parameters are corrected. Results show that the spatialized parameter estimation approach allows for a successful reconstruction of observed fireline position and shape as well as a substantial improvement in the forecast performance compared to the standalone fire spread model. Results also show that the inferred wind parameters may not be accurate and should be viewed as effective values that incorporate multiple sources of uncertainties. Developing a better representation of fire-wind interactions is thus viewed as a key aspect to improve the FIREFLY forecast capability.},

note = {Fire Safety Science: Proceedings of the 12th International Symposium},

keywords = {Data assimilation, Fire modeling, Fire spread, Parameter estimation, Wildfires},

pubstate = {published},

tppubtype = {article}

}

@article{MILLER2017123,

author = {Colin H Miller and Wei Tang and Mark A Finney and Sara S McAllister and Jason M Forthofer and Michael J Gollner},

url = {http://www.sciencedirect.com/science/article/pii/S0010218017300998},

doi = {https://doi.org/10.1016/j.combustflame.2017.03.007},

issn = {0010-2180},

year  = {2017},

date = {2017-01-01},

journal = {Combustion and Flame},

volume = {181},

pages = {123 - 135},

keywords = {Boundary layer, Coherent structures, Diffusion flame, Instability, Laminar, Streak},

pubstate = {published},

tppubtype = {article}

}

@article{GOLLNER201768,

title = {The effect of flow and geometry on concurrent flame spread},

author = {Michael J Gollner and Colin H Miller and Wei Tang and Ajay V Singh},

url = {http://www.sciencedirect.com/science/article/pii/S0379711217303454},

doi = {https://doi.org/10.1016/j.firesaf.2017.05.007},

issn = {0379-7112},

year  = {2017},

date = {2017-01-01},

journal = {Fire Safety Journal},

volume = {91},

pages = {68 - 78},

abstract = {Flame spread is an important parameter used in the evaluation of hazards for fire safety applications. The problem of understanding and modeling flame spread has been approached before, however new developments continue to challenge our current view of the subject, necessitating future research efforts in the field. In this review, the problem of flame spread will be revisited, with a particular emphasis on the effect of flow and geometry on concurrent flame spread over solid fuels. The majority of this research is based on that of the senior author, who has worked on wind-driven flame spread, inclined fire spread, flame spread through discrete fuels and the particular problem of wildland fires, where all of the above scenarios play an important role. Recent developments in these areas have improved our understanding of flame-spread processes and will be reviewed, and areas for future research will be highlighted.},

note = {Fire Safety Science: Proceedings of the 12th International Symposium},

keywords = {Burning rate, Concurrent, Flame spread, Inclined, Wildland fires, wind-driven},

pubstate = {published},

tppubtype = {article}

}

@article{Xiao2016,

title = {From fire whirls to blue whirls and combustion with reduced pollution},

author = {H Xiao and M J Gollner and E S Oran},

doi = {10.1073/pnas.1605860113},

issn = {10916490},

year  = {2016},

date = {2016-01-01},

journal = {Proceedings of the National Academy of Sciences of the United States of America},

volume = {113},

number = {34},

abstract = {textcopyright 2016, National Academy of Sciences. All rights reserved. Fire whirls are powerful, spinning disasters for people and surroundings when they occur in large urban and wildland fires. Whereas fire whirls have been studied for fire-safety applications, previous research has yet to harness their potential burning efficiency for enhanced combustion. This article presents laboratory studies of fire whirls initiated as pool fires, but where the fuel sits on a water surface, suggesting the idea of exploiting the high efficiency of fire whirls for oil-spill remediation. We show the transition from a pool fire, to a fire whirl, and then to a previously unobserved state, a "blue whirl." A blue whirl is smaller, very stable, and burns completely blue as a hydrocarbon flame, indicating sootfree burning. The combination of fast mixing, intense swirl, and the water-surface boundary creates the conditions leading to nearly soot-free combustion. With the worldwide need to reduce emissions from both wanted and unwanted combustion, discovery of this state points to possible new pathways for reduced-emission combustion and fuel-spill cleanup. Because current methods to generate a stable vortex are difficult, we also propose that the blue whirl may serve as a research platform for fundamental studies of vortices and vortex breakdown in fluid mechanics.},

keywords = {Blue whirl, Combustion, Fire whirl, Soot free, Vortex breakdown},

pubstate = {published},

tppubtype = {article}

}

@article{Gollner2016,

title = {Detection and Suppression of Fires: A Cornerstone of Fire Protection Engineering},

author = {M J Gollner},

doi = {10.1007/s10694-016-0606-2},

issn = {15728099},

year  = {2016},

date = {2016-01-01},

journal = {Fire Technology},

volume = {52},

number = {5},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{singh2016experimental,

title = {Experimental methodology for estimation of local heat fluxes and burning rates in steady laminar boundary layer diffusion flames},

author = {Ajay V Singh and Michael J Gollner},

year  = {2016},

date = {2016-01-01},

journal = {JoVE (Journal of Visualized Experiments)},

number = {112},

pages = {e54029},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Singh2015c,

title = {Local Burning Rates and Heat Flux for Forced Flow Boundary-Layer Diffusion Flames},

author = {Ajay V Singh and Michael J Gollner},

url = {http://arc.aiaa.org/doi/10.2514/1.J054283},

doi = {10.2514/1.J054283},

issn = {0001-1452},

year  = {2015},

date = {2015-08-01},

journal = {AIAA Journal},

pages = {1--11},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Altintas2015,

title = {Towards an Integrated Cyberinfrastructure for Scalable Data-driven Monitoring, Dynamic Prediction and Resilience of Wildfires},

author = {Ilkay Altintas and Jessica Block and Raymond de Callafon and Daniel Crawl and Charles Cowart and Amarnath Gupta and Mai Nguyen and Hans-Werner Braun and Jurgen Schulze and Michael Gollner and Arnaud Trouve and Larry Smarr},

url = {http://linkinghub.elsevier.com/retrieve/pii/S1877050915011047},

doi = {10.1016/j.procs.2015.05.296},

issn = {18770509},

year  = {2015},

date = {2015-01-01},

journal = {Procedia Computer Science},

volume = {51},

pages = {1633--1642},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Singh2015b,

title = {A methodology for estimation of local heat fluxes in steady laminar boundary layer diffusion flames},

author = {Ajay V Singh and Michael J Gollner},

doi = {10.1016/j.proci.2014.05.040},

issn = {15407489},

year  = {2015},

date = {2015-01-01},

journal = {Combustion and Flame},

volume = {162},

number = {5},

pages = {2214--2230},

abstract = {A thorough numerical and experimental investigation of laminar boundary-layer diffusion flames established over the surface of a condensed fuel is presented. By extension of the Reynold's Analogy, it is hypothesized that the non-dimensional temperature gradient at the surface of a condensed fuel is related to the local mass-burning rate through some constant of proportionality. First, this proportionality is tested by using a validated numerical model for a steady flame established over a condensed fuel surface, under free and forced convective conditions. Second, the relationship is tested by conducting experiments in a free-convective environment (vertical wall) using methanol and ethanol as liquid fuels and PMMA as a solid fuel, where a detailed temperature profile is mapped during steady burning using fine-wire thermocouples mounted to a precision two-axis traverse mechanism. The results from the present study suggests that there is indeed a unique correlation between the mass burning rates of liquid/solid fuels and the temperature gradients at the fuel surface. The correlating factor depends upon the Spalding mass transfer number and gas-phase thermo-physical properties and works in the prediction of both integrated as well as local variations of the mass burning rate as a function of non-dimensional temperature gradient. Additional results from precise measurements of the thermal field are also presented. ?? 2014 The Combustion Institute.},

keywords = {Diffusion flame, Flame spread, Laminar burning, Vertical wall},

pubstate = {published},

tppubtype = {article}

}

@article{Singh2015a,

title = {Estimation of local mass burning rates for steady laminar boundary layer diffusion flames},

author = {Ajay V Singh and Michael J Gollner},

url = {http://linkinghub.elsevier.com/retrieve/pii/S1540748914000431},

doi = {10.1016/j.proci.2014.05.040},

issn = {15407489},

year  = {2015},

date = {2015-01-01},

journal = {Proceedings of the Combustion Institute},

volume = {35},

number = {3},

pages = {2527--2534},

keywords = {},

pubstate = {published},

tppubtype = {article}

}