Michael John Gollner

University of California, Berkeley | UCB · Department of Mechanical Engineering

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 initi...

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 f...

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 scal...

Large wildfires of increasing frequency and severity threaten local populations and natural resources and contribute carbon emissions into the earth-climate system. Although wildfires have been researched and modeled for decades, no verifiable physical theory of spread is available to form the basis for the precise predictions needed to manage fire...

Fire spread is known to accelerate uphill over inclined surfaces due to an intrinsic coupling between geometry and fire-induced flows, especially when the slope exceeds a critical angle. The fundamental relationships which govern this close coupling, however, are not yet fully understood. To investigate these relationships, propane-fueled fires wer...

Modeling the burning processes of biomass such as wood, grass, and crops is crucial for the modeling and prediction of wildland and urban fire behavior. Despite its importance, the burning of solid fuels remains poorly understood, which can be partly attributed to the unknown chemical kinetics of most solid fuels. Most available kinetic models were...

Experiments were conducted to quantify downstream heating from inclined fires generated by a 25 cm wide, 5 cm deep gaseous line burner. A variety of orientation angles (θ) and fire heat-release rates (HRR) were employed simulating, at reduced scale, the dynamics of two-dimensional (2-D) inclined flame spread as found in wildland or building fires....

There are multiple situations in which fires may occur at environmental conditions that are different than standard atmospheric conditions. Changes in ambient pressure, oxygen concentration, flow velocity, the presence of an external heat source or gravity may change the flammability and fire dynamics of materials. The objective of this work is to...

Fires occurring at the wildland-urban interface (WUI) have rapidly increased in frequency and severity over the past few decades. As a result of these extreme fires, multiple communities, including thousands of structures, are destroyed every year. The majority of these losses have been found to stem from ignition due to firebrands, small smolderin...

In the United States, the prevalence and severity of wildland-urban interface fires impacting communities is increasing. Post-fire studies indicate that firebrand exposure has been associated with a large fraction of structure losses during wildfire events. A bench-scale wind tunnel was developed to elucidate the mechanisms contributing to the igni...

This study investigates the role of turbulence induced instabilities on three-dimensional boundary-layer flames. Boundary-layer diffusion flames under 0.99–2.43 m/s crossflow velocities were produced over a gaseous propane line burner. Incoming flows with turbulence intensities ranging from 0.5% to 16.8% were generated in a wind tunnel with fine wi...

Ignition of materials by a point source of heating plays an important role in initiating many structure and wildland fires, such as spotting by hot particles, lightning, laser, and concentrated irradiation. Herein, we study the smoldering ignition of tissue paper by a concentrated sunlight spot with heat fluxes up to 780 kW/m 2 , which is focused b...

The current study presents a series of experiments investigating the smoldering behavior of woody fuel arrays at various porosities under the influence of wind. Wildland fuels are simulated using wooden cribs burned inside a bench scale wind tunnel. Smoldering behavior was characterized using measurements of both mass loss and emissions. Results sh...

In the USA, the frequency of devastating wildfires are on the rise. Post-fire studies indicate that firebrand exposure has significantly contributed to the rapid spread of multiple wildfires and has been associated with a large fraction of structure losses during wildfire events. A bench-scale experimental protocol was developed to elucidate the ro...

Emission measurements are available in the literature for a wide variety of field burns and laboratory experiments, although previous studies do not always isolate the effect of individual features such as fuel moisture content (FMC). This study explores the effect of FMC on gaseous and particulate emissions from flaming and smouldering combustion...

Flame spread over solid fuels is a canonical problem in fire science, due to its direct implications on material flammability and importance in fire development. In a microgravity environment, such as onboard a spacecraft, flames can behave very differently than on Earth. This is concerning for spaceflight life safety, especially in higher-oxygen e...

The influence of different air entrainment conditions on burning behavior of fire whirls and their emissions of combustion products was experimentally investigated. Fire whirls were formed in a fixed-frame configuration in fuel pool of 70 cm in diameter with a water sublayer. Four different natural entrainment (NE) conditions with gap sizes varying...

Modeling the burning processes of biomass such as wood, grass, and crops is crucial for the modeling and prediction of wildland and urban fire behavior. Despite its importance, the burning of solid fuels remains poorly understood, which can be partly attributed to the unknown chemical kinetics of most solid fuels. Most available kinetic models were...

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 partic...

Number: 1141152 In situ burning is an efficient response method that quickly removes large quantities of oil from the marine environment eliminating the need for collection, storage, and transport. The combustion of hydrocarbons mainly yields carbon dioxide and water; however, it also creates large plumes of black carbon soot and residues of incomp...

Over the past few years, numerous large-scale disasters have occurred due to wildfires at the wildland-urban interface (WUI). In these fires, spread via the transport of firebrands (burning embers) plays a significant role. Several models have been developed to describe the transport of firebrands but few, if any, are available which can provide a...

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 t...

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 c...

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 configurati...

Cambridge Core - Thermal-Fluids Engineering - A Gallery of Combustion and Fire - by Charles Baukal, Jr.

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 sensit...

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...

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 vegetat...

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 t...

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 ter...

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 co...

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 f...

During wildland fires, firebrands form once they break off of burning vegetation or structures. Many are then lofted into the fire plume where they are transported long distances ahead of the fire front, igniting new “spot” fires as they land. To date, very few studies have been conducted on the breakage mechanism of thermally-degraded vegetative e...

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 an...

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...

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...

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 work-shop 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 experim...

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 w...

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, lab...

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 thermoco...

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...

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...

An accurate representation of sub-grid scale turbulent mixing is critical for modeling fire plumes and smoke transport. In this study, PLIF and PIV diagnostics are used with the saltwater modeling technique to provide highly-resolved instantaneous field measurements in unconfined turbulent plumes useful for statistical analysis, physical insight, a...

Firefighter safety challenges with 'green' construction.

A scale-modelling study was carried out on a ceiling jet flowing along an unconfined sloped surface with angles ranging from horizontal to 40 degrees. A quantitative saltwater modelling technique, utilizing laser diagnostics, was applied to visualize the flow. Measurements were taken using multiple planar laser sheets around the plume impingement r...

Observations of coherent structures in boundary layer flames, particularly wildland fires, motivated an investigation on instabilities in a boundary layer flame. This experimental study examined streaklike structures in a stationary diffusion flame stabilized within a laminar boundary layer. The incoming flow was characterized with a hotwire anemom...

Observations of streaklike coherent structures have been consistently made in boundary layer flames at various scales, including wildland fires and laboratory-scale tests. In order to scale the influence of buoyancy on these boundary layer instabilities, analogous streaks have been reproduced on a horizontal hot plate placed in a wind tunnel at the...

During wildfires, firebrands form when they break off of burning vegetation or structures. Many are then lofted into the fire plume where they are transported long distances, igniting new " spot " fires as they land. To date, very few studies have been conducted on the breakage mechanism of thermally degraded vegetative elements. Knowledge of these...

While forward heating from flames in wind-driven conditions has previously been studied to help understand flame spread, past measurements only report time-averaged values that do not give a picture of the truly dynamic processes occurring. In this study, we investigate the intermittent movement of flames, namely the flame forward pulsation frequen...

During a fire event in a building, heated currents comprised of smoke and combustion products rise up in the form of a buoyant plume, eventually impacting and radiating as a ceiling jet. While impinging ceiling jets have been well studied for horizontal configurations, many real-life ceilings are actually inclined from the horizontal. Knowledge of...