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Journal articleZhu J, Jahn W, Rein G, 2019,
Computer simulation of sunlight concentration due to façade shape: application to the 2013 Death Ray at Fenchurch Street, London, Journal of Building Performance Simulation, Vol: 12, Pages: 378-387, ISSN: 1940-1507
Reflected sunlight from the Walkie-Talkie building in 20 Fenchurch Street, London, was reported to have caused the melting of plastic components of a car parked at street level in late August of 2013. The incident was explained by the concave-shaped south façade of the building, which converges solar radiation into a hotspot. In this study, we test the sunlight concentation hypothesis with a lighting simulation. A geometry model with material properties was created, and different weather situations were modelled. The results are illustrated in irradiance maps indicating time, position and peak heat fluxes. The highest simulated flux on the day of the incident was 3320 Wm−2 (10 to 15 fold increase compared to direct solar radiation). Additionally, the specific time and day for maximum heat fluxes between June and December were determined . For the worst scenario, which was avoided becuase the sky was partially cover with clouds that day and the hotspot did not fall on street level, the simulations showed that the peak heat flux would have reached well over 4000 Wm−2.
Journal articleHeidari M, Robert F, Lange D, et al., 2019,
Probabilistic study of the resistance of a simply-supported reinforced concrete slab according to Eurocode parametric fire, Fire Technology, Vol: 55, Pages: 1377-1404, ISSN: 0015-2684
We present the application of a simple probabilistic methodology to determine the reliability of a structural element exposed to fire when designed following Eurocode 1-1-2 (EC1). Eurocodes are being used extensively within the European Union in the design of many buildings and structures. Here, the methodology is applied to a simply-supported, reinforced concrete slab 180 mm thick, with a standard load bearing fire resistance of 90 min. The slab is subjected to a fire in an office compartment of 420 m 2 floor area and 4 m height. Temperature time curves are produced using the EC1 parametric fire curve, which assumes uniform temperature and a uniform burning condition for the fire. Heat transfer calculations identify the plausible worst case scenarios in terms of maximum rebar temperature. We found that a ventilation-controlled fire with opening factor 0.02 m 1/2 results in a maximum rebar temperature of 448°C after 102 min of fire exposure. Sensitivity analyses to the main parameters in the EC1 fire curves and in the EC1 heat transfer calculations are performed using a one-at-a-time (OAT) method. The failure probability is then calculated for a series of input parameters using the Monte Carlo method. The results show that this slab has a 0.3% probability of failure when the compartment is designed with all layers of safety in place (detection and sprinkler systems, safe access route, and fire fighting devices are available). Unavailability of sprinkler systems results in a 1% probability of failure. When both sprinkler system and detection are not available in the building, the probability of failure is 8%. This novel study conducts for the first time a probabilistic calculation using the EC1 parametric curve, helping engineers to identify the most critical design fires and the probabilistic resistance assumed in EC1.
Journal articleRichter F, Rein G, 2019,
Timber is becoming a popular construction material even for high-rise buildings despite its poorly understood fire behaviour. In a fire, timber—a natural polymer—degrades in the thermochemical process of charring, causing it to lose structural strength. In spite of significant research on the physics of charring, the chemical kinetics—reactions and kinetic parameters for pyrolysis and oxidation—remains a scientific challenge to model accurately. Current kinetic models are either computationally too expensive or neglect key chemical pathways. Here we derive a new appropriate kinetic model for fire science at the microscale using a novel methodology. First, we built a kinetic model for each component of timber (cellulose, hemicellulose, and lignin) from literature studies and experiments of the components. Then, we combined these three models into one kinetic model (8 reactions, 8 chemical species) for timber. This approach accounts for chemical differences among timber species. However, the timber model is only able to reproduce the trend in the experiments when literature parameters are used. Using multi-objective inverse modelling, we extract a new set of optimised kinetic parameters from 16 high-quality experiments from the literature. The novel optimised kinetic model is able to reproduce these 16 and a further 64 (blind predictions) experiments nearly within the experimental uncertainty, spanning different heating rates (1–60 K/min), oxygen concentrations (0–60 %), and even isothermal experiments (220–300 °C). Furthermore, the model outperforms current kinetic models for fire science in accuracy across a wide range of conditions without an increase in complexity. Incorporated into a model of heat and mass transfer, this new and optmised kinetic model could improve the understanding of timber burning and has the potenial to lead to safer designs of timber buildings.
Journal articleRackauskaite E, Kotsovinos P, Jeffers A, et al., 2019,
Computational analysis of thermal and structural failure criteria of a multi-storey steel frame exposed to fire, Engineering Structures, Vol: 180, Pages: 524-543, ISSN: 0141-0296
Structural fire design, until recently, has only assumed uniform fires inside the compartment, and the assessment of structural failure has been often based on a critical temperature criterion. While this criterion, to some extent, may be able to indicate the temperature at which the structural element is near to failure, it is based on standard fire tests and, therefore, its validity is limited to individual members exposed to uniform temperatures. It is unclear how representative a critical temperature criterion is of structural failure in the case of multi-story structures, particularly in the case of non-uniform fires such as travelling fires. Therefore, the aim of this study is to assess the validity of the critical temperature criterion for structures exposed to non-uniform fires and compare it to uniform fires. A generic 10-storey steel framed building is modelled using the finite element software LS-DYNA. In total, 117 different scenarios are investigated to cover a wide range of conditions of interest for design of modern steel buildings, varying the fire exposure (travelling fires, Eurocode parametric fires, ISO-834 standard fire, and SFPE standard), floor where the fire is burning, beam section size, and applied fire protection to the beams. For the different fire exposures considered, the analysis predicts structural failure at different times, in different locations and floors, and different failure mechanisms. Moreover, it is shown that there is no single worst case fire scenario: different fires can lead to failure in different structural ways. The comparison of the various structural and thermal failure criteria (ultimate strain, utilization, mid-span deflection, and critical temperature) show that there is no consistency between them, revealing a far more complex problem than reported in the literature. Lastly, this work has illustrated that the critical temperature criterion does not predict accurately the structural failure in time, space or failu
Journal articleYuan H, Restuccia F, Richter F, et al., 2019,
A computational model to simulate self-heating ignition across scales, configurations, and coal origins, Fuel, Vol: 236, Pages: 1100-1109, ISSN: 0016-2361
Self-heating of fuel layers can trigger ignition when the temperature of the surroundings is sufficiently high. Self-heating ignition has been a hazard and safety concern in raw materials production, transportation, and storage facilities for centuries. Hot plate and oven-basket experiments are the two most used lab-scale experiments to assess the hazard of self-heating ignition. While extensive experiments have been done to study this phenomenon, modelling of the experiments is substantially lagging behind. A computational model that can accurately simulate self-heating ignition under the two experimental configurations has not been developed yet. In this study, we build such a model by coupling heat transfer, mass transfer, and chemistry using the open-source code Gpyro. Due to the accessibility of large amount of experimental data, coal is chosen as the material for model validation. A literature review of the kinetic parameters for coal samples from different origins reveals that there is a compensation effect between the activation energy and exponential factor. Combining the compensation effect with our model, we simulate 6 different experimental studies covering the two experimental configurations, a wide range of sample sizes (heights ranging from 5 mm to 126 mm), and various coal origins (6 countries). The model accurately predicts critical ignition temperature (Tig) for all 24 experiments with an error below 7 °C. This computational model unifies for the first time the two most used self-heating ignition experiments and provides theoretical insights to understand self-ignition for different fuels under different conditions.
Journal articleRestuccia F, Masek O, Hadden R, et al., 2019,
Quantifying self-heating ignition of biochar as a function of feedstock and the pyrolysis reactor temperature, Fuel, Vol: 236, Pages: 201-213, ISSN: 0016-2361
Biochar is produced from biomass through pyrolysis in a reactor under controlled conditions. Different feedstock and reactor temperatures produce materials with different physical and chemical properties. Because biomass, biochar and torrefied biomass are reactive porous media and can undergo self-heating, there is a fire hazard associated to their production, transport, and storage. This hazard needs to be tackled in biomass industries like power generation, where self-heating of biomass can cause significant problems, like the 2012 fire at Tilbury Power Plant (UK). Using basket experiments inside a thermostatically controlled laboratory oven, augmented with thermogravimetry and conductivity measurements, we experimentally study the ignition conditions of pellets and biochar made of softwood, wheat and rice husk. For softwood, we also study biochar produced at different reactor temperatures ranging from 350 to 800 °C. In total, 173 experiments were conducted with 1036 h of oven run time. By investigating the self-heating behaviour of these samples via the Frank-Kamenetskii theory, we quantify and upscale for the first time the reactivity of biochar as a function of feedstock and also of the reactor temperature. The results show that in order from higher to lower tendency to self-heating, the rank is softwood, wheat and rice husk. The reactivity of the softwood is not a monotonic function of pyrolysis reactor temperature but that biochar is most prone to self-heating when produced at 450 °C. Reactivity decreases at higher reactor temperatures, and at 600 °C the biochar is less reactive than the original feedstock. This work improves the fundamental understanding of the fire hazard posed by biomass self-heating, providing insights necessary for successful and safer biomass industries.
Journal articleRoenner N, Rein G, 2019,
A new convective ignition apparatus for polymers has been developed with measured flow and temperature fields. Polymer degradation and ignition is typically studied in fire science under radiative heating or direct contact with a pilot flame but this new apparatus allows for research to be conducted in a convective setting providing a missing piece of knowledge on flammability. Convective heating is a main mode of heat transfer in many real fires such as in the built or natural environment, like building fires or wildfires. The apparatus exposes one side of a sample to air between lab ambient and 735 °C at 0.7 to 5 m/s whilst measuring the sample 2D back side temperature via calibrated infrared. The 2D temperature and flow fields, convective heat transfer, and irradiation were studied under various operating conditions of temperature and flow. Polybutylene terephthalate (PBT) samples with glass fibre were ignited using a 735 °C hot stream. Samples of 2 mm thickness ignited after 30 s with a standard deviation lower than 1 s. The experimental work was augmented with numerical modelling of heat and mass transfer with pyrolysis chemistry in Gpyro, allowing for insight into the temperatures across the sample. Combining experimental with numerical work shows that ignition was observed at a surface temperature of 320 °C. Using this rig, ignition can be studied under a range of temperature and flow conditions filling the gaps of the literature which relies primarily on irradiated samples in natural convection conditions.
Journal articleHu Y, Christensen E, Restuccia F, et al., 2019,
Smouldering combustion of peat drives the largest fires on Earth, and their emissions play an important role in global carbon balance and regional air quality. Here we report a series of controlled laboratory experiments of peat fires. Peat samples of 100% moisture content in dry basis were burnt in an open-top reactor with dimensions of 20 × 20 × 10 cm. The diagnostics are a unique set of simultaneous measurements consisting of real-time mass loss, up to 20 different gas species concentration, size-fractioned particle mass (PM10, PM2.5and PM1), temperature profile, and visual and infrared imaging. This comprehensive framework of measurements reveals that the evolution of the emissions varies in time with four observed stages (ignition, growth, steady and burn out) which are characterised by different combustion dynamics. Mass flux measurements show that CO2, CO, CH4and NH3are the four most predominant gas species emitted in the steady stage. Incorporating the mass loss rate, the transient emission factors (EFm) of both gas and particle species are calculated and reported here for the first time. Averaging the steady stage, the EFm of PM2.5reached 23.12 g kg-1, which accounts for 87.2% of the total particle mass, and PM1EFmwas reported to be 15.04 g kg-1. The EFm of alkane species (CH4, C2H6, C3H8, C4H10) were found to peak within the ignition stage, whereas the EFmof CO2, CO and NH3kept increasing during the steady stage. Because of these measurements, for the first time we were able to validate the EF calculated by assuming averaged values and a carbon balance, which is the preferred method used in remote sensing and atmospheric sciences. This work contributes to a better understanding of peat fire emissions and could help develop strategies tackling regional haze.
Journal articleHuang X, Rein G, 2019,
Smoldering is the dominant combustion process in peat fire, releasing a large amount of carbon and smoke into the atmosphere. The spread of smoldering in peatland is a multi-dimensional process, which is slow, low-temperature, persistent, and difficult to detect. In this work, we investigate the upward spread of peat fire from the underground to the surface after forced ignition which is a relevant configuration but rarely studied. In the experiment, ignition is not possible if the igniter is deeper than 15 cm below the free surface, regardless of moisture content or density. Once ignited, the 1st-stage upward fire spread is initiated towards the free surface (opposed smoldering) with a peak temperature of 300 °C, leaving behind a char structure that does not collapse. Then, a 2nd-stage downward spread (forward smoldering) is activated with a peak temperature of 600 °C and regression of free surface. The upward spread is faster than the downward spread. The rates of both upward and downward spread decrease as the peat density or depth is increased. These experimental observations are successfully captured by a 1D computational model of heat and mass transfer with 5-step kinetics. Modelling results further suggest that (1) the oxygen diffusion controls the entire upward-to-downward spread of peat fire, (2) the oxidation of peat sustains the 1st-stage upward spread, and (3) the oxidation of char sustains the 2nd-stage downward spread. This is the first study investigating the upward spread of peat fire, which helps understand the persistence of peat fire and guide the fire prevention and suppression strategies.
Journal articleRichter F, Atreya A, Kotsovinos P, et al., 2019,
Structural softwood (timber) recently gained attention by architects and engineers as a construction material for high-rise buildings. Regulations restrict the height of these buildings due to safety concerns as their fire behaviour is poorly understood. The fire behaviour and loss of loadbearing capacity of timber is controlled by charring, whose chemical kinetics has rarely been studied. Current models of charring assume, without proof, the same reaction scheme and kinetic parameters apply to all wood species, which potentially introduces a large uncertainty. Here, the hypothesis is tested that the kinetics of different wood species insignificantly affects their charring behaviour. The kinetics is modelled by a microscale kinetic model—including pyrolysis and char oxidation reactions—which assumes that the three main components (cellulose, hemicellulose, and lignin) of wood degrade independently. Variation in the kinetics between different wood species is captured by their different chemical compositions within a wood group (softwood or hardwood). Hardwood is included for comparison. A database of over 600 compositions was compiled from literature, and studied across scales using a microscale (mg-samples) and mesoscale (kg-samples) model. All reactions, kinetic parameters, and physical properties were selected from literature. Both models were validated using blind predictions of high-fidelity experiments from literature. Variation in kinetics were found to have a small effect on the predicted mass loss rate at both scales (±1 g/m2-s) and a negligible effect on the predicted temperatures (±16 K) across different depths, heat fluxes, and oxygen concentrations at the mesoscale. These results prove, for the first time, that the variation in kinetics is negligible for predicting charring across scales. A kinetic model of charring derived for one wood species should be valid for all wood species within softwood or hardwood. Modellers should, t
Journal articleWang Z, You F, Rein G, et al., 2018,
This study aims to develop a complete methodology for assessing flammability hazards of typical fuels (ie, transformer oil, hydraulic oil, gear oil, and lubricating grease) used in a wind turbine nacelle by combining different experimental techniques such as thermogravimetric analysis and cone calorimetry. Pyrolysis properties (onset temperature, temperature of maximum mass loss rate, and mass residue) and reaction‐to‐fire properties (ignition time, heat release rate, mass loss rate, and smoke release rate) were determined and used for a preliminary assessment of thermal stability and flammability hazards. Additional indices, for ignition and thermal behavior (effective heat of combustion, average smoke yield, and smoke point height, heat release capacity, fire hazard parameter, and smoke parameter, were calculated to provide a more advanced assessment of the hazards in a wind turbine. Results show that pyrolysis of transformer oil, lubricating grease, hydraulic oil, and gear oil occur in the range of 150°C to 550°C. Lubricating grease and transformer oil show the higher and lower thermal stabilities with maximum pyrolysis rate temperatures of 471°C and 282°C, respectively. The measured relation between ignition time and radiant heat flux agrees well with Janssens method (a power of 0.55). The aforementioned indices appear to provide a reasonable prediction of performance under real fire conditions according to a full‐scale fire test documented by Declercq and Van Schevensteen. The results of the study indicate that transformer oil is the easiest to ignite while lubricating grease is the most difficult to ignite but also has the highest smoke production rate; that transformer oil has the highest heat release rate while gear oil has the lowest; and that the fire hazard parameter is the highest for transformer oil and the smoke parameter is the highest for lubricating grease. The potential of this type of work to design safer wind turbines under perfor
Journal articleAyala P, Cantizano A, Rein G, et al., 2018,
In case of fire, constructive features of typical atria could favor the spread of smoke. This makes the design of their smoke control and management systems a challenging task. Five full-scale fire experiments in the literature have been analyzed and numerically compared in FDS v6 to explore the influence of the make-up air. However, these fire experiments cover only a limited number of set-ups and conditions, and require further numerical modeling to obtain a deeper understanding of the makeup air influence. Subsequently, 84 simulations with FDS v6 have been carried out, considering different vent areas (air velocity from 0.4 to 5.3 m/s) and configurations, two heat release rates (2.5 and 5 MW), and two pan locations. It is demonstrated that make-up air velocities lower than the prescribed limit of 1 m/s, by the international codes, may induce adverse conditions. Based on our results, we recommended fire engineers to numerically assess the fire scenario with even lower velocity values. The results also show that asymmetric configurations are prone to induce circulation around the flame which can contribute to the formation of longer flames and fire whirls. Thus, this numerical study links two fire types allowing the connection of pool fires to fire whirls, which completely differ in behaviour and smoke filling, for the sake of design of fire safety.
Journal articleRoulston C, Paton-Walsh C, Smith TEL, et al., 2018,
Southeast Asia experiences frequent fires in fuel-rich tropical peatlands, leading to extremeepisodes of regional haze with high concentrations of fine particulate matter (PM2.5) impacting humanhealth. In a study published recently, the first field measurements of PM2.5 emission factors for tropical peatfires showed larger emissions than from other fuel types. Here we report even higher PM2.5 emission factors,measured at newly ignited peat fires in Malaysia, suggesting that current estimates of fine particulateemissions from peat fires may be underestimated by a factor of 3 or more. In addition, we use both field andlaboratory measurements of burning peat to provide the first mechanistic explanation for the high variabilityin PM2.5 emission factors, demonstrating that buildup of a surface ash layer causes the emissions of PM2.5 todecrease as the peat fire progresses. This finding implies that peat fires are more hazardous (in terms ofaerosol emissions) when first ignited than when still burning many days later. Varying emission factors forPM2.5 also have implications for our ability to correctly model the climate and air quality impacts downwindof the peat fires. For modelers able to implement a time-varying emission factor, we recommend an emissionfactor for PM2.5 from newly ignited tropical peat fires of 58 g of PM2.5 per kilogram of dry fuel consumed (g/kg), reducing exponentially at a rate of 9%/day. If the age of the fire is unknown or only a single value may beused, we recommend an average value of 24 g/kg.Plain Language Summary This paper provides evidence that peat fire emissions of fineparticulates are much larger than for other fires when the peat is newly ignited but decrease rapidly as thefire progresses. This is important because it means that newly ignited fires are particularly detrimental toambient air quality in impacted regions.
Journal articleHu Y, Fernandez-Anez N, Smith TEL, et al., 2018,
Smouldering peat fires, the largest fires on Earth in terms of fuel consumption, are reported in six continents and are responsible for regional haze episodes. Haze is the large-scale accumulation of smoke at low altitudes in the atmosphere. It decreases air quality, disrupts transportation and causes health emergencies. Research on peat emissions and haze is modest at best and many key aspects remain poorly understood. Here, we compile an up-to-date inter-study of peat fire emission factors (EFs) found in the literature both from laboratory and from field studies. Tropical peat fires yield larger EFs for the prominent organic compounds than boreal and temperate peat fires, possibly due to the higher fuel carbon content (56.0 vs 44.2%). In contrast, tropical peat fires present slightly lower EFs for particulate matter with diameter ≤2.5 μm (PM2.5) for unknown reasons but are probably related to combustion dynamics. An analysis of the modified combustion efficiency, a parameter widely used for determining the combustion regime of wildfires, shows it is partially misunderstood and highly sensitive to unknown field variables. This is the first review of the literature on smouldering peat emissions. Our integration of the existing literature allows the identification of existing gaps in knowledge and is expected to accelerate progress towards mitigation strategies.
Journal articlehuang X, Rein G, 2017,
Smouldering fires in peatland are different from the flames in wildland fires. Smouldering peat fire is slow, low-temperature and more persistent, releasing large amounts of smoke into the atmosphere. In this work, we experimentally and computationally investigate the vertical downward spread of smouldering fire in a column of 30 cm-tall moss peat under variable moisture content (MC) and bulk density. The measured downward spread rate decreases with depth and wet bulk density, and is ~1 cm h−1 equivalent to a carbon emission flux of 200 tonnes day−1 ha−1. We observe that downward spread increases as MC increases substantially at least inside the range from 10 to 70%, which is not intuitive and goes against the trend observed for the horizontal spread in the same peat. We also conduct one-dimensional computational simulations to successfully reproduce the experimental observations. The analysis shows that the spread rate increases with MC and decreases with density because smouldering spread is controlled by the oxygen supply. The volume of the porous peat expands when absorbing water, which reduces the density of organic matter and decreases the heat release rate. This shows that the widely assumed conclusion that the spread rate of wildfire decreases with MC is not universal when applied to smouldering fires.
Journal articleRackauskaite E, Kotsovinos P, Jeffers A, et al., 2017,
Structural analysis of multi-story steel frames exposed to travelling fires and tradition design fires, Engineering Structures, Vol: 150, Pages: 271-287, ISSN: 1873-7323
Most of the current understanding of building behaviour in fire is based on the adoption of the standard and parametric temperature-time fire curves. However, these design fires are based on small scale tests and idealize the thermal environment as uniform. Thus, they have important limitations on their applicability to large enclosures. Instead, in large open-plan compartments, travelling fires have been observed. To account for such fires, a design tool called Travelling Fires Methodology (TFM) has been developed and used for design. The aim of the present study is to compare computationally the structural response of a multi-storey steel frame subjected to both uniform design fires (available in current standards) and travelling fires. A two-dimensional 10-storey 5-bay steel frame designed according to ASCE 7-02 is modelled in the general finite element program LS-DYNA. Different fire exposures are investigated. They include travelling fires, Eurocode parametric curves, ISO-834 standard fire and the constant compartment temperature curve from the SFPE standard. These fires are applied to different floors, one at a time, to explore the influence on the structural response, resulting in a total of 80 different scenarios. The development of deflections, axial forces and bending moments is analysed. Uniform fires are found to result in approx. 15–55 kN (3–13%) higher compressive axial forces in beams compared to small travelling fires. However, the results show irregular oscillations in member utilization levels in the range of 2–38% for the smallest travelling fire sizes, which are not observed for any of the uniform fires. Peak beam mid-span deflections are similar for both travelling fires and uniform fires and depend mainly on the fire duration, but the locations in the frame and times when these peak displacements occur are different. The results indicate that travelling fires and uniform fires trigger substantially different structural respons
Journal articleRein G, Huang X, Restuccia F, et al., 2017,
Detection of landmines in peat soils by controlled smouldering combustion: Experimental proof of concept of O-Revealer, Experimental Thermal and Fluid Science, Vol: 88, Pages: 632-638, ISSN: 0894-1777
We study a novel landmine detection technology, called O-Revealer, which uses controlled smouldering combustion and is valid for minefields in peat soils. We have conducted laboratory experiments with two types of dummy landmines buried in peat, the plastic SB-33 and the metal PROM-1. The ignition and spread of a smouldering front was monitored under different soil moisture and wind conditions. Special attention was paid to the thermal conditions that could trigger thermal runaway of the explosive charge. In all experiments, the smouldering fire burned across the peat, leaving the dummy completely exposed to the open for easy identification and quick demining. The spread rate and peak temperature both decrease with soil moisture, and both increase with wind speed. The results show that for the SB-33 landmine, the heat damage to the shell can be significant, and the chance of thermal runaway ranges between low (moist peat and no wind) to high (dry peat and wind). For PROM-1 landmine, the damage and chance of runaway are always very low. In addition, using rock samples, we show that O-Revealer helps identify objects buried in the soil, thereby avoiding false detections. These experiments show the benefits of the technology and its feasibility for field application in peat minefields worldwide like Falkland Islands, Vietnam, Burma, Laos, Uganda, Zimbabwe or former Yugoslavia.
Journal articleRoenner N, Hutheesing K, Fergusson A, et al., 2017,
Simultaneous improvements in flammability and mechanical toughening of epoxy resins through nano-silica addition, Fire Safety Journal, Vol: 91, Pages: 200-207, ISSN: 0379-7112
Polymers in transport, and many other engineering applications, are required to be mechanically tough as well as resistant to ignition and flame spread. These demands are often for many polymer types in competition, especially when adding flame retardants. With nano-silica addition, we show that improvements in both properties of a polymer can be achieved simultaneously. In this study, an epoxy resin is evaluated for its flammability and mechanical properties with step wise additions of nano-silica. The fracture toughness was significantly improved. In the single edge notch bending test, the addition of 36% nano-silica particles doubled the toughness and increased the flexure modulus by 50%. Flammability was studied via time to ignition at constant irradiation, and via a UL94 test coupled with mass loss and surface temperature measurements. Modelling for the heat transport and chemical kinetics in Gpyro was done and yielded good agreement with the temperatures measured. Adding up to 36% nano-silica, the time to ignition increased by 38% although a sharp decrease was observed around 24% SiO2 addition. We show that the increased time to ignition is mostly due to a higher thermal diffusivity, increased inert content, as well as a strengthening of the residue outer skin, which acts as a mass barrier for pyrolysate. This outer skin was analysed using a scanning electron microscope coupled with an energy dispersive X-ray spectrometer. We found that in the skin the nano-silica particles agglomerate at the surface forming a strong continuous structure together with the char residue from the epoxy. Improvements in the flammability as seen in the UL94 test were measured with mass loss showing a 30% reduction after 20 s, and surface temperatures at the ignited end being up to 75 K lower compared to the pure epoxy. Modelling in Gpyro supported the temperature measurements taken. Despite the improvements seen, all samples ignited, failing the test with dripping and showing that
Journal articlerichter F, Rein G, 2017,
The chemistry of pyrolysis, together with heat transfer, drives ignition and flame spread of biomass materials under many fire conditions, but it is poorly understood. Cellulose is the main component of biomass and is often taken as its surrogate. Its chemistry of pyrolysisis simpler and dominates the pyrolysis of biomass. Many reaction schemes with corresponding kinetic parameters can be found in the literature for the pyrolysis of cellulose, but their appropriatenessfor fire is unknown. This study investigated inverse modelling andthe blind prediction of six reaction schemes of different complexitiesfor isothermal and non-isothermal thermogravimetric experiments. We used multi-objective optimisation to simultaneously and separatelyinverse model the kinetic parameters of each reaction schemeto several experiments. Afterwards we tested these parameters with blind predictions. For the first time, we reveal a set of equally good solutions for the modelling of pyrolysis chemistry of different experiments. This set of solutions is called a Pareto front, and represents a trade-off between predictions of different experiments. It stems from the uncertainty in the experiments and in the modelling. Parameters derived from non-isothermal experiments compared well with the literature, and performed well in blind predictions of both isothermal and non-isothermal experiments. Complexity beyond the Broido-Shafizadeh scheme with seven parameters proved to beunnecessary to predict the mass loss of cellulose; hence, simplereaction schemes are most appropriate for macroscale fire models.Our results show that modellers should use simple reaction schemes to model pyrolysis in macroscale fire models.
Journal articlevermesi I, Didomizio M, richter F, et al., 2017,
Pyrolysis and spontaneous ignition of wood under transientirradiation: experiments and a-priori predictions, Fire Safety Journal, Vol: 91, Pages: 218-225, ISSN: 1873-7226
Wood is a material widely used in the built environment, but its flammability and response to fire are adisadvantage. Therefore, it is essential to have substantial knowledge of the behavior of wood undergoingexternal heating such as in a fire. The majority of studies in the literature use constant irradiation. Althoughthis assumption simplifies both modelling and experimental endeavors, it is important to assess the behaviorof materials under more comprehensive heating scenarios which might challenge the validity of solid-phaseignition criteria developed previously. These criteria are evaluated here for the spontaneous ignition undertransient irradiation by combining experimental measurements and a-priori predictions from a model of heattransfer and pyrolysis. We have applied a two-step transient irradiation in the cone calorimeter in the formof a growth curve followed by a threshold of constant irradiation. We used white spruce samples of size 100x 100 mm thickness of 38 mm measured the temperature at different depths and the mass loss. A one di-mensional model written in the open source code Gpyro is used to predict the pyrolysis behavior. The modelhas a chemical scheme in which the virgin components of wood (hemicellulose, cellulose, lignin) becomeactive, then decompose in two competing reactions: char and gas, and tar. The kinetic parameters, as wellas the thermal properties of the wood and char are taken from the literature, whileρand moisture contentare measured experimentally. A priori predictions of the temperature, made prior to the experiments, showexcellent agreement with the measurements, being within the experimental uncertainty range. The mass lossrate (MLR) predictions are qualitatively similar to the measurements, but there is a large uncertainty in themeasurements. For a-posteriori simulations, certain parameters are changed after having access to the mea-surements to improve the simulations. We found that the heat of reaction
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