Abstract Structure of vegetation significantly influences its flammability and resulting fire spr... more Abstract Structure of vegetation significantly influences its flammability and resulting fire spread. Despite considerable amount of laboratory studies, experimental works carried out with full plant specimens, representative of field conditions, are still limited. Present study aims to collect meaningful experimental data on structure and flammability of shrub of rockrose and evaluate the predictions of a fire model (WFDS) against this dataset. Spatial distribution of fuel elements, sorted according to their characteristic thickness, was established from destructive measurements. 28 fire tests were conducted with full plants under a calorimeter. Foliar moisture content was in the range of 4–18% on dry basis. Radiant panels were used as source of ignition. Flammability was investigated using ignitability, sustainability, combustibility and consumability. Comparison to previous studies highlighted the necessity of standardization among test procedures. Principal component analysis revealed four flammability regimes depending on proportion of thin fuel elements within the crown, position of ignition and duration of preheating. Finally, combustion dynamics of a shrub was numerically investigated with WFDS. A bulk density model was developed from the characterization study and used as input data for the numerical code. Predicted HRR was in good agreement with experiments, although simulation results need improvement in initiation phase of burning.
ABSTRACT This study focuses on localized ignition by external radiant flux and subsequent flame g... more ABSTRACT This study focuses on localized ignition by external radiant flux and subsequent flame growth over thin polymeric materials (plastic and paper) in microgravity. Two transition stages were observed. The first transition stage covers the period from the onset of ignition to the formation of stabilized flame near the ignited area. This is followed by the second transition of the flame growth stage from the initial stabilized flame to sustained fire growth away from the ignited area. For the first stage, ignition experiments of thin PMMA sheets were conducted using a CO2 laser as an external source in the 10 s drop tower. The results of front side surface ignition and of backside surface ignition were observed. The effects of imposed flow velocity, sample thickness, and ambient oxygen concentration on ignition are obtained. Numerical study was conducted to investigate to understand and predict ignition behavior observed in the experiments. For the second stage, numerical study is being conducted to describe the effects of gravity on heat release rate of a PMMA sheet. The gravity level was varied from zero to normal gravity. The preliminary results show that the maximum heat release occurs at around 0.02 g.
Abstract Structure of vegetation significantly influences its flammability and resulting fire spr... more Abstract Structure of vegetation significantly influences its flammability and resulting fire spread. Despite considerable amount of laboratory studies, experimental works carried out with full plant specimens, representative of field conditions, are still limited. Present study aims to collect meaningful experimental data on structure and flammability of shrub of rockrose and evaluate the predictions of a fire model (WFDS) against this dataset. Spatial distribution of fuel elements, sorted according to their characteristic thickness, was established from destructive measurements. 28 fire tests were conducted with full plants under a calorimeter. Foliar moisture content was in the range of 4–18% on dry basis. Radiant panels were used as source of ignition. Flammability was investigated using ignitability, sustainability, combustibility and consumability. Comparison to previous studies highlighted the necessity of standardization among test procedures. Principal component analysis revealed four flammability regimes depending on proportion of thin fuel elements within the crown, position of ignition and duration of preheating. Finally, combustion dynamics of a shrub was numerically investigated with WFDS. A bulk density model was developed from the characterization study and used as input data for the numerical code. Predicted HRR was in good agreement with experiments, although simulation results need improvement in initiation phase of burning.
ABSTRACT This study focuses on localized ignition by external radiant flux and subsequent flame g... more ABSTRACT This study focuses on localized ignition by external radiant flux and subsequent flame growth over thin polymeric materials (plastic and paper) in microgravity. Two transition stages were observed. The first transition stage covers the period from the onset of ignition to the formation of stabilized flame near the ignited area. This is followed by the second transition of the flame growth stage from the initial stabilized flame to sustained fire growth away from the ignited area. For the first stage, ignition experiments of thin PMMA sheets were conducted using a CO2 laser as an external source in the 10 s drop tower. The results of front side surface ignition and of backside surface ignition were observed. The effects of imposed flow velocity, sample thickness, and ambient oxygen concentration on ignition are obtained. Numerical study was conducted to investigate to understand and predict ignition behavior observed in the experiments. For the second stage, numerical study is being conducted to describe the effects of gravity on heat release rate of a PMMA sheet. The gravity level was varied from zero to normal gravity. The preliminary results show that the maximum heat release occurs at around 0.02 g.
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Papers by William Mell