RE-IGNITION OF MULTI-SPECIES SOOT CLOUDS IN BUILDING FIRES

The re-ignition potential of multi-species soot clouds in building fires were investigated based on their extinction characteristics. The investigation was carried out theoretically using an adaptation of Semenov’s thermal explosion theory. The critical sizes of soot particles in the cloud were found to be strongly affected by the particle temperature, shape, and reactivity, as well as the mass fraction of each species, and ambient conditions. The cloud shape, cloud particle number density, fuel mass fraction, and soot reactivity were identified as the major parameters impacting upon the cloud extinction potential. Our analysis indicate that blending of a base soot with a less reactive soot generally increases the extinction potential of the cloud (i.e. likelihood of extinction) while addition of a more reactive secondary soot to the base one minimises the probability of cloud extinction

EFFECTS OF POROSITY ON RE-IGNITION CHARACTERISTICS OF A SURROGATE MATERIAL

This study is part of a larger project which aims at studying the re-ignition behaviour of charring solid fuels under fire conditions. The main objective of this part of the work was to investigate the role of material porosity on the re-ignition characteristics of the fuel. For this purpose, experiments were carried out on a set of surrogate ceramic samples to de-couple the pyrolysis and combustion processes from those associated with heat transfer. The surrogate samples were made out of magnesia silica ceramic with porosity levels of 72.9%, 53.5%, and 35%. Experiments were conducted in a modified cone calorimeter over a range of heat fluxes between 40 to 60 kW/m2. The re-ignition delay was found to be significantly affected by the material porosity. The higher the porosity, the longer the re-ignition delay time. For samples having the same porosity level, the re-ignition delay time was primarily a function of sample thickness and the external heat flux. Thicker samples generally showed shorter reignition delays. The results of this study will be used in future work to quantify the impact of porosity on the re-ignition behaviour of real samples

Effect of Porosity on Re-ignition Characteristics of a Surrogate

ABSTRACT This study is part of a larger project which aims at studying the re-ignition behaviour of charring solid fuels under fire conditions. The main objective of this part of the work was to investigate the role of material porosity on the re-ignition characteristics of the fuel. For this purpose, experiments were carried out on a set of surrogate ceramic samples to de-couple the pyrolysis and combustion processes from those associated with heat transfer. The surrogate samples were made out of magnesia silica ceramic with porosity levels of 72.9%, 53.5%, and 35%. Experiments were conducted in a modified cone calorimeter over a range of heat fluxes between 40 to 60 kW/m 2 . The re-ignition delay was found to be significantly affected by the material porosity. The higher the porosity, the longer the re-ignition delay time. For samples having the same porosity level, the re-ignition delay time was primarily a function of sample thickness and the external heat flux. Thicker samples generally showed shorter reignition delays. The results of this study will be used in future work to quantify the impact of porosity on the re-ignition behaviour of real samples

RE-IGNITION OF MULTI-SPECIES SOOT CLOUDS IN BUILDING FIRES

The re-ignition potential of multi-species soot clouds in building fires were investigated based on their extinction characteristics. The investigation was carried out theoretically using an adaptation of Semenov’s thermal explosion theory. The critical sizes of soot particles in the cloud were found to be strongly affected by the particle temperature, shape, and reactivity, as well as the mass fraction of each species, and ambient conditions. The cloud shape, cloud particle number density, fuel mass fraction, and soot reactivity were identified as the major parameters impacting upon the cloud extinction potential. Our analysis indicate that blending of a base soot with a less reactive soot generally increases the extinction potential of the cloud (i.e. likelihood of extinction) while addition of a more reactive secondary soot to the base one minimises the probability of cloud extinction

Re-ignition of multi-species soot clouds in building fires

The re-ignition potential of multi-species soot clouds in building fires were investigated  based on their extinction characteristics. The investigation was carried out theoretically using the adaptation of Semenov`s thermal explotion theory. The critical sizes of soot particles in the cloud were found to be strongly effected by  the particle temperature., shape, and reactivity, as the mass fraction of each species, and ambient conditions. The clous shape, cloud particle number density, fuel mass fraction and soot reactivity were identified as the major parameters impacting upon the cloud extinction potential. Our analysis indicate that blending of a base soot with a less reactive soot generally increases extinction potential of the cloud ( i.e. likelihood of extinction) while addition of a more reactive secondary soot to the base one minimizes the probability of cloud extinction. Keywords: extinction, clouds, re-ignition, soo

The role of extinction on the re-ignition potential of wood-based embers in bushfires

The re-ignition potential of partially burnt wood-based embers was investigated theoretically by studying their extinction characteristics. An adaptation of Semenov's thermal explosion theory was used in conjunction with a linear stability analysis to determine the critical particle size at which extinction occurs. Particles of various shapes were studied and the analysis was carried out for both thermally thin and thermally thick particles. The results of our analysis indicate that thermally thick embers are less susceptible to extinction than thermally thin ones and, as such, are more prone to re-ignition. The results also show that the extinction of wood embers is strongly affected by the particle temperature, particle shape, and reaction kinetics. The effects of ambient conditions were found to be less pronounced than particle properties

Short Communication: application of a surrogate material in assessing the impact of porosity on re-ignition of wood-based materials

Re-ignition behaviour of charred solid fuels after extinction by water is studied. In this communication the effect of material porosity on re-ignition is investigated. A surrogate ceramic material is used so as to separate the pyrolysis and combustion processes from those associated with heat transfer. Experimental data are reported for different sample thickness and porosity, and varying heat flux and water application time