Léo Courty

Flammability limits of biogenic volatile organic compounds emitted by fire-heated vegetation (Rosmarinus officinalis) and their potential link with accelerating forest fires in canyons: a Froude-scaling approach

The accelerating forest fire phenomenon for two real accidents is studied. This phenomenon is investigated using the thermochemical hypothesis, based on the ignition of a biogenic volatile organic compounds cloud accumulated in canyons. By heating a Rosmarinus officinalis plant in a specific hermetic enclosure, a mixture of 14 biogenic volatile organic compounds is identified and their mass fractions determined as temperature functions. The theoretical flammability limits of those components are calculated by means of empirical correlations. Froude-scaling law is applied to laboratory emission results to find the concentrations of biogenic volatile organic compounds at field scale. The comparison of the flammability limits with the calculated concentrations at real scale using this changing-scale analysis shows that the emitted biogenic volatile organic compounds can lead to an accelerating forest fire.

External heating of electrical cables and auto-ignition investigation

Electric cables are now extensively used for both residential and industrial applications. During more than twenty years, multi-scale approaches have been developed to study fire behavior of such cables that represents a serious challenge. Cables are rather complicated materials because they consist of an insulated part and jacket of polymeric materials. These polymeric materials can have various chemical structures, thicknesses and additives and generally have a char-forming tendency when exposed to heat source. In this work, two test methods are used for the characterization of cable pyrolysis and flammability. The first one permits the investigation of cable pyrolysis. A description of the cable mass loss is obtained, coupling an Arrhenius expression with a 1D thermal model of cables heating. Numerical results are successfully compared with experimental data obtained for two types of cable commonly used in French nuclear power plants. The second one is devoted to ignition investigations (spontaneous or piloted) of these cables. All these basic observations, measurements and modelling efforts are of major interest for a more comprehensive fire resistance evaluation of electric cables.

Estimation of species concentrations during a fire in a reduced-scale room

An approach to estimate species production during a compartment fire is proposed. Semi-empirical correlations based on oxygen concentration are given. They give an estimate of the concentrations of carbon monoxide, carbon dioxide, hydrogen, and hydrocarbons with a carbon chain length lower than five. Three intervals of oxygen concentration are noted, and they correspond to sufficiently ventilated, underventilated, and very underventilated fires. In order to validate these correlations, fire experiments are performed in a reduced-scale room. Species concentrations predicted by the model are in good agreement with our experimental data and with those of the literature. Coefficients used in the correlations are obtained for heptane and dodecane fires.

DETERMINATION OF LAMINAR BURNING SPEEDS AND MARKSTEIN LENGTHS OF p-CYMENE/AIR MIXTURES USING THREE MODELS

The aim of this article is to determine the laminar burning speeds and Markstein lengths of p-cymene. This fuel is emitted by a typical vegetal species of the Mediterranean region often involved in forest fires. Experiments are performed in a spherical vessel for different equivalence ratios ranging from 0.7 to 1.4 at 180 °C and at atmospheric pressure. The effect of temperature (85 to 180 °C) at the stoichiometry is also studied. Three models (one linear and two nonlinear) are used in the extraction process. Depending on the equivalence ratio, the more accurate models are adopted to determine the laminar burning speeds and Markstein lengths of p-cymene. Results are compared favorably to experimental values of a similar fuel (α-pinene) and to numerical data of n-decane computed using the in-house code A-SURF.

Biogenic volatile organic compounds emissions at high temperatures of common plants from Mediterranean regions affected by forest fires

Vegetal species emit biogenic volatile organic compounds at elevated temperatures. Because of their combustibility, biogenic volatile organic compounds can modify the wildland fires propagation dynamics, changing them from a moderate behavior to an explosive propagation. This phenomenon is known as an accelerating forest fire. The origin of such phenomena can be the accumulation of biogenic volatile organic compounds in concentrations close to their lower flammability limit in seasons where the plants are themselves very flammable. There is a lack of information on the biogenic volatile organic compounds emissions of vegetal species typically found in wildland fires at temperatures higher than ambient temperature. In this work, we used a flash pyrolysis device linked to a gas chromatograph/mass spectrometer to investigate experimentally the biogenic volatile organic compounds emissions of Thymus vulgaris, Lavandula stœchas, and Cistus albidus between 70°C and 180°C. High amounts of terpenoid compounds were found, except for C. albidus emissions, including thymol, l-fenchone, and 3-hexen-1-ol. The information provided in this work could help to improve the characterization of thermal degradation of vegetal fuels and to incorporate the biogenic volatile organic compounds combustion in physical forest fires models. They also show that under the right circumstances, biogenic volatile organic compounds from these vegetal species could contribute to the development of an accelerating forest fire.

Combustion Characteristics of Two Biogenic Volatile Organic Compounds: L-Fenchone and 3-Hexen-1-OL

This article deals with the emissions and combustion of l-fenchone and 3-hexen-1-ol. These biogenic volatile organic compounds (BVOCs) are the main compounds emitted respectively by two vegetal species often involved in forest fires: Lavandula stœchas and Cistus albidus. Two types of experimental setups are used: a flash-pyrolysis device to study the emissions at elevated temperatures and a spherical chamber to study the combustion characteristics. Emission results are compared to literature data for the same vegetal species at ambient temperature. Laminar burning speeds and Markstein lengths of these two BVOCs are determined at 453 K for different equivalence ratios. Results are compared to the ones obtained in our previous works for two other BVOCs at the same temperature.