A flame propagation model for nanopowders

International audience; The determination of explosion severity should be made from intrinsic properties of the fuel-air mixture in order to avoid the influence of external parameters, such as the vessel volume or the initial turbulence. To overcome such limitations, the flame propagation of gaseous mixtures is often studied in order to estimate their laminar burning velocity, which is independent of external factors and is a useful input for CFD simulation and for the sizing of protective devices. Experimentally, this parameter is difficult to evaluate when it comes to dust explosion due to the inherent turbulence during the dispersion of the cloud. However, the low inertia of nanoparticles allows performing tests at very low turbulence without sedimentation. Knowledge on flame propagation concerning nanoparticles may then be modelled and, under certain conditions, extrapolated to microparticles, for which an experimental measurement is a delicate task. This work then focused a nanocellulose with primary fiber dimensions of 3 nm width and 70 nm length. A one-dimensional model was developed to estimate the flame velocity of a nanocellulose explosion, based on an existing model already validated for hybrid mixtures of gas and carbonaceous nanopowders similar to soot. Due to the fast devolatilization of organic powders, the chemical reactions considered are limited to the combustion of the pyrolysis gases. The finite volume method was used to solve the mass and energy balances equations and mass reactions rates constituting the numerical system. Finally, the radiative heat transfer was also considered, highlighting the influence of the total surface area of the particles on the thermal radiation. Flame velocities of nanocellulose from 17.5 to 20.8 cm.s-1 were obtained numerically depending on the radiative heat transfer, which proves a good agreement with the values around 21 cm.s-1 measured experimentally by flame visualization and allows the validation of the model for nanoparticles.