Ignition sensitivity of gas-vapor/dust hybrid mixtures
Résumé
The explosion sensitivity of various gas or vapor/dust mixtures has been studied thanks to specifically modified apparatuses based on a 20 L sphere and a Hartmann tube. Experiments have shown that concentration of gas/vapors as low as 1% vol. causes a significant decrease of the minimum ignition energy and induces changes in the rate-limiting step of the combustion reaction, from boundary diffusion to homogeneous gas phase reaction. They also confirm that a hybrid mixture explosion is possible even when both dust and vapor concentrations are respectively lower than their minimum explosion concentration and lower explosivity limit. Comparisons have been done between our experimental data and classical models such as those developed by Bartknecht or Le Chatelier. It appears that these laws are not always conservative from a safety point of view. The influences of the diameter, of the adiabatic flame temperatures and of the critical ignition kernel, directly related to the quenching distance, have also been highlighted. This work demonstrates the peculiar behavior of gas or vapor/dust explosions and proposes simple models in order to estimate their ignition sensitivity.