A comparative study between two ignition sources: electric igniter versus pyrotechnic igniter
Résumé
The risk assessment of combustible explosive dust is based on the determination of the probability of dust dispersion, the identification of potential ignition sources and the evaluation of explosion severity. It is achieved in most of cases with the two main experimental normalized devices such as the Hartmann tube (spark ignition) and the 20L spherical bomb (with the 5 kJ pyrotechnic ignitors). Ignition energy of the 5kJ ignitor is well calibrated and generates a reproducible ignition. But on the other hand this ignition is not punctual and the over pressure produced is nearly 2 bars. Moreover, the pyrotechnic igniter accelerates the combustion with multi ignition points in a large volume and that disturbs the kinetics. In this way, this ignition source does not allow to analyse the combustion products because the composition of the pyrotechnic igniter was found in the combustion products. This article deals with the comparison of two ignition sources in the 20 L spherical bomb. A large panel of classical explosive dusts is studied with electrical and pyrotechnic ignitors, in order to evaluate the possibility to establish a correspondence between parameters obtained with these two ignition technics. Severity parameters of Aluminium powder, titanium alloy and nicotinic acid CaRo 11 were measured by using the two types of ignition system in our 20 L spherical bomb equipped with the Kühner dihedral injector. The maximum explosion overpressure P max and dust deflagration index K st were measured in a large range of concentration allowing to propose correlations between electrical and pyrotechnic ignition for each parameter and each type of powder. The relevance of these correlations will be discussed.
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