(388ae) Effect of Ignition Energy On Dust Explosion Behavior: Phenomena of Under-Driving and Over-Driving

The dust explosion prevention first requires reliable data on explosion hazards. Energy of pyrotechnic ignition sources used to determinate the critical explosion characteristics such as the thermodynamic parameter pressure ratio PR and the kinetic parameter explosion index K_st is always prescribed as a fixed value according to the specifications of current testing standards. However, authors’ previous studies indicated that explosion behaviors are strongly affected by ignition energy. To complete current testing procedures and yield more realistic data, experiments were carried out to gain an insight into the explosion behaviors of carbonaceous and light metal dusts induced by different ignition energies by using the Siwek 20 L spherical vessel. Both the under-driving phenomenon in thermodynamics and the over-driving in kinetics were investigated systematically. The pronounced influence of ignition energy on the typical brisance parameter PR for carbonaceous dust means that the strong dependency of volatile yield on the strength of ignition source is verified. The Incomplete deflagration of carbonaceous dust under weak ignition energy results in the under-driving phenomenon, the adverse effect yielding under-estimated thermodynamic data. Moreover, the under-driving phenomenon appears to be inconspicuous as the dust concentration is raised because the weak activation of low ignition energy is partially balanced by the quite efficient particle preheat process under the fuel-rich condition. Nevertheless, the under-driving usually occurring for carbonaceous material is not notable for magnesium dust. This is because the amount of energy liberated from the surface heterogeneous oxidation of magnesium particles is not so sensitive to ignition energy. The measured K_st increases monotonically with the rise of ignition energy but fails to represent a horizontal asymptote, which gives the idea that the dust flame propagation is over-driven by strong ignition sources and thereby the typical kinetic parameter K_st as well as the burning velocity is somewhat over-estimated. Based on the analysis of flame propagation in dust cloud, a practical method was proposed to evaluate the occurrence of over-driving. The over-driving can be verified when the reduction of dimensionless flame thickness turns to augment again. Moreover, the light metal dust is much easier to be over-driven than carbonaceous dust. Authors suggest that the most appropriate ignition energy to gain realistic data in both thermodynamics and kinetics may be the energy at which the thinnest dimensionless flame thickness is attained.