On the pyrotechnic ignitors role in dust explosion testing: Comparison between 20 L and 1 m3 explosion vessels

Several phenomena (e.g., initial turbulence level, overdriving, underdriving, etc.) affect the measurement of dust explosion parameters in the 20 L and 1 m(3) standard test vessels. Estimating the role of each phenomenon is crucial to understand the discrepancies observed over the years between the data collected using these vessels. In this work, we focus on the role of the pyrotechnic ignitors on the pressure trend and the temperature distribution. We run explosion tests in the 20 L vessel to measure the pressure-time history generated by the explosion of pyrotechnic ignitors. Moreover, we performed CFD simulations to simulate the spatial/temporal evolution of the temperature map from the hot core due to the igniter explosion toward the vessel walls. The explosion of the pyrotechnic ignitors shows a significant increase of pressure in the 20 L vessel, suggesting that flame propagation is occurring inside the vessel. Furthermore, the localized increase of temperature due to the ignitor explosions, diffuse, and then uniformize much more rapidly in the 20 L vessel than in the 1 m(3) vessel. The flame propagation generated by the ignitors is very relevant in the 20 L sphere leading to the overdriving phenomenon. This result justifies the fact that for many organic dusts, the deflagration index values measured in the 20 L are much higher than those measured in the 1 m(3) vessel. CFD simulations show that the hot core generated by the ignitors dissipate much faster in the 20 L vessel than in the 1 m(3) vessel, due to the higher turbulence level of the smaller vessel. Therefore, dusts whose combustion is controlled by particle heating are more prone to sustain combustion in the 1 m(3) than in the 20 L vessel.