A New Method to Evaluate the Suitability of Ignitor Strength Used in the Tests of Dust Explosions

Abstract

Based on systematic experiments in the 20-L Siwek sphere, the explosion behaviors of bituminous coal dust were investigated by changing the strength of pyrotechnic ignitor. The effect on the maximum explosion pressure (Pex) and maximum rate of pressure rise ((dp/dt)ex) of the ignitor strength is analyzed. Due to the under-or over-driven phenomena, the overly low or high ignitor strength may result in unrealisticPexand (dp/dt)ex, especially for lower dust concentration. To evaluate the suitability of ignitor strength, the time scales (i.e. the effective action time,teff, and the induction time,ti,) of the ignitor combustion and flame kernel development are introduced by analyzing the ignition process of dust cloud. It can be found that theteffsignificantly heightens and thetigradually decreases with the rise of ignitor strength. Moreover, when theteffis much lower than theti, the under-driven phenomenon will occur, which leads to the underestimatedPexand (dp/dt)ex. Conversely, when theteffis much higher than theti, the explosion tests may be over-driven to cause the overestimatedPexand (dp/dt)ex. For ideal ignitor strength, theteffwould be comparable to theti. Based on these facts, the under-and over-driven phenomena can be effectively verified by comparing theteffand theti. As a result, when the dimensionless time ratioteff/tiis 0.52 or 1.42, the explosion tests in the 20-L sphere would be, respectively, under-driven or over-driven. To obtain the realistic test results in the 20-L sphere, it is suggested that theteff/tivalue should be in the range of 0.8~1.2 as much as possible.