Transition to detonation in corn starch dust-oxygen and -air mixtures

Abstract

In the transition to detonation of some organic dust-gas oxidizer mixtures four stages can be distinguished: (1) initial particle ignition; (2) compression wave amplification by coherent energy release; (3) unsteady reaction shock; and (4) spin detonation. By decreasing the initiation energy the monotonous acceleration of the whole process turns into a multistage one. Within the stage of the reaction shock the symmetrical smooth wavefront structure is transformed into a three-dimensional one, and the spin detonation forms. The transition with an abrupt onset of detonation and retonation wave formation, as observed normally in gaseous mixtures, exists in dust mixtures too, since propagation of dust detonations is also dominated by transverse waves. For detonations in lean corn starch dust-oxygen mixtures at initial pressure p 0 = 0.4 bar, the minimum tube diameter is d min = 0.14 m. But for corn starch dust-air mixtures, the same value of d min holds only at p 0 = 2–2.5 bar.