Jadwiga Fangrat, Wiesław Glinka, Piotr Wolański, Marek Woliński


The deflagration to detonation transition process as well as the structure of detonation were studied in vertical tubes for organic dust-oxygen mixtures (wood dust, brown and black coal dusts). Two vertioal tubes were used: one with rectangular
cross-section of 0.05 m and with the length of 3.2 m and the other with circular oross-section of 0.08 m and the length of 4.5 m. Weak initiation souroes, i.e. exploding wire, weak eleotric arc or electrical fuse heads were applied.

It was found that transition to detonation was gradual for all mixtures. In some cases, however, the ignition spots were visible ahead of original flame front. Retonation waves were not observed. Recorded detonation velocities are within the range of 1550 m/s to 2160 m/s.

The detonation structure was examined by means of pressure measurements, recording of the radiation emission in three
different wavelengths and by direct streak photography. It was found that a few pressure peaks were usually present in the detonation front; the distanoe between the leading shock and C - J plane varied from 5 cm to 15 cm and the mаximum temperature did not exceed 2900 K.

In the case of highly reacting brown coal dust sticking initially to the tube walls, the quasi-detonation combustion was also observed.

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