ARTICLE:

• CRITERIA FOR TRANSITION FROM DEFLAGRATION TO DETONATION IN H₂-AIR-STEAM MIXTURES  download article

C. K. Chan
AECL, Whiteshell Laboratories, Pinawa, Manitoba ROE 1L0, CANADA

W. A. Dewit
AECL, Whiteshell Laboratories, Pinawa, Manitoba ROE 1L0, CANADA

G. W. Koroll
AECL, Whiteshell Laboratories, Pinawa, Manitoba ROE 1L0, CANADA

ABSTRACT

Flame acceleration and transition to detonation were examined for various H₂-air-steam mixtures in a 28 cm diameter, 6.4 m-long, combustion duct filled with obstacles. The run-up distances for DDT (distance between ignition and onset of detonation) were measured for these mixtures and found to be inversely proportional to the laminar burning velocities of the corresponding mixtures. Based on these results, experimental DDT limits were established. Instead of relying on the detonability limits as the conservative criteria for DDT, the experimental DDT limits offer a set of less restrictive criteria. Results also showed that DDT did not occur if a flame had not accelerated to a speed corresponding to a flame Mach number greater than 1.5. This critical value indicates that for H₂-air-steam mixtures, the mechanism for DDT is closely related to the strength of its leading shock. Comparison with other experiments confirms that initiation of detonation by shock focusing caused by the reflection of the leading shock off obstacles is the dominant mechanism for DDT in these insensitive mixtures.

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