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1 1998

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Influence of initial temperature, dilution and scale on DDT conditions in hydrogen - air mixtures

Sidorov V.P., Dorofeev S.B.

Archivum Combustionis

1998

Vol. 18 nr 1-4

87-103

Results of large scale experiments on deflagration to detonation transition (DDT) in hydrogen - air - stream mixtures at elevated temperature are presented. The objectives of the tests were (1) study of conditions for DDT at large scale, (2) evaluation of DDT scaling criteria for steam diluted hydrogen - air mixtures at elevated initial temperatures. Experiments were carried out in the RUT facility, Russia. Total volume of mixture was about 480 m3. Inner volume of the facility was preheated by specially designed heating system in tests with steam. Initial gas temperature inside the facility was 370-380 K. Ignition was made by weak electric spark. The combustion modes observed include shock-less (slow) deflagration, fast turbulent deflagration, and DDT. Onset of detonations was observed either in the obstructed channel, or in the largest compartment of the enclosure. Results of the present tests were comapred with tests carried out in the same facility at normal initial temperature (285 K) with hydrogen - air mixtures. Critical conditions for DDT were analysed in terms of the detonation cell size as a measure of mixture sensitivity to detonation initiation. Avaible measured data on detonation sell sizes for different initial conditions and hydrogen - air - steam mixture compositions have been approximated by an analytical function. This function was used to estimate detonation sell size for mixtures within composition range where the measured data are not avaible. It was shown that the compositions with the cell size close to 1 m are the critical compositions for DDT in the RUT facility. The critical compositions expressed in terms of detonation cell size appeared to be very similar in hydrogen - air DDT experiments at 285 K, and in hydrogen - air - steam tests at 375 K in the same facility.