Critical energy of initiation of a multifront detonation

Conclusions On the basis of the theoretical cell model and the experimental data on the emergence of the detonation from narrow channels into a half-space, we have constructed a model of the “direct” initiation of the detonation. The formulas obtained enable us to estimate the critical initiation energy practically for any experimental conditions. As the initial data, in the formulas we use only the density of the mixture, the velocity and dimension of a cell of the self-sustaining detonation, and also the time and space characteristics of the energy generation. The use of the model is based on a relatively simple experimental determination of the cell dimension for the mixture being investigated. In other models available today, for example [1–7], kinetic data on ignition delays are used; the inaccuracy in determining these may lead to considerable errors in the calculation of the initiation energy. A verification of the proposed model on the basis of existing experimental results is difficult because there are not enough data given in the published studies. Depending on the completeness of the information we have shown the quantitative or qualitative agreement between model and experiment. Novosibirsk. Translated from Fizika Goreniya i Vzryva, Vol. 15, No. 6, pp. 94–104, November–December, 1979.     

Cellular structures of a multifront detonation wave and initiation (Review)

Combustion, Explosion, and Shock Waves - The state of the art in the field of initiation of combustible mixtures is overviewed. Recommendations on using various formulas for estimating the critical...     

Energy release in multifront detonation

A method is proposed for determining the energy release in a combustible mixture, which is based on processing the trajectory of the expanding wave from the viewpoint of the strong explosion model. The wave trajectory in the case of critical initiation of multifront detonation in a combustible mixture is compared with the trajectory of a blast wave generated by the same initiator in an inert mixture whose gas-dynamic parameters are equivalent to those of the combustible mixture. The energy release is defined as the difference between the joint energy release of the initiator and combustible mixture in the case of critical initiation and the energy release of the initiator in the case of blast wave excitation in the inert mixture. Results of experimental validation of the method by an example of a stoichiometric acetylene–oxygen mixture are presented. Noticeable deviations of the experimental profile of energy release from available model concepts are observed.     

Diffraction of a multifront detonation wave

Moscow. Translated from Fizika Goreniya i Vzryva, Vol. 25, No. 5, pp. 137–141, September–October, 1989.     

Effect of nitrogen on multifront detonation parameters

A faster increase in the cell size and other very important multifront detonation parameters compared with that predicted by the kinetic calculations has been shown for nitrogen-diluted fuel-oxygen mixtures of hydrogen and typical hydrocarbons. Dilution of mixtures with other inert gases does not lead to a similar effect. This may be associated with the increase in the chemical reactivity of nitrogen under the action of the electric field of a detonation wave. A more correct method of calculating the ignition delays of various nitrogen-containing mixtures for detonation conditions is proposed. Translated fromFizika Goreniya i Vzryva, Vol. 34, No. 1, pp. 79–83, January–February, 1998     

Reliability of kinetic data used for estimating multifront detonation parameters

A faster increase in the cell size and other important parameters of multifront detonation than that predicted by kinetic calculations is obtained for fuel-oxygen mixtures of hydrogen and typical hydrocarbons diluted by nitrogen. In a stoichiometric hydrogen-oxygen mixture diluted by an additional amount of oxygen or hydrogen, experimental and calculated data are also found to diverge with increasing concentration of the added species. This effect, however, is not observed if these mixtures are diluted by helium or argon. An assumption about the reason for this difference in data is put forward. A conclusion is made that kinetic data should be corrected as applied to detonation conditions. __________ Translated from Fizika Goreniya i Vzryva, Vol. 45, No. 3, pp. 89–94, May–June, 2009.     

Effects of initiation conditions on detonation development

Combustion, Explosion, and Shock Waves -     

Critical energy of bubble detonation wave initiation by a wire explosion

Initiation of bubble detonation by a short shock wave generated by exploding a wire located in a chemically active bubbled medium is studied experimentally. Critical energies of detonation initiation are determined for different volume fractions of bubbles. It is demonstrated that this method of initiation transforms the compression wave to a detonation wave at a length of ≈0.3 m. In the case of a wire explosion in a gas-liquid medium, the critical energy of bubble detonation initiation can be reduced by more than two orders of magnitude, as compared with initiation by a gas detonation wave.     

Gap effect on the initiation of detonation of gas mixtures in cylindrical combustion chambers

A new mechanism is proposed for the occurrence of a number of phenomena in combustible gas mixtures described in the literature. This mechanism takes into account the possibility of reaction-zone propagation by pathways that were not envisaged in designing experimental setups. The process discovered more than 25 yr. ago and identified previously as autoignition of a shock-heated gas is considered in detail. This process has recently been used as experimental evidence for the existence of spontaneous (gradient and induction) flames. It is shown that this process actually involves mixture ignition by hot reaction products which issue into the chamber from the side of the detonation wave rather than combustible-mixture autoignition. Lavrent’ev Institute of Hydrodynamics, Siberian Division, Russian Academy of Sciences, Novosibirsk 630090. Translated from Fizika Goreniya i Vzryva, Vol. 34, No. 2, pp. 86–97, March–April, 1997.