Vol 14, No 1 (2021)

The autoignition delays of stoichiometric methane–ethylene–air mixtures in the initial temperature range T₀ = 760–1000 K and at a pressure P₀ = 1 and 3 atm were determined experimentally by the method of autoignition in a static reactor and by kinetic modeling. It was found that increasing the pressure reduces the autoignition delay without changing the general nature of its dependence on the concentration of ethylene in the mixture. The effective activation energy of the autoignition delay of methane–ethylene–air mixtures within the measurement error weakly depends on pressure which is confirmed by kinetic calculations. The calculated values of the effective activation energy are in a good agreement with the experimental results.

The paper is devoted to the numerical and theoretical analysis of the mechanisms of generation and amplification of shock waves in the process of unconfined flame propagation. Two basic mechanisms of shock wave generation corresponding to the linear and nonlinear stages of hydrodynamic instability development are distinguished. The role of thermoacoustic instability in shock wave amplification and the establishment of the conditions for deflagration-to-detonation transition is demonstrated on the example of a highly chemically active mixture.

The study is aimed at clarifying and eliminating the reasons of cycle-to-cycle variability during the operation of an innovative pulsed detonation hydroramjet (PDH) which reduces its thrust performance. An experimental sample of the PDH in the form of a pulsed detonation tube connected to an optically transparent water guide has been designed and manufactured. Experimental studies were performed with the vertical immersion of the sample in water. It was found that the cycle-to-cycle variability is associated with the overexpansion of gaseous detonation products in the detonation tube due to the inertia of the water column in the water guide. Gas overexpansion causes a reverse flow of the gas–water mixture which fills the water guide and penetrates the detonation tube, thus exerting a strong effect on the cyclic operation of the PDH. To eliminate the cycle-to-cycle variability, a new PDH model was developed, manufactured, and tested. The model is equipped with a rotary mechanical valve and operates on a propane–oxygen mixture. Its test fires showed that the use of the valve makes it possible to eliminate the cycle-to-cycle variability and to increase more than twice the average specific impulse: up to 550 s instead of 250 s at an operating frequency of 14 Hz.

The mechanism of HMX combustion at pressures of 0.05–5.0 MPa is investigated. Itis shown that HMX burns in the focal (hot-spot) mode. In the article “HMX combustion mechanism” byV. N. Marshakov, V. G. Krupkin, and S. A. Rashkovsky (2020. Russ. J. Phys. Chem. B 14(6):934–939. doi: 10.1134/S1990793120060111), the scale of inhomogeneity of the combustion surface — the characteristic size of hot spots is determined. The dependence of the size of the hot spots on the average burning rate of the sample is obtained. In the present article, the temperature distributions in the combustion wave obtained using thermocouples are analyzed. The local burning rates are obtained from the analysis of temperature distributions in the condensed phase (close to the Mikchelson distribution). It is shown that the scatter of the burning rate values is explained by the registration of the velocity at different points of the transverse wave front. The values of the local burning rates exceeding the average burning rate are caused by the elevated initial temperature of the sample ahead of the flame front and the smaller values are explained by the curvature of the flame front and by the buckling mode of combustion.

A method for recording light flashes during the initiation of an explosion in energy-intensive materials by a laser monopulse is proposed. Two methods of measuring the explosion delay are implemented. In the first, the photocell is installed on the back side of the test sample and luminocity is recorded in the infrared range (> 700 nm). On the register diagram, two separate peaks are clearly observed corresponding to the moment of generation (1064 nm) and the expansion of the explosion products. In the second, two photocells are used: the first one is located similarly and the second one is located on the side, in front of the sample. Luminocity is recorded in the range of 400–440 nm. The direct and scattered (explosion products) light fluxes emitted by the discharge of a pulsed pump lamp are measured. The delay is determined by the time shift of the signals of both photocells. The delay times for the selected chemical compound were 10 and 20 µs for monopulses with an energy of ∼50 and ∼ 60 mJ, respectively. The time of expansion of the explosion products is estimated in the interval from the beginning to the peak of the photocurrent. The specified value was ∼ 35 µs and did not depend on the initiation energy.

The mechanism of the modifying effect of rotational forces on the structure of the SHS-wave (SHS — self-propagating high-temperature synthesis) front in a cylindrical reactor with a compressed aluminothermic mixture rotating around a vertical axis is presented. It is shown that under the action of centrifugal forces, the particles of the reduced metal produced in the reaction zone of the SHS-wave move to the region ahead of the wave front and initiate new ignition sites in the fresh mixture, thus increasing the propagation velocity of the SHS-wave. This process opens up the possibilities for the synthesis of new nonequilibrium inorganic compounds with high temperature stability and a set of useful properties. As an example, the modifying effect of the addition of inorganic radicals (0.036% Al₂₀B₄O₃₆) on the crystallization of the silumin melt with a significant decrease in the size of crystals in the cooled melt is demonstrated.