T. V. Bazhenova

Self-ignition of a fuel gas upon pulsed efflux into an oxidative medium

It is demonstrated that hydrogen can exhibit self-ignition when a starting shock wave, on which the temperature increases above the stagnation temperature, appears in front of a cold expanding gas jet. This heating leads to the ignition of the hydrogen-air mixture formed at the contact surface. The results of numerical simulations show that, at a gas pressure in the vessel on the order of 300–600 bar, the intensity of a shock wave formed in air is sufficient to produce self-ignition of the hydrogen-air mixture formed behind the front of the jet of compressed hydrogen.

The Shock-Wave Mechanism of Spontaneous Ignition of Hydrogen under Conditions of Sudden Efflux from Reservoir at High Pressure

Analysis is made of the conditions of spontaneous ignition of hydrogen as a result of emergence of a starting shock wave in air before an expanding cold flow of gas. The rise of temperature behind the shock wave causes ignition of the mixture of combustible gas with air, which forms on the contact surface. The condition for spontaneous ignition is the sufficient time of residence of mixture at high temperature for mixing and ignition. The calculations of spontaneous ignition of hydrogen jet are based on a model which takes into account the gasdynamic transport of viscous gas, the kinetics of oxidation of hydrogen, multicomponent diffusion, and thermal conductivity. The range of pressures is determined in a reservoir, during whose depressurization the shock wave forming in air exhibits intensity sufficient for igniting the hydrogen-air mixture behind the front of propagating jet of compressed hydrogen. Results of analysis are given of the dependence of conditions of ignition on the pressure of hydrogen in the reservoir, on the size of the outlet opening, and on the initial temperature of hydrogen and air.

Shock wave effect on protective sand screens of different thicknesses

The interaction of a shock wave and a wall protected by a pressed sand layer with various thicknesses was studied in this work. The sand screen was placed at a distance of 0.1–12 cm from the end-wall of the shock tube or dead-attached to it. The attenuation of the reflected shockwave was compared when it interacted with the sand screen in the two above cases.

Study of an interaction of a blast wave with a destructible screen made of a granular material

The results of an experimental study of three cases of the interaction of a shock wave with screens made of an easily destructible material are given. The dependence of the coefficient of attenuation on the thickness and location of the screen is obtained.

An Investigation of Surface Energy Input to Gas during Initiation of a Nanosecond Distributed Surface Discharge

The fraction of energy, directly introduced into gas during the initiation of a distributed pulsed surface discharge of the plasma sheet type, is analyzed using the results of investigation of the dynamics of resultant shock waves. Results are given of numerical calculation of development of flow within the model of thermal energy input. It is demonstrated that the experimentally obtained values of the velocity of motion of perturbations agree well with the calculation results assuming that 40 ± 10% of the energy of surface electric discharge of nanosecond duration changes to thermal energy in the stage of energy input, i.e., during the time which is much shorter than 1 μs.

Increasing the force with which a shock wave discharged from the channel acts on an obstacle by way of converting a normal pressure shock to a system of oblique shocks

The results are given of experimental and numerical investigations of the effect produced on an obstacle by shock waves discharged from channels of different cross-sectional shapes (circle, square, cross). The pressure distribution on an obstacle mounted normally to the flow axis is measured. The experimental results are compared to the data of numerical calculation for determining the optimal modes as regards the duration of calculation and the cell size that produce the least difference between the experimental and numerical data. Calculations are performed of the gas flow behind a shock wave discharged from a channel of X-shaped cross section, and the distribution of pressure and temperature over the obstacle surface is plotted. It is found that the force with which a flow acts on an obstacle when discharged from a channel of X-shaped cross section is much greater than in the case of being discharged from a channel of round or square cross section. Shadow photographs show that this is due to the reduction of the loss of total pressure in the flow because of the conversion of the normal pressure shock to a system of oblique shocks.

Three-Dimensional Effects and the Interaction between an Obstacle and a Shock Wave Discharged from a Channel

The results are given of experimental and numerical investigations of the total pressure across a stagnation shock in the flow behind a shock wave discharged from open ends of round and square channels. It is found that the loss of total pressure behind a stagnation wave before an obstacle when discharged from a square channel exceeds that in the case of a round channel. The observed effect is attributed to the fact that, when a shock wave is discharged from a square channel, the flow separation occurs at a greater angle, which is accompanied by an increase in the Mach number of the flow.

Flow Expansion behind a Shock Wave Discharged from a Channel

The results are given of experimental and numerical investigations of the structure of flow behind a shock wave discharged from open ends of round and square channels. It is demonstrated that the expansion regions arising in a flow behind a diffracted wave are characterized by a larger volume and a higher expansion ratio than those arising in a stationary underexpanded jet with the same value of the Mach number of flow at the channel exit section.

Diffusive self-ignition of hydrogen upon efflux from a nozzle array

It is experimentally demonstrated that the efflux of hydrogen at a high pressure into air via a nozzle array is accompanied by the interaction of jets, which results in the conditions for self-ignition at a nozzle diameter below the values for which self-ignition is possible in a single jet. Conditions for the safe efflux of hydrogen via a nozzle array from a reservoir at a pressure of 400 bar (and below) are established.

Diffusion-controlled autoignition of hydrogen outflowing into an air-filled channel

The results of a numerical study of the pulsed outflow of hydrogen into an air-filled channel are presented. The adjustable parameters were the initial pressure of hydrogen in the reservoir and the distance from the diaphragm to the ignition point. The pressure, temperature, and water vapor mass fraction profiles along the channel wall at various moments of time were calculated. The autoignition parameters were calculated with account of turbulence, boundary layer formation, heat transfer, and diaphragm opening time. It was demonstrated that the boundary layer effect promotes hydrogen autoignition. The dependence of the distance from the diaphragm to the autoignition point was calculated as a function of the pressure in the reservoir with hydrogen. The simulation results were found to be in close agreement with the available experimental data.