Collision Plane Research Articles

The ignition of a fuel droplet in the stagnant gas region produced by colliding shock waves

Observations were made of the behavior of a fuel droplet suspended in air in the collision plane of oppositely facing shock waves of equal strengths. In such situation the gas surrounding the droplet is brought almost instantaneously to a high-temperature stagnation state, and the rapid atomization process observed in the incident-shock experiment does not take place. Three kinds of liquid fuels were used. The temperature of the stagnant region ranged from 1000 to 3000°K, strong emissions indicating exothermic reactions being observed except near the lower temperature limit. A fairly short but definite induction period for the onset of strong emission, exhibiting an Arrhenius-type dependence on temperature, was found to exist, during which the droplet remained seemingly unaffected. The breakup of the droplet set in only after the emission, whereby the whole liquid mass exploded symmetrically into minute fragments, luminous zones spreading out with them. While the present experiment might be regarded as the extension of quasistatic ignition studies in furnace to higher temperatures, the features disclosed seem to indicate that a substantial role is played by the strong turbulence behind the reflected shock waves, resulting in an abnormally rapid heating of the droplet.

The screening effect in the interaction of blast waves

1. The authors have obtained experimental confirmation of the feasibility of screening stress waves by the counterexplosion method. 2. Simultaneous firing of the main charge and of additional charges which form a plane wave front enables one to reduce the stresses in the wave front of the main explosion. The additional charges must be located at the boundary of degeneration of the plastic wave of the main explosion into an elastic compression wave. 3. The approach of the collision plane of the main and screening explosion fronts to the additional charge lines enables one to improve the screening conditions and to obtain a more effective screening effect at a lower weight of the additional charges. Collision of the fronts must occur after formation of the plane wave of the screening explosion; this enables the differences between the divergences of the fronts of central and axial symmetry to be utilized. 4. Use of the method of artificial “aging” of piezoceramic plates of TsTS-19 material under a load of 800 kg/cm2 for 72 h enables the linearity of the dependence of the piezoelectric charge Q on the stress σ33 to be extended up to a pressure of 550 kg/cm2, thus reducing the measurement error.

Rotational Relaxation of Homonuclear Diatomic Molecules

Through the use of Wang Chang and Uhlenbeck's theory of polyatomic gases, rotational relaxation times for homonuclear diatomic molecules have been calculated. The model adopted is that of two molecules rotating in the same plane which also serves as the collision plane. The intermolecular potential used is Parker's modification of the Morse potential, where the molecular orientations are taken into account only in the repulsive part. This leads to a relaxation time, for which the ``collision number'' Zrot is essentially independent of temperature. Owing to the lack of any experimental information concerning the temperature dependence of rotational relaxation the discussion has been limited to a few comments about earlier calculations.

Classical scattering of an atom from an asymmetric molecule

Using the methods of classical mechanics, we have calculated the cross sections for inelastic scattering of an atom 4He, in collisions with a diatomic rigid rotator HT. The molecule has an asymmetric mass distribution, and as a consequence, a rotating potential model was introduced. This involves a potential field spherically symmetrical about the geometrical midpoint of the molecule which rotates around its centre of mass. The results show large deviations from the cross sections obtained with a simple spherical potential. These deviations depend strongly on the orientation and the angular momentum J of the molecule. An analysis of the effect of the space orientation of J reveals a considerable polarization of the deviations of the cross sections. A reasonable approximation to an orientation averaged cross section can be obtained by taking the positions of J perpendicular to the collision plane as representative, which permits simplification to a two-dimensional collision calculation. There is a positive increase in the diffusion cross section which can be as much as 20% for low relative velocities and high angular momentum values. It is possible to calculate the probability for change of the rotational state, showing how correctly a calculation based on classical mechanics can describe a quantum phenomenon. The new calculations predict an increase in the transition probabilities from 10 -3 to about 5·10 -2. This is in accordance with the value expected from experiments.