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On the Determination of the Gas Temperature From the Velocity of the Muzzle Rarefaction Wave

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Final rept. Jul 1981-May 1982

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The temperature of the propellant gas as it flows out of the muzzle of a gun is a principal factor in respect to the strength of the air blast which accompanies the discharge of the projectile. The temperature also plays a dominant role in respect to the occurrence of secondary combustion of flash. We discuss the fundamental basis for a method of determining the temperature from measurements of the velocity of the unloading wave or rarefaction created by the discharge of the projectile. The method is, of course, restricted to cases in which the projectile velocity is less than the speed of sound in the gas directly behind it. For charges which are completely burnt and in which the products of combustion at the muzzle are purely gaseous, three sources of error are identified. First, the measurement time may be approximately equal to the relaxation time for changes in chemical composition. This will result in dispersion and since the unloading wave contains components of all frequencies, part of the wave will move with the frozen wave speed and part move with the equilibrium speed. Due to dissipation the faster frozen components will be less detectable at increasing distances from the muzzle. Second, the unloading wave is not one-dimensional and the radial relaxation time is of the same order as the measurement time. Significant geometrical dispersion will result and will be superimposed on the chemical relaxation. Third, the temperature of the gas in the measurement zone may differ significantly from the space-mean value as a consequence of a non-uniform release of chemical energy by the propellant and the deviation may be to higher or to lower values.

Subject Categories:

  • Test Facilities, Equipment and Methods
  • Ballistics

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