Molecular Dynamics of Propellant Gases. Part 2,
ARMY ARMAMENT RESEARCH AND DEVELOPMENT CENTER DOVER NJ
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For an accurate description of the interior ballistic event, the equation of state for the propellant gas is very important. This is because the burning rate is pressure dependent and it is that pressure the performs work on the projectile. The technique of molecular dynamics is used to calculate the pressure for nitrogen gas in the density range of 0.2 to 1.0 gcm and in the temperature range of 500K to 3000K. The calculations assume that the motion of nitrogen gas molecules can be described using the laws of classical mechanics. Lennard-Jones and exponential-6 potentials are used to describe the molecular interactions. A system of 256 particles, in conjunction with a periodic boundary condition, is employed to simulate the bulk material. A predictor-corrector type of algorithm is used to integrate the equation of motion. The calculated pressures are compared with available equations of state and perturbation theory. It is found that the Lennard-Jones potential works well at 3000K and that the Hansen perturbation theory could become an effective method for calculating the pressure for real gases.