The Thermodynamics of Interior Ballistics and Propellant Performance

Report No. ARL-TR-6709
Authors: Anthony J. Kotlar
Date/Pages: November 2013; 46 pages
Abstract: The equilibrium thermodynamic properties of propellants are routinely calculated by standard computer codes such as NASA-Lewis, BAGHEERA, or BLAKE. This thermodynamic information is also "packaged" by the interior ballistic (IB)-oriented codes BLAKE and BAGHEERA and transferred to IB performance codes via several parameters (mainly ϒ, impetus [I], and the covolume). A related quantity called the chemical energy [CE = I/(ϒ - 1)] is also usually calculated, since it is sometimes viewed as one of the traditional measures of propellant performance. In cases like the electrothermochemical (ETC) gun, where energy (electrical) is added to the system, the CE appears not to adequately account for the additional energy. This study takes a critical look at the concept of CE as it is calculated for use in IB applications. Using a JA2 + 1-kJ/g system as an example, the missing energy, as reflected in the value of the CE, is found to be tied up in a composition change of the system; the energy scale used for the CE and IB calculations is incapable of directly accounting for this chemical effect. The relationship of the IB energy scale to the thermochemical energy scale is discussed. Using BLAKE (which is based on the thermochemical scale), the energies of several changes of state are calculated as alternatives to (as opposed to substitutes for) the CE. Also, for an often-used idealized gun model—constant breech pressure before burnout, Lagrange gradient, no losses—the processes delineating propellant performance (and the conditions at muzzle) are calculated via BLAKE using full variable-composition equilibrium thermodynamics.
Distribution: Approved for public release
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Last Update / Reviewed: November 1, 2013