Can the Accuracy of BKW EOS be Improved?

摘要

Due to its mathematical simplicity and ease of implementation, the Becker- Kistiakowski-Wilson (BKW) equation of state is still used in thermochemical computer codes to predict detonation parameters, despite its lack of rigorous theoretical background. It gives satisfactory agreement between calculated and experimentally obtained detonation parameters for many standard high explosives having densities in the range 1 - 1.9 g/cm~3 . However, beyond these density limits, agreement is generally poor. A number of different parameter sets in BKW EOS have been proposed in order to overcome its limitations and shortcomings, unfortunately with limited success. To address this problem we applied an alternative approach which includes optimization of the covolume factors of detonation products obtained by ab-initio calculations to match experimental shock Hugoniot data, adjustments of the BKW coefficients so as to reproduce not only experimental detonation pressures and velocities but also other detonation parameters, introduction of a new concept of density/pressure-dependent covolume factors, as well as modification of the BKW EOS by adding an exponent to the covolume term x. To validate the approach we incorporated the modified BKW EOS into the thermochemical equilibrium code EXPLO5 and carried out calculations on a series of explosives having densities ranging from 0.25 to 1.9 g/cm~3 . The calculation shows a palpable improvement in accuracy at lower densities of explosives. The overall error in predicting detonation pressure and velocity for the studied explosives, expressed by the root mean square percent error (RMS), is 7.26% and 2.59%, respectively. We found the accuracy of modified BKW EOS to be close to the accuracy of the physically-based EOS.