a] Jouguet state. It particularly applies to oxygen-deficient explosives and at higher densities, where formic acid appears to be an important detonation product.

One of the most important tasks of thermochemical codes for the calculation of detonation properties is the accurate description of the state of gaseous products within a rather wide range of pressures and temperatures – from several hundreds of kbar and several thousands of K to atmospheric pressure and temperature. Due to its simplicity and convenience, the Becker-Kistiakowski-Wilson (BKW) equation of state is used in many practical applications in the explosives field, despite its lack of rigorous theoretical background. The BKW EOS gives good agreement between calculated and experimentally obtained detonation parameters for many standard high explosives having densities in the range 1.2 – 2 g/cm3. However, it fails to predict accurately detonation properties at lower densities. To overcome this problem, we introduced the concept of density dependent molecular covolumes in the BKW EOS instead of invariant. The applicability of the approach is verified by comparing experimental and calculated values of detonation parameters for a series of explosives having different formulations and densities. It was found that by applying this approach the accuracy of the calculations for lower densities can be significantly improved.

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A hundred years ago (in 1921) Becker proposed an equation of state in which the repulsive term in van der Waals equation of state was replaced by an exponential function. Twenty years later, Kistiakowsky and Wilson modified Becker's equation and used it to calculate the detonation properties of nitroglycerine and mercury fulminate. The resulting equation of state, commonly called the BKW equation of state, is attributed to Becker, Kistiakowsky, and Wilson. Although it was not founded on a strict theoretical background, the BKW equation of state has been widely adopted in thermochemical codes to predict the detonation properties of explosives. Throughout the years, the accuracy of BKW has been significantly improved through proper calibration of the BKW constants and covolumes. This paper presents the concept of temperature-dependent covolumes of polar molecules (H 2 O and NH 3 ) as a way to improve the accuracy of prediction of detonation properties of explosives, especially those explosives producing larger amounts of H 2 O and NH 3 . It was demonstrated that temperature-dependent covolumes describe more accurately experimental shock Hugoniots of polar molecules than constant covolumes, and the accuracy of prediction of detonation properties of HNO types of explosives is greatly improved.

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