Estimation of the Exothermic Reaction Rates for Nonideal Detonation of Triple Nitromethane/Ammonium Perchlorate/Aluminum Mixtures

The nonideal detonation of ternary mixtures of nitromethane (NM) and ammonium perchlorate (AP) with a large excess of aluminum (Al) is numerically modelled. A theoretical model developed earlier, in which the exothermic transformation of the mixture proceeds in three stages, including the decomposition of NM and AP, as well as the diffusion combustion of Al, is used. The calculation results are in close agreement with the experimental data on the detonation velocity recorded in steel tubes with a diameter of 18 mm, varying in a wide range of the NM content and Al/AP ratio in the mixtures. The values of the coefficients of the conversion rates of NM and AP, which are used in modeling the detonation of triple mixtures, are determined from the closest agreement of the calculations with the experiments on the charge diameter effect on the detonation velocity of a mixture of NM with 54% AP. The pressure exponents were set equal to 1. When changing the ratio of components, the calculations carried out with the same conversion rate coefficients closely agree with the experimental data. This is the reason why the selected values are used to calculate the detonation of triple mixtures. The low conversion rate of AP in comparison with NM leads to the length of the detonation wave reaction zone increasing up to 10 mm. The share of burnt AP is slightly less than half in mixtures with an Al/AP ratio of 1 : 1, and slightly more than one-third with an Al/AP ratio of 2 : 1.