The afterburning is a complex chemical process which stems from the reaction of the detonation products with the oxygen in the air when appropriate conditions exist. TNT is a very fuel-rich explosive as indicated by the large negative oxygen balance value of −74%. It means that there is not enough oxygen in its initial chemical compound and extra oxygen is needed to make the afterburning energy release possible. This article describes in details the calculation process for evaluating the amount of energy release in a confined TNT explosion. Moreover, partial afterburning energy release is also calculated for cases of oxygen deficiency. Commonly, numerical simulations take into account only the detonation energy in blast pressure analysis and it is responsible for under prediction of blast pressures in a confined explosion. Accounting for the afterburning energy as well considerably improves the predictions and yields pressures that are in good correspondence with measured data. The calculation time however increases by an order of magnitude. An afterburning coefficient was defined as the relation between the total energy released and the detonation energy. This coefficient was found useful for correcting numerical simulation results of TNT confined explosion which take into account only the detonation energy. This correction can be achieved by multiplying the pressure-time history with the afterburning coefficient. In addition, an analytic method, based on thermodynamic rules, was developed for calculating the gas pressure resulted by TNT confined explosion. This unique method takes into account the variation of the total energy released and the heat capacity ratio depending on the ratio between the charge weight divided by the confined air volume. The gas pressure obtained using this method was shown to be in good agreement with experimental results that are published in the literature.
This paper presents a first stage of a study aimed at understanding some characteristics of an interior explosion within a room with limited venting. An interior explosion may occur accidentally in ammunition storage, or due to a terrorist action, or as a result of a warhead explosion that follows its penetration into a closed space. The full scale experimental study is focusing on a single room sized space with rigid boundaries, at the center of which a TNT charge is detonated. The room has a limited size opening for venting at the ceiling. The effect of the charge size on the blast pressures has been investigated and a new insight with regard to the pressure distribution on the walls as well as the pressure attenuation depending on these parameters has been gained.
This paper aims at extending our understanding with regard to some characteristics of an interior explosion within a room with limited venting. An interior explosion may be the result of an ammunition storage explosion, or an explosive charge as part of a terrorist action or a warhead explosion that follows its penetration into a closed space in a military action. Full scale experiments have been performed with a TNT charge detonated at the center of a single room sized space with rigid boundaries. The room has a limited size opening for venting at the ceiling. Numerical simulations of the problem have been performed using AUTODYN Ver. 12.1 and compared with the experimental measurements. Some deviations between the measured pressure and the predicted pressure motivated the present study in an attempt to study the effect of the additional energy released due to the burning of the detonation products reacting with the surrounding oxygen. The study that is described in this paper enhanced our understanding. Incorporation of this effect considerably improved the predictions. The present study clarified when, how and to what extent the afterburning should be introduced in the analysis.
Peak overpressure and impulse are the most important parameters in the explosive performance estimation. Available models commonly consider trinitrotoluene explosive as the standard charge. In this article, the trinitrotoluene equivalency factor is studied through verified one-dimensional numerical simulations. The equivalency factors for impulse and overpressure are different and found to be constant with the scaled distance (3-40 m/kg 1/3), which means that a unique value for the equivalency factor is suitable for the equivalency factor calculation for each distance. Comparison of the equivalency factor with available models shows that it strongly depends on the internal energy ratio of the explosive in interest, relative to trinitrotoluene, and a new formula for equivalency factor for overpressure is proposed. A verified simulation method is presented in which the explosive is modeled with an equivalent "air bubble" with the same internal energy and ideal gas equation of state. A new approach using the energy flux density calculation is presented to calculate the equivalency factor for impulse and overpressure from a single gauge measurement of overpressure-time history, at a specific distance.
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