Afterburning Aspects in an Internal TNT Explosion

Abstract

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.

On the effectiveness of ventilation to mitigate the damage of spherical membrane vessels subjected to internal detonations

“…All the studied cases refer to deficiency in oxygen chambers (i.e. W/V vessel > 0.387 kg-TNT/m 3 , Table 1) and should show a final QS temperature of 2800 K in agreement with the chemical equilibrium (Edri et al, 2013). Nevertheless, it can be observed that the QS temperature that is calculated from the 3D model disagrees with those from the chemical equilibrium approach because gases are modeled by independent EOS and are not described such as a unique gas that should be modeled by a variable gamma ideal gas EOS (Edri et al, 2013;Hernandez et al, 2016).…”

“…After the dynamic response of the chamber, a significant final temperature is observed for the FC chambers associated with the QS state. For example, the chemical equilibrium predicts that the final temperature of the gas mixture is approximately equal to T QS = 2800 K when chambers are deficient in oxygen, that is, W/V vessel > 0.387 kg-TNT/m 3 (Edri et al, 2013). This temperature is so high that ventilation seems to be mandatory, taking into account that the forging temperature for carbon steels is approximately 1500 K. Figure 12 shows the temperature time-history obtained from the 3D model associated with the FC and PC chambers.…”

Prediction of Confined Blast Loading in Single-Layer Lattice Shells

“…It is quite possible caused by neglecting the afterburning effect. During the simulation in AUTODYN, the standard JWL equation (Eqn 4) takes no account of the afterburning energy due to additional combustion processes (Edri et al 2012(Edri et al , 2013. On the other hand, the subsequent reflected values of the simulation are a bit larger than those recorded in the chamber test.…”

Prediction of blast loading in an internal environment using artificial neural networks

“…As such, preliminary testing led to a domain of 10 7 5 × × m being specified, with rigid surfaces placed on the upper and lower surfaces (ceiling and floor), and two of the four walls, see Figure 8. The two remaining boundaries were specified to be ambient so sufficient venting is provided to the domain and energy increase through afterburning (Edri et al, 2013) and quasi-static pressure development (Anderson et al, 1983) is negligible. The domain can therefore be considered as 'fully vented' according to the definition in UFC 3-340-02 (US DOD, 2008).…”