Scaling of light emission from detonating bare Composition B, 2,4,6-trinitrotoluene [C7H5(NO2)3], and PE4 plastic explosive charges

Abstract

It is well known that an intense flash of light is emitted when an explosive charge is detonated. The light emission continues well beyond the actual detonation process due to shock excitation of the air molecules around the charge, as well as post-detonation reactions in the expanding products of the detonation. Various researchers have studied these emissions, and it has been established that there are features in such emission spectra that can be regarded as characteristic for a specific explosive composition and configuration. In this study, the emission characteristics at wavelengths between 650 and 940 nm were experimentally investigated for cylindrical bare Composition B, 2,4,6-trinitrotoluene [C7H5(NO2)3], and PE4 plastic explosive charges in the mass (M) range of 0.5 kg to 4 kg. The results show that the light emission parameters scale to M1/3 consistent with other explosive blast parameters such as pressure and impulse (so-called Hopkinson’s scaling). It is also shown that for bare charges, two distinct regions in time can be distinguished for the light emission, namely, light from the early time frame, while the charge is detonating (and slightly beyond), and light from the expanding products of the explosive (the “fireball”). It is argued that in the first region, ionization effects and shock excitation of the air molecules around the charge dominate the light emission. The dominance of these effects fizzles out rapidly as the blast wave expands from the charge, leaving only light emission from the expanding products of the detonation.