Thermal Behavior of Explosive Fireballs as a Function of Charge Size

ABSTRACT Post‐detonation fireball temperatures were measured as a function of charge size for pentolite spheres ranging from 13 to 165 g using video pyrometry. The charges were detonated in an open environment with diagnostics positioned to monitor the optical emission intensity as a function of time. The emission data was analyzed for temperature and a threshold intensity was used to identify the thermal growth and decay of a fireball as a function of explosive charge size. Experiments used three‐color imaging pyrometry (i.e., spatially and temporally resolved measurements) and spectrograph‐based pyrometry (i.e., spatially averaged measurements over a broader spectral range) to calculate temperatures. Results show fireball growth and decay rates are similar for the larger charge masses (55 and 165 g) and reduced by about 50% for the smaller charge mass (13 g). When the data are normalized spatially and temporally, the scaling of thermal growth and decay are nearly identical.