Influence of Air-Fuel Ratio on Turbulent Fireball Temperatures

We predict the explosion fields from the detonation of different spherical HE charges. Our high-order Godunov code is used for this purpose. Thermodynamics of the gaseous products are predicted by tabulated Cheetah code results. Initial conditions are provided by a similarity solution for a constant velocity Chapman-Jouguet detonation wave, which is mapped onto the Cartesian grid when the wave reaches the radius of the charge. Adaptive Mesh Refinement is used to follow the dynamics of the turbulent mixing structures on the computational mesh. Three different 1-kg charges are studied: TNT, Comp B and LX-14. These have very different Heats of Combustion (3473, 2667, 2292 cal/g) and Air-Fuel ratios (3.14, 2.37, 1.13 g/g) for TNT, Comp B and LX-14, respectively. The computed vorticity fields in the fireballs are similar—which means that the turbulent mixing rates are similar. But to reach stoichiometric conditions, it takes 1.1 units of time for LX-14, 2.4 units of time for Comp B, and 3.1 units of time for TNT. After achieving stoichiometric conditions, further turbulent entrainment of air simply cools the fireball. This is reflected in the mean fireball temperatures, for example: the LX-14 fireball cools to room temperature in 26 milliseconds, while the Comp B fireball remains at 1,500 K until 260 milliseconds. So, while the mean fireball temperatures at stoichiometric conditions are similar, the late-time fireball temperatures are strongly dependent on the air-fuel ratio. LLNL-ABS-832910