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Effects of confinement on combustion of TNT explosion products in air

Kuhl A. L., Ferguson R. E., Oppenheim A. K., Sum T-H.J., Reichenbach H., Neuwald P., Kuhl A. L., Ferguson R. E., Oppenheim A.

Archivum Combustionis

2001

Vol. 21 nr 1

3-25

A numerical study of turbulent combustion following detonative explosions of TNT in geometrically similar cylinders filled with air reveals that the combustion rate depends significantly on the size of the chamber (confinement). The fluid-dynamic solution provides an insight into the evolution of combustion fields dominated by strong interactions between turbulence and shock waves. Time profiles of fuel consumption, extracted from this solution, demonstrate the dynamic (thermokinetic) features of the system, expressed by the rate of combustion (akin to velocity) and its change (akin to acceleration). Their evolution is described by means of bi-parametric life functions.

Gasdynamics of combustion of TNT products in air

Kuhl A. L., Ferguson R. E.

Archivum Combustionis

1999

Vol. 19 nr 1-4

67-89

Effects of turbulent combustion induced by explosion of a 0.8-kg cylindrical charge ot TNT in a 17 m3 chamber filled with air, are investigated. The detonation wave in the charge transforms the solid explosiwe (TNT: C7H5N3O6) to gaseous products rich (`20% each) in carbon monoxide. The detonation pressure (`210 kb) thereby engendered causes the products to expand rapidly, driving a blast wave into the surrouding air. The interface between the products and air, being essentially unstable as a consequence of the strong acceleration inducted by the blast wave, evolves into a turbulent mixing layer - a process enhaced by shock reflections from the walls. Under such circumstances rapid combustion takes place where the expanded detonation products play the role of fuel. Its dynamic effect is manifested by the experimental measurement of ` 3 bar pressure increase in the chamber, in contrast to ` 1 bar attained by a corresponding TNT explosion in nitrogen. The experiments were modeled as turbulent combustion in an unmixed system at infinite Reynolds, Peclet and Damkohler numbers. The numerical solution was obtained by a high-order Godunov scheme using Adaptive Mesh Refinement to trace the turbulent mixing on the computational grid in as much detail as possible. The evolution of the calculared mass-fraction of fuel consumed by combustion began with a finite (non-zero) rate associated with strong initiation, followed by an exponential decay. Calculated pressures are in good agreement with measurements. The results thus reveal details of a combustion process that is controlled by fluid-mechanic transport in a higly turbulent field, in contrast to the conventional reaction-diffusion machanism of laminar flames.