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Numerical simulations were performed to study the impact of thermal radiation and particle diameter on layered coal-dust explosions. The geometrical setup considered the interaction of a primary explosion with a thin layer of coal dust inside of a closed channel. The simulations solved the compressible reacting Navier–Stokes equations coupled to an Eulerian granular multiphase model. Thermal radiation was included by solving the radiation transfer equation using the filtered spherical harmonics approximation. The results show that the impact of radiation on the dust explosion is situation specific. Radiation can promote, inhibit, or have little impact on the explosion depending on the particle diameter. Radiation has a slight inhibiting effect on dust layers comprised of 30 and 100 μ m-diameter coal particles. Radiation quenched the explosion when particles were 5 μ m in diameter. Radiation promoted stable burning for larger 150 μ m-diameter coal particles, while simulations excluding radiation for 150 μ m-diameter coal particles produced a failed explosion. The influence of particle diameter on the dispersibility characteristics of dust layers has a significant impact on the explosion. Small 5 μ m-diameter coal particles are dispersed poorly by the leading shock and are too highly concentrated to burn. Large 150 μ m-diameter particles disperse higher into the channel and show improved mixing, but have large thermal time scales that inhibit vigorous reaction. Cases with 30 and 100 μ m-diameter particles show a good compromise between dispersibility, mixing, and thermal time scales which produce stable combustion with or without the inclusion of thermal radiation in the model. [ABSTRACT FROM AUTHOR]

A quantum-cascade-laser-absorption-spectroscopy (QCLAS) diagnostic was used to characterize post-detonation fireballs of RP-80 detonators via measurements of temperature, pressure, and CO column pressure at a repetition rate of 1 MHz. Scanned-wavelength direct-absorption spectroscopy was used to measure CO absorbance spectra near 2008.5 cm − 1 which are dominated by the P (0 , 31) , P (2 , 20) , and P (3 , 14) transitions. Line-of-sight (LOS) measurements were acquired 51 and 91 mm above the detonator surface. Three strategies were employed to facilitate interpretation of the LAS measurements in this highly nonuniform environment and to evaluate the accuracy of four post-detonation fireball models: (1) High-energy transitions were used to deliberately bias the measurements to the high-temperature outer shell, (2) a novel dual-zone absorption model was used to extract temperature, pressure, and CO measurements in two distinct regions of the fireball at times where pressure variations along the LOS were pronounced, and (3) the LAS measurements were compared with synthetic LAS measurements produced using the simulated distributions of temperature, pressure, and gas composition predicted by reactive CFD modeling. The results indicate that the QCLAS diagnostic provides high-fidelity data for evaluating post-detonation fireball models, and that assumptions regarding thermochemical equilibrium and carbon freeze-out during expansion of detonation gases have a large impact on the predicted chemical composition of the fireball. [ABSTRACT FROM AUTHOR]

Vented flash tubes have often been used in the ignition train of medium and large caliber weapon systems. Despite their long history of ballistic usage, there are undesirable features associated with uneven venting of the combustion products. Pressure measurements at various locations from the flash tube have shown severe variations with time, which is associated with spatially nonuniform mass discharging rate from the vent holes. Measured pressure profiles in the flash tube show counterintuitive, nonmonotonic pressure distributions with the lowest pressure in the middle of the venting section of the flash tube. A model of the flash tube venting process was developed to explain these phenomena using modern, high-order numerical schemes. Source terms accounting for mass addition from the black powder pellets, mass loss through the vent holes, wall friction, differential area changes, and volume changes from surface regression of black powder pellets were fully coupled in the model. The numerical results of this model reproduced the severe pressure variations and nonmonotonic pressure profiles observed in experiments. In general, they are caused by gas dynamic effects from a slowly moving normal shock wave in the middle portion of the venting section of the flash tube. As the driving pressure from the burning black powder pellets changes, the location of the normal shock wave jumps from one vent hole set to another, producing pressure variations observed in experiments. The physical understanding gained from this model solution has provided guidance for achieving more uniform mass discharging rate by varying the vent hole sizes as a function of distance along the flash tube. [DOI: 10.1115/1.4001285]

Vented flash tubes have often been used in the ignition train of medium and large caliber weapon systems. Despite their long history of ballistic usage, there are undesirable features associated with uneven venting of the combustion products. Pressure measurements at various locations from the flash tube have shown severe variations with time, which is associated with spatially nonuniform mass discharging rate from the vent holes. Measured pressure profiles in the flash tube show counterintuitive, nonmonotonic pressure distributions with the lowest pressure in the middle of the venting section of the flash tube. A model of the flash tube venting process was developed to explain these phenomena using modern, high-order numerical schemes. Source terms accounting for mass addition from the black powder pellets, mass loss through the vent holes, wall friction, differential area changes, and volume changes from surface regression of black powder pellets were fully coupled in the model. The numerical results of this model reproduced the severe pressure variations and nonmonotonic pressure profiles observed in experiments. In general, they are caused by gas dynamic effects from a slowly moving normal shock wave in the middle portion of the venting section of the flash tube. As the driving pressure from the burning black powder pellets changes, the location of the normal shock wave jumps from one vent hole set to another producing pressure variations observed in experiments. The physical understanding gained from this model solution has provided guidance for achieving more uniform mass discharging rate by varying the vent hole sizes as a function of distance along the flash tube. [ABSTRACT FROM AUTHOR]