Temperature measurements of high-explosive and combustion processes are difficult to obtain due to the speed and environment of the events. To overcome these challenges, we have characterized and calibrated a digital high-speed color camera that may be used to measure the temperature of such events. A two-color ratio method is used to calculate a temperature using the color filter array raw image data and a graybody assumption. If the raw image data are not available, temperatures may be calculated from the processed images or movies, depending on proper analysis of the digital color imaging pipeline. We analyze three transformations within the pipeline (demosaicing, white balance, and gamma correction) to determine their effect on the calculated temperature. Using this technique with a Phantom color camera, we have measured the temperature of exploded C-4 charges. The surface temperature of the resulting fireball was found to rapidly increase after detonation, and subsequently decayed to a constant value of approximately 1980 K.
A high-speed imaging pyrometer was developed to investigate the behavior of flames and explosive events. The instrument consists of two monochrome high-speed Phantom v7.3 m cameras made by Vision Research Inc. arranged so that one lens assembly collects light for both cameras. The cameras are filtered at 700 or 900 nm with a 10 nm bandpass. The high irradiance produced by blackbody emission combined with variable shutter time and f-stop produces properly exposed images. The wavelengths were chosen with the expected temperatures in mind, and also to avoid any molecular or atomic gas phase emission. Temperatures measured using this pyrometer of exploded TNT charges are presented.
Articles you may be interested inThe role of microstructure refinement on the impact ignition and combustion behavior of mechanically activated Ni/Al reactive composites Bottom-up modeling of Al/Ni multilayer combustion: Effect of intermixing and role of vacancy defects on the ignition process Investigations on the self propagating reactions of nickel and aluminum multilayered foils Combustion temperatures from impact initiated nickel-aluminum (NiAl) and aluminumpolytetrafluoroethylene (Al-PTFE) materials have been measured using a high-speed two-camera imaging pyrometer. The materials were launched with a nominal velocity of 1700 m/s into a sealed chamber. Upon impact into a steel anvil chemical reactions were initiated and a flame propagated through the chamber. The measured temperature after impact was 3600 K (NiAl) and 3300 K (Al-PTFE).
High speed video and streak camera imaging are used to measure peak pressures for explosions of spherical charges of the high explosive C‐4 (92 % trimethylenetrinitramine, C3H6N6O6). The technique measures the velocity of the air shock produced by the detonation of the explosive charges, converts this velocity to a Mach number, and uses the Mach number to determine a peak shock pressure. Peak pressure measurements are reported from a few millimeters to approximately one meter from the charge surface. Optical peak pressure measurements are compared to peak pressures measured using piezoelectric pressure transducers, and to peak pressure measurements estimated using the blast computer code CONWEP. A discussion of accuracy of peak pressures determined optically is provided.
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