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High-speed movies of solid propellant deflagration have long provided useful qualitative information on propellant behavior. Consequently, an extension of performance to include quantitative behavior of the surface, particularly the spatial relationships of particles across the surface, the temporal behavior of particles through extended periods of time, and accurate measurements of particle sizes, is highly desirable. Such measurements require the ability to take detailed movies across an extensive surface through the propellant flame for periods longer than the residence time of a given particle. For such experiments, camera optics employing magnification are undesirable, since they severely limit both the field-of-view and the depth-of-field, and hence, the useful duration of a flame sequence. Unfortunately, high resolution without magnification pushes both the diffraction limits and the performance capabilities of standard lenses. At this limit, the modulation transfer function (MTF) of the camera optics and film will greatly affect performace. High-speed movies of propellant deflagration have been made at pressures up to 500 psi. High resolution at unity magnification is achieved by the use of 1.4 mJ of illumination energy per pulse in conjunction with a fine-grain film. This approach has worked well on both aluminized and pure aluminum perchlorate propellants. Since the laser pulses provide enough light to expose tine-grain film at unity magnification, it is possible to encompass an entire 1/4-inch strand surface in our field-of-view. Motion blur at 7 kHz framing rates and unity magnification is negligible (1 μm) due to the 25 ns width of the laser pulses. The short pulse width is also helpful in circumventing flame turbulence. Front-lit high-speed stereo movies have been made of the burning surfaces of solid propellant strands at operating pressures up to 350 psi. Movies were made at viewing angles separated by 90 degrees to achieve a high-depth resolution. These movies, which were recorded through flames across a 1/4 in. field-of-view, have a resolution of 25 gm. The stereo images were simultaneously recorded side by side on the same 16-mm frame by using X2 demagniying optics and a mirror arrangement.
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