Pulsed-Laser, High Speed Photography of Rocket Propellant Surface Deflagration

摘要

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 relationship 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 longer periods 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 frame 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 performance. The MTF of the optics can be improved by a factor of two or more at practical spatial frequencies by the use of monochromatic light, such as the reflected light from a laser. This is especially true for off-axis rays, and important consideration when an extended field-of-view is required. The use of an intense, short-pulsed laser has the additional advantage of suppressing flame brightness and motion blur. Such a light source must retain a high repetition rate to follow temporal behavior in detail.