Journal of the Society of Motion Picture and Television Engineers (1950-1954)

the surface of this plastic, forming a liquid film which radically reduced the rate of heat transfer and left the main body intact. Furthermore, the relatively plentiful and inexpensive Plexiglas permitted the construction of motors larger than the usual 100 Ib thrust small-scale research types.3 Useful knowledge about injector and flame behavior was obtained with these Plexiglas motors with high-speed motionpicture photography (black-and-white and color). Flame pulsations and uneven combustion patterns were readily detected, in at least one case, and were related to a particular type of injector.3 The cameras used in this work were Eastman Type III, 16mm motionpicture at 3000 fps. Film speeds were measured by noting the movement of a timing disk shown on each frame or by using film timing pips. Kodak Super XX black-and-white and Kodachrome color film were used. Berman and Logan2 of General Electric photographed rocket motor combustion through a j-in. quartz slit using either a 1 6mm, 8000-fps camera or a General Radio Co. Type 651 35mm continuous strip with a 2-in. focallength lens at film speeds of 8 to 80 fps. The flame front velocity was readily measured this way. In order to obtain a more rigorous and detailed picture of the events in the rocket combustion chamber it was decided at Bell Aircraft Corp. to develop a schlieren or shadowgraph method of combustion analysis. It was believed that the inherent sensitivity and resolving power of the shadowgraph method would permit the detection and analysis of the fluid stream-to-vapor-to-gas mechanism. This in turn would lead to a fuller understanding of the effect of fluid interaction with the actual combustion gases and could possibly indicate remedial measures in the case of rough combustion. Furthermore, the path of vapor recycling and turbulence might be detected. Pilot studies were undertaken with a miniature propane-air motor which roughly simulated normal motor burning. The basic research on the optical alignment, photographic techniques, chromatic and polarigraphic schlieren methods and glass employment was done with this motor. The transparent walls consisted of 2 X 4 X i-in. pieces of Vycor glass. The optical system for normal shadow studies consisted of two //6, 12-in. dia front-surface parabolized mirrors, a 100-w zirconium arc point light source and rotating prism camera. Several preliminary attempts were made to improve upon normal schlieren or shadow techniques. Two of these consisted of polarigraphic control of background light intensity, using two crossed Polaroid filters, one in front of the light source and the other in front of the camera. Another was the positioning of two adjoining color filters (in this case, red and green) at the normal location of the knife edge. The junction served as a knife edge or block for on-axis rays, while all off-axis rays, deviated by the differential refraction within the chamber, passed either through the red or green filter. This yielded a schlieren image whose color striae indicated the direction of deviation of the light rays. Since it was desired to obtain shadowgraph information quickly, the above methods were temporarily suspended for the conventional methods. A series of shadowgraph and schlieren motion pictures at 1000 fps was then obtained with a small 8-in. flat-sided motor with Vycor walls. The lens settings used were usually //1. 5. Operating difficulties with a small motor of this type and constant breakage and blowout of the Vycor walls prevented a full utilization of the inherent possibilities of the schlieren method. However, enough information on the behavior of the structure and combustion process was obtained to warrant further research in the field. Stratton and Stehling: Rocket Motor Research 601