Pulsed illumination, closed circuit television system for real-time viewing of unsteady (> 1 micros) events.
A pulsed illumination closed circuit television system is described whereby fast (times <<33 ms), unsteady events can be observed in real time. A low-power helium-neon laser beam is modulated to send a short duration light pulse through the unsteady test medium. The light is refracted according to the instantaneous optical properties of the medium. The refracted light travels to a solid state television camera, known as a charge injection device (CID), in which the sensor array is charged within microseconds. The scanning of the charged array then follows, requiring the standard 33 ms for information transfer to video tape and a TV monitor. The image is thus formed during the laser pulse duration (which presently is 10 to 100 micros, but shorter duration pulses are possible with more powerful lasers), but no more than one image every 33 ms can be observed and recorded. Thus this method is particularly suited for the investigation of high frequency periodic events in which one can observe both a single image, or an ensemble average of as many as 100 images, occurring at corresponding times in different cycles. The reported applications include the recording of steady and transient propane torch flames, of the transient fuel injection process in a motored internal combustion engine, and of the propagation of a flame under firing conditions in the engine. In the shadowgraph and Schlieren modes the method is particularly suited for application to periodic combustion events such as those occurring in internal combustion engines. The method then presents the following advantages over high-speed filming (> 3000 pictures/s); real-time observation and recording of chamber events at any crankangle; real-time observation and recording of the effects of changes in the engine variables (speed, load, spark timing, injection pressure and duration, chamber swirl, etc.) on the combustion events; real-time observation and recording of ensemble averages and cycle-to-cycle variations. The technique also eliminates the delays and unknowns of film processing. Finally, the cost of this system is similar to that of a high-speed camera.
Marden
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Department of Mechanical and Aerospace Engineering, Princeton University, Princeton, NJ 08540, USA.
Steinberger
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Bracco
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