A NONINTRUSIVE DIAGNOSITC FOR WATER VAPOR IN HIGH TEMPERATURE FLOW FIELDS

A FAST-RESPONSE METHOD FOR MEASUREMENT OF WATER VAPOR CONCENTRATIONS IN HIGH TEMPERATURE FLOWS IS NEEDED FOR RESEARCH ON HYPERSONI AIRBREATHING ENGINES AS WELL AS OTHER APPLICATIONS IN COMBUSTION RESEARCH OR CONTROL. THE PROPOSED INNOVATION WILL UTILIZE INEXPENSIVE ROOM TEMPERATURE LASER DIODES TO MEASURE ABSORPTION BY WATER VAPOR AT NEAR-INFRARED WAVELENGTHS. THESE LASERS WILL BE USED IN COMBINATION WITH HIGH FREQUENCY DETECTION TECHNIQUES TO DEVELOP A WATER VAPOR DIAGNOSTIC WITH HIGH SENSITIVITY, WIDE DYNAMIC RANGE, AND THE CAPABILITY FOR EXTREMELY FAST TIME RESPONSE. THE DIAGNOSTIC COULD ALSO BE USED FOR MEASUREMENT OF TEMPERATURE AND FLOW VELOCITY IN HYPERSONIC FLOWS. AN IMPORTANT CHARACTERISTIC OF THIS INNOVATION IS THAT THE MEASUREMENTS ARE NONINTRUSIVE. IN COMPARISON WITH OTHER POTENTIAL OPTICALLY-BASED METHODS FOR MEASURING WATER VAPOR CONCENTRATIONS, THE PROPOSED APPROACH USES EXCEPTIONALLY RELIABLE AND INEXPENSIVE LASER SOURCES WHICH CAN READILY BE COMBINED WITH FIBER OPTICS FOR MULTI-POINTING MONITORING. THE FEASIBILITY OF THE TECHNIQUE WILL BE DEMONSTRATED IN PHASE I BY MEASURMENTS IN A ROOM TEMPERATURE ABSORPTION CELL AND IN THE POST-FLAME GASES OF A METHANE-AIR FLAME.