Continuous Water Vapor Mass Flux and Temperature Measurements in a Model Scramjet Combustor Using a Diode Laser Sensor

A sensor for simultaneous measurements of water determinations. vapor density, temperature and velocity has been developed based on absorption techniques using room Introduction temperature diode lasers (InGaAsP) operating at 1.31 μm. Sensor calibrations of density and temperContinuous measurements of in-stream data for gas ature were acquired in a laboratory hot absorption cell dynamic and chemical processes are required for and on a H -air flat flame burner from 500 K to 2200 K. development and optimization of advanced propulsion 2 In the laboratory with 0.3 Hz bandwidth and a pathsystems. In the case of SCRAMJET engines, measurelength of 70 cm in the flame, the sensor provided a ments of such data are complicated by the high precision of better than 5% in temperature and better enthalpy of the gas streams. Intrusive probes either do than 10 % in molecular density, and velocity. Optical not survive or introduce unacceptable flow disturbinstrumentation was developed for integrating the ances. The ultimate objective is to measure the net sensor to a model SCRAMJET combustor at the Air thrust produced by the propulsion system. Especially in Force Research Laboratory Wright-Patterson AFB. SCRAMJET engines, the net thrust provided by the Preliminary measurements in the Mach 2.1 flowfield at engine is often a relatively small increase in the expanded temperatures of 540, 650, and 740 K across momentum flux ('V ) between large inlet and exhaust an 18 cm pathlength provided a temperature agreement values. Thus, thrust determinations require a sensitive with predictions ranging from 7 to 11%, a density technique capable of simultaneous measurements of gas agreement ranging from 17 to 56% and a velocity stream density, velocity and temperature in high agreement of 25%. Measurements at higher enthalpy enthalpy flows. flow gave similar results for water density and temperature, but generated increasingly difficult beam Optical sensors and diagnostics for combustion _______________ during the previous decade because of their inherently *Principal Research Scientist, Member AIAA non-intrusive nature, and their ability to probe relevant Aerospace Engineer species such as O , CO, CO NO, OH, and H O. † Research Scientist Laser-based optical techniques for measurements in ‡ Copyright © 1998 by Physical Sciences Inc. Published by high enthalpy flows have undergone extensive developthe American Institute of Aeronautics and Astronautics, ment. Many of the optical diagnostics have the Inc. with permission. added value of flow field mapping using planar imaging steering influences that degraded accurate flow velocity