Optically Based Flame Detection in the NASA Langley 8-FT High Temperature Wind Tunnel

Two optically based flame-detection systems have been developed for use in NASA Langley’s 8-Foot High-Temperature Tunnel (8-ft HTT). These systems are used to detect the presence and stability of the main-burner and pilot-level flames during facility operation. System design considerations will be discussed, and a detailed description of the system components and circuit diagrams will be provided in the Appendices of this report. A more detailed description of the manufacturing process used in the fabrication of the fiber-optic probes is covered in NASA TM-2001-211233. DEFINITIONS 8-ft HTT NASA Langley Research Center’s 8-ft High Temperature Tunnel (B1265) OFD Optical Flameout Detector OPFD Optical Pilot Flame Detector PMT Photomultiplier Tube NO/NC Normally Open/Normally Closed Tr % Transmittance ND Neutral Density # INTRODUCTION This paper documents the design, fabrication and integration of the various optically based flame-detection systems developed for use in the combustor of NASA Langley Research Center’s 8-ft High-Temperature Wind Tunnel. The original optical system was designed to detect the presence of the combustor’s main-burner flame during facility operations. Eventually a derivative of this system was developed to monitor the pilot-level flame, replacing a less reliable thermocouple-based sensing system. The technical specifications and other pertinent data for both systems are covered in this report. A more detailed description of the manufacturing process used to fabricate the optical probes is covered in a separate report, NASA TM-2001-211233 [1]. BACKGROUND NASA Langley Research Center’s 8-Foot HighTemperature Tunnel (8-ft. HTT) is a large-scale hypersonic facility that utilizes a large air/methane combustor which can be configured to generate test section free-stream flow velocities of Mach Numbers 4, 5, or 7. This facility uses an open-jet test section that can simulate atmospheric conditions from 18 to 38 kilometers (60,000 to 125,000 feet) in altitude. [2] (Figure 1) Concerns over an unplanned combustor flameout and re-ignition led to the development of several new flame-detection technologies with response times of less than 100 milliseconds. Results of these studies yielded two new flameout detection techniques – an acoustic-based and an optical-based system. The acoustic-based system detects the presence of selected acoustic resonances within the