Fluorescence Rise Time Measurements for High Temperature Fluorescence-Based Thermometry (original) (raw)
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Fluorescence thermometry for advanced high-temperature materials
1996
Advanced high-temperature materials, such as ceramics, metals, and composites, are of critical importance to the development of new and improved technologies worldwide. For aircraft, automobiles, or other combustion-engine powered systems, major efficiency improvements depend on the ability to operate at temperatures closer to the adiabatic limit of the chemical processes involved. Materials able to function at higher temperatures must therefore be introduced into improved designs. Jet turbine engines, for example, already require air cooled rotors and stators in order that the nickel alloys used will not deteriorate and fail from overheating. In the case of ceramics, optimum temperature usage will often cause the refractory surfaces to glow red hot and the material itself to become partially translucent. For composites, especially where structural integrity, vibration resistance, and strength are concerned, the temperature behavior of dissimilar components must be well known and we...
Development of Fluorescent Coatings for High Temperature Aerospace Applications
For many years, phosphor thermometry has been used for non-contact measurements in hostile high temperature environments, including large blackbody radiation backgrounds, vibration, rotation, fire/flame, pressure, or noise. Often these environments restrict the use of more common thermocouples or infrared thermometric techniques. In particular, temperature measurements inside jet turbines, rocket engines, or similar devices are especially amenable to fluorescence techniques. Often the fluorescent materials are used as powders, either suspended in binders and applied like paint or applied as high temperature sprays. These coatings will quickly assume the same temperature as the surface to which they are applied. The temperature dependence of fluorescent materials is a function of the base matrix atoms and a small quantity of added activator or "dopant" ions. Often for high temperature applications, the selected materials are refractory and include rare earth ions. Phosphors...
LED-induced fluorescence diagnostics for turbine and combustion engine thermometry
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Fluorescence from phosphor coatings is the basis of an established technique for measuring temperature in a wide variety of turbine and combustion engine applications. Example surfaces include blades, vanes, combustors, intake valves, pistons, and rotors. Many situations that are remote and noncontact require the high intensity of a laser to illuminate the phosphor, especially if the surface is moving. Thermometric resolutions of 0.1 C are obtainable, and some laboratory versions of these systems have been calibrated against NIST standards to even higher precision. To improve the measurement signal-to-noise ratio, synchronous detection timing has been used to repeatedly interrogate the same blade in a high speed rotating turbine. High spatial resolution can be obtained by tightly focusing the interrogation beam in measurements of static surfaces, and by precise differential timing of the laser pulses on rotating surfaces. We report here the use of blue light emitting diodes (LEDs) as an illumination source for producing useable fluorescence from phosphors for temperature measurements. An LED can excite most of the same phosphors used to cover the temperature range from 8 to 1400 C. The advantages of using LEDs are obvious in terms of size, power requirements, space requirements and cost. There can also be advantages associated with very long operating lifetimes, wide range of available colors, and their broader emission bandwidths as compared to laser diodes. Temperature may be inferred either from phase or time-decay determinations.
The overall goal of the Aeronautics Research Mission Directorate (ARMD) Seedling Phase II effort was to build on the promising temperature-sensing characteristics of the ultrabright thermographic phosphor Cr-doped gadolinium aluminum perovskite (Cr:GAP) demonstrated in Phase I by transitioning towards an engine environment implementation. The strategy adopted was to take advantage of the unprecedented retention of ultra-bright luminescence from Cr:GAP at temperatures over 1000 C to enable fast 2D temperature mapping of actual component surfaces as well as to utilize inexpensive low-power laser-diode excitation suitable for on-wing diagnostics. A special emphasis was placed on establishing Cr:GAP luminescence-based surface temperature mapping as a new tool for evaluating engine component surface cooling effectiveness.
Advances in High Temperature Phosphor Thermometry for Aerospace Applications
39th AIAA/ASME/SAE/ASEE Joint Propulsion Conference and Exhibit, 2003
Phosphor thermometry has been used for many years for non-contact temperature measurements in hostile environments. Aerospace systems are particularly prone to adverse high temperature environments, including large blackbody background, vibration, rotation, fire/flame, pressure, or noise. These environments often restrict the use of more common thermocouples or infrared thermometric techniques. Temperature measurements inside jet turbines, rocket engines, or similar devices are especially amenable to fluorescence techniques. Often the phosphor powders are suspended in binders and applied like paint or applied as high temperature sprays. Thin coatings will quickly assume the same temperature as the surface to which they are applied. The temperature dependence of phosphors is a function of the base matrix atoms and a small quantity of added activator or "dopant" ions. Often for high temperature applications, the selected materials are refractory and include rare earth ions. Phosphors like Y 3 Al 5 O 12 (YAG) doped with Eu, Dy, or Tm, Y 2 O 3 doped with Eu, or similar rare earth compounds, will survive high temperatures and can be configured to emit light that changes rapidly in lifetime and intensity. Recently, a YAG:Cr phosphor paint emitted fluorescence during short duration tests in a high Mach number hydrogen flame at 2,200 °C. One of the biggest challenges is to locate a binder material that can withstand tremendous variations in temperature in an adverse aerospace environment. This presentation will give research results applicable to the use of phosphors for aerospace thermometry. Emphasis will be placed on the selection of phosphor and binder combinations that can withstand high temperatures.
Phosphorescent thermal history sensors
Sensors and Actuators A: Physical, 2011
The operating temperatures of surfaces in the hot sections of gas turbines are of great practical importance, but are often very hard to measure. Thermal indicating paints offer one possible and practical way, but they have many disadvantages. A novel concept for the utilisation of phosphorescent coatings as thermal history sensors was proposed by Feist et al. [1] in 2007. These phosphor coatings undergo irreversible changes when exposed to high temperatures that affect their photoluminescent properties and are a function of both the temperature and duration of exposure. If care is taken to ensure steady state conditions during exposure, subsequent off-line analysis of emission in the laboratory can reveal the temperature experienced by the coating. In this paper, an investigation of the amorphous-to-crystalline change of Y 2 SiO 5 :Tb is reported and used to provide a proof of concept for a phosphorescent thermal history sensor. Phosphor powder was calcined at different temperatures and for different periods, and characterised using photoluminescence spectroscopy. A calibration curve was generated and shows that this phosphor is suitable for temperature measurements over a temperature range from 600 • C to at least 1000 • C. With more advanced signal processing routines it is anticipated that the dynamic range might be extended to 1400 • C. Such routines and other materials/physical processes are the subject of ongoing research in the area at Imperial College and Southside Thermal Sciences.
AIP Conference …, 2003
Phosphor materials are, by design, capable of efficiently converting excitation energy into fluorescence. The temperature-dependent characteristics of this fluorescence provide the basis for noncontact thermometry. In the past decade this approach has been applied to turbine engine diagnostics, liquid temperature measurements for heat pump research, combustion engine intake valve and piston measurements, galvanneal steel processing, transient thermometry of particle beam targets, and microcantilevers used in MEMS devices. The temperatures involved range from ambient to in excess of 1200 C. Some of these applications have involved fiber optics for light delivery and/or fluorescence signal collection. In addition to fielding these applications, there has been considerable work in the laboratory aimed at exploring further improvements and adding to the database of temperature-characterized phosphors. The activities involve investigation of short-decay time phosphors for use on imaging surfaces moving at high speeds, measuring and modeling pressure as well as temperature dependence, developing to phosphor adhesion methods, developing phasebased data acquisition approaches. A significant advance is that light-emitting diodes can now be used to provide adequate stimulation of fluorescence in some applications. Recently nanophosphors have become available. The spectral properties and, by implication, thermal dependence of these properties change which particle size. This has ramifications that need to be explored. The ways in which such materials can be exploited for micro-and nanotechnology are just now being addressed. These applications and developments mentioned above will be surveyed and discussed as well as envisioned future improvements and new uses for this thermometry technique.
Remote thermometry with thermographic phosphors: Instrumentation and applications
Review of Scientific Instruments, 1997
The temperature-dependent characteristics of fluorescence of several rare-earth-doped ceramic phosphors has made these materials the focus of a major effort in the field of noncontact thermometry over the past few decades. These ''thermographic phosphors,'' e.g., Y 2 O 3 :Eu, have been used for remote measurements of the temperatures of both static and moving surfaces, and have performed many other tasks that standard sensors ͑thermocouples, thermistors, etc.͒ cannot. The range of usefulness of this class of materials extends from cryogenic temperatures to those approaching 2000°C. The instrumentation needed for this type of thermometry has followed many different lines of development, and this evolution has produced a wide variety of both field-and laboratory-grade systems that are now described in the literature. In general, the technique offers high sensitivity (Ϸ0.05°C), robustness ͑e.g., stability of the sensor sample in harsh environments͒, and NIST traceability. In addition, such systems have been successfully adapted to make remotely sensed measurements of pressure, heat flux, shear stress, and strain. In this review, we summarize the physical mechanisms that form the basis for the technique, and then catalog and discuss the instrumentation-related aspects of several different remote thermometry systems that employ thermographic phosphors as the sensors.
Fluorescence-Based Thermometry:Principles and Applications
Reviews in Analytical Chemistry, 1999
The temperature-sensitive nature of molecular fluoresence provides the basis for designing optical detection systems whereby changes in fluorescent intensity, peak position, or other spectral attributes can provide a local measurement of temperature. This review details the underlying photophysics responsible for the effects of temperature, compares their relative utilities for temperature sensing, and provides an overview of the instrumentational requirements for performing multi-dimensional temperature sensing. The requisite integration of chemistry and optics for this application helps define the desired properties for the fluorescent probe. In particular, bichromophoric fluorophores offer notable advantages by providing an internal reference for fluorometric temperature sensing. The review focuses its description on the operation and properties of this class of fluorescent compounds and summarizes the reported probes and their operating ranges. A model one-dimensional system for measuring spatial and temporal changes in temperatures using a bipyrenyl fluorophore is presented as demonstration of the ability to perform remote detection using a bichromophoric fluorescent probe. The selection of light source and detector are highlighted as are specific designs employing lasers and CCD cameras for expanding the ability of fluorometric sensing to produce three-dimensional profiles of temperature.
On the thermal sensitivity and resolution of a YSZ:Er3+/YSZ:Eu3+ fluorescent thermal history sensor
Sensors and Actuators A: Physical
This paper deals with the problem of thermal history analysis of high temperature components for applications such as furnaces, nuclear reactors and jet engines. It focuses on fluorescent thermal history sensors, which exhibit permanent changes in their luminescence properties when exposed to high temperature. These changes can then be quantitatively evaluated to determine the temperature of exposure from a previous thermal event. The main objective of this paper is to investigate the thermal sensitivity and the thermal resolution of a yttria-stabilized zirconia (YSZ) Er 3+-doped phosphor produced by a solgel route and combined with a thermal history insensitive YSZ:Eu 3+ reference, which was selected for its high sensitivity to thermal history above 1173 K. In particular, the interest of this YSZ:Er 3+ /YSZ:Eu 3+ sensor is discussed in the view of the physical properties of sol-gel deposited YSZ coatings, the selection of an appropriate excitation wavelength and the practical measurement of coatings fluorescence properties. The sensitivity and the resolution of two thermal history measurement fluorescence methods, based on intensity ratios and lifetime analysis, were determined and compared. A comparison is also made with standard non-contact temperature measurement methods such as infrared thermography and thermochromic paints.