High Range, and Durable Thermocouples for Turbine Engines

The harsh chemically reacting environments associated with turbine inlets offer significant measurement challenges.  Gas inlet temperatures of 2200oC and violent chemical reactions pose challenges in instrumentation development and application, which in turn can force design and maintenance compromises.  In this proposal we use ultrasonic thermometry to measure the turbine gas inlet temperature at 2200oC.   Ultrasonic temperature sensing methods suitable for extreme thermal environments have been available for several years.  Until recently, ultrasonic instrumentation has been size and cost prohibitive.  With the advent of low cost, high speed A/D, improved high temperature piezoelectric sensors, and compact ultrasonic instrumentation this technology is now affordable, reliable and practical.  In this proposal two approaches will be evaluated.  Both configurations rely on the variation of material modulus (ultrasonic velocity) with temperature.  The first configuration uses high frequency bulk waves propagating in sensor bars with reflectors at the sensor tip.  These probes can be designed to achieve spatial resolution from 1 mm to 25 mm and response times from 0.1 millisecond to 10 milliseconds. The second configuration uses guided waves.  These sensors have slower response times and poorer spatial resolution but can be flexible and allow longer working distances. The precision of these sensors is relatively independent of the operating temperature.  It should be possible to obtain precision of +/- 1oC at 2200oC. BENEFITS: Turbine inlet temperature is one of the most critical parameters in the operation of gas turbine engines, but is seldom used in design or health monitoring because of the lack of accurate, reliable measurement techniques.  Current commercially available high temperature thermocouples are unable to measure turbine inlet temperatures in most large gas turbine engines. Ultrasonic thermometry offers unique capabilities in extreme environments where conditions preclude the use of thermocouples, resistance devices or optical pyrometers. Applications include thermal transport studies in hypersonic research, high temperature process control for military turbine engines and for on board control of commercial turbine engines.  In addition to the applications in hypersonic vehicle and propulsion systems, the ultrasonic temperature sensor technology has applications in the areas of space lift, space platform, combustion research, and missiles.  There is also a potential commercial market in areas where thermal transport data is needed in relatively inaccessible regions such as combustion chambers, reactors and in some glass molding operations.