High Temperature Sensors for Small Gas Turbines

Abstract

This Command has reviewed this report and concursIn the conclusions contained herein. The findings and recomnendatlons of this report wll'i be used to guide future programs of temperature sensor development. Several material systems were identified and experimentally shown capable of sensing air temperatures at 2500 o F with transients to 3000°F. Since thermocouples measure temperature at one point in the flow path, a large number of junctions are necessary to obtain proper averaging due to burner streaking (the T-56 uses 16 junctions). A method of determining the effect of gas blockage on engine cycle efficiency is presented and shown to be significant. A proposed protected thermocouple junction offers best reliability and durability, but has relatively slow response to changes in gas temperature. A suggested exposed junction has greatly improved response rate, however, the reliability and durability are much less than the protected junction. MMi « TaskFive commercial radiation pyrometers were evaluated and one concept chosen as having, by far, the greatest potential for application to turbine engines. Detailed experiments on environmental effects cm all materials led to the design and purchase of a miniaturized model especially for this program. The sensor consists of a sapphire window, a quartz lens and a silicon p-n junction detector which must sight on an emissive body in the gas stream. Thus, hardware, rather than air temperature, is measured. The rotating buckets are chosen since they will register close to average temperature. The sensor tested demonstrated microsecond response, good accuracy, and good reliability as long as the environmental temperature for the silicon chip was kept below 250 S F and the window was maintained clean. A unique gas -collimator lens (gel) system was devised which acts as an Interface between the turbine gas path and the sensor head window. An experimental gas-collimator lens operating on a simulated turbine rig was able to keep the sensor head window perfectly clean after many hours of operation interfaced with a high soot-laden gas stream.Recommendations are included for continued development of three approaches which have potential value to the high temperature advanced gas turbines: the protected thermocouple junction which employs advanced high temperature material systems. including a TNV-7 coated tantalum alloy sheath, diffusion bonded to a W-Re junction; the bare PT-RN thermocouple, using in-series junctions, to give the fastest possible response rate; the radiation pyrometer, in conjunction with the gas-collimator lens devised to measure individual bucket temperatures. m -■um iinBM -

High Temperature Sensors for Gas Turbines

“…The information presented in this paper was generated during the course of a program "High Temperature Sensors for Small Gas Turbines," performed at Solar Division of International Harvester, San Diego, Calif., for the U.S. Army Aviation Materiel Laboratories (AVLABS) Fort Eustis, Va. (7). This program surveyed many types of sensors and finally concentrated on two types of thermocouple probes and a specific radiation sensor.…”