Multi-Color Pyrometry Techniques for Characterization of Spall in Heavy Duty Gas Turbine Engines

Abstract

Current gas turbine engine Pyrometers are typically broadband Si-detector line-of-sight (LOS) systems. They have been used in the past to identify areas with spall in the stage-one blade (S1B) and bucket passages by detection of bursts of higher voltage signals at the Pyrometer output. However, the single color signal can be misleading for estimating temperature and emissivity variations in these bursts. This paper summarizes the testing results from a heavy duty gas turbine engine using the Multi-Color Pyrometry (MCP) developed at GE Global Research Center (GRC). The objective of the test is to detect the burst from the spall and characterize its temperature and emissivity. Results of the radiant temperature, multi-color temperature and apparent emissivity are presented. The results indicate that at the spall regions the temperature typically drops and the emissivity increases and that differentiates from the emissivity of the normal regions. Five distinct burst signals corresponding to known five blades with spall areas are clearly identified with three colors and the various changes corresponding to suction side, trailing edge, pressure side, fillet and platform seen in the LOS clearly detected. MCP algorithms are applied to characterize the temperature and emissivity changes in these areas and compared to normal passages. Data gathered from stage-two blade pyrometers indicated no spall.