Developments and Experiences With Pulsation Measurements for Heavy-Duty Gas Turbines

Abstract

The dynamical combustion processes (pulsations) of heavy-duty gas turbines must be supervised by suitable instrumentation for optimal operation of the engine regarding emissions and component life. But the hostile environment of the combustor makes it difficult to perform the measurements. There are two possible approaches to measure the combustor pulsations. Either a high temperature sensor is placed as close as possible to the combustion chamber to measure the acoustics directly (Cavity Type Probe), or the acoustic signal is led to the outside of the engine by means of a reflection free waveguide, where a dynamic pressure sensor picks up the passing signal (Long Line Probe). Both approaches were developed and investigated in detail. This paper describes the past and current efforts in refining the probe designs for use in the harsh operational environment while maintaining sensor accuracy, measurement range and lifetime as a rugged probe. Theoretical and laboratory investigations were undertaken to increase the useable frequency range of the Cavity Type Probe up to 8kHz under engine operation conditions. This was made possible with a smaller high temperature transducer, which is the result of a cooperative development project with a sensor manufacturer. Experiences with both probe concepts on Alstom’s GT26 Test Power Plant in Birr and on field engines provided clear confirmation that the Cavity Type Probe design with an advanced sensor now fulfils all initially defined requirements of acoustic combustion measurements on heavy-duty gas turbines. On the contrary, the waveguide design principle has fundamental limitations in the direct measurement of the combustion acoustics at gas turbine operating conditions.