The use of microelectromechanical systems for surge detection in gas turbine engines

Compressor surge results from the instability of highly undesirable oscillations occurring at specific frequencies and at low compressor flow rates in the system. Research has shown that by stabilizing the small-perturbation dynamics, the large-amplitude surge event can be prevented in these systems. In order to completely avoid the initiations of conditions that will lead to surge or stall, engine designs conservatively determine operational stability margins that are far from the stability limit of the compression system. Advanced turbine engines operate with reduced stability margins to increase performance. This reduction in stability margin must be limited to such an extent that does not compromise the operational capability of the engine. Pressure probes equipped with fast-response transducers have been successfully used in axial-flow compressors and turbines but have been rarely used in centrifugal compressors. The harsh thermal environment of operation has limited the use of pressure transducers to operational ranges below 250/spl deg/C effectively precluding measurement at the final stage exit where temperatures are typically in excess 280/spl deg/C depending on the turbine. This paper proposes a hybrid processing method in which a piezoresistive chromium strain gauge is embedded between two thin film silicon carbide (SiC-MEMS) or silicon carbon nitride microelectromechanical (SiCN-MEMS) membranes as an enhanced technique for the design of high temperature pressure transducers. The hybrid process technology, which enables fabrication of such structure, along with the novel packaging principles represents the main contribution of the present report.