Abstract
Mechanically robust turbine design with respect to blade vibration is challenging when dealing with nozzle-ring fouling and wear. Especially for engines operating with heavy fuel oil (HFO), the nozzle rings of the turbocharger turbines are prone to severe degradation in terms of contamination with unburned fuel deposits. This contamination will lead to an increased excitation of blade resonances in comparison to the nominal design. Due to the statistical character of contamination, long-term monitoring of blade vibration amplitudes would be beneficial. In the harsh environment of HFO operation, however, conventional blade vibration measurement techniques, such as those using strain gauges or blade tip timing, cannot work reliably for a long period. Thus, the objective of this research is to develop a method that enables the monitoring of turbine blades using pulsation or vibration sensors installed on the stator side. Almost a dozen turbines, both radial and axial, have been examined in order to determine a proper measurement chain/position and analytical method. Even though the challenges specific to the turbocharger turbine application—that high-frequency (up to 50 kHz) acoustic radiation from turbine blades has to be detected by a sensor on the stator side—were demanding, in the course of the investigations several clear examples of turbine blades engine-order resonance detection were gathered. Finally, the proposed method has been tested successfully in a power plant for over one year.
Highlights
IntroductionIn heavy fuel oil (HFO) operation, the vaned turbocharger nozzle ring might be the first major flow obstruction after the engine cylinder outlets, making it prone to contamination by fuel residuals
In heavy fuel oil (HFO) operation, the vaned turbocharger nozzle ring might be the first major flow obstruction after the engine cylinder outlets, making it prone to contamination by fuel residuals.The degree of contamination depends on various factors, such as the properties of the HFO, temperature, or the frequency and quality of prescribed turbine washings by end users
This study provides sound evidence that integral mode turbine blade vibration can be principally detected by a pulsation sensor installed on the stator side away from turbine trailing edge, when vibration stress reaches a critical level from an high-cycle fatigue (HCF) point of view
Summary
In heavy fuel oil (HFO) operation, the vaned turbocharger nozzle ring might be the first major flow obstruction after the engine cylinder outlets, making it prone to contamination by fuel residuals. The degree of contamination depends on various factors, such as the properties of the HFO, temperature, or the frequency and quality of prescribed turbine washings by end users. A contamination state, as shown, in which some sectors of the nozzle ring are clogged almost completely, is not uncommon. As well as being the cause of a drop in turbine stage efficiency, nozzle-ring fouling is considered to be the major cause of turbine blade failures due to high-cycle fatigue (HCF).
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