In this study, an assessment of the performance of an industrial gas turbine during compressor fouling conditions is undertaken. The assessment is carried out through performance diagnostic and ...prognostic methods. The diagnostic technique identifies and isolates faults in the components of the gas turbine, and considers the health parameter of the compressor (efficiency). The remaining useful life of the compressor is estimated by a degradation model that also considers the compressor efficiency health index. Compressor efficiency is estimated using a gas turbine real-time executable digital-twin. The digital-twin is integrated within a gas turbine system operating in the field. Data processing of the compressor efficiency is required to obtain a meaningful trend of the compressor health index. Results demonstrate that the diagnostic and prognostic methods applied to the problem of compressor health parameter estimated by the digital-twin can be a powerful tool to initiate maintenance actions on associated axial compressors prior to significant performance deterioration.
In this study, an impedance model represented as an equivalent electrical circuit (EEC) and comprised of a transmission line circuit and a frequency dispersion Warburg component is developed for the ...study of the electrochemical impedance spectroscopy (EIS) of Li-ion batteries. The model considers the impedance response of a porous cathode electrode comprised of solid particles surrounded by solution. Theory of diffusion of charge carriers in the solid and solution phases of the cathode composite electrode has been considered in the impedance model. The simulated impedance response predicted by the impedance model is compared with EIS measurements carried out in a LiPo battery pack. In addition, a theoretical comparison between the simulated EIS response from the developed model with the simulated impedance response of an EEC representing a Li-ion battery and reported in the literature is carried out as well. The effect of increasing and decreasing the cathodic diffusion distance of lithium ions across the solution and solid phases on the Nyquist impedance complex-plot is simulated. The impedance model is able to decouple diffusion mechanisms in the solid and solution phases of the cathode electrode represented at different frequencies of the Nyquist complex-plot. The results show that the impedance model can provide an insight into the different electrochemical mechanisms of the Li-ion battery represented in the Nyquist complex impedance plot at different frequencies. The model could assist the understanding of the different phenomenological processes in the electrode during the decrease of state of charge of Li-ion batteries using EIS.
•Development of an impedance model to analyse EIS in Li-ion batteries.•Impedance model is developed from fundamental electrochemical theory.•Experimental and theoretical validation of the impedance model is carried out.•Analysis of diffusion mechanisms in the cathode composite electrode is carried out.
In this study, an analysis of the current distribution and oxygen diffusion in the Polymer Electrolyte Fuel Cell (PEFC) Cathode Catalyst Layer (CCL) has been carried out using Electrochemical ...Impedance Spectroscopy (EIS) measurements. Cathode EIS measurements obtained through a three-electrode configuration in the measurement system are compared with simulated EIS data from a previously validated numerical model, which subsequently allows the diagnostics of spatio-temporal electrochemical performance of the PEFC cathode. The results show that low frequency EIS measurements commonly related to mass transport limitations are attributed to the low oxygen equilibrium concentration in the CCL–Gas Diffusion Layer (GDL) interface and the low diffusivity of oxygen through the CCL. Once the electrochemical and diffusion mechanisms of the CCL are calculated from the EIS measurements, a further analysis of the current density and oxygen concentration distributions through the CCL thickness is carried out. The results show that high ionic resistance within the CCL electrolyte skews the current distribution towards the membrane interface. Therefore the same average current density has to be provided by few catalyst sites near the membrane. The increase in ionic resistance results in a poor catalyst utilization through the CCL thickness. The results also show that non-steady oxygen diffusion in the CCL allows equilibrium to be established between the equilibrium oxygen concentration supplied at the GDL boundary and the surface concentration of the oxygen within the CCL. Overall, the study newly demonstrates that the developed technique can be applied to estimate the factors that influence the nature of polarization curves and to reveal the effect of kinetic, ohmic and mass transport mechanisms on current distribution through the thickness of the CCL from experimental EIS measurements.
► Cathode impedance measurements gathered with a three-electrode configuration. ► Comparison between measured and simulated data using a validated impedance model. ► Electrochemical and diffusion mechanisms calculated from impedance measurements. ► Analysis of current density and oxygen distributions in the cathode catalyst layer. ► Effect of kinetic, ohmic and mass transport mechanisms on current distribution.
•Electrochemical impedance model for estimation of oxygen diffusion in PEFC.•Development of a cathodic impedance model comprising the CCL and GDL.•EIS and polarisation curves measured in PEFC ...operated with nitrox and heliox.•Estimation of oxygen diffusion resistance from EIS in PEFC with nitrox and heliox.•Analysis of oxygen diffusion resistance in catalyst layer and gas diffusion layer.
In this study, a new electrochemical impedance model to predict oxygen diffusion resistance in the cathode catalyst layer (CCL) and in the gas diffusion layer (GDL) of polymer electrolyte fuel cells (PEFCs) is proposed. The impedance model of the PEFC is validated with electrochemical impedance spectroscopy (EIS) measurements carried out in a single PEFC operated with oxygen diluted in nitrogen (nitrox) and diluted in helium (heliox) at different relative humidity (RH). The PEFC impedance model combines the impedance model for the CCL reported in the authors’ previous study with a diffusion impedance model for the GDL reported in the literature. The EIS measurements in the PEFC represent lumped parameters (total oxygen diffusion resistance RO2_PEFC) from the different layers comprising the PEFC. The impedance model ignores the effect of oxygen transport in the flow field plates on EIS measurements, as this effect is apparent on EIS measurements carried out in PEFCs with low oxygen stoichiometry. The results from this study demonstrate that the estimated oxygen diffusion resistances in the CCL and GDL are distributed in the total oxygen diffusion resistance RO2_PEFC=RO2_CCL+RO2_GDL. This is demonstrated by analysing the EIS measurements carried out in the PEFC with nitrox and heliox as cathode gas reactants and neglecting oxygen transport resistance in either the CCL RO2_PEFC≈RO2_GDL or GDL RO2_PEFC≈RO2_CCL from the PEFC impedance model. It is possible to obtain a deeper understanding of the influence of the electrochemical mechanisms from the different layers comprising the PEFC on EIS measurements by combining fundamental theory and experimental measurements in a complimentary manner.
•Analysis of inductive loops in EIS measurements of an open-cathode PEFC stack.•Impedance model to predict inductive loops in PEFC-EIS measurements.•Inductive loops associated to water vapour ...diffusion in cathode catalyst layer.•Relation between trend of inductive loops and phase angle in EIS measurements.
In this study, an impedance model of a polymer electrolyte fuel cell (PEFC) is considered to simulate inductive loops at low frequencies from electrochemical impedance spectroscopy (EIS) measurements carried out in an open-cathode PEFC stack. The new impedance model proposed in this study is derived from the hypothesis that water vapour transport in the cathode catalyst layer (CCL) yields the formation of inductive loops at low frequencies. The impedance model of the PEFC considers the impedance model of the CCL reported in a previous study and considers an analytical expression for the impedance of water vapour diffusion in the CCL. The developed PEFC impedance model is validated with EIS measurements featuring inductive loops at low frequencies and carried out in the individual cells comprising an open-cathode PEFC stack at two current densities. The parameters related to the impedance of water vapour diffusion simulate the inductive loops at low frequencies and simulate a change of the size of the impedance spectrum of the PEFC. Therefore, the formation of inductive loops at low frequencies can be attributed to not only water vapour transport, but also ionomer swelling/shrinking (hydration/dehydration) in the CCL. The impedance model can provide an insight into the relation between the trend of the inductive loops at low frequency and the change in the phase angle in the EIS measurements which can indicate the hydrated state in the membrane-electrode assembly of the individual cells of the open-cathode PEFC stack.
In this study, a sensor fault diagnostic system to detect/isolate and accommodate faults in sensors from an industrial gas turbine has been developed. The sensor fault diagnostic module is integrated ...with a gas turbine real-time executable digital-twin (RT xDT) reported in a previous study. The sensor fault diagnostic module of the digital-twin considers analytical sensor redundancy using a reference engine model to provide redundant estimates of measured engine variables. A Software-in-the-Loop (S-i-L) architecture and Hardware-in-the-Loop (H-i-L) facility are constructed to assess the sensor diagnostic module (fault detection/ fault isolation) during failure in sensors from the engine. The results demonstrated that if the discrepancy between virtual measurement (provided by digital-twin) and sensor measurement exceeds the prescribed tolerance levels, the sensor fault diagnostic logic determines the state of switching between the virtual and engine sensor measurements in a dual lane control configuration of the gas turbine control system. The sensor fault detection system implemented in the gas turbine RT xDT can be deployed onto a distributed control system of industrial gas turbines to diagnose sensor deficiencies and ensure continuous and safe operation of the gas turbine. Consequently, the developed system will increase engine availability and reliability by diagnosing engine operational deficiencies before severe failure.
In this study, an assessment of degradation and failure modes in the gas-path components of twin-shaft industrial gas turbines (IGTs) has been carried out through a model-based analysis. Measurements ...from twin-shaft IGTs operated in the field and denoting reduction in engine performance attributed to compressor fouling conditions, hot-end blade turbine damage, and failure in the variable stator guide vane (VSGV) mechanism of the compressor have been considered for the analysis. The measurements were compared with simulated data from a thermodynamic model constructed in a Simulink environment, which predicts the physical parameters (pressure and temperature) across the different stations of the IGT. The model predicts engine health parameters, e.g., component efficiencies and flow capacities, which are not available in the engine field data. The results show that it is possible to simulate the change in physical parameters across the IGT during degradation and failure in the components by varying component efficiencies and flow capacities during IGT simulation. The results also demonstrate that the model can predict the measured field data attributed to failure in the gas-path components of twin-shaft IGTs. The estimated health parameters during degradation or failure in the gas-path components can assist the development of health-index prognostic methods for operational engine performance prediction.
Based on fundamental electrode theory, an analytical transfer function to simulate the frequency impedance spectrum of the finite-length Warburg (FLW) impedance and the dynamic potential response of ...the FLW impedance in the time-domain has been developed in this study. Parameters reported in the literature estimated from experimental measurements carried out in polymer electrolyte fuel cells (PEFCs) have been considered to validate the new analytical transfer function. The analytical transfer function representing the FLW impedance can be considered in different equivalent electrical circuit configurations to simulate a more accurate dynamic output voltage of an electrochemical power system under the effect of diffusion phenomena. A Simulink model based on the Randles circuit and the new transfer function representing the FLW impedance is constructed to simulate the dynamic output voltage of a PEFC during a current-interrupt incident. In addition, a Simulink model based on an electrical circuit configuration and the new transfer function representing the FLW impedance is constructed to simulate the dynamic output voltage of a Li-ion battery. This study establishes a wider scope to relate the electrochemical impedance spectroscopy to the dynamic output voltage response of electrochemical power systems.
•Analytical transfer function representing the finite-length Warburg (FLW) impedance•Simulation of dynamic potential response of the FLW impedance in the time-domain•Simulink model considering the Randles circuit and analytical FLW transfer function•Simulation of voltage output of a polymer electrolyte fuel cell and a Li-Po battery
► Generic electrical circuit derived from fundamental electrode and diffusion theory. ► Simulation of cathode catalyst layer impedance response using generic circuit. ► Theoretical and experimental ...validation of the developed generic circuit. ► Theoretical validation using three circuits commonly reported in the literature. ► Experimental validation with cathode EIS measurements of an H2/air PEFC.
In this study, a generic electrical circuit is presented to characterise the frequency response of the Polymer Electrolyte Fuel Cell (PEFC), Cathode Catalyst Layer (CCL) at different current densities. The new electrical circuit is derived from fundamental electrochemical and diffusion theory. It consists of a transmission line in combination with distributed Warburg elements. The validation of this study is divided into a theoretical validation and an experimental validation. In the theoretical validation the impedance response of the CCL generated from three different circuits reported in the literature was compared with the simulated data from the generic electrical circuit. In the experimental validation, Electrochemical Impedance Spectroscopy (EIS) measurements were carried out in an H2/air PEFC through a three-electrode configuration in the measurement system and were compared with the simulated data from the generic circuit. The results show that the generic circuit is able to accurately reproduce the measured data of the CCL at different current densities and is able to represent the electrochemical and diffusion mechanisms of the CCL in the frequency domain. It is possible to generate a deeper understanding of how and where the chemical energy that is released from the redox reaction is being dissipated and retained within the real physical system.
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