Aircraft Engine On-Line Diagnostics Through Dual-Channel Sensor Measurements: Development of an Enhanced System

In this paper, an enhanced on-line diagnostic system which utilizes dual-channel sensor measurements is developed for the aircraft engine application. The enhanced system is composed of a nonlinear on-board engine model (NOBEM), the hybrid Kalman filter (HKF) algorithm, and fault detection and isolation (FDI) logic. The NOBEM provides the analytical third channel against which the dual-channel measurements are compared. The NOBEM is further utilized as part of the HKF algorithm which estimates measured engine parameters. Engine parameters obtained from the dual-channel measurements, the NOBEM, and the HKF are compared against each other. When the discrepancy among the signals exceeds a tolerance level, the FDI logic determines the cause of discrepancy. Through this approach, the enhanced system achieves the following objectives: 1) anomaly detection, 2) component fault detection, and 3) sensor fault detection and isolation. The performance of the enhanced system is evaluated in a simulation environment using faults in sensors and components, and it is compared to an existing baseline system.

Modeling and Analysis of Power Conversion System for High Temperature Gas Cooled Reactor With Cogeneration

A gas turbine in combination with a nuclear heat source has been subject of study for some years. This paper describes the advantages of a gas turbine combined with an inherently safe and well-proven nuclear heat source. The design of the power conversion system is based on a regenerative, non-intercooled, closed, direct Brayton cycle with high temperature gas-cooled reactor (HTGR), as heat source and helium gas as the working fluid. The plant produces electricity and hot water for district heating (DH). Variation of specific heat, enthalpy and entropy of working fluid with pressure and temperature are included in this model. Advanced blade cooling technology is used in order to allow for a high turbine inlet temperature. The paper starts with an overview of the main characteristics of the nuclear heat source, Then presents a study to determine the specifications of a closed-cycle gas turbine for the HTGR installation. Attention is given to the way such a closed-cycle gas turbine can be modeled. Subsequently the sensitivity of the efficiency to several design choices is investigated. This model is developed in Fortran.

Aircraft Engine On-Line Diagnostics Through Dual-Channel Sensor Measurements: Development of a Baseline System

In this paper, a baseline system which utilizes dual-channel sensor measurements for aircraft engine on-line diagnostics is developed. This system is composed of a linear on-board engine model (LOBEM) and fault detection and isolation (FDI) logic. The LOBEM provides the analytical third channel against which the dual-channel measurements are compared. When the discrepancy among the triplex channels exceeds a tolerance level, the FDI logic determines the cause of the discrepancy. Through this approach, the baseline system achieves the following objectives: 1) anomaly detection, 2) component fault detection, and 3) sensor fault detection and isolation. The performance of the baseline system is evaluated in a simulation environment using faults in sensors and components.

Review of Metrics and Assignment of Confidence Intervals for Health Management of Gas Turbine Engines

The development and evaluation of new diagnostic systems requires statistically-based methods to measure performance. Various metrics are in use by developers and users of diagnostic systems. Current metrics practices are reviewed, including receiver operating characteristics, confusion matrices, Kappa coefficients and various entropy techniques. A set of metrics is then proposed for assessment of diverse gas path diagnostic systems. The use of bootstrap statistics to compare metric results is developed, and demonstrated for a set of hypothetical data sets with a range of relevant characteristics. The bootstrap technique allows the expected range of the metric to be assessed without assuming a probability distribution. A method is proposed to develop confidence intervals for the calculated metrics. The application of a confidence interval could prevent a good diagnostic technique being discarded because of a lower value metric in one test instance. The strengths and weaknesses of the various metrics with derived confidence intervals are discussed. Recommendations are made for further work.

Analysis of Intermediate Temperature Combined Cycles With a Carbon Dioxide Topping Cycle

The development of high efficiency solar power plants based on gas turbine technology presents two problems, both of them directly associated with the solar power plant receiver design and the power plant size: lower turbine intake temperature and higher pressure drops in heat exchangers than in a conventional gas turbine. To partially solve these problems, different configurations of combined cycles composed of a closed cycle carbon dioxide gas turbine as topping cycle have been analyzed. The main advantage of the Brayton carbon dioxide cycle is its high net shaft work to expansion work ratio, in the range of 0.7–0.85 at supercritical compressor intake pressures, which is very close to that of the Rankine cycle. This feature will reduce the negative effects of pressure drops and will be also very interesting for cycles with moderate turbine inlet temperature (800–1000 K). Intercooling and reheat options are also considered. Furthermore, different working fluids have been analyzed for the bottoming cycle, seeking the best performance of the combined cycle in the ranges of temperatures considered.

Employing Inverted Brayton Cycle to Solve Stack Temperature Problems After Water Recovery From HAT Cycle Exhaust Gas

By adding an induced draft fan or exhaust compressor between flue gas condenser and stack to make the turbine expand to a pressure much lower than ambient pressure, this paper actually employed inverted Brayton cycle to solve stack temperature problems after water recovery from Humid Air Turbine (HAT) cycle exhaust gas and compare the effect of different discharging methods on the system’s performance. Comparing with the methods of gas discharged directly or recuperated, this scenario can obtain the highest electrical efficiency under certain pressure ratio and turbine inlet temperature. Due to the introduction of induced draft fan, in spite of one intercooler, there are twice intercoolings during the whole compression since the flue gas condenser is equivalent to an intercooler but without additional pressure loss. So the compression work decreases. In addition, the working pressure of humidifier and its outlet water temperature are lowered for certain total pressure ratio to recover more exhaust heat. These enhance the electrical efficiency altogether. Calculation results show that the electrical efficiency is about 49% when the pressure ratio of the induced draft fan is 1.3∼1.5 and 1.5 percentage points higher than that of HAT with exhaust gas recuperated. The specific works among different discharging methods are very closely. However, water recovery is some extent difficult for HAT employing inverted Brayton cycle.

Design Details of a 600 MW Graz Cycle Thermal Power Plant for CO2 Capture

The high power highest efficiency zero-emission Graz Cycle plant of 400 MW was presented at ASME IGTI conference 2006 and at CIMAC conference 2007. In continuation of these works a raise of power output to 600 MW is presented and important design details are discussed. The cycle pressure ratio is increased from 40 to 50 bar by a half-speed stage connected via gears to the main compressor shaft allowing to keep the volume flow to the main compressors constant. The compressors are driven by the transonic compressor turbine stage. Mass flow to the compressors is increased by the factor of 1.27, density in blades of the main compressors is raised by the same factor. The turbine inlet temperature is raised to 1500°C together with the increase in the cycle pressure ratio, both are well accepted values in gas turbine technology today. Most important development problems have to be solved in designing the oxy-fuel burners. They are presented here in the form of coaxial jets of fuel (natural gas or coal gas alternatively) held together by a steam vortex providing coherent flow and flame is ignited by its strong suction. Combustion is finalized by the mixing with a counter-rotating outer vortex flow of working gas leading to a well defined position of vortex break down. The transonic stage of the compressor turbine is supplied with innovative steam cooling forming coherent layers outside of the blade shell of which stress deliberations will be presented.

Simulation of Performance Deterioration of a Microturbine and Application of Neural Network to Its Performance Diagnosis

This study aims to simulate performance deterioration of a microturbine and apply artificial neural network to its performance diagnosis. As it is hard to obtain test data with degraded component performance, the degraded engine data have been acquired through simulation. Artificial neural network is adopted as the diagnosis tool. First, the microturbine has been tested to get reference operation data, assumed to be degradation free. Then, a simulation program was set up to regenerate the performance test data. Deterioration of each component (compressor, turbine and recuperator) was modeled by changes in the component characteristic parameters such as compressor and turbine efficiency, their flow capacities and recuperator effectiveness and pressure drop. Single and double faults (deterioration of single and two components) were simulated to generate fault data. The neural network was trained with majority of the data sets. Then, the remaining data sets were used to check the predictability of the neural network. Given measurable performance parameters (power, temperatures, pressures) as inputs to the neural network, characteristic parameters of each component were predicted as outputs and compared with original data. The neural network produced sufficiently accurate prediction. Reducing the number of input data decreased prediction accuracy. However, excluding up to a couple of input data still produced acceptable accuracy.

A Systematic Comparison and Multi-Objective Optimisation of Humid Power Cycles: Part II—Economics

The STIG, HAT and TOPHAT cycles lie at the centre of the debate on which humid power cycle will deliver optimal performance when applied to an aero-derivative gas turbine and, indeed, when such cycles will be implemented. Of these humid cycles, it has been claimed that the TOPHAT cycle has the highest efficiency and specific work, followed closely by the HAT (Humid Air Turbine) and then the STIG (STeam Injected Gas turbine) cycle. In this study, the systems have been simulated using consistent thermodynamic and economic models for the components and working fluid properties, allowing a consistent and non-biased appraisal of these systems. Part 1 of these two papers focussed on the thermodynamic performance and the impact of the system parameters on the performance, part 2 studies the economic performance of these cycles. The three humid power systems and up to ten system parameters are optimised using a multi-objective Tabu Search algorithm, developed in the Cambridge Engineering Design Centre.

A Parametrical Study of a Seven Serpentine Channel PEM Fuel Cell

Proton exchange membrane (PEM) fuel cells have been identified as a viable emerging technology for future power generation systems in terms of both stationary and mobile applications since it offers a significant economical and environmental potential in future power production. This paper presents the development of a PEM fuel cell system using a full three-dimensional computational fluid dynamics model for the system optimization. The fuel cell investigated is a seven serpentine channel cell of 100cm2 active area. The model includes a complete set of mathematical equations for the fluid flow, multi-component species transport, electrochemistry, and the transport of protons and electrical currents throughout the PEM fuel cell. The results obtained from the parametric analyses of the cell performance at different current loads have been presented. The model results provide us detailed information on the fluid dynamics and electrochemical processes that occur in the fuel cell. This generates a clear picture on the fuel/oxidant distribution, consumption, and the current density distribution in the fuel cell. This assists us in identifying the critical parameters that influence the cell performance and sheds light onto the physical mechanisms leading to the improvement of the fuel cell system performance.