Micro Gas Turbine With Ceramic Nozzle and Rotor

A series of operation tests of a ceramic micro gas turbine has been successfully carried out. The baseline machine is a small single-shaft turbojet engine (J-850, Sophia Precision Corp.) with a centrifugal compressor, an annular type combustor, and a radial turbine. As a first step, an Inconel 713C alloy turbine rotor of 55 mm in diameter was replaced with a ceramic rotor (SN-235, Kyocera Corporation). A running test was conducted at rotational speeds of up to 140,000 rpm in atmospheric air. At this rotor speed, the compression pressure ratio and the thrust were 3 and 100 N, respectively. The total energy level (enthalpy and kinetic energy) of the exhaust gas jet was 240 kW. If, for example, it is assumed that 10% of the total power of the exhaust jet gas was converted into electricity, the present system would correspond to a generator with 24 kW output power. The measured turbine outlet temperature was 950°C (1,740°F) and the turbine inlet temperature was estimated to be 1,280°C (2,340°F). Although the ceramic rotor showed no evidence of degradation, the Inconel nozzle immediately in front of the turbine rotor partially melted in this rotor condition. As a second step, the Inconel turbine nozzle and casing were replaced with ceramic parts (SN-01, Ohtsuka Ceramics Inc.). The ceramic nozzle and case were supported by metal parts. Through tests with the ceramic nozzle, it became evident that one of the key technologies for the development of ceramic gas turbines is the design of the interface between the ceramic components and the metallic components, because the difference between the coefficients of linear thermal expansion of the ceramic and metal produces large thermal stress at their interface in the high-temperature condition. A buffer material made of alumina fiber was therefore introduced at the interface between the ceramic and metal.

Turbofan Engine Robust H-∞ Dynamical Output Feedback Control Design Based on LMI Method

This paper presents an approach to turbofan engine dynamical output feedback controller (DOFC) design in the framework of LMI (Linear Matrix Inequality)-based H∞ control. In combination with loop shaping and internal model principle, the linear state space model of a turbofan engine is converted into that of some augmented plant, which is used to establish the LMI formulations of the standard H∞ control problem with respect to this augmented plant. Furthermore, by solving optimal H∞ controller for the augmented plant, we indirectly obtain the H∞ DOFC of turbofan engine which successfully achieves the tracking of reference instructions and effective constraints on control inputs. This design method is applied to the H∞ DOFC design for the linear models of an advanced multivariate turbofan engine. The obtained H∞ DOFC is only in control of the steady state of this turbofan engine. Simulation results from the linear and nonlinear models of this turbofan engine show that the resulting controller has such properties as good tracking performance, strong disturbance rejection, and satisfying robustness.

Performance of Oxidation and Creep Resistant Alloys for Primary Surface Recuperators for the Mercury 50 Gas Turbine

Recuperation is a means for increasing the efficiency of a simple-cycle gas turbine, allowing for heat transfer between the exhaust and compressor discharge gas streams to occur in a highly efficient, relatively compact package. The primary surface recuperator operates at high temperatures and gas pressures and is constructed from thin metal sections, presenting challenges for high temperature materials selection. This paper discusses a joint Solar Turbines-ATI Allegheny Ludlum project which was undertaken to address the issue of elevated temperature attack in the presence of high levels of water vapor and its relevance to alloys intended for use in primary surface recuperators. An overview of the alloy selection process will be presented, followed by a detailed study of the two most promising alloy candidates. Breakaway oxidation was mitigated by using alloys with higher nickel and chromium content, and oxide scale evaporation was controlled with selected minor element additions.

Influence of Flow Characteristics on the Discharge Coefficient of a Multiperforated Wall

The aim of this study is to determine the discharge coefficient of a multiperforated wall sample designed by AVIO, and more precisely to show the influence of each surrounding flow (inside holes, coolant and main flows). Results obtained are compared to correlations from literature. As previously observed, it is found that the discharge coefficient is strongly dependent on the Reynolds number relative to the hole flow (Reh). The influence of the coolant flow has been proved. The comparison with classical correlations shows many differences: i) on the expected asymptotic value ii) on the rate of increase for the lowest values of Reh. This influence is not taken into account by classical correlations deduced from experiments carried out without crossflow. Based on our experiments, we determined a general expression of Cd. Experimental data are fitted with a function of type Cd = A(1−exp(−B.Reh)), where A and B are expressed as functions of the Reynolds number (Re2) of the coolant flow.

Preliminary Multidisciplinary Design Optimization System: A Software Solution for Early Gas Turbine Conception

Preliminary Multidisciplinary Design Optimization (PMDO) project addresses the development and implementation of the Multidisciplinary Design Optimization (MDO) methodology in the Concept/Preliminary stages of the gas turbine design process. These initial phases encompass a wide range of coupled engineering disciplines. The PMDO System is a software tool intended to integrate existing design and analysis tools, decompose coupled multidisciplinary problems and, therefore, allow optimizers to speed-up preliminary engine design process. The current paper is a brief presentation of the specifications for the PMDO System as well as a description of the prototype being developed and evaluated. The current assumed e xible architecture is based on three software components that can be installed on different computers: a Java/XML MultiServer, a Java Graphical User Interface and a commercial optimization software.

Engine Testing of an Advanced Alloy for Microturbine Primary Surface Recuperators

HAYNES® alloy HR-120® has been identified as a potential alloy for the manufacture of primary surface recuperators. Primary surface recuperator components have been manufactured from HR-120, and actual microturbine testing is on going. Initial engine test results indicate the formation of a protective oxide scale that is resistant to both steady-state and cyclic operation with no evidence of accelerated attack, and which is likely to meet or exceed the desired 80,000 hour component life.

Assessment of Technologies for Biomass Conversion to Electricity at the Wild Land-Urban Interface

In the near term, biomass in various forms is the most available renewable energy source in the USA, particularly in the wild land-urban interface (WUI). With current high natural gas (NG) prices the possibility of gasifying biomass and developing a local Biomass Alliance with Natural Gas (BANG) so that the biomass gas (BG) can supplement natural gas (NG) could have many energy, environmental and economic (EEE) benefits. An analytic cost estimation (ACE) method is used to assess various BANG technologies potentially applicable at the WUI and to determine NG prices at which BG capable systems can deliver electricity at competitive costs. ACE is based upon the approximate linear relationship between cost of electricity (COE = Y), and cost of fuel (COF = X), i.e., Y = K + SX, as seen in many detailed cost analyses of electrical generating systems. ACE is here used to guide efforts directed towards energy sustainability in the WUI where nearby biomass stores are abundant. Thermal conversion and the use of the fuel to supplement NG is considered here at various power (P) levels to lower the cost of electricity. A reasonable K(P) and S(P) for NG fired electrical generation systems is first established. Then using an Antares Group Inc. report (AGIR) analyses of eleven biomass fueled technologies K(P) and S(P) are identified using only three adjusted parameters for each technology. An accurate analytical equation is also found for AGIR calculations of net present value (NPV = Z) vs. P and Y. These equations are then used to interpolate and extrapolate the AGIR economic analyses to other Ps and X or Y in some cases leading to other conclusions than in the AGIR. We conclude that BANG can save energy costs in many communities at the WUI and lead the way to: the development of economically competitive woody biomass supply and applications industries provide jobs, stabilize local economies, reduce USA’s dependence on imported fuels and lower greenhouse gas emissions.

Model-Based Control of Combustion Instabilities

Model-based control has been successfully implemented on an atmospheric pressure lean premixed combustion rig. The rig incorporated a pressure transducer in the combustor to provide a sensor measurement, with actuation provided by a fuel valve. Controller design was based on experimental measurement of the open loop transfer function. This was achieved using a valve input signal which was the sum of an identification signal and a control signal from an empirical controller to eliminate the non-linear limit cycle. The transfer function was measured for the main instability occurring at a variety of operating conditions, and was found to be fairly similar in all cases. Using Nyquist and H∞-loop shaping techniques, several robust controllers were designed, based on a mathematical approximation to the measured transfer function. These were implemented experimentally on the rig, and were found to stabilise it under a variety of operating conditions, with a greater reduction in the pressure spectrum than had been achieved by the empirical controller.

Use of Hybrid Engine Modeling for On-Board Module Performance Tracking

A practical consideration for implementing a real-time on-board Module performance tracking system is the development of a high fidelity engine model capable of providing a reference level from which performance changes can be tracked. Real-time engine models made their advent with the State Variable Model (SVM) in the mid-80’s which provided a piecewise linear model that granted a reasonable representation of the engine during steady state operation and mild transients. Increased processor speeds over the next decade allowed more complex models to be considered which were combinations of linear and non-linear physics based components. While the latter may provide greater fidelity over transient operation and flight envelope excursions, it bears the limitation of potential model obsolescence as performance improvements in the form of hardware modifications, bleed and stator vane schedules alterations, cooling flow adjustments, and the like are made during an engine’s life cycle. Over time, these models may deviate enough from the actual engine being monitored that the module performance estimations are inaccurate and misleading. This paper describes an alternate approach to engine modeling by applying a hybrid engine model architecture that incorporates both physics-based and empirical components. This methodology provides a means to tune the engine model to a particular configuration as the engine development matures and furthermore, aligns the model to the particular engine being monitored to insure accurate performance tracking while not compromising real-time operation.

The Potential of Electronic High Temperature Devices Based Upon Polymer Derived Ceramics

In this paper, we describe the potential use of polymer-derived ceramics (PDCs) for micro-sensors for high-temperature gas turbine applications. PDCs have several unique properties such as ease of microfabrication, excellent mechanical, materials and thermal properties, and tunable electrical conductivity. The electrical conductivity of PDCs with varied composition is measured as a function of temperature from room temperature upon to 700°C. Our results reveal that with suitable doping, the electrical conductivity could be controlled from insulating to semiconducting. Next, we measure the cure depth of the precursors as a function of UV intensity and exposure time. A model is developed to predict the cure depth as a function of photoinitiator concentration and light intensity. Good agreement between theory and experimental data is obtained. Finally, a few typical micro parts are fabricated by lithography technique.