Mark van Roode

Ceramic Composite Development for Gas Turbine Engine Hot Section Components

The development of ceramic materials for incorporation into the hot section of gas turbine engines has been ongoing for about fifty years. Researchers have designed, developed, and tested ceramic gas turbine components in rigs and engines for automotive, aero-propulsion, industrial, and utility power applications. Today, primarily because of materials limitations and/or economic factors, major challenges still remain for the implementation of ceramic components in gas turbines. For example, because of low fracture toughness, monolithic ceramics continue to suffer from the risk of failure due to unknown extrinsic damage events during engine service. On the other hand, ceramic matrix composites (CMC) with their ability to display much higher damage tolerance appear to be the materials of choice for current and future engine components. The objective of this paper is to briefly review the design and property status of CMC materials for implementation within the combustor and turbine sections for gas turbine engine applications. It is shown that although CMC systems have advanced significantly in thermo-structural performance within recent years, certain challenges still exist in terms of producibility, design, and affordability for commercial CMC turbine components. Nevertheless, there exist some recent successful efforts for prototype CMC components within different engine types.Copyright

Ceramic Matrix Composite Combustor Liners: A Summary of Field Evaluations

Solar Turbines Incorporated, under U.S. government sponsored programs, has been evaluating ceramic matrix composite combustor liners in test rigs and Solars Centaur® 50S gas turbine engines since 1992. The objective is to evaluate and improve the performance and durability of CMCs as high-temperature materials for advanced low emissions combustors. Field testing of CMC combustor liners started in May of 1997 and by the end of 2004, over 67,000 operating hours had been accumulated on SiC/SiC and oxide/oxide CMC liners. NO X and CO emissions have been consistently <15 ppmv and <10 ppmv, respectively. Maximum test durations of 15,144 h and 13,937 h have been logged for SiC/SiC liners with protective environmental barrier coatings. An oxide/oxide CMC liner with a Friable Graded Insulation coating has been tested for 12,582 h. EBCs significantly improve SiC/SiC CMC liner life. The basic three-layer EBC consists of consecutive layers of Si, mullite, and BSAS. The durability of the baseline EBC can be improved by mixing BSAS with mullite in the intermediate coating layer. The efficacy of replacing BSAS with SAS has not been demonstrated yet. Heavy degradation was observed for two-layer Si/BSAS and Si/SAS EBCs, indicating that the elimination of the intermediate layer is detrimental to EBC durability. Equivalent performance was observed when the Hi-Nicalon fiber reinforcement was replaced with Tyranno ZM or ZMI fiber. Melt infiltrated SiC/SiC CMCs have improved durability compared to SiC/SiC CMCs fabricated by Chemical Vapor Infiltration of the matrix, in the absence of an EBC. However, the presence of an EBC results in roughly equivalent service life for Ml and CVI CMCs. Results to date indicate that oxide/oxide CMCs with protective FG1 show minor degradation under Centaur® 50S gas turbine engine operating conditions. The results of, and lessons learned from CMC combustor liner engine field testing, conducted through 2004, have been summarized.

X-ray diffraction measurement of glass content in fly and slags☆

Abstract The purpose of this study is to develop an accurate procedure for measuring the glass content of some mineral wastes to assist in predicting their behaviour in concrete. Several X-ray diffraction methods were used for analyzing the source materials of this study. The present investigation involves only a quantitative X-ray diffraction (QXRD) method which is used to compute the mass percentages of α-quartz, mullite, magnetite and hematite, and the glass content by difference. The technique was improved in the course of this study. Glass contents determined with this method ranged from 53.5 to 94.5 per cent.

Ceramic Gas Turbine Development: Need for a 10Year Plan

Ceramic gas turbine development that started in the 1950s has slowed considerably since most of the large-scale ceramic gas turbine development programs of the 1970s-1990s ended. While component durability still does not meet expectations, the prospect of significant energy savings and emission reductions, potentially achievable with ceramic gas turbines, continues to justify development efforts. Four gas turbine applications have been identified that could be commercially attractive: a small recuperated gas turbine (microturbine) with ~35% electrical efficiency, a recuperated gas turbine for transportation applications with ~40% electrical efficiency with potential applications for efficient small engine cogeneration, a ~40% efficient midsize industrial gas turbine, and a ~63% (combined cycle) efficient utility turbine. Key technologies have been identified to ensure performance and component durability targets can be met over the expected life cycle for these applications. These technologies include a Si 3 N 4 or SiC with high fracture toughness, durable EBCs for Si 3 N 4 and SiC, an effective EBC/TBC for SiC/SiC, a durable oxide/oxide ceramic matrix composite (CMC) with thermally insulating coating, and the next generation CMCs with high strength that can be used as structural materials for turbine components for small engines and for rotating components in engines of various sizes. The programs will require integrated partnerships between government, national laboratories, universities, and industry. The overall cost of the proposed development programs is estimated at U.S.

Ceramic Stationary Gas Turbine Program: Combustor Liner Development Summary

110M over 10 years, i.e., an annual average of U.S.

Ceramic Stationary Gas Turbine Development

10M.

Ceramic Gas Turbine Materials Impact Evaluation

Under the Ceramic Stationary Gas Turbine Program sponsored by the U. S. Department of Energy, Solar Turbines Incorporated has successfully designed and developed ceramic combustor liners. Their potential for low emissions has been demonstrated in five field-engine tests for a total duration of over 30,000 hours, with over 13,000 hours on EBC protected liners in one engine test. The ceramic combustor development under the CSGT Program (1992–2000), including design, material selection, testing and evaluation are discussed.Copyright

Durability of Oxide/Oxide Ceramic Matrix Composites in Gas Turbine Combustors

A program has been initiated under the sponsorship of the Department of Energy (DOE), Office of Industrial Technology, to improve the performance of stationary gas turbines in cogeneration through the selective replacement of metallic hot section parts with uncooled ceramic components. It is envisioned that the successful demonstration of ceramic gas turbine technology, and the systematic incorporation of ceramics in existing and future gas turbines will enable more efficient engine operation, resulting in significant fuel savings, increased output power, and reduced emissions. The program which started in September, 1992, takes an engine of the Solar Centaur family of industrial gas turbines, and modifies the design of the hot section to accept ceramic first stage blades and first stage nozzles, and a ceramic combustor liner. The ceramic materials selected for the blade are silicon nitride, for the nozzle silicon nitride and silicon carbide, and for the combustor liner silicon carbide as well as two continuous fiber reinforced ceramic composites, one with a silicon carbide matrix and another with an oxide matrix.This paper outlines the approach, conceptual component design, and materials selection for the program.Copyright

Comparative evaluation of high temperature coatings for corrosion protection of fuel injector tips

Impact of foreign or domestic material on components in the hot section of gas turbines with ceramic components is a common cause of catastrophic failure. Several such occurrences were observed during engine testing under the Ceramic Stationary Gas Turbine program sponsored by the U.S. Department of Energy. A limited analysis was carried out at Solar Turbines Incorporated (Solar), which involved modeling of the impact in the hot section. Based on the results of this study an experimental investigation was carried out at the University of Dayton Research Institute Impact Physics Laboratory to establish the conditions leading to significant impact damage in silicon-based ceramics. The experimental set up involved impacting ceramic flexure bars with spherical metal particulates under conditions of elevated temperature and controlled velocity. The results of the study showed a better correlation of impact damage with momentum than with kinetic energy. Increased test specimen mass and fracture toughness were found to improve impact resistance. Continuous fiber-reinforced ceramic composite (CFCC) materials have better impact resistance than monolithics. A threshold velocity was established for impacting particles of a defined mass. Post-impact metallography was carried out at Oak Ridge National Laboratory to further establish the impact mechanism.© 2002 ASME

Ceramic Stationary Gas Turbine Development Program: Third Annual Summary

An integrated creep rupture strength degradation and water vapor degradation model for gas turbine oxide-based ceramic matrix composite (CMC) combustor liners was expanded with heat transfer computations to establish the maximum turbine rotor inlet temperature (TRIT) for gas turbines with 10:1 pressure ratio. Recession rates and average CMC operating temperatures were calculated for an existing baseline N720/A (N720/Al2O3) CMC combustor liner system with and without protective Al2O3 friable graded insulation (FGI) for 30,000-h liner service life. The potential for increasing TRIT by Y3Al5O12 (YAG) substitution for the fiber, matrix, and FGI constituents of the CMC system was explored, because of the known superior creep and water vapor degradation resistance of YAG compared to Al2O3. It was predicted that uncoated N720/A can be used as a combustor liner material up to a TRIT of ∼1200 °C, offering no TRIT advantage over a conventional metal + thermal barrier coating (TBC) combustor liner. A similar conclusion was previously reached for a SiC/SiC CMC liner with barium strontium aluminum silicate (BSAS)-type environmental barrier coating (EBC). The existing N720/A + Al2O3 FGI combustor liner system can be used at a maximum TRIT of ∼1350 °C, a TRIT increase over metal + TBC, and uncoated N720/A of ∼150 °C. Replacing the Al2O3 with YAG is predicted to increase the maximum allowable TRIT. Substitution of the fiber or matrix in N720/A increases TRIT by ∼100 °C. A YAG FGI improves the TRIT of the N720/A + Al2O3 FGI by ∼50 °C, enabling a TRIT of ∼1400 °C, similar to that predicted for SiC/SiC CMCs with protective rare earth monosilicate EBCs.