Durability Evaluation of Ceramic Components Using Cares/Life

The computer program CARES/LIFE calculates the time-dependent reliability of monolithic ceramic components subjected to thermomechanical and/or proof test loading. This program is an extension of the CARES (Ceramics Analysis and Reliability Evaluation of Structures) computer program. CARES/LIFE accounts for the phenomenon of subcritical crack growth (SCG) by utilizing the power law, Paris law, or Walker equation. The two-parameter Weibull cumulative distribution function is used to characterize the variation in component strength. The effects of multiaxial stresses are modeled using either the principle of independent action (PIA), the Weibull normal stress averaging method (NSA), or the Batdorf theory. Inert strength and fatigue parameters are estimated from rupture strength data of naturally flawed specimens loaded in static, dynamic, or cyclic fatigue. Application of this design methodology is demonstrated using experimental data from alumina bar and disk flexure specimens which exhibit SCG when exposed to water.

Future Vehicular Recuperator Technology Projections

The Department of Defense and NASA have funded a major gas turbine development program, Integrated High Performance Turbine Engine Technology (IHPTET), to double the power density and fuel economy of gas turbines by the turn of the century. Seven major US gas turbine developers participated in this program. While the focus of IHPTET activity has been aircraft propulsion, the same underlying technology can be applied to water craft and terrestrial vehicle propulsion applications, such as the future main battle tank. For these applications, the gas turbines must be equipped with recuperators. Currently, there is no technology roadmap or set of goals to guide industry and government in the development of a next generation recuperator for such applications.

Progress on the Advanced Turbine Technology Applications Project (ATTAP)

This technology project, sponsored by the U.S. Department of Energy, is intended to advance the technological readiness of the ceramic automotive gas turbine engine. Of the several technologies requiring development before such an engine becomes a commercial reality, structural ceramic components represent the greatest technical challenge, and are the prime project focus. The ATTAP aims at developing and demonstrating such ceramic components that have a potential for: (1) competitive automotive engine life cycle cost and (2) operating for 3500 hr in a turbine engine environment at turbine inlet temperatures up to 1371°C (2500°F). Allison is addressing the ATTAP goal using internal technical resources, an extensive technology and data base from General Motors (GM), technical resources from several subcontracted domestic ceramic suppliers, and supporting technology developments from Oak Ridge and other federal programs. The development activities have resulted in the fabrication and delivery of numerous ceramic engine components, which have been characterized through laboratory evaluation, cold spin testing, hot rig testing, and finally through engine testing as appropriate. These component deliveries are the result of the ATTAP design/process development/fabrication/characterization/test cycles. Ceramic components and materials have been characterized in an on-going program using nondestructive and destructive techniques. So far in ATTAP, significant advancements include: • evolution of a correlated design procedure for monolithic ceramic components • evolution of materials and processes to meet the demanding design and operational requirements of high temperature turbines • demonstration of ceramic component viability through thousands of hours of both steady-slate and transient testing while operating at up to full design speed, and at turbine inlet temperatures up to 1371°C (2500°F) • completion of hundreds of hours of durability cyclic testing utilizing several “all ceramic” gasifier turbine assemblies • demonstration of ceramic rotor survivability under conditions of extreme foreign object ingestion, high speed turbine tip rub, severe start-up transients, and a very demanding durability cycle In addition to the ceramic component technology, progress has been made in the areas of low emission combustion technology and regenerator design and development.

The Flight Testing of Natural and Hybrid Laminar Flow Nacelles

The achievement of large areas of laminar flow over aircraft engine nacelles offers significant savings in aircraft fuel consumption. Based upon current engine configurations nett sfc benefits of up to 2% are possible. In addition the engine nacelle is ideally suited to the early inclusion of laminar flow technology, being relatively self contained with the possibility of application to existing airframes. In September 1992 a European Consortium managed by Rolls-Royce including MTU and DLR began flight testing of a natural laminar flow nacelle. This programme was later extended by R-R and DLR to flight test a hybrid laminar flow nacelle featuring boundary layer suction and insect contamination protection. The tests evaluated the effects of flight and engine environment, boundary layer transition phenomena, suction system operation and insect contamination avoidance strategies. This paper describes the global conclusions from these flight tests which are a significant milestone leading to the future application of laminar flow technology to engine nacelles.

300 kW Class Ceramic Gas Turbine Development (CGT 301)

CGT 301 is a recuperated, single-shaft, ceramic gas turbine for cogeneration capable of continuous full load application. In order to reduce its size, thermal stress, and deformations, ceramic parts are designed axi-symmetrically. The combustor is located on a shaft axis just before the turbine, therefore it does not have a large scroll. The turbine is a two-stage axial flow-type with ceramic blades. For the first phase of the program, the primary-type gas turbine with all-metallic parts was fabricated and tested under various conditions. The test results confirmed the rotation stability of the gas turbine. After the test of preliminary metallic gas turbine, all-ceramic parts were fabricated and various tests were carried out to confirm their reliability. The configuration and structure of the ceramic turbine were improved based on the data obtained from the tests of the primary-type gas turbine and the fundamental tests for ceramic components. The primary-type ceramic gas turbine of TIT 1200°C was designed and fabricated for the second phase of the program. This paper outlines the concept of the ceramic component design, test results of ceramic parts in the hot section, and the engine test.

Status of the Automotive Ceramic Gas Turbine Development Program: Year 3 Progress

Under the ongoing seven-year program, designated “Research and Development of Automotive Ceramic Gas Turbine Engine (CGT Program)”, started in June 1990. Japan Automobile Research Institute. Inc. (JARI) is continuing to address the issues of developing and demonstrating the advantageous potentials of ceramic gas turbines for automotive use. This program has been conducted by the Petroleum Energy Center (PEC) with the financial support of MITI. The basic engine is a 100 kW, single-shaft regenerative engine having a turbine inlet temperature of 1350°C and a rotor speed of 110,000 rpm. In the third year of this program, the experimental evaluation of the individual engine components and various assembly tests in a static thermal test rig were continued. Exhaust emissions were also measured in a performance test rig for an initially designed pre-mixed, pre-vaporized lean (PPL) combustor. A maximum speed of 130,700 rpm was obtained during hot spin tests of delivered ceramic turbine rotors, which was almost the same level as during cold spin tests. A dynamic thermal test including a centrifugal compressor, a ceramic radial turbine rotor and all the ceramic stationary hot parts was initiated.

Regenerator Effectiveness During Transient Operation

The transient response of regenerators is considered. The time required for regenerators to reach steady-state effectiveness is determined. Theoretical results are presented. Also, experimental results that confirm the theory are presented. It is concluded that the time required for a regenerator to reach steady-state effectiveness is τss∼NTU1+hA′1+As′CRAT4As′1-SCkN×ρcDH2RNuH1-pp This expression indicates how regenerator cores can be designed for fast effectiveness response. In dimensionless form, τXss*∼1 where τXss* is the greater of the cool-flow and warm-flow heat-capacity rates, times τss, divided by the heat capacity of the core material. This expression gives a general method for calculation of the effectiveness-response time of regenerator cores. The dimensionless response time is nearly constant with variations in regenerator system-parameter values. Also, for sufficiently high dimensionless core-rotation rates, the dimensionless response time is independent of dimensionless core-rotation rate.

Plasticity Considerations in Probabilistic Ceramic-to-Metal Joint Design

A new probabilistic failure criterion was developed for the design of high-temperature ceramic-to-metal joints. The essential feature of the theory is the inclusion of the energy dissipated during plastic deformation of the adjacent braze layer in the joint. A large number of bi-material interface fracture simulations were performed for different crack positions and orientations near the bimaterial interface to determine the effect on stresses in the ceramic near the interface. The effective stress values were then ported to a probabilistic failure analysis code, which permitted simple inclusion of the new failure criterion. Brazed joints were made and failure tested in torsion to verify the failure criterion. Results show that the new failure criterion more closely approximates the failure of the ceramic-to-metal joints over the entire range of ultimate loads, an is a significant improvement in the failures criteria previously used for this type of joint design. Aspects of the failure criterion, material systems, residual stresses, mechanical behavior, and strength predictions will be presented.

Development of 300kW Class Ceramic Gas Turbine (CGT303)

CCT303 is a two-shaft regenerative ceramic gas turbine with rotary heat exchangers for the purpose of mobile power generator. It is also widely adaptable for industrial machinery and construction machinery as well. The development program of CGT303 is funded by New Energy and Industrial Technology Development Organization (NEDO). The maximum output power of 300kW and thermal efficiency of 42% at TiT 1350C are the objectives of this development. The high TiT requires for the material of all gas passage components to use ceramics which are designed appropriately to keep sufficient strength by using sophisticated computer analysis. Hot spin tests on ceramic turbine rotors and thermal shock tests on stationary ceramic components have been carried out to prove their strength. The paper covers the design concept of CGT303 and results of analysis.

Testing an APU for Potential Service Aboard a U.S. Naval Destroyer

Incentives exist for replacing ships high pressure gas turbine emergency start air systems with auxiliary power units (APUs). The Allied Signal, Model GTCP 100-82 is one option. It is currently used in Naval aircraft start carts. Interest has been kindled in a shipboard application primarily for emergency starting Ship Service Gas Turbine Generator Sets. This APU is tested at the Naval Surface Warfare Center Carderock Division facility in Philadelphia. The target ships for this application is the future addition to the DDG-51 Class, AEGIS Destroyers. Advantages from both financial and life cycle management perspectives are expected from standardized air and sea service. This APU application concept, and variations of it, are overtly suited to a broad array of similar installations.