High-temperature Engine Research Articles

NASA’s high-temperature engine materials program for civil aeronautics

The Advanced High-Temperature Engine Materials Technology Program is described in terms of its research initiatives and its goal of developing propulsion systems for civil aeronautics with low levels of noise, pollution, and fuel consumption. The program emphasizes the analysis and implementation of structural materials such as polymer-matrix composites in fans, casings, and engine-control systems. Also investigated in the program are intermetallic- and metal-matrix composites for uses in compressors and turbine disks as well as ceramic-matrix composites for extremely high-temperature applications such as turbine vanes.

A program of equivalent tests for turbine blades under laboratory conditions

A method of conducting equivalent tests of turbine blades under laboratory conditions, which ensures reproduction of the operational pattern of the loading in its most heavily loaded components, is proposed. A method for construction of the equivalent-test program is analyzed on a stage-I turbine blade of one of the high-temperature aviation gas-turbine engines.

Synthesizing Oils Is a Slippery Job

Synthesizing Oils Is a Slippery Job

Selecting high-temperature structural intermetallic compounds: The materials science approach

Some 300 intermetallic compounds with high melting temperatures are candidate materials for the high-temperature turbines and engines of the future. Before these applications can be realized, however, the limited ductility of intermetallic materials must be overcome. Using melting temperature and density as figures of merit, and considering the effects of composition and crystal structure, the most likely candidates for these high-performance applications may be identified.

Thermal cycling of tungsten-fibre-reinforced superalloy composites

The thermal cycling of a tungsten-fibre-reinforced superalloy (TFRS) composite is typical of its application in high-temperature engine environments. The mismatch in thermal expansion coefficients between fibre and matrix causes substantial longitudinal (0°) stresses in the composite, which can produce inelastic damage-producing matrix strains. The case of thermal fatigue is explored as a “worst case” of the possible matrix damage in comparison with specimens which are also mechanically loaded in tension. The thermally generated cyclic stresses and the attendant matrix plasticity may be estimated using a non-linear finite-element program by proposing a physical analogue to the micro-mechanics equations. A damage metric for the matrix is proposed using the Coffin-Manson criterion, which metric can facilitate comparisons of damage among different candidate materials, and also comparisons for a given material subjected to different temperature cycles. An experimental programme was carried out for thermal cycling of a 37 vol % TFRS composite to different maximum temperatures. The results confirm the prediction that thermal cycling produces matrix degradation and composite strength reduction, which become more pronounced with increasing maximum cyclic temperature. The strength of the fibre is shown to be identical for the as-fabricated and thermally cycled specimens, suggesting that the reduction in composite strength is due to the loss of matrix contribution and also to notching effects of the matrix voids on the fibre.

Future Application Trends - a Case for Mechanistic Approaches

AbstractThis paper reviews moving mechanical assembly (MMA) and component technology shortfalls imposed by demanding ground, naval and aerospace system requirements of the future. The tribology development needs for specific harsh environment applications such as high temperature engines, chemical reactant turbopumps, precision acquisition, tracking and pointing MMAs surveillance systems and laser communications components are identified. Development goals for lightweight bearing and gear alloys and ceramics, ultra low friction and wide temperature range solid lubricants, self lubricating composites and real time health monitoring devices are translated into a rationale for mechanistic, more fundamental research approaches.

Surface and Bulk Oxidizing Species for Self Lubricating Ceramics

AbstractThe use of ceramic materials for high temperature engine applications has prompted interest in the friction and wear characteristics of ceramicceramic pairs in mating contact. This interest has led to both surface and bulk material modifications aimed at improving the lubricity and wear resistance of these materials. This paper will discuss two basic systems developed to allow self-lubrication at high temperatures in ceramic materials through the formation of a lubricious oxide film. Both methods operate under the assumption that the oxide chemistry of the system controls the lubricity and wear properties. Relevant issues for each system will be presented and discussed.

Analysis of grain boundaries for reaction-bonded silicon nitride with yttria addition

Silicon nitride is often the developmental ceramic of choice for high-temperature engine components. Sintering this ceramic, however, is very difficult due to the covalent nature of the bonding. Complicating the matter, Si3N 4 tends to dissociate at temperatures above 1700 ° C. Dissociation can be impeded by application of a nitrogen overpressure, while the general sintering problem is overcome by the addition of small amounts of various oxides. These sintering aids react with the silicon nitride and each other to form liquid phases, allowing sintering at temperatures between 1600 and 1900°C. Common additives include magnesia, yttria, alumina, and their various combinations. Normal additive content is in the range of 1 to 10% by weight. Although these sintering aids produce highly dense structures, they also lead to the formation of secondary phases along grain boundaries. The resulting materials are very strong at room temperature, but they rapidly lose their strength at high temperature (> 1000°C) because high-temperature mechanical properties such as creep are controlled by the grain boundary phases. The grain-boundary phases, in turn, are determined by the quantity and combination of sintering aids, by the firing cycle, and by the densification process (e.g. hot-pressed or reaction-bonded). Thus, by correlating the microstructure with the physical properties and processing/composition with microstructure, the effect of processing and compositional factors upon the physical properties can be determined and controlled. Although MgO was initially used as a sintering aid in the past, Y203 and YaO3-A1203 yield greater hightemperature strength [1, 2]. Yttria is an attractive additive because at low temperatures it reacts with the SiO2 (and some Si3N4) on the surface of the Si3N4 to form a liquid, greatly enhancing the sintering rate [3]. At higher temperatures when densification is complete, the liquid reacts with more Si 3 N 4 to give a highly refractory bonding phase along the grain boundaries. Tsuge et al. [4] showed that crystallization of the grain-boundary phase could improve high-temperature strength. Investigations of Si3N4-Y203 and Si3Na-Y203SiO2 phase diagrams [3, 5, 6] have been used to predict and explain the various grain-boundary constitutents and resulting properties. Using hot-pressed materials, Lange and co-workers [5, 7] found that the phases within the Si3N4 Si2N20 Y2Si207 compatibility triangle (in the Si3N4 Y203 SiO2 phase diagram) were extremely oxidation resistant, while Si3Y203N4, YSiOzN (K-phase), YxoSiyO23N4 (H-phase) and Y48i207N2 (J-phase) readily oxidize at 1000 ° C. Richer-

Canadian Petroleum Research —Digging In For The Long Term

Abstract Canadian petroleum research ranges from exploration technology to development of highly refined petrochemicals. Studies on permafrost and ice mechanics are examples of diversified Arctic research programs being undertaken by many industry, university and governmental research groups. New seismic evaluation methods, the forerunner of advanced expert systems, are assisting exploration directed toward relatively small complicated oil reservoirs in the western basin. More efficient processes for recovering the large resources of heavy crude and natural bitumen are under active testing, including horizontal wells and follow-up processes to apply after steam stimulation. Research on the extraction of mined oil sands is improving the commercially applied technologies as well as providing technology alternatives for new projects. New approaches for upgrading heavy oil and bitumen have been identified and are under active study. Research in the petroleum products area has led to the introduction of new, high-detergency gasoline. Field testing of various alternative fuels, including oxygenated fuels and dual gaseous/liquid fuels, is under way. The severity of Canadian winters has provided fertile ground for the development of advanced low temperature lubricants, and increased attention is being applied to lubricants suitable for the new high-temperature engines coming on the market. Introduction The recent downturn in the petroleum industry has had a significant effect on the level, and nature, of the industry's commitment to research and development. Many companies have trimmed their R&D budgets and focused more of their remaining effort on shorter-term projects closer to the mainstream of their business. In spite of this retrenchment, technology development and application is still recognized as a key ingredient for competitive survival. Significant research activity in the core areas continues, and important longer term step-out technologies are being aggressively pursued. The shortage of funds has put renewed emphasis on collaborative work, and a number of joint industry programs have been established. One of the remarkable features of petroleum R&D in Canada is its breadth, From off-shore exploration to the development of highly refined petrochemical products, It has not been possible to include all current projects in the following summary statements, but the ones which have been described amply demonstrate the scope and complexity of the research under way. Expected impacts of the projects are provided in Table 1. Upstream R&D Exploration Research in the Arctic The earliest application of marine technology in Canada's Arctic (at least by Europeans) was in support of whaling or for exploration (such as the search for the Northwest Passage). Today, the major incentive to Arctic operations is the recovery of minerals, primarily oil and gas, and this has led to a complex set of research requirements. Under the auspices of the Arctic Petroleum Operator's Association (APOA) (now Frontier Division of the Canadian Petroleum Association) well over 200 joint industry research studies have been conducted in the general topic areas of:—permafrost,—ice mechanics and ice forces,—waves and wave action of islands,—offshore soils and foundations,—oil spill control,—environmental base line studies,—offshore platforms, including caisson islands, and—pipelines.

The Influence of Several Combined High/Low Cycle Loading Parameters on the Crack Growth of a Turbine Disk Alloy

The interactive effects of high- and low-cycle loading on crack growth were evaluated for a high-temperature engine disk alloy (Inconel 718) over a wide range of low-cycle hold times, low-cycle stress intensity factor range (ΔK), high-cycle ΔK, and high-cycle frequency up to 1825 Hz. A series of fatigue crack growth experiments were carried out with a constant low-cycle ΔK and an increasing high-cycle ΔK. The high-frequency ΔK and crack length were measured with sufficient precision to capture details of the transition from the low-cycle dominated regime to the high-cycle dominated regime. In these experiments, the low- and high-cycle dominated growth regimes remained distinct over the entire range of low cycle ΔK, low cycle hold time and frequency investigated. An interactive effect apparent in the low-cycle dominated regime, was a retardation of the low-cycle growth rate when high-cycle loading was applied. The degree of retardation varied with low-cycle ΔK and frequency.

Polymer, metal, and ceramic matrix composites for advanced aircraft engine applications

Advanced aircraft engine research within NASA Lewis focuses on propulsion systems for subsonic, supersonic, and hypersonic aircraft. Each of these flight regimes requires different types of engines, but all require advanced materials to meet their goals of performance, thrust-to-weight ratio, and fuel efficiency. The high strength/weight and stiffness/weight properties of resin, metal, and ceramic matrix composites will play an increasingly key role in meeting these performance requirements. At NASA Lewis, research is ongoing to apply graphite/polyimide composites to engine components and to develop polymer matrices with higher operating temperature capabilities. Metal matrix composites, using magnesium, aluminum, titanium, and superalloy matrices, are being developed for application to static and rotating engine components, as well as for space applications, over a broad temperature range. Ceramic matrix composites are also being examined to increase the toughness and reliability of ceramics for application to high-temperature engine structures and components.

舶用熱水フラッシュ発電プラント

The hot-water flash power generating plant recently developed by Mitsubishi Heavy Industries for diesel ship application far exceeds the conventional economizer-steam power generating plant in terms of waste heat recovery rate, and hence can adequately do its job even with the limited waste heat energy available from the lean exhaust of the increasingly fuel-efficient marine diesel engines which are also smaller for the ship size than hitherto and which are frequently run at part loads for slow steaming. Thus, it is believed that the hot-water flash power generating plant will prove especially worthwhile for ships powered by diesel engines 12, 000 PS and above in output, all these ships now finding it almost practically impossible to employ the conventional economizer-steam power plant.Mitsubishi's hot-water flash power generating plant comes in two types; MARK-N1 and MARK-N2. The former recovers the engine exhaust gas energy all with pressurized water in the exhaust-gas economizer and produces steam by flashing pressurized hot water to drive its generator turbine: The latter, though also equipped with the economizer, recovers high-temperature engine exhaust gas energy as steam and heat of low-temperature exhaust gas and scavenging air with pressurized water to drive the generator turbine with both superheated steam and flash steam.

Film Cooling of Insert Turbine Vane Trailing Edges

Modern high temperature engines require a very efficient cooling process for the turbine guide vanes which are directly exposed to the combustion gases. The use of an internal insert, both for cooling air distribution within the vane and also for protection of the trailing edge by film cooling, offers a satisfactory solution to the problem. Analysis and experiment show that the trailing edge film cooling technique is superior to forced convection. The gain can reach or exceed 200°C and tests indicate that aerodynamic performance of the turbine is not affected. Transient thermal stress analysis indicates that leading and trailing edges are adequately cooled for a life of over 10,000 cycles. The point which is subject to the maximum total mechanical strain range during the first cycle lies on the suction side and coincides with the maximum temperature point. Nomenclature A = coefficient obtained from tests Ae = trailing edge slot area for one vane c = chord length d = trailing edge base thickness h = airfoil span k = ratio of hot gas side to film side heat-transfer coefficients / = distance from last cooling hole to trailing edge tip. Distance from film injection slot to trailing edge tip. m = injection parameter TV = rotational speed P — total pressure p = static pressure q = coolant flow-rate in one blade or vane r = exponent obtained from tests ^ = equivalent slot width T = total temperature / = metal thickness between cooling holes and outer skin V = flow velocity x = abscissa, positive from base to trailing edge tip z = spanwise position of an airfoil section

Application of Thermal Barriers to High-Temperature Engine Components

Application of Thermal Barriers to High-Temperature Engine Components

2750 Deg F Engine Test of a Transpiration Air-Cooled Turbine

The development of gas turbine engines for advanced subsonic and supersonic aircraft as well as for potential utilization of these high performance engines for stationary and marine applications requires, as a key element, the ability to operate at turbine inlet temperatures above the actual melting temperatures of the turbine materials. A limit on gas temperature levels is imposed by the fact that current alloys available for use in turbines, exhibit inadequate strength and oxidation characteristics above 1600–1800 deg F. However, the performance gains offered by operating engines at a high turbine inlet temperature may be realized through the application of an efficient method of cooling the highly stressed turbine components. As a step toward demonstrating that transpiration cooling of turbine blading is an effective means for achieving reliable and efficient gas turbine operation in a high gas temperature environment, a full-scale engine was tested at average gas temperatures of 2750–2800 deg F with a transpiration cooled turbine fabricated from normally used turbine alloys which are limited to metal temperatures of 1600–1800 deg F. The authors discuss the design of the transpiration air-cooled turbine, the technique used in fabricating the porous turbine blading, and the experimental test results obtained from operating the high-temperature engine. Furthermore, correlation of the test results on blade cooling with analytical predictions is presented.

Ignition of aircraft fluids on high temperature engine surfaces

Temperatures created in aircraft jet engines have given rise to concern over hot surface ignition of flammable fluids. For some time, 500° F has been accepted as the maximum safe surface temperature. Under the specific conditions reported here, it appears that this figure can be increased significantly.