The Development of Gas Turbine Materials

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When hooked up to a steam turbine, the setup reached a record-breaking It can go from zero to full throttle in less than half an hour, enabling the plant operator, EDF Energy, to quickly respond to changing demand, as well as supply from intermittent sources such as wind and the sun. Earlier this year, a plant in Japan with an HA turbine inside clocked in at A world record is more than just bragging rights.

As of August , they have accumulated more than , fired hours of operation. Earlier this summer, for example, an HA turbine at a power plant encountered an oxidation issue that affects the lifespan of a single blade component. The minor adjustments that we need to make do not make the HA any less of a record setting turbine — they are meeting — and in many cases exceeding — their performance goals at every customer site today.

Images credit: GE Power. GE Power tests its turbines and their latest upgrades at a unique test bed next to its state of the art manufacturing facility in Greenville, South Carolina. The test stand, which is disconnected from the power system to prevent wreaking havoc on the local grid, comes equipped with its own gas plant and 4, sensors monitoring the complex machine as engineers run it through a litany of stressful conditions, such as operating the turbine at percent of its rated speed, mimicking a power surge in Mexico or extreme heat in Saudi Arabia.

The HA turbine was tested at ambient temperatures ranging from minus 37 degrees Celsius to 85 degrees Celsius — far beyond what it would encounter in service. Besides working closely with customers and learning from their experience, GE engineers are busy testing ideas to make the machine even better. We have confirmed that the EBCs effectively work for the recession resistance. Fukudome et al. Request Permissions. Tanaka, M. Yoshida, T.

Kubo, H. Terazono, S. Fukudome, S. Tsuruzono, W. Karasawa, Y. Etori, T.

Turbine blade

Hisamatsu, I. Yuri, Y. Yasutomi, T. Machida and K. Ferber, H. Lin, V. Parthasarathy and W. More, P. Tortorelli, M. Ferber, L. Walker, J. Keiser, N. Miriyala, W. Brenrnall and J. Wenglarz and K. Schenk, T. Stangman, E.

  • Microscopy of Semiconducting Materials: Proceedings of the 14th Conference, April 11-14, 2005, Oxford, UK: 107 (Springer Proceedings in Physics).
  • General characteristics.
  • The Development of Gas Turbine Materials.

Opila, R. Robinson, D. Fox, H. Klemm, C. Taut, K. More and P. Miriyala, A. Fahme and M. Price, O. Jimenez, N. Miriyala, J. Kimmel, D.

The Development of Gas Turbine Materials | G.W. Meetham | Springer

Leroux and T. Corman, A. Dean, S. Even though an aircraft engine application may justify material costs of hundreds or even thousands of dollars per kilogram, cost-benefit is still a major consideration. For example, a large national investment in metal-matrix composites in the s and s resulted in both a technically viable manufacturing process and several successful demonstrations of metal matrix components in engines. Nevertheless, when projected to wide-scale adoption, the parts appeared to be too expensive to be viable. Even at a conceptual level, it is often difficult to distinguish between materials development and the manufacturing technology required to fabricate parts from that material.

This is especially true for many high-temperature materials such as single-crystal turbine airfoils, powder metal disks, and high-temperature coatings as well as some polymer composites. This is not the case for materials adopted from other applications such as steel, aluminum, and some nickel alloys, where the material manufacturing is distinct from the part fabrication. New manufacturing methods such as the additive manufacture of high-temperature materials like titanium and nickel superalloys can be considered either an innovation or a confluence of the additive manufacture of plastics in use since the early s with the powder metal processing long used for disks.

In either case, it represents an alternative path to the realization of complex parts and new materials. It offers intriguing possibilities to realize structures or properties that would otherwise be prohibitively expensive. This technology is in its infancy in terms of dimensional control, surface finish, and material properties, so significant progress should be possible. Manufacturing technology advances such as this may be a significant contributor to improving engine performance, weight, and perhaps cost. While advanced materials can reduce fuel burn by reducing weight, they can be especially valuable when they improve temperature capability and reduce cooling requirements.

This is true for compressor materials to. Materials can also improve part durability to retain rather than increase fuel burn as an engine ages. The most fruitful areas of materials research at this time appear to be in advanced high-temperature metals, ceramics, and coatings:. The state of the art in compressor and turbine turbomachinery efficiency is about 90 percent, while studies suggest that efficiencies of better than 95 percent may be possible.

Applications of interest include aerodynamics, aeromechanics, and the mechanical arrangements of complete components, especially those that enable higher compressor discharge temperatures. Improved analysis tools and emerging manufacturing technologies may open new approaches or make old ideas feasible. Historically, turbomachinery efficiency improved as machine size increased, all else remaining equal. As engine and airplane efficiency improves, less thrust is needed for a given mission, so the size of engine turbomachinery shrinks.

Also, as the overall pressure ratios OPRs of engines have been increased to improve thermodynamic efficiency, the flow areas and thus the dimensions of airfoils in the core, especially at the rear of the compressor and in the high-pressure turbine, have shrunk dramatically. Indeed, the newest engines entering service at the 30, lb thrust level have the same core diameter as older designs that are still in production and deliver only one-fifth the thrust. Current turbomachinery design trades between size and efficiency are based on empirical practice rather than first principles limitations.

Obvious areas of concern include sensitivity to geometry variations such as tip clear-.

Epstein, , Aeropropulsion for commercial aircraft in the 21st century and research directions needed, AIAA Journal 52 5 Manufacturing technology investments could assist here. Work on analytical tools can help progress in this area. Significant investments over 40 years have yielded complex computer simulations that analyze turbomachinery aerodynamics at the design point.

These tools are inadequate at important operating conditions away from the design point, such as idle. Mechanical analysis tools suffer from inadequate models of nonlinear mechanical interactions such as friction, sliding interactions, and plastic deformation. Aeromechanics is another turbomachinery discipline in which physics-based simulations are not yet capable of adequately predicting engine behavior over the entire operating regime.

Overall, the advancement in the accuracy and speed of simulation tools so that they can be better used to optimize the overall engine system in a timely manner during design may add several percentage points of improvement in fuel burn and certainly reduce development cost and time. In conclusion, although there have been substantial investments in turbomachinery over many decades, efficiency, weight, and cost could still be improved significantly. A modern engine uses percent of the compressor core flow for hot section cooling and purging. This is a direct debit to engine efficiency since the work that must be done to compress this air is only partially recovered as thrust.

Turbine cooling is another area that has received considerable attention over decades. Improved methods have reduced the amount of cooling air required and enabled longer engine life even at higher temperatures. Manufacturing technologies to realize sophisticated cooling schemes have been one area of progress, but more can be done here, especially for nonmetallic materials. Another constraint on cooling is the clogging of small passages and holes over time by dirt ingested by the engine. Thus, technologies that improve dirt separation and rejection could contribute to a reduction in fuel burn.

These challenges are exacerbated as engine size is reduced. Current combustion systems are better than 99 percent efficient in converting the chemical energy in fuel to heat. Both lean burn and rich burn approaches have proven competitive to date. Continued emissions work will be needed given the expected tightening of emissions requirements coupled with the increase in engine pressure ratio that will be needed to further reduce fuel burn. As engine overall pressure ratios are increased to improve thermodynamic efficiency and reduce CO 2 , combustor design will be further challenged to meet both emissions and mechanical integrity goals.

Areas that may be helpful include new design concepts and improved modeling tools, especially physics-based approaches capable of accurate prediction of regulated emissions. Alternative fuels to date are compatible with existing combustor technology. New approaches to combustor design may be able to significantly shorten combustor length, thus reducing engine weight and CO 2 emissions.

Overcoming the limitations and constraints of existing engine controls and accessories such as generators, pumps, and heat exchangers offers the potential to improve fuel consumption, reduce weight, and reduce cost. Dirt can also cause erosion that increases tip clearance, which increases fuel burn, and dirt can clog cooling holes in the turbine. These effects are much worse in places with poor air quality.

Lefebvre, , Gas Turbine Combustion , second ed.

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While many advanced engine control architectures have been proposed and analyzed, the lack of enabling hardware, including processors, sensors, and actuators with the needed temperature capabilities, has inhibited practical application. As aircraft subsystems become more electrical and as fan pressure ratios drop to improve propulsive efficiency, this challenge will be exacerbated. The inefficiency of current fuel pumps consumes much of the heat capacity of the fuel flow that would otherwise be available for the cooling needed by other aircraft heat sources.

Therefore, improving fuel pump efficiency, especially at low fuel flows, would reduce the size and pressure drops associated with other engine and aircraft cooling requirements. Heat exchangers, which are addressed in more detail below, are far from their theoretical maximum performance.

Taken together, engine accessories occupy a significant portion of the propulsion system volume, especially on smaller engines; this problem becomes more challenging as fan pressure ratio is lowered to improve propulsive efficiency. Reducing the volume of these accessories could lead to lower fan pressure ratios by enabling better nacelle designs. Overall, improving the performance, efficiency, and size of external components such as pumps, heat exchangers, and controls would help to reduce CO 2 emissions.

Reliable gas turbines

Gas turbine mechanical components such as bearings and seals offer many opportunities for improvement. Bearings and their need for cooling and lubrication add considerable complexity to an engine. The bearings in a midsized gas turbine dissipate about kW into the oil, heat that must be rejected to the fuel or the environment.

The oil system of a modern gas turbine is exceedingly complex. One reason is that bearings are located where the ambient temperatures exceed the autoignition temperature of the oils. Thus the bearing compartments must be cooled with seals to inhibit oil leakage. Efforts to replace oil-lubricated, rolling-element bearings have not been successful to date, but the combination of smaller engine cores, advanced analytical techniques, and new materials may permit the use of either air bearings or magnetic bearings on smaller commercial aircraft.

Air bearings have been used for decades on aircraft environmental control systems and some auxiliary power units, so safe, long-term service has already been demonstrated, albeit in less thermally demanding environments. Modeling and materials work could help here. Industrial magnetic bearings are used on some ground-based power turbines and on industrial pumps and compressors. In addition to elimination of oil and the oil system, they offer the potential advantage of active control of rotor dynamics, a serious issue for aircraft engines.

Challenges in the past include the weight and volume of the power electronics needed, as well as high-temperature capabilities of the magnets themselves. There has been much progress here in the past two decades, especially in power electronics, so this may be another area that could contribute significantly to improving aircraft engines. Engines in commercial service today use simple Brayton cycles. There are many variations of the Brayton cycle that could theoretically offer improvement.

Regenerative cycles capture heat from the exhaust and move it to the compressor to improve engine performance when operating off the design point. Intercooled cycles cool the air during compression to improve compressor efficiency while reducing compressor discharge temperature. Combined cycles capture some of the exhaust heat, which is then routed to a Rankine cycle to produce additional power for a given fuel burn.

These cycles all require large relative to the motor heat exchangers, which add considerable weight, volume, cost, and maintenance burdens. While prevalent in ground power plants, to date they have not been used in aircraft engine applications because these cycles have not appeared attractive given the current state of the art of components. Intercooled and combined cycle gas turbines are extensively used in ground-based power generation, where size, weight, and on-off cycling are lesser issues. Significant improvements in heat exchanger technology would be required to make such approaches viable for low-carbon propulsion of commercial transport aircraft.

These advanced engine cycle concepts are constrained by the capabilities of current heat exchanger technology. Intermittent combustion approaches and those that use shock waves have been studied for many decades and in some cases have been brought to the point of laboratory demonstration. For example, the Humphrey cycle uses. The Humphrey cycle poses several engineering challenges, including the mechanical integrity of the system with large pressure pulses.

The potential value of various hybrid cycles to commercial aircraft propulsion for fuel burn reduction has yet to be clearly established. The committee determined that hybrid cycles should not currently be considered a high-priority research area for subsonic commercial aircraft compared to other investment opportunities. Heat exchangers are an important part of any propulsion system, air-breathing or electric. Their temperature capability, life, volume, and weight are limiting in many applications.

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Current turbofan engines use heat exchangers to cool engine oil, generator coolant, and bleed air to the aircraft. In the near future, some engines will soon use heat exchanges to produce cooling air for the turbines. As cores get smaller and electrical demands grow, more heat must be rejected to the fan stream. At the same time, as fan pressure ratios drop, this heat rejection becomes increasingly expensive in terms of fuel burn, weight, and volume.

Some advanced cycle concepts are even more dependent on heat exchanger technology.

The Evolution of Jet Engine Turbine Blades

Indeed, the viability of airborne intercooled and regenerative cycles is constrained by heat exchanger penalties. This may be an even larger constraint on electric and hybrid-electric approaches in which the heat is of low quality, exacerbating heat rejection penalties. Airborne heat exchangers have not seen much progress over many decades. Heat exchangers used on ground-based engines are often the largest and most expensive component and the one requiring the most maintenance.

Airborne concepts are needed that reduce pressure drop, weight, and volume per unit heat transferred; work at high temperatures; and have longer life and lower cost. New manufacturing technology, such as additive manufacturing, may enable new concepts.

The overall efficiency of commercial aircraft engines has been improving at a rate of about 7 percent per decade since see Figures 3. Today, the overall efficiency of commercial aircraft propulsion is approaching 40 percent. Aircraft engines are not mature: Given sufficient investment, there is a potential to continue this rate of improvement for the next several decades.

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Additional benefit may be realized by innovative propulsion—airframe integration technologies, discussed in Chapter 2. Rationale for Gas Turbine Engine Research. Gas turbine engines have considerable room for improvement, with a potential to reach overall efficiencies perhaps 30 percent better than the best engines in service today, with a concomitant reduction in CO 2 emissions. This magnitude of gain requires investment in a host of technologies to improve thermodynamic and propulsive efficiency of engines, with each discrete technology contributing only a few percent or less.

Aircraft gas turbine challenges were discussed above to elucidate some of the many opportunities available to improve engine performance. These opportunities are often presented in a traditional, disciplinary sense:. To focus on improving efficiency and CO 2 as fast as possible at given levels of investment, it is useful to consider the challenges and research opportunities by topical area.

Overcoming the challenges will require a mix of disciplines to become an engineering reality and will involve work on both scientific advances and design concepts.

The Development of Gas Turbine Materials The Development of Gas Turbine Materials
The Development of Gas Turbine Materials The Development of Gas Turbine Materials
The Development of Gas Turbine Materials The Development of Gas Turbine Materials
The Development of Gas Turbine Materials The Development of Gas Turbine Materials
The Development of Gas Turbine Materials The Development of Gas Turbine Materials

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