Transportation Materials
Growth in total jet fuel consumption, however, has remained at a mere 3%, and the corresponding specific consumption rate (per passenger mile) has decreased 2–3% annually. These improvements in efficiency have come principally from the application of modern by-pass engine technology, which is based on elevated combustion temperatures and increased engine pressures.
Advances in thermostructural materials have lead to sustained improvements in engine efficiency of aeropropulsion systems. (consumption data from Intergovernmental Panel on Climate Change) Future gains will rely on use of ceramic composites, intermetallic alloys and new generations of thermal and environmental barrier coatings
Despite the sustained progress in jet engine technology, some of the greatest challenges lie ahead. Continuing expansion of the world economy will escalate demand for air travel, placing ever-greater demands on our limited supply of hydrocarbon fuels and exacerbating the ever-growing problem of greenhouse gasses. At current rates of economic growth and engine efficiency, worldwide consumption of jet fuel will double in the next 25 years – from about 60 billion to 120 billion gallons annually. The environmental, economic, and geopolitical ramifications of this growth are daunting.
Holding fuel consumption growth even to this level will require continued improvements in engine efficiency sufficient to cut specific fuel consumption by half in the next two decades. Slowing or reversing the trend will require an even more ambitious agenda. The technology to achieve these goals will be based on new materials that can successfully operate in thermal and environmental conditions within the engine that are far more severe than those encountered today.
The transportation focus within the Institute for Energy Efficiency specifically targets propulsion system efficiency through developing materials which will allow those higher operating temperatures while also providing reductions in weight and cost. Currently-used technologies include high-strength titanium alloys, refractory nickel superalloys, and lightweight polymer matrix composites. More recently, the most significant gains have resulted from use of oxide thermal barriers on the hottest engine components. By implementing these barrier layers, allowable turbine temperatures have increased about 100°C – comparable to that achieved through three decades of progress in alloy design. Yet additional gains in engine efficiency will be achieved through the successful implementation of high-temperature forms of carbide and oxide-composites and intermetallic compounds, coupled with barrier layers to assure protection against environmental degradation.
Tony Evans and his collegues choose the geometry of a multimaterial
lattice structure. Geometric changes due to heating and cooling can be minimized so that the lattices can be used for the hot surfaces of hypersonic aircraft.
Progress in high temperature materials has had a major impact not only on propulsion technology but also on industrial turbine-based power-generation systems. Commonalties in function and design have spurred R&D efforts that simultaneously target both industries. As a result, future progress in materials for jet engines will have direct bearing on power generation, with further implications for fuel consumption and environmental impact.
Research groups within the Materials and Mechanical Engineering departments are addressing these critical materials challenges of energy-efficient propulsion and power generation. Our research agendas are based on iterative linkages between the system, the components and the constituent materials, and our research initiatives integrate all aspects of materials technology, including design, synthesis, processing and characterization of new alloys and composites. Extensive collaboration with leading suppliers of aero and industrial turbines and with materials manufacturers, ensures that our research is relevant to industrial practice and provides a pathway for technology transition. Specifically, strong partnerships have been developed with General Electric (both aero engine and power systems divisions), United Technologies (Pratt and Whitney), Honeywell, Rolls Royce and Siemens.
