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Increasing in the turbine rotor inlet temperature improves the aviation gas turbine efficiency, while on the other hand, but also leads to a higher requirement for blade cooling air, which in turn reduces the gain in efficiency achieved by increasing temperature. Turbine rotor inlet temperature has been increasing with the entry of highly-efficient gas turbines have been developed for the last decades for the aviation market. Around one fifth of the compressed air is extracted from the compressor and is used for blade cooling purposes and is thus not used in the actual power/thrust generation process, which has a negative impact on the engine efficiency. For this reason, new cooling methods and hot-gas path component materials that will be compatible with these high temperature’s gases are among the areas being analyzed.

An “APU” (Auxiliary Power Unit) is a small gas turbine engine to provide supplementary power to an aircraft and is located at the tails of larger jets. APU generators provide auxiliary electrical power for running aircraft systems on the ground. Applications include powering environmental systems for pre-cooling or preheating the cabin, and providing power for crew functions such as preflight, cabin cleanup, and galley (kitchen) operation and long-haul airliners must be started using pneumatic power of APU compressor. The Honeywell 131-9A gas turbine APU has 440 kW shaft power and 90 kW electric generator consuming 120 kg fuel/hour. Hybrid power systems based on fuel cells are promising technology for the forthcoming power generation market. A solid oxide fuel cell (SOFC) is the perfect candidate for utilizing waste heat recovery. This case deals with waste heat recovery from fuel cell exhaust using Brayton cycle as bottoming cycle for additional power production.

The quest for achieving more efficient gas turbine engine systems (GTESs) has led the researchers to try getting into many new dimensions of research. Simple Brayton cycle-based GTESs were coupled with recuperators, regenerators and reheaters to avoid/recoup heat energy from being wasted and these were designated as complex GTESs. Multistage compression (multi-casing) in axial compressors and multistage (two-cylinder) expansions in turbines paved the path to optimize the plant design for greater thrust to weight ratio and greater efficiency of the GTESs. Since the increase in efficiency of any power plant is directly or indirectly related to temperatures at which the plant cycle is being operated, this thermodynamic constraint had led to the development of high temperature materials such as single crystal nickel-based superalloys.