Engine Design Strategies to Maximize Ceramic Turbine Life and Reliability

Abstract

Ceramic turbines have long promised to enable higher fuel efficiencies by accommodating higher temperatures without cooling, yet no engines with ceramic rotors are in production today. Studies cite life, reliability, and cost obstacles, often concluding that further improvements in the materials are required. In this paper, we assume instead that the problems could be circumvented by adjusting the engine design. Detailed analyses are conducted for two key life-limiting processes, water vapor erosion and slow crack growth, seeking engine design strategies for mitigating their effects. We show that highly recuperated engines generate extremely low levels of water vapor erosion, enabling lives exceeding 10,000 hs, without environmental barrier coatings. Recuperated engines are highly efficient at low pressure ratios, making low blade speeds practical. Many ceramic demonstration engines have had design point mean blade speeds near 550 m/s. A CARES/Life analysis of an example rotor designed for about half this value indicates vast improvements in slow crack growth-limited life and reliability. Halving the blade speed also reduces foreign object damage particle kinetic energy by a factor of four. In applications requiring very high fuel efficiency that can accept a recuperator, or in short-life simple cycle engines, ceramic turbines are ready for application today.