Multidisciplinary Design Methodology for Micro-Gas-Turbines - Part II: System Analysis and Optimization

Owing to their high specific energy capabilities, ultra micro gas turbines (UMGT) are a high-potential technology to provide portable electric power supply for applications with demand of less than 1 kW. UMGT conceptual design is challenged by small-scale effects augmenting interdisciplinary dependencies leading to highly coupled, non-linear component interactions. This work provides a novel approach to conceptual UMGT design by combining reduced order component and system modelling with constrained multi-objective optimization. Hereby, Part I presents integrated design and performance modelling of compressor, turbine, combustor and generator. In Part II, the heat engine and generator modules are merged into a system framework by establishing conceptual UMGT rotor geometry and engine design. Following bearing selection and lifetime assessment, experimentally validated reduced order models are developed for heat transfer and rotordynamic analysis. Using the elaborated framework, a constrained multi-objective system optimization of a 300W engine is performed based on ten design parameters and comparing SiAlON and Inconel 718 as potential rotor materials available for additive manufacturing. Hereby, bearing lifetime, system efficiency and specific power are maximized while meeting rotordynamic, structural and thermal requirements. Evaluating the results, interdisciplinary effects are highlighted, and two optimum engine configurations are suggested.