Ultra micro gas turbines for electric power generation below 1 kW are a viable replacement technology for lithium batteries in drones due to their high energy density. To achieve high aerodynamic efficiency, turbomachinery at centimeter scale and speeds up to 500,000 rpm are required. Previous research showed that small-scale effects disqualify design practices applied to larger gas turbines where subcomponents can be optimized isolated from system design. To appropriately capture component interdependencies of ultra micro gas turbines, an integrated design approach based on reduced order models is expedient. Therefore, a comprehensive engine design model including thermodynamic cycle analysis, compressor and turbine aerodynamic design, combustor design and high-speed generator design is presented. The design system is adapted to capture additive manufacturing constraints of small-scale components. In addition, reduced order models for rotordynamics, stress analysis and heat transfer are used to define the permissible design space.
To validate the established set of reduced order models, extensive experimental investigations have been performed. The applicability of additive manufacturing to micro gas turbines was investigated by performance comparison of two rotors manufactured with lithographic ceramic manufacturing (LCM) and selective laser sintering (SLS). To this end, compressor performance maps were recorded at speeds up to 450,000 rpm, showing significant performance benefit for the LCM processed rotor and good agreement with the reduced order model. Additionally, porous media combustion performance was measured, showing low achievable equivalence ratios but considerable radiation heat losses. Furthermore, a high-speed generator was developed and tested validating the reduced order modelling approach. Finally, system performance testing is currently on-going on a preliminary micro turbine prototype integrating generator, turbomachinery and combustor.
