Fabrication of functional mesoscopic ceramic parts for micro gas turbine engines

The demand for small-size energy sources with high power densities is increasing with the development of miniature devices. New materials and novel manufacturing techniques are essential for developing these energy sources for miniature devices.; Micro gas turbine engines can have higher power density per volume and weight due to their higher operating frequencies, which is made possible by the scaling effect. Higher power densities can also lead to redundant systems that have higher reliability than single engine systems. By replacing metal parts with lighter ceramics, power generated per unit mass can be increased further. However, since the ceramic parts are brittle, they suffer from lower reliability. Mesoscopic ceramic parts have higher reliability due to their smaller volume. This can be predicted by Weibull statistics.; A fist-size miniature gas turbine engine with silicon nitride parts called “Firefly” is being developed at the Rapid Prototyping Laboratory (RPL), Stanford University and its industrial partners. Firefly's rotor-group and turbine inlet nozzle are made of silicon nitride to achieve light weight and increased efficiency.; The Firefly engine's ceramic parts require smooth surface but their complex geometry prevents grinding. The Mold Shape Deposition Manufacturing (Mold SDM) process and its derivative, therefore, are used to fabricate the ceramic parts. Since the process was not fully developed for the fabrication of functional ceramic parts, several process improvements have been made. The manufacturing processes and the fabricated parts are characterized in terms of surface quality, strength, accuracy and build time. The results show that the processes have been developed to the extent that they produce functional ceramic parts for micro gas turbine engines.; The functionality of the Mold SDM silicon nitride parts for the Firefly engine is tested. The ceramic inlet nozzles were tested with high temperature gas. The ceramic turbine has been spin tested and it achieved 456,000 rpm. The ceramic compressor was characterized up to 420,000 rpm and the effect of compressor clearance gap for the compressor functionality was measured. Noticeable increases of compression ratio, mass flow rate and efficiency have been observed as the compressor clearance gap decreases from 180 μm to 120 μm.