Performance improvement on MEMS micropropulsion system through a novel two-depth micronozzle design

A novel micronozzle geometry with different depths at converging and diverging section was designed with the aim in mitigating viscous loss due to formation of subsonic viscous boundary layers at nozzle sidewalls. Feasible fabrication schemes based on available fabrication techniques, deep reactive ion etching (DRIE) and low temperature co-fired ceramic (LTCC) tapes, were proposed to prove practicality of the design. Numerical simulations were performed in evaluating the parameters of micronozzle performance, thrust, mass flow rate and specific impulse efficiency, for both 3D linear and two-depth micronozzles with 15° and 30° expander half-angles over a range of throat Reynolds numbers (Re_throat≈601068). Pressurized nitrogen gas was selected as propellant in this study. Comparison of numerical results shows two-depth micronozzles outperform linear micronozzles for the entire range of Re _throat and all performance parameters. The new micronozzle design has successfully reduced viscous loss through shorter expander length and mitigation of subsonic layers merging at nozzle expander section. Although the asymmetric geometry was found inducing a Z-axis thrust component, it can be offset through proper arrangement of the micronozzles. In conclusion, the design demonstrates improved performance over conventional micropropulsion system utilizing linear micronozzles by approximately 5%.