Thrust characteristics of nano-carbon/Al/oxygenated salt nanothermites for micro-energetic applications

Abstract

Combustion within small motors is key in the application-specific development of nanothermite-based micro-energetic systems. This study evaluates the performance of nanothermite mixtures in a converging-diverging nozzle and an open tube. Mixtures were prepared using nano-aluminum (n-Al), potassium perchlorate (KClO4), and different carbon nanomaterials (CNMs) including graphene-oxide (GO), reduced GO, carbon nanotubes (CNTs) and nanofibers (CNFs). The mixtures were packed at different densities and ignited by laser beam. Performance was measured using thrust measurement, high-speed imaging, and computational fluid dynamics modeling, respectively. Thrust, specific impulse (ISP), volumetric impulse (ISV), as well as normalized energy were found to increase notably with CNM content. Two distinctive reaction regimes (fast and slow) were observed in combustion of low and high packing densities (20% and 55%TMD), respectively. Total impulse (IFT) and ISP were maximized in the 5% GO/Al/KClO4 mixture, producing 7.95 mN·s and 135.20 s respectively at 20%TMD, an improvement of 57% compared to a GO-free sample (5.05 mN·s and 85.88 s). CFD analysis of the motors over predicts the thrust generated but trends in nozzle layout and packing density agree with those observed experimentally; peak force was maximized by reducing packing density and using an open tube. The numerical force profiles fit better for the nozzle cases than the open tube scenarios due to the rapid nature of combustion. This study reveals the potential of GO in improving oxygenated salt-based nanothermites, and further demonstrates their applicability for micro-propulsion and micro-energetic applications.