Prospects for endurance augmentation of small unmanned systems using butane-fueled thermoelectric generation

Abstract

We investigate the potential of enhancing small (<20 kg) drone endurance by exploiting the high energy density of hydrocarbons using a prototype generator based on commercial-off-the-shelf (COTS) thermoelectric energy conversion technology. A proof-of-concept prototype was developed to vet design and engineering challenges and to bolster validity of resultant conclusions. The combination of the prototype performance and modeling suggests that endurance augmentation remains a difficult technical challenge with no clear immediate remedy despite many expectant alternatives. Across a sample of representative drones including ground- and air-based, multicopter and fixed wing drones, we report the following: from their current maximum values of 12%, thermoelectric (TE) generator module efficiencies must increase by over two times to achieve endurance parity with lithium batteries for VTOL multicopters. On the other hand, current TE efficiencies can compete with lithium batteries for some low power fixed wing and ground-based drones. Technical contributors for these results include weight of non-energy contributing components, low specific power and the associated tradeoff between specific power and specific energy due to fuel mass fraction, and lastly, low efficiencies.