Weighing just 22 lb (10 kg), the simple engine uses a single moving piston to develop power. Beyond vehicles, Aquarius is developing the engine for use as an off-grid micro-generator.

First created in 2014, Aquarius' efficient single-piston linear engine has a single central cylinder in which the piston moves between two engine heads. In previous iterations, Aquarius used more conventional fossil fuels to create combustion, but now it's turning attention to emissions-slashing hydrogen. The company says Austrian engineering firm AVL-Schrick recently completed third-party testing, verifying that a modified version of the engine can operate purely on hydrogen.