These are variant rotary vane engines implemented as 2 separate, axially coupled stages: an intake/compression stage & a combustion/expansion stage. The primary design objective is improved fuel efficiency.
The engines are coupled to a starter motor which doubles as a dynamometer. Independent combustion & expansion ratios over 20:1 can be set to accommodate various fuels & for attaining the highest efficiency (currently ~10% & rising steadily as seals are improved).
Wear surfaces & seals are graphite-on-s