From Pinnacle Looks Beyond Detroit as the Market for Its Opposed-Piston Engine:

Pinnacle Engines' prototype Cleeves Cycle engine
Pinnacle Engines’ prototype Cleeves Cycle engine

Pinnacle Engines’ prototype Cleeves Cycle engine is a spark-ignited, opposed-piston engine capable of burning gasoline, ethanol, compressed natural gas, or diesel fuel. This prototype features a single cylinder; up to three can be combined.