Return of the efficiency 2-piston cylinder:
EcoMotors OPOC Two Stroke Engines – Opposed Piston Opposed Cylinder
"The engine can be built in a modular fashion, allowing more cylinders to be added in pairs with a clutch between the modules so one pair can be used at start or light load with the clutch adding more cylinders when required."
This type of configuration is not new, though:
EcoMotors - Wikipedia, the free encyclopedia
http://www.oldengine.org/members/diesel/Marine/doxford.htm
