The opoc engine operates on the 2-cycle principle, generating one power stroke per crank revolution per cylinder. Each module consists of two opposing cylinders per module, with a crankshaft between them; each cylinder has two pistons moving in opposite directions. With a two-module application configured at the appropriate power level (to deliver a combined 480 hp), the opoc unit could deliver about 45% better fuel efficiency compared to a conventional heavy-duty diesel engine in a Class 8 truck, the company suggests, while delivering emissions at the US Tier 2 Bin 5 level (the 50-state level in the US for diesel light duty vehicles).
The opoc engine in dual-module configuration is connected by an electrically controlled clutch. Select modules are deactivated at different points in the operating cycle to optimize fuel consumption (cylinder deactivation, but on a module basis). The clutch assembly is housed between two engine modules, and is engaged when both modules are running to deliver power from both modules through the drivetrain.
When the power of the second module is not needed, the clutch is disengaged, allowing the second engine to stop completely. This not only improves fuel economy, it also eliminates parasitic power losses in the primary module.
Here you can see the animation
SOURCE: Green Car Congress