Opposed Piston Opposed Cylinder Engine

An extremely lightweight opposed piston opposed cylinder (OPOC) engine has been developed under a Defense Advanced Research Projects Agency (DARPA) program.

FEV and Advanced Propulsion Technologies (APT) were asked by the U.S. Army Tank Automotive Research Development and Engineering Center (TARDEC) to modify this engine for heavy-truck applications. Analyzing the two stroke scavenging, the side-injection combustion, and the structure of the key components shows the potential of the OPOC concept.

It is predicted for the 465 kW (650 hp) OPOC truck engine. The OPOC engine was designed to be modular. Each module is self-contained and delivers 325 hp. The modules are connected together via the Modular Displacement Clutch, which synchronizes the modules for achieving even firing when both modules are functioning.

With an optimized scavenging process, the special design features of the OPOC engine offer a significant step towards the potential of the two-stroke engine having double the power density of a four-stroke engine. An estimated 90% scavenging efficiency has been achieved with unique gas exchange characteristics of the OPOC engine and the use of an electric assisted turbocharger.

The OPOC engine runs with almost two times the engine speed (3800 rpm) along with a large cylinder stroke (167.53 mm), as a result of the split stroke of the opposed piston structure. This also improves the power density by another factor of 2.

There's an autoplaying video here that shows just how it works realtime. I like the idea, just the length of the conrods concerns me. A supercharger instead of the "electric turbocharger" would also simplify and add power. Nice design.