More stories related to SAE DETROIT - FEV Engine Technology displays at the annual Society of Automotive Engineers World Congress here an intriguing opposed-cylinder diesel engine that leverages improvements to the 2-stroke cycle to generate thermal efficiency in excess of 41%.

The Opposed Piston-Opposed Cylinder (OPOC) design, says an FEV source, also generates extraordinary power density. A turbocharged 2-cyl. prototype on display generates 325 hp and 590 lb.-ft. (800 Nm) of torque at 2,000 rpm, yet weighs just 270 lbs. (123 kg).

Using a unique system of inner and outer connecting rods and cleverly positioned intake and exhaust ports, the OPOC design runs pistons in each opposed cylinder. The design causes the pistons to clamp together to develop compression and drive apart from the resulting combustion.

FEV says the inspiration for the OPOC design comes from both the Junkers Jumo twin-crankshaft diesel aircraft engine and the opposed-cylinder (“boxer”) design of Ferdinand Porsche.

FEV says the design, in eliminating cylinder heads and all valvetrain, has 25% fewer components, presenting the potential to dramatically reduce manufacturing cost and servicing complexity.

FEV OPOC concept engine uses opposed pistons running in opposed cylinders.

At the same time, the improvements to the 2-stroke cycle - focused largely on asymmetrically located intake and exhaust ports and a high degree of turbo boost - generates twice the power density of a typical poppet-valve 4-stroke engine.

The OPOC engine development program, conducted in conjunction with Advanced Propulsion Technologies Inc. (APT), was sponsored by the Defense Advanced Research Projects Agency as a potential power generator for military applications. (See related story: Military Humvees on Hybrid Trail)

FEV says the prototype engine has “almost no main bearing forces and very low piston side forces,” which significantly reduces operating friction. The prototype's four long connecting rods are constructed from titanium.

The engine also employs an electrically assisted turbocharger (EAT) developed by APT. An FEV source says the EAT is integral to the OPOC engine's ability to achieve the most from the 2-stroke combustion process.

The turbocharger's electrically assisted turbine can develop high levels of boost at low engine speeds that normally leave conventional turbochargers lacking. The FEV source says the EAT also can be used to precisely tailor the engine's torque output.