Pinnacle Touts Opposed-Piston Engine Design

Pinnacle Engines Inc. claims its opposed-piston, four-stroke engine has shown as much as 50% better fuel economy in lab tests than a conventional gasoline powerplant.

The San Carlos, Calif.-based firm says its high-compression spark-ignited design requires no expensive technology, can be produced with conventional production equipment and could deliver the efficiencies of a hybrid without the expense and complexity.

Dual-cam-activated reciprocating sleeve valves enable the four-stroke cycle with the engine's opposed piston architecture. Pinnacle says the design can shift between Otto cycle (constant volume combustion) and diesel cycle (constant pressure combustion), depending upon operating conditions.

Under high loads, the engine can operate with extremely delayed spark timing, enabling it to run without knock on 87-octane fuel at a compression ratio of 15:1. Pinnacle terms the mode the "Cleeves cycle" after company founder James Cleeves.

Pinnacle has focused its development work on a low-cost engine that is naturally aspirated and has fixed valve timing and a fixed compression ratio. It estimates that such a configuration under light load would be 15%-30% more efficient than a conventional engine. Simulations indicate that adding variable valve timing, direct injection and turbocharging could make the engine 50% more efficient, according to the company.

Pinnacle says it will introduce its first engines through a licensing and joint development deal with an unidentified Asian carmaker in the first quarter of 2013.

The company will present an SAE technical paper (#2012-01-0378) about its engine at the SAE World Congress in Detroit next week.