Achates Power, AVL Plan Multi-Cylinder Opposed-Piston Demo Engine

Achates Power Inc. and AVL Powertrain Engineering expect to complete work by early-2015 on a highly efficient three-cylinder, two-stroke opposed-piston engine designed for military use, Green Car Congress reports.

The companies have logged more than 3,600 hours of lab tests on their single-cylinder prototype architecture. Scaling up the design will be accomplished under a $4.9 million contract with the U.S. Army Tank Automotive Research, Development and Engineering Center in Warren, Mich.

TARDEC wants a next-generation combat engine that makes about 70 hp per liter and burns fuel at a rate of less than 0.36 lbs per horsepower-hour. Achates predicts it will surpass those goals with its technology, which has demonstrated 47.5% brake thermal efficiency in the lab.

The Achates design arranges two opposing pistons in a single cylinder. The pistons come together at top dead center and are pushed apart by combustions. The pistons alternately expose and block intake and exhaust ports, thus eliminating the need for a conventional valvetrain.

Achates says its latest design, dubbed A48, includes design tweaks to improve durability and thermal management. The company also says its work to date indicates the optimal stroke-to-bore ratio must be between 2.0 and 2.3. The company says 2-, 3-, 4- and 5-cylinder configurations are possible, but it says a three-cylinder configuration offers the best gas exchange efficiency.