Achates Power OP Engine Begins Real-World Test Phase

January 17, 2018

Matthew Borst

Achates Power's 2.7-L opposed-piston engine installed in an F-150 demonstrator on display at the 2018 North American International Auto Show. (Matt Borst)

In 2016, Achates Power received a $9 million award from the U.S. Dept. of Energy’s ARPA-E program to develop its opposed-piston gasoline compression ignition (OPGCI) engine. Through Achates' recently-announced partnership with Aramco, the engine has entered the in-vehicle development phase and is now fitted to Ford F-150 demonstrators, revealed at the 2018 North American International Auto Show.

Achates latest OP engine on display at NAIAS. The 3-cylinder engine features two crankshafts. Each cylinder set employs two pistons, sharing a common combustion chamber. A turbocharger and supercharger combine to create the pressure differential in the cylinder. (Matt Borst)

The OP design aims to achieve fuel economy levels beyond regulatory requirements with lower emissions and cost, compared with current production engines.

The 2.7-L, 3-cylinder engine (see February 2017 AE cover story: http://www.nxtbook.com/nxtbooks/sae/17AUTP02/index.php#/0) has undergone minor updates in recent months to make it more production-ready. The combustion chamber was further refined, through partnerships with Delphi and Argonne National Laboratory, and compression ratio was increased from 16:1 to 18.5:1 to achieve indicated thermal efficiencies (ITE) above 50%.

“We chose to demonstrate our ultra-clean, ultra-efficient OP engine in a full-size light-duty pickup truck because of the significant need and opportunity for improvement in this segment,” said David Johnson, president and CEO of the San Diego-based company. “These trucks are driven more miles, sold in higher volume, consume more fuel and emit more CO₂ than other light duty vehicles.”

In the F-150, the Achates engine is expected to achieve a combined 37 mpg on pump gasoline—4 mpg better than the proposed 2025 CAFE regulations—and deliver 270 hp (201 kW) and 480 lb-ft (650 N·m). Those fuel economy, power and torque numbers are superior to those produced by Ford's new 3.0-L V6 diesel that will be available in the 2018 F-150.

Energy giant Aramco, which has analyzed dozens of engine/fuel technologies at its Novi, Michigan, research and test facility since 2015, saw great potential in the Achates engine for demonstrating real-world engine efficiency improvements, noted David Cleary, the Research Center Leader. “We are big believers of testing engines on dynos and looking at the numbers," he told Automotive Engineering, "but we are even bigger believers in getting in the car and driving them.”

The GCI engine has true compression ignition; there is no spark-plug assistance like that employed in Mazda’s SpCCI system (see October 2017 AE cover story, http://www.nxtbook.com/nxtbooks/sae/17AUTP10/index.php#/ ). The Achates OPGCI injects fuel early in the compression cycle for a lean mixture, with incoming air and residual exhaust that is purposefully left in the cylinder. Then, ignition is initiated by injection of the gas just like on a diesel engine. The turbocharger and supercharger provide the pressure differential in the cylinder.

With this higher combustion efficiency comes reduced engine-out emissions, reduced aftertreatment requirements and improved cold-start-emissions, the engineers claim. Johnson and his team believe that along with an average 60% reduction in overall bill-of-material, their GCI engine achieves a 10% cost savings over a comparable supercharged V-6.

Achates Power is currently putting its OP-engine demo vehicles in customer hands. Watch Automotive Engineering for program updates and an on-road driving report later this year.