Achates Power

Achates Power is an American developer of opposed-piston, two-stroke, compression ignition engines for use in commercial and passenger vehicles. Based in San Diego, California, the company was founded in 2004 by James U Lemke.

According to Achates Power, its opposed-piston, two-stroke engine has demonstrated an increase in fuel efficiency with engine-out emissions levels sufficient to meet tailpipe emissions regulations.

In 2018, Achates Power was awarded $6,994,601 from the California Air Resources Board for the Opposed Piston Engine Class 8 Heavy Duty On-Road Demonstration. The objective of the program was to demonstrate that a heavy-duty diesel engine could meet California's ultralow NOx requirements while simultaneously increasing fuel efficiency. A 10.6L heavy-duty opposed-piston engine was installed in a Peterbilt 579 tractor and operated in fleet service by Walmart Corporation. The engine demonstrated the ability to meet every 2027 NOx emissions regulation enacted by both the United States Environmental Protection Agency and the California Air Resources Board, including new regulations for low load operation and off-cycle use. In addition, the engine demonstrated the ability to meet the 2027 EPA Green House Gas Phase 2 regulations and increased efficiency as much as 21% compared to a benchmark truck. Moreover, using the accelerated aftertreatment system aging protocol at Southwest Research Institution, the engine demonstrated the ability to meet the 2027 CARB regulations to a full useful life of 800,000 miles. Notably, these results were achieved with a conventional, underfloor aftertreatment system consisting of a diesel oxidation catalyst, a diesel particular filter, selective catalyst reduction, and an ammonia slip catalyst. No additional emissions control technology was required to achieve the ultra-low NOx levels. In 2025, the company published a technical paper at SAE World Congress summarizing these results.

In December 2012, the company announced that it had been selected as a subcontractor to AVL Powertrain Engineering, Inc. to build the next-generation combat engine for the U.S. Army. Less than a year later, in October 2013, Achates Power and Fairbanks Morse Engine signed a joint development and licensing agreement to reduce emissions and fuel consumption of Fairbanks Morse proprietary and dual-fuel opposed-piston engines. In 2017, Cummins announced that it and Achates Power had been selected by the U.S. Army to develop the 1000 hp Advanced Combat Engine based on the opposed-piston technology developed by Achates Power. The U.S. Army describes the Advanced Combat Engine as a "highly efficient, power dense engine that enables the expansion of military ground vehicle capabilities beyond current or past potential with the next-generation of propulsion power."

Achates Power is privately owned and backed by Sequoia Capital, RockPort Capital Partners, Madrone Capital Partners, Triangle Peak Partners and Interwest Partners.