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In-use emissions report for Achates heavy-duty OP diesel shows substantial margin to most stringent EPA NOx proposed regulation

Achates Power has released initial in-use NOx measurements from the cleaner, heavy-duty diesel engine it developed in a project funded by the California Air Resources Board (CARB) and several partners. Achates Power previously announced the opposed-piston has entered fleet service with WALMART Corporation in a Peterbilt 579 tractor. (Earlier post.)

It is the only diesel engine operating on the road capable of meeting CARB’s 2027 regulation, which requires a 90% reduction in NOx emissions compared to current standards. In addition, the Environmental Protection Agency (EPA) recently released its proposed rule to lower NOx emissions levels for commercial vehicles across the entire United States. (Earlier post.) Option 1 from EPA is similar in many respects to the CARB regulation.

Both CARB and EPA have introduced Low Load requirements, in-use NOx measurement updates, and limits on permissible real-world emissions.

Before entering fleet service, the 400 hp, 10.6L 3-cylinder (6 pistons) engine was extensively tested, and the ultra-low emissions and improved fuel efficiency were measured and confirmed at the Aramco Research Center-Detroit. The University of California, Riverside (UCR) provided the in-use emissions measurements, using a Portable Emissions Measurements System (PEMS).

The PEMS measurements conducted by UC-Riverside for CALSTART on the Peterbilt 579 powered by the Achates Power 10.6L heavy-duty opposed-piston engine demonstrated NOx emissions control far better than other diesel engines we have tested.

This first round of measurements performed over 3 days in December 2021 in the California San Joaquin Valley with ambient temperatures in the mid-40s °F while the vehicle was in active fleet operation showed between a 99% and 50% margin to the most stringent EPA 2031+ in-use NOx proposed Regulations, which is outstanding.

—Kent Johnson, Principal Investigator, Emissions and Fuels Research, UCR

At low speeds, typical of driving in urban and other congested areas, today’s heavy-duty vehicles by contrast can emit five times today’s higher certification limit. In-use testing is an important assessment of real-world emissions and emission control strategy practical robustness.

Achates Power is pleased with this initial in-use assessment as it confirms that opposed-piston engines have inherent advantages in both low criteria emissions and low CO2. It is particularly noteworthy that we were able to achieve the extremely stringent in-use NOx limits without any additional emissions control devices while reducing cost, complexity, and compliance risk. As our engineers refine the emissions control systems, we expect further increase in performance and emissions control.

—Dave Crompton, President, and CEO of Achates Power

The engine installed in the Peterbilt truck and operated for the demonstration is a Gen1 design. Achates Power is also testing a Gen2 design on its transient dynamometer.

The Gen1 engine uses only an underfloor aftertreatment system. No other emissions control devices (such as a close-coupled SCR) are required for the OP engine to achieve ultralow NOx compliance.

The Gen2 engine uses an even simpler aftertreatment system, a MY2021 one-box, underfloor system with a typical DOC-DPF-SCR-ASC1 configuration. As with Gen1, no other emissions control devices are used.

CALSTART managed the demonstration project team, which consisted of Achates Power and the team of technology providers. South Coast Air Quality Management District, San Joaquin Valley Air Pollution Control District, and the Sacramento Metro Air Quality Management District provided additional support and funding for the project.

In addition to lower in-use NOx, the demonstration program also shows that the opposed-piston provides a fuel economy improvement of more than 10% compared to reference trucks currently in service. Improving fuel economy both reduces the cost of operation and provides a commensurate reduction in CO2 emissions.

The opposed-piston engine can use existing manufacturing facilities, processes, and materials to allow rapid time-to-market and deployment. It also uses existing components and supply chains. It is expected to cost less than current engines, even as it meets much more stringent environmental regulations and fuel efficiency. It does not require any additional emissions control devices and has a reduced part count compared to conventional engines.

Building off these demonstrated achievements, Achates Power is conducting further testing with a fully aged catalyst (the equivalent of 800,000 miles of operation) to demonstrate sustained ability to meet CARB and EPA Option 1 stringent standards.



Seems like these big trucks should also have a electric motor and battery or supercap sized for mountain driving energy recovery (a big safety improvement) or at least stop and go driving.


It has been some time since we heard any news from Achates. Albeit that this article sounds impressive, we should also note that also conventional engines will be able to meet future CARB and US EPA emission limits. In due time, of course, since engine manufacturers are normally in no hurry to meet emission limits before they are enforced. In my quick assessment of the article, it seems as Achates might be able to meet these limits with less aftertreatment hardware and thus, reduced cost compared to a conventional engine. Nice!

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