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California ARB awards $7M for ultra-low NOx heavy-duty diesel truck demo project with Achates opposed-piston engines

The California Air Resource Board (CARB) is awarding $7 million to CALSTART to develop a Class 8 truck that will achieve a 90% reduction in NOx along with a 15-20% fuel efficiency improvement. The project will build and install diesel-fueled two-stroke compression-ignition Achates Power Opposed-Piston Engines into Class 8 demonstration trucks that will be road-road ready in 2019 and operate in fleet service in California in 2020.

California’s ultra-low NOx emissions standard is 0.02 grams per brake horsepower-hour (g/bhp/hr). This program will demonstrate the first diesel engine to comply with the state standard. In addition, the engine will emit 10% less CO2 than the 2027 federal greenhouse gas requirement.

The project is part of CARB’s Low Carbon Transportation and Fuels Investments and Air Quality Improvement Program. CALSTART will serve as the project grantee and administrator.

The project team, led by CALSTART, includes a heavy-duty truck manufacturer as well as Achates Power and leading suppliers in the powertrain and emissions industry. California’s South Coast Air Quality Management District, the San Joaquin Valley Air Pollution Control District and the Sacramento Metropolitan Air Quality Management District also are investing in the project.

Achates Power, founded in 2004, currently has a number of development projects underway spanning a variety of applications of its opposed-piston engine architecture, from light-to-heavy duty.

At the 2018 North American International Auto Show (NAIAS) in January, Achates Power and new development parter Aramco Services (earlier post) showcased a Ford F-150 fitted with a 3-cylinder, 2.7-liter Opposed-Piston Gasoline Compression Ignition (OPGCI) engine. (Earlier post.)

In 2017, engineers from Achates presented a paper (2017-01-0638) at the SAE World Congress (WCX 17) describing the development of a 55% brake thermal efficiency (BTE) commercial heavy-duty opposed-piston engine without the use of a waste heat recovery system or turbocompounding.

The two-stroke OP engine described therein employed currently available engine components, such as supercharger, turbocharger and after-treatment and featured a uniquely designed piston bowl shape to enhance mixing with a swirl-to-tumble conversion as the piston bowls approach minimum volume. This design improved fuel-air mixing and hence resulted in low soot values, increased indicated thermal efficiency (ITE)—due to better combustion phasing because of faster mixing controlled combustion—and lower NOx because of improved area-to-volume ratio and lower fueling requirement per cycle.

An optimized system included a high trapped compression ratio piston bowl, ports designed to provide best scavenging performance, thermal barrier coating on piston bowls and dual injector with an optimized spray pattern layout.

The Achates engine model destined for the Class 8 demonstration is related to the 9.8-liter unit, but with modifications, said David Johnson, Achates CEO. For one, it’s a bit bigger: 10.6 liters.

We’re aiming at the heart of the Class 8 market. The engine will deliver 450 hp and all the necessary torque, along with the ultra-low NOx.

—Dave Johnson

With the reduction in steady-state engine-out NOx from the engine, meeting the ultra-low NOx specification is really a problem of cold starts, Johnson said; i.e., warming up the aftertreatment catalyst quickly.

Achates determined in earlier work that it could run in a “catalyst light-off mode”, creating the heat required to bring the aftertreatment fully online while running the engine in a relatively clean condition. (Earlier post.)

With low engine-out NOx and high enthalpy going to the aftertreatment system, we believe that we are able to reduce the aftertreatment warmup from 600 seconds to less than 300 seconds. That will enable us to meet ultra-low NOx tailpipe standards. We also deliver a significant fuel economy improvement.

—Dave Johnson

Achates engineers will be presenting a new paper at World Congress this year describing more about this approach, and presenting test data.

Funding for the grant comes from California Climate Investments, a statewide program that puts billions of Cap-and-Trade dollars to work reducing greenhouse gas emissions, strengthening the economy and improving public health and the environment—particularly in disadvantaged communities.

The Cap-and-Trade Program also creates a financial incentive for industries to invest in clean technologies and develop innovative ways to reduce pollution. California Climate Investments projects include affordable housing, renewable energy, public transportation, zero-emission vehicles, environmental restoration, more sustainable agriculture, recycling and much more. At least 35% of these investments are made in disadvantaged and low-income communities.


  • Abani, N., Nagar, N., Zermeno, R., chiang, M. et al., (2017) “Developing a 55% BTE Commercial Heavy-Duty Opposed-Piston Engine without a Waste Heat Recovery System,” SAE Technical Paper 2017-01-0638 doi: 10.4271/2017-01-0638


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