Automotive Engineering - April 2021 - 47

Q&A

Development of Achates' 10.6-L heavy-duty diesel, shown here in a
Peterbilt tractor, was funded by California's ARB.
What's the status of the OP engine for pickups?
That's our third big project: the 2.7-L, 3-cylinder opposed-piston truck engine that's funded by the Department of Energy's
ARPA-E [https://www.sae.org/publications/magazines/
content/17autp02/).We finished the first stage of that project,
running gasoline compression-ignition. It's installed in a Ford
F-150. At the moment it's about 10 percent more efficient, on a
drive-cycle basis, than Ford's most efficient engine in the F-150.
Gasoline is hard to combust at low temperatures, but the
OP engine can run compression-ignition with gasoline without any additional heat source. We can control the degree of
cylinder scavenging; at low loads we keep most of the exhaust gas in cylinder. This has a double benefit: it keeps the
trapped gas hot for stable combustion, with inherent NOx
mitigation because we have internal EGR. So, the OP is the
perfect architecture for low-reactivity fuels as we look to cooptimize engine and fuel with Aramco.
We received a follow-on grant in late
2019 to continue the program. So, we
brought in Ricardo as the prime subcontractor. That follow-up program has two
goals. The first goal is to further improve
the efficiency. We think we can get to a
20 percent advantage over any other
production gasoline engine used in light
trucks. The second goal is to significantly reduce the weight and cost of the
engine. The prototype engine is fairly
heavy. In this next phase we're going to
reduce weight significantly, to where it's
competitive with a light-truck diesel.
Our aim for the second-generation 2.5-L
is to deliver diesel-engine efficiency
with gasoline fuel. Ricardo is a perfect
partner; they're world-class in engine
design and expert at optimizing mass in
every component.

Achates achieves low-NOx engine-out emissions through precise control
of cylinder scavenging.
Previously we talked about the potential for hybridizing the
Achates engine.
Yes - it's a great technology for both military and commercial
applications. We have a project funded by ARPA-E, for a hybrid
opposed-piston engine. We're working with the University of
Michigan on that project; they're doing development and testing
of one of our engines now. Anna Stefanopoulou [professor of
mechanical engineering, William Clay
Ford Professor of Technology, and SAE
Fellow] is the project's 'guru'. Much of the
work they're doing, on controls, is headed
by Heath Hofmann [professor, electrical
engineering and computer science].

OP is the perfect
architecture for
low-reactivity fuels
as we look to cooptimize engine and
fuel with Aramco.

AUTOMOTIVE ENGINEERING

What's your compressor strategy and
hardware?
Up until the middle of 2020, all the prototype engines used a turbocharger,
mostly off the shelf, and a supercharger
primarily from Eaton, to do our boosting work. We're a 2-stroke engine so we
have no pumping loop in the combustion cycle. Our direction now is toward
electrification - some type of e-turbo
along with an EGR pump. Our new engines under test are employing some of
those capabilities.
April 2021 47

https://www.sae.org/publications/magazines/content/17autp02/

Automotive Engineering - April 2021

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