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ARPA-E awards $2M to Achates Power for opposed-piston engine for hybrids; U Mich, Nissan partners

Achates Power was awarded $2 million in funding from the US Department of Energy’s Advanced Research Projects Agency-Energy (ARPA-E) for the development of a Highly-efficient Opposed-Piston Engine (HOPE) for Hybrid Vehicles. (Earlier post.) Achates Power has partnered with the University of Michigan and Nissan Motor Company., Ltd. for the project.

The project builds on the successful development of the OP Engine and expands our research and development into the hybrid and range-extender market. The inherent balance and power characteristics of the OP Engine makes it an ideal powertrain in a hybrid solution, providing vehicle manufacturers a cost-effective solution to improve vehicle fuel efficiency and reduce carbon dioxide emissions.

—Fabien Redon, Chief Technical Officer, Achates Power

The HOPE project will develop a unique single-cylinder OP Engine design with the goal to minimize energy losses typical in conventional internal combustion engines.

A motor-generator integrated on each engine crankshaft will provide independent control to each piston and eliminate all torque transmitted across the mechanical crankshaft connection, thus reducing engine size, mass, cost, friction, and noise.

The application of high-bandwidth power electronics will further improve engine efficiency through the real-time control of the piston motion and combustion process.

I am excited to design and optimize the controls that will free this opposed-piston engine from the mechanical constraints of the crank and gear mechanism through the electric motors; it is like breaking the shackles and unleashing its true potential. Along with the freedom, though comes the responsibility of highly precise control and coordination of the piston motions to maximize efficiency and ensure a smoother operation.

—Anna G. Stefanopoulou, Energy Institute Director and Professor of Mechanical Engineering, University of Michigan

The University of Michigan Energy Institute will contribute engineering resources and talent in the design and testing of the Highly-efficient Opposed-Piston Engine for Hybrid Vehicles, the project will look to leverage Nissan Motor Company., Ltd. experience in hybrid engine development.



Further financial support (subsidies, hand outs) for a dying technology is not justified. Supporting new technologies like SS batteries and FCs and REs would make be sense.


There are applications for range extenders and the like for military and civilian projects. We can and should have everything necessary to move forward.


I would have to agree with SJC on this - a good range extender would be a boon.
It means you can have a much smaller, lighter battery and always get home.
However, have Achates Power ever sold anything other than promises ?


A waste of money on yet another form of the ICE; developing the internal combustion engine in a never ending new configuration is moving backwards and a continuation of pollution for profits at the expense of our children's health and future well being.
The idea is to replace the ICE and our dependence on the fossil fuel it burns in the air. HD has it spot on; spend the money on developing the new, clean technology.


It sounded exciting back in 2010 when they started talking about it but 9 years later they are still developing it. Meanwhile the world keeps turning. BEVs are about 3 years away from being cost competitive with ICE sans subsidy and FCEVs may be viable in 6 years. Their window of opportunity is getting narrower.

Tim Duncan

I have been on this blog for 20 years, Battery has always been 3-5 years away. Meanwhile the much hated ICE keeps saving humanity (literally every day) exceeding ever environmental hurdle thrown at it, getting more efficient each year and staying affordable without subsidies.

I love batteries and have worked on many electric drive systems and vehicles. But we have to keep an open mind. All good ideas welcome. Because ICE utility is practically unprecedented in history & Batteries have a heavy lift.

Engines such as this can have fuel efficiency as good as a power plant. I have also worked a little with solar, wind power and grid mix. I’m just saying baseload requirements are real and not going anywhere. Thx.


I have a Niro PHEV and like it very much. About 50% of my miles are now EV. Cross country fill-ups take 5min (vs 50min) and $10,000 cheaper.

Any bets as to when BEVs reach 50% market share? Now <2%? Wake me up when it reaches 10%.

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The Achates Opposed Piston Engine is already very efficient, reaching as much as 55% BTE (153.7 g/(kW⋅h))at part load, reference:
So this would be interesting as a Range Extender in a Series Plug-In Hybrid (Nissan already uses a Series Hybrid in the e-Note).
Achates and Cummins are already using this engine in military applications so it would be great if it could be extended to HEV or PHEV for the military (Oshkosh Defense has a hybrid drive system for military vehicles).


“Battery has always been 3-5 years away. ”

In the past those saying batteries were three to five years away have mostly been either those looking for money to finance their endeavors or fans who were unrealistic. Batteries have now reached the point where they are adequate in all important aspects except two; cost and recharge time. For the next few years we can expect batteries t decline 15-20% per year. That should get the price where it needs to be in three years time.

Recharge times wil also continue to improve. Tesla’s announcement tonight puts their product line in the acceptable range. I doubt the rest of the industry is much more than three years behind Tesla.


I have a Niro PHEV and like it very much. “

Congrats. Excellent choice.

“About 50% of my miles are now EV. “

That would be typical for a PHEV with about 25 miles AER.

“Cross country fill-ups take 5min (vs 50min) “

Few people drive cross country on a regular basis who are not professional drivers. If you wanted a BEV for that purpose then the Tesla model 3 would probably be a better choice. Other viable options will be available in the coming years.

“and $10,000 cheaper.”

Locally the Niro Phevs start at a little over $29k while Chevy Bolts start at a little under $26k before subsidies. TM3s start at about 35k.

“Any bets as to when BEVs reach 50% market share? “

EVs will probably reach 50% of new car sales in the US around 2027. Norway is already there.
California will probably hit that sometime in 2023.


I'm amazed at the commenters here.  Achates comes along with an engine that achieves efficiency as good as some of the best low-speed diesels and comes close to SOFC and CCGT territory, and people are bad-mouthing it.

Come to think of it, I wouldn't be surprised if this engine could equal or even beat a CCGT if it was equipped with turbocompounding; don't underestimate the advantage from near-constant-volume combustion compared to the high entropy increase in constant-pressure combustion.

One of the best options for long-term energy storage is power-to-liquids.  An engine like this is an excellent prospect for turning liquids back to power.


“I'm amazed at the commenters here... are bad-mouthing it.”

My comments should not be misconstrued as bad mouthing the Achates HOPE engine. I’m still hopeful for them though the fact that Achates is groveling for a pittance in grant money is a reliable sign that commercialization is not imminent.

@Gryf What attributes do you think are holding it back in a REX application? Reliability? Noise? Vibrations? Emissions? Cost would not seem to be an issue in volume production.

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Good REX questions Gasbag:

Reliability: This is a "two stroke diesel" probably the the most reliable engine ever built. Originally developed by Junkers in 1930, the opposed two stroke diesel was used in aircraft, trains, and the Fairbanks-Morse 38 8-1/8 engine is used as a backup engine for nuclear submarines.

Noise: It is very quiet. The U.S. Navy used Nasty Class PT boats for covert operations during the Viet Nam War. These boats used Napier Deltic opposed piston diesel engines.

Emissions: The opposed engine is low in NOx (reference: . However, this is a sensitive issue with any diesel engine and all emissions must be accurately tested (just ask VW).

Cost is an issue since it is a diesel. Fuel injection, component materials, etc.are factors.
Also, what fuel? Probably Gasoline not diesel. Gasoline Compression Ignition or something like the Mazda spark-controlled compression ignition system. Finally, Size: this engine must be very compact, definitely less than 1 liter, 500-900cc.


Does this engine feel like a threat to all you EV fans? In the near future, probably not, since it will take a few years until we see something on the road. Development of a new concept takes time, and nothing (commercial) will happen until some big automotive player steps in (I do not refer to Cummins). However, if the competition is an EV with half a ton of batteries, this concept should have a fair chance when prices of rare elements will start to skyrocket in a few years. Considering the limited resources of rare elements, HEVs and PHEVs make much more sense than EVs, and for that we must continue to improve ICEs.


PeterXX is a partisan in this fight (he's an engine guy), but he's right.  If e.g. cobalt becomes an issue, lots of lithium battery chemistries are going to get a lot more expensive/scarce while the plain old ICE will hardly be affected.

Plugging my horse in the race for a minute, such shortages would push the sweet spot back toward PHEVs and maybe regular hybrids.  NiMH appears to use rare earths rather than cobalt, and rare earths are not rare so much as difficult and dirty to separate.

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Forgot to mention that Peter_XX (he's the real expert here on diesel tech) had a post last year in this blog on the Achates Engine which mentions "Internal EGR" which is in my reference emissions. Check:


“Does this engine feel like a threat to all you EV fans?“

Not at all. I think EV fans view it as a bigger threat to the incumbents. In a REX application it could address all the current short comings of BEVs and accelerate the migration to PHEVs. The bigger problem is that it wasn’t production ready as a REX yesterday. It is unfortunate that the are celebrating a research grant instead of opening a production facility.


“Considering the limited resources of rare elements, HEVs and PHEVs make much more sense than EVs, ”

Not to be pedantic but I think you meant BEVs instead of EVs as EVs includesBEVs, PHEVs, et al.
Most rare elements aren’t that rare. They are unprofitable. In 2016 thru the first half of 2018 we saw prices for cobalt, lithium, and spherical graphite double and triple as predicted. Additional sources came online and prices dropped in half. In spite of this industry average prices for batteries dropped by 18%.

There are designs for electric motors which don’t use any rare earth elements and batteries that use less of the more expensive elements. If the market dictates then these will come in vogue.

With that said I think PHEVs make a lot of sense but more AER is desirable.

PHEVs make a lot of sense but more AER is desirable.

Desirable is one thing, essential is another.  There are diminishing returns from additional battery capacity in any vehicle, starting with cost and going on to the weight penalty of hauling more batteries around.  From my calculations, we only need a 50% solution to get rid of petroleum entirely (the rest can be done with biofuels).  Since I'm already displacing 80% of my motor fuel with electricity, I'd say that 2013 PHEV technology is adequate to the task.  What we need at this point is to roll out more charging and systems to manage the additional demand which will result, and keep promoting the heck out of PHEVs using things like feebates and fuel consumption and emissions limits on the first 50 miles of travel.

Tim Duncan

@EP, Or we could put our crusader hats back in the museum and let the market work. Any one thinking nature must be saved from mankind clearly knows little of mother nature, she is and always will be a killer. No amount of taxes and regulations is going to change this or the climate. If and when BEVs & PHEVs fit/enhance people’s lives (many vehicles are about more than getting to a 9-5 job) better than ICE they should and will thrive.


Funny, I don't recall that "letting the market work" actually worked when Los Angeles was buried in smog every day.  Neither did it work in the seventies when the US economy was devastated by the oil price shocks.  Were the catalytic converter, smog checks, CAFE and the Strategic Petroleum Reserve "crusader hats", or sensible means of dealing with very pressing problems?

You can't fix a long-term problem with short-term thinking, and public policy is often required to get outcomes which aren't just races to the bottom.  Despite the recent surge in oil extraction, the US remains a net oil importer.  The shale boom cannot last forever, and diminishing returns will set in sooner rather than later.  Do you have a solution for this?  I do.  However, preventing another recession when the problem hits in earnest requires acting BEFORE everyone starts feeling the pain—while we still have the surplus wealth to build the replacements.  You can call that a crusader hat.  I call it being sensible and thinking ahead.

Tim Duncan

@ EP. Market driven Technological innovation will continue to find & extract oil. Predictions of Peak oil have been almost as bad as climate change and ice volumes. The enormous Canadian oil sands will also increase production when pipelines are built. Venezuela will get back to work eventually. Mexico and many other known fields will also have their shale revolutions.

As for EVs taking over soon, the only ones preaching this are AOC & other climate doomsayers and climate religion fanatics. As referenced in the article, serious predictions see increasing oil demand for a long time.

Regarding oil shocks, efficiency, emissions regulations & government cures, you need to consider/learn history. Externalities are hard to deal with prudently. Black swans that you want to fight are by definition unknowable, get over yourself a little. The link below is a start.


Too bad , they already had an engine that had better thermal efficiency than any internal combustion engine I’ve ever heard of and it’s being scrapped. This is the story of a corrupt industry with government backing in the works . “Here’s 2 million to start a new engine and forget the one you have already demonstrated until electric cars can take over or gas prices can be raised sufficiently .”

Conwell Boccia

Politics (government & private) are the greatest hurdles, not engineering. The 2 stroke delivers max RPM in 1/2 the time (getting the HP when you need it with smaller displacement) with reduction in weight, friction & complexity. 1 cylinder - 2 piston versions could power hybrids, 3 cylinder - 6 piston versions for non-hybrids. Electric vehicles aren't clean or efficient if you are making electricity burning hydrocarbon fuels. Success with Defense Dept projects may prevent seeing this in passenger vehicles for some time, again because of politics.

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