By on January 15, 2018

Achates Power Opposed Six image 1

Thus far, the North American International Auto Show has been a truck festival  – more specifically, a green-truck fest. Ram showed a hybrid 1500. Ford revealed their V6 diesel. Chevrolet surprised with an inline-six diesel. Clearly the Big Three are looking at the calendar, with a big red circle over the 2025 CAFE standards looming like a dark cloud.

Achates Power, a fourteen-year-old startup from San Diego, has a different idea. By combining a variety of existing technologies – some of which date from before World War Two – they have developed an engine that they expect to meet 2025 fuel economy standards, emissions standards, and most importantly, the performance standards of light-truck buyers.

How does 37 mpg sound in a half-ton truck? That’s on gasoline. The Achates engine can also manage 42 mpg in the same truck running on diesel.

Indeed, the diesel engine is the focus of Achates, while compression-ignition with gasoline is a later development focus. The innovation on this is with the layout of the engine itself. Rather than the typical inline or vee, this engine is:

  • Three-cylinder
  • Six-opposed-piston
  • Direct-injected
  • Two-stroke
  • Turbocharged and supercharged

In other words, a mouthful. As the cylinders are firing toward each other, there are a pair of crankshafts, but no cylinder heads. The lack of a complex valvetrain and cylinder heads will minimize heat and friction losses.

At 2.7 liters, the OP GCI (Opposed Piston Gasoline Compression Ignition) produces 270 horsepower and 480 lb-ft of torque, with a 16.5:1 compression ratio. The diesel version should deliver similar power figures, at 18.5:1 compression.

The Achates Power engine was developed with a $9 million grant from the US Department of Energy.

Achates Power Opposed Six image 1

For the aircraft buffs in the house, this powertrain configuration might seem familiar. Junkers developed an opposed-piston diesel in the 1920s to power various aircraft. It was relatively successful despite the higher relative weight to avgas-powered radial engines.

Achates Power Opposed Six image 4

I’m wondering how the engine will sound. I’m secretly hoping the exhaust note will resemble the two-stroke supercharged Detroit Diesel powerplants known as the “Screaming Jimmy.”

Achates Power announced a partnership with Aramco Services Company here at the 2018 Detroit Auto Show, as the Saudi-based oil company has an interest in making internal-combustion engines sustainable for the foreseeable future. Thus, Achates and Aramco have fitted a diesel 2.7-liter powerplant into a Ford F-150. They assure me that this isn’t a Ford-specific project – indeed, Mark Subramaniam, VP of Business Development for Achates Power, tells me that they have worked with many OEMs on various projects, and are actively shopping this engine technology to many potential partners. They expect to have the engine running and driving in the F-150 later this year.

[Images: © 2018 Chris Tonn; GIFs and truck image courtesy Achates Power]

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62 Comments on “Achates Power Brings an Efficiency Revolution To Detroit...”

  • avatar

    Cummins has been working closely with Achates on this technology to be used in certain vehicles for the Army.

  • avatar

    “When Achates Power is production-ready with its engine—expected within the next three years-existing emission after—treatment technologies will have a role.” – 29-Nov-2010 03:37 EST

    Any day now..

  • avatar

    So upright it’s an inline, if you flop it on its side, is it a boxer?

    • 0 avatar

      @Lightspeed – No. A boxer has its cylinders “flat” on each side at 180 degrees to a common crank. The two piston banks are flat. A”V” engine has its cylinders obviously in a “V” configuration to a common crank.
      An “inline” engine has only one bank of cylinders to a common crank. Whether it be straight “up” or at an angle, it doesn’t matter. Examples would be GM’s 250ci inline 6 or Chrysler’s 225ci slant 6.

    • 0 avatar
      The ultimate family-friendly hybrid vehicle is finally here.

      On one side it’s a /, and tilted the other way it’s a .

      “Slash Six” would look good in silver script on the fender panel.

  • avatar

    I eagerly await the sound, too. Noise, Vibrasion, & Harshness (NVH) may be the achilles heel for this engine.

    My tolerance for naturally aspirated two-stroke Detroit Diesels is very low. Add a ‘T’ for Turbo to end of the Detroit Diesel model designation and it is a whole new animal. The addition of a turbo makes the sound seem much more mellow. A 6V-53T in an old 1-ton flatbed would be fun.

    Search YouTube for videos of a 6V-53T since I can’t post links.

    • 0 avatar

      Flat 6s have perfect primary and secondary balance. This thing’s gonna be smooth, and given that it has 3x cylinders with 2x the firing pulses per RPM it’s gonna sound good even with low revs. At 4K this will sound like a conventional 6 cylinder at 8K.

    • 0 avatar

      @ EqauipmentJunkie

      “My tolerance for naturally aspirated two-stroke Detroit Diesels is very low. Add a ‘T’ for Turbo to end of the Detroit Diesel model designation and it is a whole new animal”

      There’s no such thing as a naturally aspirated two-stroke Detroit; they all require a supercharger for scavenging and a mild supercharging effect. But I get what you’re saying about a turbo mellowing them out, although I actually prefer the sound of a non-turbo … a 6-71 at full romp definitely gets your attention :)

      BTW some trivia for those that weren’t aware: the old-school blowers people would add to their cars, e.g. “671” or “1471” blowers, were from these Detroit Diesels. The name was from the engine model it was used on, which in turn meant the number of cylinders (e.g. 6 or 14 cylinders), and the 71 being the cubic inch displacement of each cylinder. The 71-series went from 1-cylinder all the way up to 24. These engines also share a sort of design philosophy with GM’s locomotive engines which were also two-stroke diesels, except the displacement per cylinder was 710 cubic inches (there was also a 645 cid per cylinder version).

  • avatar

    This is a tall engine. With this configuration, why not make it laying flat?

  • avatar

    In a sane world, trucks would be paying gas guzzler tax just like regular cars.

    Cars with a combined fuel economy rating under 22.5 mpg pay it. Silverado and F150 are 20 mpg.

    • 0 avatar

      In a sane world we shouldn’t be using tax payer money to subsidize 100k Tesla buyers but here we are.

      • 0 avatar

        How do you feel about the subsidy to develop this engine?

      • 0 avatar

        We are now subsidizing 70 million trucks that should be paying gas guzzler tax in order to pollute. Why do you focus instead on the in comparison minimal amount spent on Teslas to bring positive change?

        • 0 avatar

          So we love “trucks” that happen to be exempt from the gas guzzler tax, and that includes midsize pickups, minivans, SUVs and such and we’d probably buy most of them anyway, even if they weren’t. We pay dramatically more for them by various other taxes and fees for the luxury, vs a cheesy little sedan. CAFE is still cracking down on the biggest offenders. And this is America where we’re sorta treated like adults in this area, along with automakers.

        • 0 avatar

          Pretty convoluted thinking. A tax is a penalty. No tax is not a subsidy.

  • avatar

    sarcasm/So is this an interference design?

  • avatar

    Similar configuration to the OPPO engine featured a few years ago on TTAC, although they had an unwieldy double conrod arrangement replacing the gear train. Wonder where they’ve gone? Everyone was going to use an OPPO engine, by golly.

    Back in the 1920s, Junkers invented both this Achates and the OPPO configuration. Nothing new under the sun. Fairbanks-Morse had the US license for the geared cranks solution, and the result was an 1100 horsepower version used in US fleet submarine diesels during WW2. Used in the Pacific, great engine for the time.

    These days, so much effort has been expended on port and combustion chamber design on gasoline engines, this opposed piston configuration looks quaint. No central park plug or direct fuel injector location possible. Yet according to PR, a miracle has occurred. Is this engine really as efficient as the new 40% efficient 2.5l in the new Camry? Surprising if it is. C/D got 45 mpg at 75 mph in the 2018 Camry, upon which Toyota spent much more than Achates government grant. Toyota also released a 2.8l 4 cylinder diesel for worldwide use 2 years ago with 44% thermal efficiency, highest around (not available in USA). Tough hill for Achates to climb.

    • 0 avatar

      Emissions is the big unmentioned factor.
      We could all be efficiency heroes if we didn’t have to run the EPA tests.
      That’s why it might be good for the military…someday…

      In other news, Cummins just got a quarter billion DoD contract for more V903s, which was intro’d in 1967.

  • avatar

    I am skeptical of the emissions viability of two stroke diesels. I just traded traded a 2016 Ram 1500 4wd diesel. It got mid to high 20s (and the occasional 30mpg highway tank) until the last dealer update. After that it was noticeably worse. Still better than my 2013 2wd Hemi.

  • avatar

    This type of engine was used in the Soviet tanks in the 1960s.

  • avatar

    Is there really an efficiency advantage to having opposed pistons in the same cylinder?

    • 0 avatar

      Yes, because there is no head area to absorb heat. There is also an emissions advantage with respect to unburned hydrocarbons. Other advantages are the port timing possibilities along with the cylinder clearing advantages to the flow. Balance should be excellent too. Disadvantages are the geared cranks and the fact that there are 2 of them. Engine size and weight/power are not great.

      • 0 avatar

        My immediate concern was weight and rotating mass as well. Crankshafts are heavy, beefy things – having TWO of them can’t be good. Valve trains in comparison are much lighter, thus the reason the dual overhead cam setup has become so popular. I’m waiting for F1 racing style cams that operated interdependently and hydraulically, thus allowing for all kinds of intake and exhaust tricks.

    • 0 avatar

      Interesting. My first thought was that it created more surface friction, as opposed to three cylinders with three pistons. That may not have been fair. Maybe I should have compared it to a six cylinder.

      I hadn’t thought of the lack of a place for heat to go or deposits to build up. I might have to ponder it a bit more.

      The part about inherent balance is an easy one anyway.


    • 0 avatar
      Guitar man

      Its needed to compress the charge. This is a two stroke engine.

  • avatar

    I’m kind of surprised no one has mentioned the Commer TS3 that was a 3 cylinder opposed piston engine.

  • avatar

    A 14-year old company is still a start-up? I hope their engines start up faster than that.

  • avatar

    Fairbanks-Morse (now a subsidiary of EnPro) has used and still uses this OP (opposed piston) tech for 2-stroke diesels for marine propulsion and electrical generation. I operated the 10-cyl/20 piston OP’s for several years. I would think the height would be a problem – our 1600hp engines were very tall due to the long stroke (19″ for each crank). OP engines I operated were relatively vibration free considering that the majority of the upper crank power went to the supercharger and not the load – balancing the output power from both cranks would seem to make this proposed new engine somewhat smoother in my opinion due to the opposed reciprocation and equal loading of the crankshafts. I am not sure that the claims made for efficiency are realistic but Fairbanks-Morse OP 2-stroke diesel engines have been in economic and reliable use in considerable numbers since the ’30s. 4-cycle OP engine on gasoline? I guess we’ll see on that one.

  • avatar

    Kept trying to figure out how they managed to develop this for 14 years in a row with just a $9 million DOE grant, until I realized it’s most likely Aramco propping them up because they don’t want ICE to die off or they’re going to be totally screwed.

    • 0 avatar

      The oil business wouldn’t completely go away, as there will still be demand for oil for rubber, plastics, and other synthetics, among other uses. But yes, demand (and prices) will decrease.

  • avatar

    Looks pretty cool. Playing with “valve” timing will be pretty easy playing with gating of the ports as well. I’m a little disappointed with the output given the size and complexity of this thing… but 480lb-ft = high average power right in the meat of the rev range.

    I agree with whoever said they need to lay this thing flat. Lot of possibility here though. With 4 cylinders and cross plane cranks this would sound like a V8. And with double the power pulses it will have double the pitch for a given RPM. Imagine having a ~12,000 RPM “sounding” engine in a street car. Very cool stuff but we’ll see.

  • avatar

    I’m amazed to see this!

    I had thought of this as a bright idea–why have the head absorb the power stroke. It’s just the practical considerations.

    But now, that I read that Junkers did this in 1920s, and that other companies have used this principle with some success, it’s not a secret to automakers.

    If they, with their considerable resources and experience, cannot address the limitations of this design, I find it hard to believe a $14 million start-up can.

    Great article though, thanks!

  • avatar

    I wonder how reliability will be on ultra low sulfur diesel fuel.

  • avatar

    At Oshkosh 2015 I came across the Gemini 100 aircraft engine.

    It is, essentially the same design. One interesting thing on the Gemini was that the the cylinders were made of steel and fit into the block, making them easily replaceable.

    One benefit of this design is it turns the ide of a “bottom-end” overhaul on its head. Since the cranks are where the top end would be it makes inspection of the crank bearings much easier in a typical aircraft installation.

    One important note for aircraft applications is that Jet-A (used by aircraft diesel engines) weighs about one pound more per gallon. The weight savings of te Gemini design ar offset by the 25 pound increase in fuel weight in a typical application.

    Sadly, as with most innovative aircraft engines, it made a splash and then disappeared.

  • avatar

    I wonder what type of emissions equipment these will need as two-stroke gasoline engines? Also, I assume it will use oil injection, or some other way to premix? An oil tank that has to be filled periodically, like a DEF tank?

    • 0 avatar

      Agreed, emission regulations killed cylinder port engines before. They’ll have to be some way to fiddle with it to keep emissions acceptable.

    • 0 avatar

      I rather doubt a need for “premix” or oil injection in this proposed 2-cycle gas version. A pressurized oil system as used in 4-cycle engines would work fine – pressurized oil systems work well in existing 2-cycle diesels with little to no burn-off of the lubricant. Most 2-cycle engines we Gringos are familiar with that use “premix” oil/gas (trimmers, chain saws, et al) are for simplification and weight reduction to eliminate the added lubrication system hardware and complexity.

  • avatar

    Sounds interesting.

    I’ll believe it’s all that when it *ships*, though.

  • avatar

    I’ll see your two crankshafts and raise you one:
    The Napier Deltic diesel with 3 pairs of opposed pistons per bank in a delta configuration, 3 cranks, and 3 banks of cylinders, for a total of 18 pistons. See

    Although later adapted for locomotive use, the Napier Deltic was originally developed for British Motor Torpedo Boats (PT Boats), including the wonderfully named Norwegian “Nasty” Class boats.

  • avatar

    This doesn’t need pre mixing like a traditional 2 stroke as the crankshaft is like a 4 stroke aka it’s not for compressing of the combustion gas.

    That being said although this won’t have the oil consumption issues of a 2 stroke I still think it have issues with oil consumption due to using sleeve valves as the oil control ring pass.

    There are several video’s online that show how it works such as

  • avatar

    There have been a lot of opposed piston engine designs and in recent years I’ve seen maybe a half dozen different startups using some kind of opposed piston setup. So far none have come to market. Ecomotors looked promising, announced all sorts of deals with Chinese companies and now their website is offline.

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