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Achates showcases 2.7L, 3-cylinder opposed piston gasoline compression ignition engine in F-150; estimated 37 mpg combined

At the North American International Auto Show (NAIAS), 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.)

Fabien Redon, Vice President, Technology Development at Achates, said they estimate that the OPGCI pickup will achieve 37 mpg (6.35 l/100 km) on the combined cycle—nearly five MPG better than the proposed CAFE 2025 requirements for a vehicle of a similar size. The OP engine produces 270 hp and 480 lb-ft (651 N·m). This performance is achieved without vehicle modifications and is projected to cost $1,000 less per vehicle than widely accepted technology roadmaps currently being considered by OEMs, Achates said.

The Achates Power Opposed-Piston (OP) Engine is engineered to achieve superior thermal efficiency by virtue of its lower heat losses, improved combustion, and reduced pumping losses.

The OP Engine eliminates the cylinder head for an improved surface-area-to-volume ratio of the combustion chamber for reduced heat transfer and rejection. In addition, conventional engine valvetrain and related components are eliminated, and due to the architecture the OP Engine offers a reduction in the aftertreatment system size and cost. A comparison between the 2.7L OP Engine and a comparable V6 with supercharger shows a part reduction of more than 60%, enabling an approximate 10% cost reduction.

To fit the OP engine—with its fundamentally different shape—into the F-150 engine bay, Achates packaged its engine in a V-shape (approx. 30˚), with the cylinder bank angled on one side and the air handling and auxiliary units packaged on the other, Redon said. The pictures and video below illustrate the major components.

Achates Power Aramco 2-7L OP Engine Animation

Achates Power Aramco 2-7L OP Engine Animation

We chose to demonstrate our ultra-clean, ultra-efficient OP Engine in a full-size light-duty pickup truck because of the significant need and opportunity for improvement in this segment. These trucks are driven more miles, sold in higher volume, consume more fuel and emit more CO2 than other light duty vehicles. Using our OP GCI engines in light duty trucks would reduce CO2 and fuel usage in the same way as completely eliminating half of all cars sold each year. Using our OP GCI engines in future light trucks has the same fuel savings and CO2 reduction as completely eliminating more than half of the cars sold each year.

An Opposed-Piston Engine is 30-50 percent more fuel efficient than comparable diesel and gasoline engines, it is a no-excuses way to meet future efficiency and emissions standards. The technology and infrastructure to meet these future standards exists and will be available for consumers in the near future.

—David Johnson, president and CEO, Achates Power

Achates Power is showing the light duty demonstration pick up truck in the Aramco display as part of a joint development agreement, which formalizes the cooperative relationship between the companies. Achates Power and Aramco have agreed to work together on a series of projects to develop and demonstrate highly efficient and clean OP engines. The first project to be announced is the in-vehicle demonstration of the 2.7L OP Engine.

For its part, Aramco Services has been investigating gasoline compression ignition engine technology for a number of years, and came to the conclusion that it would be mutually beneficial to work with Achates, with that company’s decade-plus worth of expertise and intellectual property in the field, said David Cleary, Research Center Leader at Aramco Services Company.

Achates has been developing diesel-fueled (compression ignition) opposed piston engines since its founding in 2004. The company has demonstrated substantial fuel efficiency savings in diesel applications with a high indicated thermal efficiency of 53%. (Earlier post.)

The OP GCI engine—an effort to combine the benefits of compression ignition with a readily available fuel source (gasoline) in the highly efficient opposed-piston architecture—was designed and developed by Achates Power with a $9-million award from the Department of Energy’s ARPA-E in 2015, along with partners Delphi and Argonne National Laboratory. Testing of the OPGCI engine was conducted at Argonne, and Achates Power facilities in San Diego.

Development and testing of the new 2.7L engine will continue at Achates Power facilities, and at Aramco Services research center in metro-Detroit, for both diesel- and gasoline-fueled versions. (Earlier post.) Based on current testing, the engine is anticipated to be fully integrated into the vehicle and drivable in late 2018.






I normally never comment on ICEs gas guzzling machines, but smaller OP engines could be a way to reduce liquid fuel consumption by 30% to 40% now.

At 37+ mpg for large heavy pick ups, would represent a significant reduction in CO2 and pollution emission.

Smaller lighter cars could eventually go 50 to 55 mpg, reducing pollution and GHGs significantly.

A smaller (1.0 L to 1.5L) OP could be very efficient for HEVs and PHEVs?


This could make a good range extender for PHEV delivery trucks.


I'm am very impressed, 37mpg on the best selling vehicle in the US would no doubt raise the CAFE, i mean even sedans or much smaller vehicles might struggle to get those numbers.

The statement about being the equivalent to removing half of the cars on the road is impressive. Trucks, especially work trucks drive a lot of miles, so starting with the hungriest of all the ICEs is a smart move. I don't think they are wrong with that statement.

Hopefully they get into production, not just some aftermarket add on. I hope Ford or someone reaches out and makes an arrangement. It not unheard of for other makers to put in third party engines, or even competitor engines in cars, so hopefully they make this successful. Or just develope competing technology.

Smaller lighter cars could get into the upper 60mpg range if this truck can get into the high 30s. My car can break into the 50s, and there is a lot that they could do better with the powertrain.

if it works, this is probably the last great hurrah from the ICE, it makes sense to use gasoline, smaller particles, less emissions worry. But they'll still likely need the equivalent of DPF or a three way catalist.


Is there something about Opposed-Piston Ignition that facilitates low octane combustion?

Brian P

The surface-to-volume relationship of the combustion chamber is better during the combustion phase with this arrangement (should favor lower heat losses), but ... call me a skeptic because of the piston porting that is inherent in this design. There is lubrication - oil - on the crank side of the pistons - the piston rings and cylinder walls require lubrication. Every time the piston rings pass the ports, a little bit of oil tends to get out into the port, and that's either going into the cylinder (intake ports) or out the exhaust (exhaust ports). If the rings are supplied with adequate lubrication, the emissions are worse. If the rings are supplied with sparse lubrication, longevity suffers.

Detroit Diesel built piston-ported two-stroke diesel engines for decades, even using electronic injection control towards the end, and with all that experience, could not solve the emissions problems, and switched to four-strokes.

I see nothing about this engine that is indicative of a magic solution to the piston porting emissions versus lubrication trade-off.

I share the same skepticism about ALL of the opposed-piston two-stroke concepts and for the same reasons.


Well hopefully they have a solution that Detroit diesel failed to realize. Rings really haven't progressed too much, but spray in liners and coatings have on sidewalls of cylinders have. So they might have a trick, perhaps a certain novel way of stacking the rings, or a 3D spray pattern, or some novel material.

At least it shouldn't be as troubling as a wankle as far as apex seals go.

If this goes on sale, no doubt we'll see this engine tested and analyzed by the OEMs, the general public, and perhaps someone will run it through its paces quickly and we can get some real world insight.

The biggest problem I see is you really can't overhaul this engine. You'd have to cut the rods just to get the pistons out after a while. I mean that's a solution, but it's interesting to think about.


The ability to use compression ignition (HCCI, or whatever you want to call it) of low-octane and low-cetane fuel in an opposed piston engine has nothing to do with surface/volume ratio of the combustion chamber (though it is good for efficiency). However, it is well-known in the past that 2-stroke engines are better suited to compression ignition of low-cetane fuel than 4-stroke engines. The main enabling feature is that the level of rest gas – call it “internal EGR” if you like – can be controlled in a way which is very, very difficult on a 4-stroke engine. In essence, you control the scavenging process. It is plausible, in my mind, that an opposed piston engine is even better in this respect than a conventional 2-stroke engine. Recall that longitudinal scavenging improves with increasing stroke/bore ratio. Large marine 2-stroke engines can have a stroke to bore ratio of up to 3.5:1 and they are the most efficient combustion engines we know of (~55%). This ratio is lower for Achates but it is still a factor of 2 better than a conventional 2-stroke engine, e.g. the Detroit Diesel engines. In addition, you can use cooled and uncooled EGR. This gives you almost total control of EGR and in-cylinder temperature; crucial factors for obtaining a large speed-load area of HCCI (ideally: 100%).

Detroit Diesel once had a 92-series engine that ran compression ignition with CNG. Due to the very low cetane level of CNG, they had to use a glow plug. Glow plugs were already in use on their methanol (M100) engines. One aspect to consider here is that glow plugs at that time were unreliable, if you had to use them more than only for starting the engine. Today, this is not an issue (e.g. ceramic glow plugs). The engine was never launched in production and DDC had already then started the shift to 4-stroke engines for many other reasons. Note that a low-octane gasoline, or naphtha, should have much better properties than CNG.

In summary, we know that Achates has many advantages over the mentioned known technology with their OPGCI. Whether they will experience any show-stoppers on the road remains to be seen.


I forgot to mention that Achates consider the oil consumption problem to be solved. At least they have published data (e.g. SAE papers) on very low oil consumption. It is, for sure, more difficult to get low oil consumption on a port-scavenged 2-stroke engine than on a 4-stroke engine but if they have reached a low and acceptable level, it is fine with me. This is not a likely show-stopper anyway.


Gemini has one for aircraft.


Note that 30-50% more efficient translates to 23% to 33% fuel savings, not 50%.  (Still great but a long way from cutting it in half.)

I wonder how much of this comes from reduction in throttling losses at part-load.

The linear configuration lends itself to flat packaging of smaller engines, which would lower the center of gravity.  That's an attractive feature right there.

Liviu Giurca

52% thermal efficiency without heat recovery was obtained in 1993 by Dr. Marius Paul engine. See .
For even more efficient engines I think now is a time for heat recovery:

Tim Duncan

Peter_XX & Brian P, They have a several utubes on various design details, worth checking out. One was real time oil consumption monitoring they put in their development cell called Da Vinci Lubricant Oil Consumption (DALOC) sulfur-trace analyzer measurement system, which uses a sulfur tracing technique. It looked quite state of the art and very helpful. All the engine test cells I have been in, never seen anything like it. Before this I thought an AVL weight cart ( I have never run an oil consumption test) was what everyone did. None-the-less in 2012 they claim a weighted speed/load map FSOC of 0.018% vs 0.25-0.60% for historic 2-stroke diesels like the DDC. They have 2019 SAE paper out, but I have not read it yet.

Another aspect they discussed in an SAE paper below was liner cooling and warpage control. Titled, "Cylinder Cooling for Improved Durability on an Opposed-Piston Engine"

They had some nice CFD coolant models, reasonable heat loading assumptions as the piston traveled, etc. Paper was from ~5yrs back and design solution shown was an impingement cooling arrangement on a short band of the liner at TDC, then tailored but more conventional on out towards the ports. I believe the exhaust port partitions (can't think of proper name) were drilled axially for coolant. Anyway, very aggressive cooling, reminded me of work in turbine hot sections. Anyway they claimed a TDC to outer end of liner delta that was miniscule, vs the starting case (which may or may-not have been a valid or totally fair baseline). I don't recall the circumferential delta, but the liner temp was LOW. I am familiar with designing around diesel 4-stroke liner temps and these were chill. I don't know much about the tribology of rings and liners, but agree with comments, its no joke. I just wanted to mention their work toward a cool, straight liner & say it may be a significant enabler of low lubrication compression rings & PRL durability.

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