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US Army awards $4.9M contract to Achates Power and AVL for Next-Generation Combat Engine based on Achates two-stroke, opposed-piston technology

The US Army Tank Automotive Research, Development and Engineering Center (TARDEC) has awarded Achates Power, Inc., developer of a two-stroke, compression-ignition (CI) opposed-piston (OP) engine (earlier post) and AVL Powertrain Engineering, Inc. a $4.9-million contract for design and construction of the Next-Generation Combat Engine.

As outlined in the solicitation (TARBAATOPIC27), to serve a wide range of US combat and tactical vehicles, the engine must deliver superior fuel efficiency, high power density and low heat rejection and will be multi-fuel capable. It should also be of a scalable design to maximize value to the Government and military vehicles. To meet the program requirements, AVL proposed an engine based on the Achates Power opposed-piston, two-stroke technology, which includes more than 1,000 innovations covered by patents and patent applications. This the the sole award from the solicitation.

When benchmarked against leading, conventional diesel engines, the Achates Power engine demonstrates:

  • Lower cycle average brake-specific fuel consumption

  • Similar engine-out emissions levels

  • Less than 0.1% fuel-specific oil consumption

  • Reduced weight and complexity

Achates Power has accumulated more than 3,600 hours of dynamometer testing and achieved 47.5% brake thermal efficiency. The brake thermal efficiency advantages demonstrated by the Achates Power engine are published in SAE International Paper 2011-01-2216 (earlier post) and include:

  • Less heat transfer due to a lower ratio of surface area-to-volume in the combustion chamber caused, in part, by the elimination of the cylinder head; Leaner, faster and earlier combustion;

  • More favorable relationship between the compression and expansion ratios realized from asymmetric timing of the intake and exhaust events;

  • Higher effective flow area due to ports on each end of the cylinder; and

  • Higher scavenging efficiency from a high stroke-to-bore ratio.

Since first releasing our engine’s results, we have demonstrated a steady increase in brake thermal efficiency, all while meeting the toughest, global emissions standards. And with high brake thermal efficiency—combined with the engine’s flat fuel map, very low engine-out soot and demonstrated durability potential—we have the utmost confidence that we will meet TARDEC’s program objectives. Over the next few years, we look forward to collaborating with AVL on the final design of this Next-Generation Combat Engine.

— David Johnson, CEO, Achates Power

Achates Power has made excellent progress overcoming the challenges commonly associated with two-stroke engines: emissions, fuel economy, oil consumption and durability. The fact that their engine has very high efficiency and power density, along with low heat rejection to coolant, makes it well suited for military applications.

—David Merrion, former EVP of engineering at Detroit Diesel, Achates Power technical advisory board member, and two-stroke engine expert


  • Randy E. Herold, Michael H. Wahl, Gerhard Regner, James U. Lemke, David E. Foster (2011) Thermodynamic Benefits of Opposed-Piston Two-Stroke Engines (SAE 2011-01-2216)



At 47+% efficiency + light weight + multi-fuel etc, a small version could be an excellent unit for PHEVs?

What are our Big-3 and 20+ other car manufacturers doing?


The other big manufacturers don't want to invest in this unproven technology - they would if the government gave them money though. However, with the federal government getting out of GM, the gravy train is over and the unions have been taken care of (even though the taxpayers have NOT). Achates will continue to be responsible for all the risk - as soon the bugs have been worked out and the technology has been established to be viable, they will be snapped up by an automaker...and maybe snuffed out.


The Army will now share the risk with Achates.

If this technology proves to be viable, Achates may be snapped up by an automaker... maybe making the Achates investors a lot of money.


If it works out it will have to be shelved for national security reasons?


new engines are a hard sale

Scuderi, Opo Engines, Achates and others have reported interesting results but none have attracted Automakers attention yet (in fat only MCE5 with their variable compression ratio engine have partnership with Peugeot for real demonstration)

it is easier to potential customer in aviation, military, truck, boating, generator


I looked at their videos on youtube, bing video, google videos, lycos videos, quebecor videos, etc and they just have a small in lab small motor. I don't think that they have something good enouph and till now they didn't move a car nor a tank. I won't wait for this.

Till then postpone any expences toward any kind of new engines and hybrids and bevs actually sold everywhere by cheap poor folks like gm, nissan honda and toyota,and wait and insist for someone beginning commercialisation of a new efficient low cost engine.


Better engine efficiency = better fuel economy = better national economic security.


This is exactly what I advocated right here ten years ago. I offered it free to anyone who was willing to develop it. Nobody was willing to even look at the concept then. It could be on our roads now, reducing fuel use by nearly 50%.

I'll not hold my breath waiting for this to actualize.


Yes E-P. Increased-better national economic security may be the key to USA's future. Reducing road vehicles' (some 250 millions or so) fuel consumption by 50% or more would be an important step?

Doing without inefficient-dangerous human drivers could also do a lot towards that goal.


@ ejj

You don't have to be concerned about the unions. The Rethuglicans are taking good care of them.


Lucus...Toyota was the first to mass produce 50+ mpg HEVs using about 75% less fuel than the USA's fleet 2000 average.

The Big 3 maintained that HEVs were ridiculous and would not sell. They tried their best to block them but failed. Toyota held fast and 12+ years latter over 1 million HEVs/year are being manufactured + a growth rate of 100%/year for many models.

More efficient ICEs may follow the same resistance road?

Henry Gibson

Mr. Pescara will be pleased that long after he is dead the opposed piston engine is still being considered, to say nothing about Mr. Junkers, Commer TS3 or the DELTIC, but hydraulic hybrids greatly improve operational efficiency without engine modifications. The EC government has more reason to require the use of Artemis Digital hydraulic or other hydraulic hybids than it does to require new air-conditioning fluids. The EC should also impose very high taxes on large automotive engines.

Capstone or Bladon turbines might be combined with hydraulic technology for clean, quiet and efficient operation. ..HG..

Liviu Giurca

A new ultra-efficient low cost engine with opposed piston is presented in the site www.hybrid–engine-hope.com . Most of manufacturers reject from start a two-stroke solution. The new concept is available also as four-stroke opposite piston engine without exotic mechanisms. It is much simpler than Achates Power engine, having same advantages.

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