How a 70-year-old idea could make engines way more efficient

Posted: December 6, 2016 by oldbrew in Emissions, innovation, Travel

Achates engine design

Achates engine design

That’s the sales pitch for an opposed-piston alternative to today’s vehicle engines. No valves, no cylinder head. But will it get off the drawing board? WIRED reporting.

IF YOU POP THE hood on your car and yank out the plastic cover beneath it, you’ll see a beautiful bit of mind-boggling engineering: the internal combustion engine.

Today’s engines harness around 100 explosions of fuel and oxygen each second, generating massive power with minimal emissions. That’s great, but tightening pollution standards around the world mean automobiles must become increasingly efficient.

Electric cars offer one way forward, but they remain expensive and hobbled by range anxiety—the fear, often unfounded, that you’ll end up stranded with a dead battery. Internal combustion isn’t going anywhere anytime soon, with advancements like turbochargers, direct injection, and variable valve timing squeezing more miles from every gallon.

Achates Power in San Diego believes it has a better way: Ditch the design that has dominated engine design for the past 130 years in favor of an idea abandoned in the 1940s and see a 30 percent bump in efficiency.

Most automotive engines, from the single-cylinder, one-horsepower unit Carl Benz created in 1885 to the 16-cylinder, 1,500-horsepower beast in the Bugatti Chiron, use a four-stroke reciprocating design. It’s a relatively simple idea: A piston in a cylinder draws in air and adds fuel during the intake stroke. The compression stroke squishes that mixture and introduces a spark, creating an explosion that drives the piston down, generating power during the power stroke. The cylinder then rises during the exhaust stroke, expelling spent gasses. The cycle repeats, thousands of times each minute.

Achates wants to chuck that out the window in favor of the opposed piston engine. This setup uses two pistons in each cylinder. The ignition of fuel and air creates an explosion that drives the pistons apart, generating power. Such engines are simpler, because they don’t use valves or camshafts.

They saw some use in locomotives and military vehicles until engineers abandoned them in the 1940s because of the difficulty of making them run cleanly and efficiently. Achates thinks it has cracked that problem. We paid a visit to find out how—check out the video [see link below] to see what we learned.

Source: Achates’ Opposed Piston Engine Could Revive Pull More Power From Less Fuel | WIRED

  1. catweazle666 says:

    Yet another re-invention.

    Junkers used opposed-piston technology in their Jumo aero engines, the Commer TS3 truck engine was very common in the UK throughout the 1950s – 1970s.

    Commer Diesel most fuel efficient DIESEL Engine ever built. NO freekin valvetrain.

    TS3 Sectioned

    The most advanced design was an extremely compact marine engine by Napier, subsequently used in the very powerful Deltic diesel locomotives.

    I lived a couple of hundred yards from the Settle-Carlisle line in the 1950s (still do, actually) when the Deltic prototype was under test, it came up and down every day towing a much heavier train than any other locomotive, very impressive.

  2. dscott says:

    Fairbanks Morse made opposed piston diesel engines for marine service for decades in the US, not a new concept but maintenance intensive to my recollection.

    The Fairbanks Morse 38D8⅛

    Fairbanks Morse O-P Engine Animation:

  3. oldbrew says:

    As the headline says it’s an old idea. What they claim is that they’ve sorted out the problems that caused it be dropped decades ago.

    Whether that translates into getting it into any production machinery is obviously another matter. From the video it looks as if there are still at least two years to go with development.

  4. […] Source: How a 70-year-old idea could make engines way more efficient | Tallbloke’s Talkshop […]

  5. oldbrew says:

    Achates says it’s a re-worked two-stroke engine but a lot more efficient: 30% better than diesel, 50% better than petrol (they claim).

  6. oldbrew says:

    John Silver says: ‘Or better valves, no camshaft’

    But Achates tops that: ‘they don’t use valves or camshafts’.

  7. Mike Flynn says:

    Complicated – two crankshafts. Combustion occurring in the centre of the engine increases the difficulty of cooling. Air has mass, and hence inertia – if it’s normally aspirated, port design restricts efficient operating range. That’s why all useful larger two stroke diesels require artificial aspiration. I’m not aware of any that use poppet valves – just ports.

    An example of a useable small two stroke diesel is the model aero engine.

    Up to 22,000 rpm or so, with relatively high specific power output. Normally aspirated, so used reed valve (springy metal flap), or rotary slide valve (from memory). Restricted RPM range – usually off, or maximum.

    Lots of two stroke diesels produced, usually big ones. Can’t see that opposed piston design confers any economic benefits here. Might be wrong, so I wish them well. I’ll keep my money in my pocket for the moment.


  8. Richard111 says:

    I think electric cars and such may take off shortly.
    Do a search on ‘supercapacitor batteries’.

  9. John Silver says:

    ‘supercapacitor batteries’
    Real soon now, as always.

  10. AlecM says:

    The opposed piston engine design has never made it into commercial automotive production.

    Why not, if it’s so good?

  11. USteiner says:

    Yet another “OPOC” engine, like this one:
    Good to see that there is competition. Good luck to both of them!

  12. Dave Ward says:

    @Mike Flynn – “That’s why all useful larger two stroke diesels require artificial aspiration. I’m not aware of any that use poppet valves – just ports”

    Depends on what your idea of “larger” is. The legendary GM “Detroit” 2 stroke diesels all use the “Uniflow” principle, with a mechanical blower (and often turbocharging) to provide scavenging via ports at the bottom of the piston stroke, and mechanically operated poppet exhaust valves in the cylinder head. Their power output & reliability is legendary, but fuel efficiency is not good, and I believe they have mostly been replaced by conventional 4 stroke engines. In this country Foden made inline 2 strokes during the same period as the Commer TS3 “Knocker” referred to above, also using the uniflow design.

    Come to think of it, I’m sure that the vast majority of really large marine engines also use the port and valve arrangement.

  13. oldbrew says:

    The point is, if true, that the old problems of this type of engine have been largely overcome.

    ‘With the help of modern technology California-based Achates Power has given new life to the concept of the opposed-piston engine, mostly abandoned after the second World War.’

  14. Dave Ward says:

    Opposed piston engines will always have a downside – the need to have 2 crankshafts, or one plus extra connecting rods, like the Commer. These have to be made of steel, and are therefore heavy – just the thing manufacturers are trying to reduce these days. The Napier Deltic is a possible exception, but the triangular layout is not ideal for most vehicle installations, and makes for very complicated access. It also needed a large gear train to synchronise the 3 cranks, rather like the Achates design, although I guess modern composites could be used instead. Uniflow designs also suffer cylinder and piston ring wear due to the ports at the bottom of each stroke. The other improvements in modern diesel engines are thanks to electronic control and common rail injection – which can be applied to any layout.

  15. Mike Flynn says:

    Dave Ward,

    You’re right, I’m wrong.

    Memory’s a wonderful thing, except when you depend on it.

    I’ll grovel in mortification, and slink away to cancel my membership of the Cult of Stupidity and Failure to Check.


  16. Dave Ward says:

    Absolutely no problem, Mike.

    Memory’s a wonderful thing, except when you depend on it”

    Don’t I know it…

    Having spent some time on YouTube the other night, I think the only “diesels” (i.e. compression ignition engines) which don’t use valves are ones like the Field Marshal tractor, and earlier “semi-diesels” like the Lanz Bulldog, and many old marine engines. These all employ crankcase compression and transfer ports, like petrol 2 strokes, with the semi-diesels requiring “hot bulbs” to make the fuel ignite. As this involves several minutes preheating with a large blowtorch, I doubt the average motorist is going to be driving about in one…

    You might find these interesting:

    The Field Marshal can also be started with a modified shotgun cartridge!

  17. oldbrew says:

    Saab had a 2-stroke car in the 50s and 60s, even a sport version.

    Saab 96 Sport [credit: Lukasz19930915 / Wikipedia]

  18. ulric lyons says:

    Diesel powered cars need to be phased out.

  19. catweazle666 says:

    Talking of 2-stroke cars, the Trabant was one too, introduced in 1957 and produced into the 1990s.

    If I lived in London, I would absolutely have to have one, zero road tax and zero congestion charge due to its capacity and with its premix 16:1 petroil and poor combustion efficiency, the finest mobile pollution generator a man could wish for, proceeding in its own little choking cloud of partially combusted hydrocarbons and chucking out more polluting per mile than any ten thousand SUVs.

    Then there is its predilection for oiling its plugs or seizing up, especially in stop-go traffic, thus expiring in the most inconvenient possible locations and causing huge traffic jams.

    Not forgetting the smell and feel of its authentic Glorious Socialist Workers’ Revolution driving experience, the shiny plastic seats, compressed cardboard bodywork and six volt lighting that makes even Joe Lucas the Prince of Darkness’ efforts seem positively thermonuclear by comparison.

    What’s not to like!

  20. oldbrew says:

    @ catweazle
    I was stuck in a traffic jam for two hours due to a bad crash on the Berlin transit motorway in the 80s.
    A lot of the Trabbies kept their engines running and the stench was dire, nowhere to hide. When we finally started rolling again there was a monster queue of Trabbies waiting to re-fuel at the next services. Some Wartburgs too IIRC.

  21. oldbrew says:

    @ ulric lyons

    Looks like doctors in London agree with you.

    BBC: Doctors call for ban on diesel engines in London
    1 hour ago

    Professor Jonathan Grigg from Doctors Against Diesel told the BBC: “Deaths from paediatric asthma are disproportionately much higher in London than the rest of Europe.”

    What would happen about commercial vehicles?

  22. oldbrew says:

    Energy firms back investment into diesel engine
    October 27, 2017

    As major carmakers shift towards electric vehicles, a group of major oil and gas firms announced Friday an investment into a diesel engine.

    The Oil and Gas Climate Initiative (OGCI), which includes BP, Saudi Aramco, Royal Dutch Shell and Total and has a $1-billion investment fund for low-carbon technologies, said it was putting money into Achates Power.

    The US company promotes a high-efficiency combustion engine that it says increases fuel efficiency while reducing greenhouse gasses emitted by vehicles at an affordable cost to consumers.

    “Pure electric vehicles and their fuel cell powered counterparts are unaffordable to the average car buyer; as such, they will remain a market novelty,” Achates Power says on its website.

    Read more at: