CoAxe Opposed Piston Diesel Engine

CoAxe opposed piston diesel engine

CoAxe opposed piston diesel engine

Opposed piston engines are getting to be the rage and this one, the CoAxe, from a company in Australia, looks like another interesting entry. It's initially being developed as a 100 horsepower unit for use in unmanned aerial vehicles.

The unit is relatively small, lightweight and low maintenance. It's also extremely low vibration since all moving parts have their opposite part moving in the reverse direction. They're not talking about use in motor vehicles and I wonder if the reason may be that it's better suited to continuous rpm operation, though you might think the shaft drive would fit the bill.

The video shows the idea in computer generated form along with see thru models for demonstrating the moving parts, but there's no actual engine, and like so many other similar projects, there may never be an engine.

You know, if even half of the concept engines we've covered here on The Kneeslider were to get built, we would be awash in new or revived designs. Take a run through our articles in the engines category and see what I mean.

Thanks for the tip, Joel.

Link: CoAxe Engine Company


  1. Mark L. says

    Looks very similar to the Dynacam engine from a decade ago, which actually made it to production as a certified aircraft engine.

  2. Paulinator says

    The cam engine has been around for a long, long time as a sub-type of the barrel engine. I believe it to be an excellent layout, but there are a few compromises that need to be dealt with, too. The video omits certain details in the areas of concern…like the guide that isolates cam-follower side-load from the piston wall, for instance. I’m really curious about what improvements they’re developing behind closed doors.

  3. GenWaylaid says

    Opposed piston engines can have excellent balance, and this variation takes that even farther. I can’t tell whether the crossheads were omitted from this design, or if the long piston skirt with two sets of rings is intended to fill that role. Note that the whole piston/crank assembly is one piece that only moves linearly.

    The most obvious reason they’re not talking about motor vehicle applications would be emissions. Opposed piston designs rely on exhaust ports in the cylinder walls which are covered and uncovered by the pistons. That’s going to push some of the oil lubricating the cylinder out the exhaust port, making for exhaust that is very difficult to keep clean. Opposed piston designs are going to share the emissions and oil consumption challenges of a Wankel rotary, but without the sealing issues.

    Realistically, I don’t see any way to meet modern emissions requirements with a combustion engine unless the combustion chamber and exhaust gases are kept separated from lubrication at all times. The poppet valve is an amazing solution to this problem, and its complexity shouldn’t be underestimated.

  4. Gildas says

    @ GenWaylaid
    Side port engines can be pretty clean, in fact you “build in” the NOX reduction…
    In marine use the lubrication is alkali, so a small quantity is meant/needs to burn, thus reducing the acidity of the exhaust gases, allowing more energy to be extracted.
    However, the efficient zone (that is also the least polluting one) is very small. These engines are made to run a fixed and rather slow Rpm (better fill rate and avoiding the need for a gear box).
    Within that available zone you must also stay in load parameters (torque goes is modulated by fuel injected, the engines are always run above stoichiometric)…
    And you need some form of charging, these engines won’t even start without!

    This is all fine and dandy on a boat, but I don’t see this being much fun or compact on a motorbike…

  5. says


    The problem is the reliability.

    Another Australian company (REVETEC) uses cam lobes to move the pistons, achieveing good fuel efficiency and bad reliability.
    In Revetec’s arrangement the cams have linear contact with the track roller bearings.
    A simpler engine (based on the same principle with the Revetec) is presented at the pattakon web site (at the section: Crankless engine).

    There are other, more conventional, opposed piston engines: the OPOC of Ecomotors (Bill Gates among the main investors), the opposed piston of Achates Power (Wallmart), the OPRE and the PatOP of pattakon. The last three are of the crosshead type and have “four stroke like” lubrication.

    Manolis Pattakos

  6. todd says

    It looks like you’d need to load both shafts equally. That’s easy on a counter-rotating twin prop motor but not so much with a single rear wheel.


    • says

      Hello Todd

      If you talk about the OPRE opposed piston engine, it depends on the application.

      In case of “a single rear wheel”, the one crankshaft could drive the gearbox, the other crankshaft could drive, through the (robust) sunchronizing gearing, the first crankshaft.

      In such a case, the single-crankshaft PatOP engine, presented at the pattakon web site, seems preferable: both pistons are connected to the unique crankshaft, no need for synchronizing gearing, no need for passing a part of the energy through gears..

      Manolis Pattakos

  7. Lee Wilcox says

    Fairbanks Morse made several opposed piston 2 stroke diesels. The applications were diesel electric subs and trains. The comments about the emissions requirements were probably right on. Intake/exhaust were ports like most two stroke bikes had.

  8. Paul Ellis says

    Don’t worry. My company is developing a radical two-stroke opposed piston engine for a motorcycle…..and it’s a diesel !!!!!
    500cc liquid-cooled 320 bhp at 16,000rpm. Low emissions too. Yes, really!