An Open Source Two Stroke Diesel

With a welder and a bunch of scrap, you can build just about anything that moves. Want a dune buggy? That’s just some tube and a pipe bender. Need a water pump? You might need a grinder. A small tractor? Just find some big knobby tires in a junkyard. Of course, the one thing left out of all these builds is a small motor, preferably one that can run on everything from kerosene to used cooking oil. This is the problem [Shane] is tackling for his entry to the 2016 Hackaday Prize. It’s an Open Source Two-Stroke Diesel Engine that’s easy for anyone to build and has minimal moving parts.

[Shane]’s engine is based on the Junkers Jumo 205 motor, a highly successful aircraft engine first produced in the early 1930s and continued production through World War II. This is a weird engine, with two opposed pistons in one cylinder that come very close to slamming together. It’s a great design for aircraft engines due to it’s lightweight construction. And the simplicity of the system lends itself easily to wartime field maintenance.

The Jumo 205 was a monstrous 12-piston, 6-cylinder engine, but for [Shane]’s first attempt, he’s scaling the design down to a 50cc motor with the intent of scaling the design up to 125cc and 250cc. So far, [Shane] has about 30 hours of simple CAD work behind him and a ton of high-level FEA work ahead of him. Then [Shane] will actually need to build a prototype.

This is actually [Shane]’s second entry to the Hackaday Prize with this idea. Last year, he threw his hat into the ring with the same idea, but building a working diesel power plant is a lot of work. Too much for one man-year, certainly, so we can’t wait to see the progress [Shane] makes this year.

The HackadayPrize2016 is Sponsored by:

42 thoughts on “An Open Source Two Stroke Diesel

    1. That video is not correct.
      IMHO as a native German “kers” shouldn’t be pronounced like the English word “curse” but more like the English word “cares”.

      1. In the U.S. beginning in the 1960’s there was a curriculum called ALS German. One of the creators was my German teacher – not that I paid any attention. But I do recall a big emphasis on “High German” and I found over the years that Germans I met were not using ALM High German :-) Nor the archaic colloquialisms of the dialogs. “Get off you goose!”

  1. Opposing piston model engine are notoriously difficult to get running. Engines do not scale well, in general, so just shrinking things does not often work with IC. There are a lot of very simple diesel engines out there like the Lister and Listeroid variants, replicate that, a known working design.

      1. From what I understand the fluid dynamics and other things just dont work if you just directly scale. For example if you took a chevy 350 V8 print and made everything 1/10th the size the engine would just not run. A lot of things have to be changed to get those little engines to work. There is more detailed info on some of the forums dedicated to small IC engines.

        There are are tiny little diesels out there, you see them for model airplanes, a lot of them came out of the old soviet union. They are different than glow ignition engines like many are familiar with, they use a counter piston in the head that you screw in to increase the compression once it is started.

        There are just so many old, working, reliable designs out there that are public domain that making something this complex is just kind of silly. And I have no idea what he is going to do for an injector pump. Injector pumps are probably more complex than the engines. And there is that thing that looks like a little roots blower on his drawings….

        If it were me I would design the engine to the size you want to start with. Making smaller prototypes just means you are making three separate engines. Just because they are smaller does not mean they will be cheaper to build.

        1. I have two of those old, soviet RC engines. One is glow engine, the other one is two-stroke Diesel. They need different fuel to run, because of lower pressures inside, Diesel one after starting up requires a bit of precision when adjusting compression, because if one pushes counterpiston too far, it will simply jam. But they are cool, simple designs made of aluminum, steel and cast iron.
          And engines don’t scale up or down very well, the main issue is the nature of combustion. Air-fuel mix must be uniformly spread inside cylinder for it to work properly, otherwise combustion won’t be complete and engine won’t be efficient. That’s also reason why fuel injectors need precise adjustments. And rocket engineers had the same problem with combustion in their engines which caused those engines to either stop working or explode.
          [Shane] should read some books on engine design and construction before attempting this project…

          1. I read only one of them, but it had rich bibliography. Unfortunately it was 18 years ago, and the book was in polish, so probably not too useful for you, Shane.

      2. A few issue I can think of that might effect the scaled engine. The fluid dynamics, I do not think air/fuel would flow and mix the same as it scaled. As cylinder volume shrinks, power shrinks at a faster rate. Like wise I believe frictional forces increase relative to power. You still need the same injector pressure as compression ratio hasn’t changed.

        1. The deltic is just three opposed engines rammed together, it’s actually a really compact and clever way to make a lot of power compared to the source engines or a basic inline or V engine. For its uses in trains and boats, it actually really is one of the better engine designs ever.

    1. Hot bulb engine? Would burn a lot more than a diesel engine. Is his aim to burn refined diesel ? If going to the trouble of an open source engine, it suggests that your fuel supply might not be well refined.
      I run veg oil in a road going diesel engine. But I’d rather run veg oil in a veg oil engine if you see what I mean. I’ve adapted enough that it works well, but if I had the capacity to design one things would be different from the outset.

    1. Trying to make the timing on both pistons adjustable is proving to be a lot more complex than I care for. It will most likely go away. Please keep in mind that this project is still in the conceptualization phase.

    1. I always prefer K.I.S.S. over complexity, I’ve been trying to figure out how to simplify some of the more complicated features. If I am unable to do so then they will have to go. I am trying to avoid feature creep where I can while in the conceptualization phase which is hard to do sometimes.

  2. I’m not very knowledgeable about the subject, but I think that reducing the number of cylinders compared to original might be a problem. Original engine with many cylinders always had combustion going on somewhere, making it easy to power through some points. This small guy only has one cylinder, so it might be difficult to start and easy to shut down at the least provocation.

  3. For a simple two stroke engine, he’s really made it overly complex with the opposed piston layout. He’d be better off using something like a Detroit Diesel engine as they’re basically conventional with a few minor differences, and the series 51 is valveless entirely, simplifying things further.
    Also his electric blower and crankcase volume look to be too small, there should be a bit of air reserve so the thing doesn’t have to suddenly work full power to scavenge the cylinder. The direct path right from the blower to the cylinder is just incorrect, he needs more space for the air to take up for there to be a reserve. The engine needs the blown air and the blower, without the blower a two stroke will not run.

    1. You are correct, the blower, crankcase, port position, port configuration, direct blower path are not correct. This was a “quick and dirty” model to show a proof of concept. Please keep in mind that this project is still in the conceptualization phase and any input is greatly appreciated. Feel free to provide feedback on the project page.

  4. Creating a precision, complex (read “difficult to produce”) design is its own punishment but I can understand the attraction.

    A better approach for global open-source production would be to design something that can be made from scrap, repaired easily and will run more or less reliably. A hot-bulb diesel does this pretty well, but they’re usually enormous and dirty.

    Not surprisingly , there is already a broad range of small diesel engines ranging from ~3 hp on up (scratch list here: for both land and marine use, as well as tiny model engines and various conversion schemes.

    Here’s a video of one running: Note the compression release and flywheel cranking involved.

  5. By all means, have your fun with this, but… I come from a rural, poor area, and I can tell you that the problem is not a lack of good designs for small engines. If we could get someone in an urban manufacturing center to build something affordable we’d be fine. But die cast parts, complex gears to cut, and electronic engine management will never be cheap to produce anywhere.

Leave a Reply

Please be kind and respectful to help make the comments section excellent. (Comment Policy)

This site uses Akismet to reduce spam. Learn how your comment data is processed.