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  1. #16
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    I like the idea of what could almost be called a compound turbo.
    Here is a video of the insides. He claims in one of the videos that because the pistons only move half as far they can run it twice as fast, I'm not so sure about that with conrods that long.
    It needs three conrods a cylinder, so I guess he will save money on a flywheel
    Also don't you end up with a combustion chamber that is a horrible shape?
    http://www.ecomotors.com/videos/introduction-opoc-powertrain

    Stuart

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  3. #17
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    Ok I watched the video and it cleared some stuff up. Here is what I think based on the tiny amount of information available.

    1. First problem that occurres to me is the weight of the pivot in the outer pistons and the strength of the side by side conrods.

    2. The idea that you can run it twice as fast with a half stroke is an oversimplification but it's more or less true. In a slider crank mechanism the piston is reciprocating and the conrods and crank are sort of half rotating and half reciprocating. Yes the crank is one piece and rotating but it's out of balance so you get forces along it's length within the structure. So you have to calculate the forces in the assembly at your design rpm and make it strong enough not to break. At some point you cross into diminishing returnes where making it strong enough increases the out of balance weight and cuts the efficiency of the engine. If your chasing efficiency then rpm isn't necessarily the way to go. You have to find a balance of everything to get a nice result.

    Length of conrod compared to stroke is a factor in side thrust on the piston. They need to keep the conriod length reasonably long on the inner normal ones to get decent engine life, all else being equal. High rpm is not conducive to long life either. You can solve a lot of problems with materials but they usually add cost.

    3. The layout produces a very wide engine. It's low but the layout does not suit all installations. Subaru make a big fuss about low c of g in thier boxers but they have always had to design their cars around the very wide engine. Again, compromise. Mind my forester has fantastic access to peripherals.

    4. The peripherals have legs. I like the turbo idea although you have to look hard at every aspect of it's inclusion. How much will it push up the cost of each engine ? What are the real efficiency gains ? The reason I mention this is it's not exactly a revolutionary idea, so I'm suspicious as to why it's not been implemented before. Still it could just be no one has bothered to chase up that option before and it will be nice.

    You shouldn't worry about the combustion chamber shape. You can make it an ok shape. Combustion chambers terrify me. I studied them for years and have only ever met a couple of people who properly understand them, and read texts by a few more. They are by far the most complex mechanical system I have ever seen and anyone who says otherwise doesn't understand the problem.

    The big issue here is waste heat. You'll be dumping twice as much into the pistons. In a normal engine the combustion chamber is static and can be kept at a relatively high temperature, both through materials, cooling system and carbon deposites. Here a very large part of the surface has to be designed for movement, light weight, expansion, and it's only indirectly cooled. To get good thermal efficiency I bet they end up going to ceramic coatings to insulate the piston crowns.

    I would be looking either to timed port injection very near the cylinder or better yet direct injection. That opens up air overrun into the exhaust for more complete filling, lower emmissions (because of the stupid way they are measured) and cooling. It also permits better fuel regulation.

    It's an interesting project and I hope it goes somewhere.
    I'm just a startled bunny in the headlights of life. L.J. Young.
    We live in a free country. We have freedom of choice. You can choose to agree with me, or you can choose to be wrong.
    Wait! No one told you your government was a sitcom?

  4. #18
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    Quote Originally Posted by damian View Post
    1. First problem that occurres to me is the weight of the pivot in the outer pistons and the strength of the side by side conrods.

    This is that part I was worried about with his "double the rpm" comment. But one thing those rods have going for them is under load that are always under tension.(at least I think that's a good thing)
    Quote Originally Posted by damian View Post
    I like the turbo idea although you have to look hard at every aspect of it's inclusion. How much will it push up the cost of each engine ? What are the real efficiency gains ? The reason I mention this is it's not exactly a revolutionary idea, so I'm suspicious as to why it's not been implemented before. Still it could just be no one has bothered to chase up that option before and it will be nice.

    It has been done in another form on a much larger engine. I think you could pretty much run the car electrics for "free". On a hybrid you might even get a little more. Must be fun to get a motor/alternator to live between the turbines of a turbo

  5. #19
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    Yes but given they are long you get whipping which is probably worse than column effect in compression.

    VW have I believe fitted twin staged turbos to some of their petrol engines to get some of the advantages he's talking about and those engines get good fuel efficiency.

    Dunno. I'd need a lot more information to comment in detail. Interesting thing though.
    I'm just a startled bunny in the headlights of life. L.J. Young.
    We live in a free country. We have freedom of choice. You can choose to agree with me, or you can choose to be wrong.
    Wait! No one told you your government was a sitcom?

  6. #20
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    I thought fast revving engines were less efficient as they cannot suck in a full amount of air and there is not enough time to burn everything properly..

    Along with the fact that high revs equals low torque..

  7. #21
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    Yes and no.

    1. An aspirated engine relies on atmospheric pressure to push the air in, which is about 14.7 psi. Because air has weight and the inlet tract has obstructions at high speed the inertia of the air prevents complete filling. If you add a pump, even adding a small amount of pressure, you can get 100% filling (at atmospheric pressure) to very high revs. Sort of like how my knees give out going upstairs but if an insistent woman gets behind me (no names) I can speed right up again

    Generally high revving engines have shorter strokes to reduce the forces on the crank and rods (and to a lesser extent the piston). The shorter stroke gives less leverage so less turning effort or torque AT THE CRANK. Because you have more revs you can gear lower and get your torque back at the wheels.

    As I say it's all swings and roundabouts and designing a really sweet engine fit for purpose is all about balancing a lot of compromises.
    I'm just a startled bunny in the headlights of life. L.J. Young.
    We live in a free country. We have freedom of choice. You can choose to agree with me, or you can choose to be wrong.
    Wait! No one told you your government was a sitcom?

  8. #22
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    [QUOTE=damian;1300833] atmospheric pressure to push the air in, which is about 14.7 psi. /QUOTE]

    to be a little more precise...its psia as opposed to psig which would then be zero (when reading a normal gauge for pressure)

  9. #23
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    eskimo, the exhast would work well

    turbo-compound (like I said, much bigger engines)
    Turbo-compound engine - Wikipedia, the free encyclopedia

    If you're going to build a knocker, why not go all out
    Napier Deltic - Wikipedia, the free encyclopedia

    Stuart

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