opposed (free) piston engine(s)

Discussion in 'Propulsion' started by yipster, Sep 17, 2004.

  1. yipster
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    yipster designer

    [​IMG][​IMG]
    this looks interesting, specs on the site seem to be made for boaters
     
  2. Thunderhead19
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    Thunderhead19 Senior Member

    That looks familiar. I've seen that design in a MUSEUM somewhere! I think that for a small engine it is probably very good, but I also think that there were some inherently weak parts in it. Modern metalurgy may have fixed this though. The Wankel rotary engine had some weak parts in it too at the beginning, but it's as popular as ever these days (thank you Mazda).
     
  3. fcfc

    fcfc Guest

    First : Devil lies in details.
    Second : The road to hell is paved with good intentions.

    The drawing seems for me a bit too simple.
    First, 2 or 4 stroke ?

    If 2 stroke, where the scavenging come from. If 4 stroke, where is the valve gear ?

    The sliding bearing on the sinusoidal power cam. Will it last 240 millions revolutions (2000 hours at 2000 rpm)

    Another worse point.
    Their page http://www.dynacam.com/Product/Torque_vs__Horsepower/torque_vs__horsepower.html is for monkeys.

    They compare a 300 hp car engine and a 300 hp truck engine. They just omit to say that if you put the car engine in the truck with the *CORRECT* gearing, it will move the truck like the truck engine. (TBO and BSFC another point).
    If you want to see very heavy vehicules with high revving engines, very light and very compact, go to military equipement. The only caveat is TBO is in the hundred of hours. MAN reciprocating diesel remplacement for turbine powered tanks.

    The only interest of their engine is that it can be put where classical configuration engines (I, O, V) cannot be put. Eg torpedoes.

    fc
     
  4. yipster
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    yipster designer

    reading up i find the idea is old, junker airplanes used these engines long ago, naval ships use(d?) them in 2 stroke diesel and indeed in torpedos. they are used in pressure jets and wild claims on e-bay where water augmentation in the exhoust can double thrust to 200HP with a gross weight of 42 lbs? here a non-technical description of the pulse engine. still digesting torque while reading Sandia PDF
     
  5. Ilan Voyager
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    Ilan Voyager Senior Member

    In 45 years I have read hundred of superlative reports about this kind of engine. None worked. As fcfc pointed out sliding bear cam won't last.

    The Wankel engine is perfectly logical and its problems were only in fabrication, not in conception. The Dynacam has some problems in conception, and the little statement written by their lawyer on the home page of the internet site has such a flavor! Please read it, it's worth...

    "FORWARD LOOKING STATEMENT DISCLAIMER
    This website contains "forward-looking statements" which involve risks and uncertainties and include, but are not limited to, statements regarding future events and Dyna-Cam's™ plans and expectations. Our actual results may differ materially from such statements. Factors that may cause or contribute to such differences include, but are not limited to, those discussed in "Risk Factors" as well as those discussed elsewhere in this Memorandum and the documents referenced herein.
    Although we believe that the assumptions underlying the forward-looking statements are reasonable, any of the assumptions could prove inaccurate. There can be no assurance that the results contemplated in such forward-looking statements will be realized. In addition, as disclosed under "Risk Factors," the business and operations of Dyna-Cam are subject to substantial risks which increase the uncertainties inherent in the forward-looking statements included in this Memorandum.
    The inclusion of such forward-looking information should not be regarded as a representation by Dyna-Cam or any other person that the future events, plans or expectations contemplated will be achieved. We disclaim any obligation to subsequently revise forward-looking statements to reflect subsequent events or circumstances or the occurrence of unanticipated events."

    I can make the foward looking statement that, in spite of my age, after a 3 year training, after loosing 60 pounds and with 1 million bucks I'll run on my short legs the 100 m in 9.2 seconds, crushing the world record. Give the money. Thanks. My lawyer wrote for me the same disclaimer on the sponsor's contract.

    Next time I do some engineering, I'll use it. Good stuff, is n't?

    PS fcfc I do not agree with you; the page horsepower is for ILLITERATE monkeys, a normal chimpanzee sitten in the bush will laugh reading such statements.

    PPS
    The bad Joke;
    "Yipster, pulse jets are old and dead end stuff. The german V1 had one. I've even made one for a model plane long time ago. Waoh, some got 400 km/h on models. But have you heard one??? You start your pulse jet driven boat at Rotterdam, the Scottish think it's the end of the world, and everybody in Paris knows that Yipster is gone fishing".

    A part this bad joke, Yipster, you are a "puits de science", I love your intellectual curiosity.

    CORRECTION I've made a confusion between pulse jets and free piston engine but I keep it for the joke. The internet page about the pulse free piston engine with only 10/1 compression ( so more reliable, curious assertion) and it's hydraulic transmission for a 3 wheeled "bicycle-car" is a summit of unvolontary humour...Thanks Yipster for finding such pages.
     
  6. yipster
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    yipster designer

    that's a compliment! must say i feel more like a parrot coming up with those links, i got this thurst for knowledge. you learned your lesson and i come to school, thanks! Boyle's law dont count underwater i know but was thinking of muffling that sound but at present i still have to build a "normal" pulse-jet. have to check on that junkers free piston but see the point on sliding bear cam shaft. i'm not so sure pulse jets are old and dead end stuff reading http://www.popsci.com/popsci/aviation/article/0,12543,473272-3,00.html ok, no engineer yet i see beauty in some of those odd designs and whenever you feel like going for that 100 meters in 9.2 seconds please let me know, just dont ask me for sponsor...
     
  7. Ilan Voyager
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    Ilan Voyager Senior Member

    Very interesting page, but it's an hybrid for military purposes where noise and TBO is not a concern.

    I'm a bit afraid for the poor valves they'll have a hard life...the article is authentic vulgarisation stuff: the "Ferrari spark plug" is an example, Ferrari does not make its spark plugs, Ferrari buys them like everybody (probably a Bosch or NGK iridium-platinium for high perf engines) but Ferrari spark plug sound s better than automotive spark plug.

    The article has not a word about the stresses induced by "supersonic waves" and pulsations that make that the TBO is of a few hours.

    For the SR71 Blackbird, the team driven by the great Kelly Johnson spent hours to figure how to slow the flow air inside the engines so it won't be destroyed. At 3500 km/h 54% of the power comes from the air rushing at undersonic speed in the engines. That's efficiency.

    Military like to throw some money away in this kind of stuff to see if it may work for a "kleenex" supersonic drone for example. It's called "sugaring" the Universities, none result is actually expected, just public relations. The funds given will be probably a very small fraction of the cost of a new last generation radar on a Hornet.

    I forgot a detail for the 9.2 secong challenge; I have to stop smoking.
     
  8. yipster
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    yipster designer

    yeah, it's a nice concept, but does perhaps fall on the shaft drive.

    no one seem to have succeeded making a really good swash-plate drive by transferring linear motion into rotation while it's been tried and done many times before, in stirling engines also.

    on the other hand; for a simpel high hp to weight, small and chiep say two stroke diesel, 2000 hours on a pleasure boat can mean decades.

    than again, better yet is a real free virtual piston as in a jet pulse, made a moddest start with some on methanol running jam jars
    or check the http://www.swissrocketman.com for real high performance and danger...
     
  9. DiverDown
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    DiverDown Junior Member

    Interesting info:the Junkers Jumo 207 opposed airplane engine was quite odd but worked very well.Six long cylinders but with 2 cranks and 12 pistons- 2 stroke supercharge scavenged ,turbo charged diesel.The cranks were on opposite ends of the cylinders,one side's pistons with the intake port and the other with the exhaust port.The pistons would travel towards each other (the cranks being geared together) and injection would occur near TDC for both. 16.6 litre capacity, with 1000 hp available for short bursts and 800 continuous.The Jumo 223 was a stack of 4 of these,all geared together.The Jumo 224 was a larger engine,stacked 4 high with 4500 hp-not sure if many were made.
     
  10. yipster
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    yipster designer

    DiverDown thanks. i looked them up on the net and from one odd engine to the next i came across some (taken from planes) exellent PT boat engines as well that seem to be forgotten nowadays.

    above i was yeppin about virtual piston blows and found this vortex trust article http://enstrophy.colorado.edu/~mohseni/VortexDynamics1.html with propulsion like a squid very interesting.
     
  11. yipster
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    yipster designer

    a good cutaway pic of that jumo, a 205 at vintage aero engines.
    also found free (liquid) pistons in dancing stirling engines.
     
  12. DiverDown
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    DiverDown Junior Member

  13. D'ARTOIS
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    D'ARTOIS Senior Member

    You came across an (illegal?) war relics collector. What interests me is that one in the back, just visible a 88mm FLAK Gun, one of the most versatile weopons from the German Armed WWII forces. Those guns are very rare. Museum pieces they are.
     

  14. yipster
    Joined: Oct 2002
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    yipster designer

    www.milweb.net go vehicles and artillery and the flak is top of the list, heavy trailors yes, no boats
    and that may be a good thing as i recall myself bidding on a 40 meter navy ship
     
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