Wet sump 2 stroke??

Discussion in 'The light stuff area' started by ryanjames170, Aug 19, 2012.

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  1. Aug 19, 2012 #1

    ryanjames170

    ryanjames170

    ryanjames170

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    Have any of you ever heard of or seen a wet sump 2 stroke before? im not sure how it would work on a gas engine i know it works in a desile but im not sure on a gas engine though.
     
  2. Aug 19, 2012 #2

    TFF

    TFF

    TFF

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    The diesels, I know of, have superchargers to move the air in and out of the cylinder; I would think gas would have to do the same. You have to have something to move the air if you are not using the crankcase as a pump.
     
  3. Aug 19, 2012 #3

    Tony

    Tony

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    Its the piston in the cylinder that create air movement not the crankcase. You have cylinders that hold pressure. As they move up and down they cause air to move within the intake system. The crankcase is vented to the intake by means of the airbreathers in the valve covers. In years past before the EPA airbreathers dumped to the atmosphere by means of a tube. You see this system used today in truck and tracktor pulls. When the thing is up on the back wheels and you see the steam or smoke coming out of those two pipes under by the oil pan. You are seeing the blow-by off the pistons in the crankcase.

    This blow-by was vented to atmosphere then they found you could reburn it and lower emissions. If you did nothing and allowed this blow-by to just build you could blow a motor apart.

    This is what I know of the engine crankcase system.

    Tony
     
  4. Aug 19, 2012 #4

    Tony

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    Superchargers do not move the air in and out of the cylinder. A supercharger or blower by some, not turbo, but blower, puts the air in the cylinder at above atomsphric pressure. Its the Valve train along with the pistons moving that force the exhaust out of a cylinder. This is why we have valve overlap. With out this overlap the engine can not get all the old exhaust out nor can it draw in all the frsh intake charge.
    Now using a supercharger you can reduce some of this overlap becuase you are blowing that charge into the cylinder instead of depending on the design of the engine to do this work. This is why when you go to a supercharger I install what I call a supercharger cam. I tell everyone you MUST replace the cam in order for this supercharger to work correctly. Will it work without replacing the cam, yes, but it will not be correct.
    A supercharger is a supplement to the intake system to up the power by means of forced air.

    Tony

    Tony
     
  5. Aug 19, 2012 #5

    Himat

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    Not quite sure, but i do think I have seen a sketch of such an engine in some book on obscure engine designs. Anyway, it could be done with a two part con rod and the cylinder sealed at both ends like on a double acting steam engine. On top of the piston the combustion chamber would reside as usual, the enclosed volume below the piston would serve as the charge blower. The crank and lower to higher con rod joint would then be in the crankcase which could incorporate a wet or dry sump.

    The other possibility for a wet sump two stroke would be as in the Jumo and others with two pistons opposing each other in one bore and two cranks. These designs do require an external blower to charge the cylinders. Diesel air made a 100hp aircraft engine like this, but I don’t know what happened to them.
     
  6. Aug 20, 2012 #6

    TFF

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  7. Aug 20, 2012 #7

    KeithO

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    Every big marine 2 stroke engine is sump lubricated. They all use blowers (scavenge air) to purge the cylinder of exhaust gas and refill with fresh air. This all happens just before and after bottom dead center. Turbochargers are not ruled out, but they must have much lower back pressure than the ones used on 4 strokes since it is the blower pushing the exhaust and not the pistons. EMD uses turbos on their locomotive engines, but the engines won't run without the blower in the first place.
     
  8. Aug 20, 2012 #8
    I've been thinking about this for a few years - these are my main conclusions.

    1) Supercharged - probably be electrically driven into a plenum to give boost at engine start.

    2) Fuel injected - get the right amount in at the right time.

    3) Inlet valve (in the head - no transfer ports) - opens as the cylinder pressure drops below the supercharger pressure (?active timing?) -normal 2-stroke exhaust.

    4) Running it at sensible revs for direct drive would mean a ludicrously long exhaust if you wanted to tune it like a normal 2-stroke but that shouldn't be necessary with the right inlet timing for the inlet pressure to push the last of the burned mixture out. I still wouldn't add a turbocharger though.

    Just so you don't make the mistake of thinking this is a completely sane idea, I would also use a modified version of this (Aero 35 In-line Piston Engine) with double ended pistons to make it effectively a 1-stroke ;^}
     
    Last edited by a moderator: Aug 21, 2012
  9. Aug 23, 2012 #9

    DaveK

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    There are wet sump 2 strokes out there, of interest are the direct injection 2 strokes that don't use fuel to distribute oil through the crankcase. If you are using a wet sump then crankcase scavenging can't be used to push air into the cylinder and these engines usually use some other method such as a blower or a separate piston to force the air into the combustion chamber. For a UL the total loss oil systems used by some of the smaller DI 2 strokes is likely the way to go. Maybe something like the Rotax E-Tec engines.
     

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