4 Stroke Cleaner Than 2, Really?

Discussion in 'Propulsion' started by Jet_Love, Jun 17, 2013.

  1. daiquiri
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    daiquiri Engineering and Design

    It doesn't just sink to the bottom - it gets dispersed all around in the volume of water, bottom included.

    Normally, molecules of grease and oil are hydrophobic, due to some particular molecular characteristics (http://en.wikipedia.org/wiki/Hydrophobe). Detergent binds to oil and grease molecules and wraps around them, lowering the interfacial tension between water and oil molecules (so-called surfactant action), and thus making oil molecules soluble in water. That's exactly how they allow you to wash greasy dishes. The grease which is attached to the dish surface gets dissolved in the water, and then rinsed away, thanks to the surfatant action of detergent.

    In conclusion, the oil does not go to the bottom when mixed with a detergent. It dissolves all around, bottom included, and intoxicates the living organisms in the nearby area.

    Cheers
     
  2. CDK
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    CDK retired engineer

    Yes Slavi, that is the way soap works, at least in our part of the world. I can also add that the amount of oil or grease a surfactant can handle is temperature dependent. Also motion greatly improves the process.
    Although some manufacturers (Dreft) claim their product can disperse 10-15 times their own volume of oil, I think 3-5 times is a more realistic value. That means that one drop of detergent can handle up to 5 drops of oil. The giant oil spot on the water is clearly only one molecule thick, otherwise the effect of a drop of detergent would not be so stunning.

    The volume of the water under the spot is many billion times larger, even in shallow areas, so the concentration of oil molecules there is near zero. Frankly I doubt that any can reach the bottom before being digested by bacteria.
     
  3. Jet_Love
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    Jet_Love Junior Member

    Just because someone says it doesn't make me believe and a test is just that, a test. Regardless of how I'm trained or taught I try to keep my mind open. I dont want to be that race horse with blinders running on a track that was laid out for him.

    Respectfully,
    Shawn
     
  4. BMcF
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    BMcF Senior Member

    Willfully disregarding a wealth of empirical data is keeping an "open mind"?

    Mmm..kay.

    Older-generation 2-stroke outboards eject relatively large quantities of oil in their exhaust by design. Latest generation fuel-injection 2-strokes are much better, but they are still 2-strokes and the lubricating oil still has to be mixed with the combustion air and some unburnt oil still passes out in the exhaust.

    There are a lot of very good environmental reasons why 2-stroke engines are been phased out of existence in the world of marine propulsion. The oil content in the exhaust is only one of those reasons.;)

    That said...I still love my stinky, smokey oil-spewing, sheen-leaving 1978 115HP Evinrude because a) it's reliable as hammer and b) Its going to be hugely expensive to replace with a 4-stroke 115. Last year I replaced the ancient (but still very healthy running) 35 Evinrude on my 15' Whaler for a new Honda 50HP 4-stroke. What a huge difference in both "clean" and fuel economy that was!
     
  5. djaus
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    djaus Salted Nut!

    Fuel, oil and grease are all derived from the same product. Crude. Every single internal combustion engine ever made will have trace amounts of oil exit the exhaust pipe. When you consider that a piston must be lubricated in order to function, there is always a tiny trace amount of oil that remains in the combustion chamber after combustion and the piston retracts into the engine block. If engines didn't do this we would never need to check oil levels. 2 stroke engines are oil & carbon spewing nightmares that should be outlawed or at least restricted to gardening equipement only. Next time you put earmuffs on your outboard to flush it, place a piece of white laminated wood close to the exhaust and rev the engine. Then see what lands on the wood.
     
  6. BMcF
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    BMcF Senior Member

    That.

    One of my older Evinrude outboards currently has a rotted out intermediate exhaust housing. That's the chunk of aluminum that mounts between the bottom of the engine and the lower unit housing; where all the real "mixing" of exhaust and spent (warmed) cooling water occurs. The housing has corroded to the point where it leaks out the side rather than directing everything down through the housing and out the prop hub like it's supposed to.

    The extensive brown-black sticky mess of mixed exhaust oil, carbon and water crud that stains the outside of lower unit housing is a real eye-opener for anyone who might doubt how much crud that 2-stroke routinely ejects in its exhaust stream.
     
  7. sdowney717
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    sdowney717 Senior Member

    yes, I am with you on this too, that is I agree.
    The law has been written to the point where it feels like a capital offense to spill even a drop. The USCG will view adding detergent as an attempt to hide your transgression.

    The bacteria in water do eat the oils we spill. Earth eventually cleans itself up. There are natural oil seeps under the sea polluting naturally and it just does not cause a problem. When the letter of the Law of men becomes involved, common sense need not apply. The law as written and their application against an offender IMO is unduly harsh reality which some unfortunate accidental transgressors bear the brunt of.
     
  8. jonr
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    jonr Senior Member

    Do you really think that none of the oil get burned?
     
  9. BMcF
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    BMcF Senior Member

    I believe he is referring to the most prevalent case..the classic 6-gallon motorboat tank and the older generation motors. Every full tank receives a full pint of 2-stroke oil to mix, and about half of that ends up going out unburnt through the exhaust. Of course the rest ends up as noxious blue/grey smoke in the atmosphere...:D
     
  10. DCockey
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    DCockey Senior Member

    Is any of the oil in the gasoline-oil mixture used in 2-stroke engines burned during the combustion of the mixture, or does it all go out the exhaust?
     
  11. Ike
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    Ike Senior Member

    That depends on when they were made. All the newer ones very little goes out the exhaust. The manufacturers have redesigned them so that exhaust is recirculated and almost completely burned. If you have an old one though most of it goes out the exhaust. I can't remember when all the refinements were made but it was around 2004 give or take a few years.

    For instance Yamaha has something they call HPDI (High Pressure Direct Injection) Basically this describes what all 2 stroke now have, they just give it different names like Optimax (merc), E-Tec (Evinrude) and so on. They directly inject the fuel into the combustion chamber, electronics meter the fuel for the exact amount. So is the oil. It is precisely metered and injected. No more fuel and oil coming in while exhaust ports are still open. So you don't have gobs of fuel and oil blowing out open exhaust ports. They are a lot cleaner than they used to be.

    But I suppose 4 strokes still beat them on clean. But they weigh more and cost more. For shear power/weight 2 strokes are better, but 4 strokes are smoother. So you pays your money and you takes your choice.

    A good page to look at for the differences; http://www.marineenginedigest.com/specialreports/2versus4stroke.htm
     
    Last edited: Jun 24, 2013
  12. jonr
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    jonr Senior Member

    Last edited: Jun 26, 2013
  13. Duane P Wetick
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    Duane P Wetick Junior Member

    4 Strokes over 2 strokes

    Most OB's will be 4 strokes in the very near future...the last 2-stroke engine on the highways of the world was the East German produced Trebant and the last one was made in 1973...a copy in the Air Force museum in Dayton, Ohio...Go Look!
    When the last 2-stroke engine disappears from the world, I will breath a huge sigh of relief!
    The Bumper Boat pond at Waldameer Park here used 2 stroke Suzukis (2 HP) and in spite of a very large filter system, the water always looked DIRTY! (It has since been scrapped due to our local Health Dept's objections).

    Cheers, DPW [Everything has limitations...and I hate limitations.]
     
  14. Ike
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    Ike Senior Member

    sure no more two strokes.
    Just like we wouldn't have radio after tV was invented. Or no sailing ships after steamships were built.

    As long as we have gasoline or it's equivalent (how long will that be, 10. 20 years?) I am sure there will be two strokes. They are lighter, have higher power to weight ratios and are relatively simple compared to 4 strokes. They are less expensive. Maybe they will not be used in outboards, but in small engines (garden tractors, snow mobiles, lawnmowers, and so on) they will be around for along time. Engine manufacturers have figured out how to clean them up.
     

  15. Jet_Love
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    Jet_Love Junior Member

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