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  1.  
    I have built single cylinder and 4 cylinder engines in the last two years that I hoped would perform nicely on propane. I am somewhat disappointed. While propane fuel emits very low odor in engine exhaust, and engines run well on it, it has a very undesirable side effect on 4 stroke engines with eclosed crankcases. It produces significantly more moisture in the exhaust than do liquid fuels like camp fuel and gasoline. The result is that the excessive moisture in the blowby gases quickly condense in the crankcase. This causes lube oil to cloud up quickly. This condensed moisture (probably acidic) is obviously not good inside an engine. From my experience with the one cylinder engine, if it is allowed to operate for longer periods of time, the oil becomes hot enough so the oil doesn't get cloudy very quickly. One the 4 cylinder, the crankcase is proportionally larger than in the one cylinder, and moisture accumulates rather quickly requiring frequent oil changes. In both engines, I believe my rings have seated very well, and blowby is actually quite minimal. My crankcases are well ventilated, but the 4 cylinder emits very little crankcase gas due to the balanced pressures inside. I use two compression rings, and have thought about adding one more but don't like the idea of adding internal friction. So I am hoping someone might have an answer to this problem before I decide to abandon propane, and switch back to liquid fuel.

    Jeff
    • CommentAuthordavid
    • CommentTimeMay 9th 2010
     
    Jeff,
    I like propane as a fuel. As I read your posting, I wonder if you crankcase may be sealed too well and the small amounts of moist exhaust, it all has water in it, condenses in you crank case. Small engines have a bunch of issues larger one don’t have relating to heat. Have you thought about crankcase ventilation?
    David
  2.  
    David,
    I like propane as a fuel also. It has a lot of benefits, but they don't balance out the condensation problem. Both of my engines are well ventilated. The 1 cylinder has a check valve in the crankcase vent. The 4 cylinder doesn't pump the crankcase gases like the 1 cylinder because you always have two pistons traveling in the opposite directions. This keeps crankcase pressures low, and doesn't provide any pressure pulsations to pump the gases out. The 4 cylinder would need some sort of power ventilation to be effective. It also runs cooler which accelerates the condensate accumulation in the oil. I have talked with other model builders that have noticed the same problem with propane fuels in enclosed crankcase engines. This necessitates an oil change and flush with WD-40 each time you show your engine. I am hopeful there is a better solution.

    Jeff
    • CommentAuthordavid
    • CommentTimeMay 9th 2010
     
    My current series of verticals are continual reductions in displacement until the y get difficult to run. Then I plan to go to multiple cylinder designs and I will see what happens.
    David
  3.  
    what about using a negitve vent system, like the ones used on top fuel dragsters... they use a type o siphon in the exaust headers to pull vapors and moisture from the crankcases


    just a thought

    jason
  4.  
    Jason,
    That may be a good idea. It would not work on the single cylinder engine, but it could possibly work on the 4 cylinder if I added another a second vent. I will give the idea a bit more thought to see if I can work it into the design. Thanks.

    Jeff