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Old 12-04-2010, 08:02 PM   #101 (permalink)
autoteach
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Quote:
Originally Posted by NeilBlanchard View Post
Two things: the exhaust flow is nearly constant because it is a 2 cylinder opposed 2 stroke, and the turbo could be sized appropriately? The RPM's are low, so there is some time. Also, each piston is pushing the other through exhaust, and there is no throttle, so pumping losses are low.

What is it about compression that is required for favorable combustion? Is it heat only, or is the pressure required? I was hoping to avoid the "work" of compression.

Your point about the offset causing low power on the upstroke is key -- the whole aim of this is gain the downstroke advantage, and not really need the upstroke power. Otherwise, it would seem that a crankshaft design for ICE is inherently and fatally flawed in that it cannot achieve any better efficiency than it already has?

(It was invented for steam power after all, which has a large back pressure reserve, so the piston is pushed nearly constantly through the whole stroke; instead of a burst at the very beginning.)
Efficiency goes up with compression, but I guess you could stand to reduce the chemical reaction efficiency as well as mechanical efficiency (I believed that I linked it) to gain back some mechanical from the non compression stroke. I would say that compression is important. Here is some more reference on this for another "less mechanically" efficient engine.
http://www.cast-safety.org/pdf/3_eng...ndamentals.pdf

I NEVER said anything about low power up stroke. What I did say that there was a significant thrust issue with your cylinder arrangement. Forcing a piston up against the side of the cylinder will use some of its life and some energy up.

As for mech's link on efficiency, the audi and vw engines putting up 41 and 44% efficiency (50% never being achievable by our antiquated modified steam engines) are 2.5 and 3.3 liters. It would seem that these would fit in cars.

And, so you know, they have gotten 2 stroke DI engines up to 20mpg in snowmobiles.

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