Practical solution to variable compression

[Roger Heflin]

> 
> I was thinking about this while designing a model of a 200cc
> two stroke engine (single bore only) that uses opposing pistons...
> 
> What if one tied the cranks together with a gear drive mechanism
> having a gear on each crank and a pair of idler gears coupled
> together with a clutch that could only slip say, 15 degrees.  By
> effectively putting the two cranks out of exact synchronization,
> wouldn't you change the engine's compression?
> 
> Think about it a minute.  If at exact alignment, the two pistons
> reach TDC at the same time, then you have MAX compression.
> If the alignment is offset by allowing the clutch to slip just a little
> and then lock back up say ten degrees off sync, then you would
> never have the two pistons reaching TDC at the same time.  Thus,
> your compression ratio would drop.
> 
> Now, my next question is...  Would you gain significant performance
> by allowing high compression at low throttle settings and then use
> a lower compression at WOT?
> 
> Having variable compression seems like a cool idea, and I
> believe an engine and management system could be built to
> do it.  Looking this whole thing over, I'm pretty sure that
> MAX performance would still be limited the way any other
> engine is, but couldn't the whole power curve starting from
> way down low near idle be boosted considerably?
> 
> Does this idea warrant any merit?
> 
> Can anyone shoot BIG holes in it?
>

The only real problem I can see is that one of the pistons would
be potentially moving into the flame front, which could be a
problem.  I think it would be more useful with a gas engine,
where too much compression detonates things, and less useful in a
diesel engine where this is mostly normal operation.   Still
it may be a problem with the piston trying to compress an expanding
gas, knowing what knock does to an engine

			Roger
> Matt
> ______
> 
> 
>