Miller cycle engines

"Ron Calls on his years of experience....and freezes at the controls" (internerdstuff) 07/09/2015 at 10:45 • Filed to: None

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I have a slight brain block while pondering miller cycle engines. Just to clarify- the specific type i’m referring to is like a forced induction version of the atkinson cycle.

So my thought is this- I know the atkinson cycle engine gains efficicancy by allowing some intake charge to escape(therefore increasing the expansion ratio),and that the miller variant makes up for the inherent power losses by adding forced induction. But why is a miller engine more efficient than any normal ICE?
The Miller uses forced induction but lets some of that intake charge back out again.... which doesnt sound much different to the end result a normal engine does! So where is the advantage?

ShiroZ31 > Ron Calls on his years of experience....and freezes at the controls 07/09/2015 at 11:09

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Maths! http://repositorium.sdum.uminho.pt/handle/1822/99…

orcim > Ron Calls on his years of experience....and freezes at the controls 07/10/2015 at 03:29

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Not apropos of anything, so dismiss, delete, ignore, whatever.

But do you remember those devices in elementary physics that looked like:

I kinda see this like that. The “obvious” solution to which way it turns (or which cycle is more efficient if you could lay hands on it) was never obvious, to me. Miller Cycle has the same thing going on, in my mind, though once explained, I get it what’s being said, but couldn’t understand it before the explanation of unharvested potential energy or the change in PV=NRT [sic] that occurs because the gases are cooler.

Anyway - hopefully my shared confusion helps you not to feel anything except that you’re human. It’s all still a little like analog TV’s - a little bit spooky.

samssun > Ron Calls on his years of experience....and freezes at the controls 07/20/2015 at 14:48

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I believe it’s because you still have a high expansion:compression ratio. So assuming friction and heat from supercharging don’t overcome the savings, whatever amount of charge you put into the engine (whether X or 2X) still gets to expand longer and therefore have more work extracted.

samssun > orcim 07/20/2015 at 14:51

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Atkinson lets whatever charge you compressed expand further, getting more work out of it before you release it out the exhaust. Miller or supercharged Atkinson starts with more charge, but still lets it expand further.

So it’s just scaling up the same idea, and relative to your output should be more efficient. Atkinson by itself means crippled performance (see: Mazda’s SkyActiv)