Half a croissant, on a plate, with a sign in front of it saying '50c'
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Ultimate Atkinson Cycle

I figure it's been long enough not posting an engine idea
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Well, Atkinson Cycle engines are somewhat interesting. What happens is the intake charge is sucked into the engine, then the intake valve remains open for a short period of time on the compression stroke so some of the charge is pushed out. This allows for greater efficiency with the trade-off of reduced power. But I believe there is a lot of un-harnessed potential in the Atkinson Cycle.

First off, in my design it would have to be variable. I propose a system like VTEC in Honda engines where there are separate rocker arms that lock together to control the same valves (in this case there would be two rocker arms for two valves and one in the center for the atkinson affect). Then, the center rocker arm would be controlled by a device like Valvetronic found in some BMW engines to continuosly vary valve lift. This is all possible stuff, hardly inventitive however necissary to the engine, as it allows the variable lift to be isolated to only the Atkinson effect, while the other two lobes control the intake function normally.

Next, there is a feature similar to my proposed idea for variable squish tabs, which would have a small tab in each cylinder that allows for a very high compression ratio when at the top of the head, but can be raised even further up to create a cavity and therefore a lower compression ratio but increased volume. This would seem like a half-assed rather than half-baked way of controlling compression ratio, however with a variable Atkinson Cycle, the extra volume added by raising the tab could be expelled in the compression stroke when necissary, effectively maintaining a constant displacement for the engine. This would be useful because it would allow for much greater power at high RPMs, as engines can handle a higher compression ratio at higher RPMs without detonation because there is less time for it in the compression stroke. It goes without saying that this would be direct-injected, so picture something like a starting compression ratio of around 12:1 with the cavity as high up as possible, increasing to as high as 15:1 in its lowest position (which would be at the top of the head as mentioned, not protruding into the cylinder).

And with greater power would come greater efficiency. A continuosly variable Atkinson Cycle would mean that the intake lobes could provide maximum lift (meaning minimum resistance) so that the pistons would suck in the charge using much less energy than with a restrictive throttle or even variable valve lift device on its own, since a lower valve lift would still create a non-trivial amount of resistance. Of course the amount of charge that would stay in the cylinder to be compressed would rely on the throttle position, which would control how much valve lift there is on the Atkinson lobe (the more lift, the more is pushed out; the less lift, the less is pushed out). The neat thing about devices like Valvetronic is that they allow for a wide range of lift.

In a nutshell, this would undoubtebly provide better efficiency and better power capability than an equivalent Otto Cycle. Oh and as a side-note, there would be a sparkplug on the tab itself in addition to the one in the head simply for better combustion.

acurafan07, May 22 2008

Rotary Atkinson Cycle Engine http://white-smoke..../page/Rotary+Engine
asymmetrical chamber mechanism for complete expansion and maximized yet shorter intake and compression [rotary, May 23 2008]

The Ultimate Atkinson Cycle Image http://www.flickr.c...026@N08/7020089179/
[AusCan531, May 31 2012]


       Wouldn't it be easier to vary when the valve closes for adjustment of that effect rather than how far it opens?   

       However the idea of a variable compression ratio atkinson cycle is sound. A variable compression/variable timing atkinson cycle engine with a turbo would have to be a pretty good thing too.
BLSTIC, May 22 2008

       I get it and I think it has merit but there's just too many things going on in that head. It makes my frontal lobes itch just imagining all those moving parts. My caveman engineering instincts recommend I smash it all with a rock. <looks around for rock>   

       I guess this is your lucky day. Bun, until the timing chain snaps.
elhigh, May 22 2008

       worked well when valves were small and piston velocities were low but i just don't see the point in a modern penthead. VCR is a neat idea but hopelessly unreliable.
WcW, May 23 2008

       Hey wait this is the HB, since when do ideas get boned for being too complicated and unreliable?
acurafan07, May 23 2008

       So, not an excercise machine for people on a low-carb diet, then?
MaxwellBuchanan, May 23 2008


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