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Old 03-30-2011, 03:40 PM   #11 (permalink)
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I'm trying to find out why no manufacture has implemented variable compression ratio technology. In part load conditions most engines only have an effective compression ratio of 6:1 or less (The published compression ratio only applies in high load conditions) So this makes me think of using a sliding plate that dynamically slides in a controlled manner into the combustion chamber (to displace some of the unoccupied volume) in part load conditions bringing the effective ratio back to 9.5:1 and slides out in high load conditions. It's probably not as simple as attaching this "slider" to an accelerator cable and I see lubrication and getting really tight tolerances as one of several challenges to be overcome. While I may be over simplistic here, why this low hanging fruit is still not implemented by any manufacturer as this idea has been floated for decades.
I just found some info here. This site www dot prodrive.com/up/vcr.pdf


Last edited by briank; 03-30-2011 at 03:49 PM..
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Old 03-31-2011, 10:34 PM   #12 (permalink)
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I recall seeing an old magazine from the late 1940's that had an article about variable CR.
It was done on a flathead Olds engine, I think, and CR could be varied to go higher with light load.
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Old 03-31-2011, 11:02 PM   #13 (permalink)
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I was mistaken. The engine this was done on was a '40s flathead Olds but the article was in the Aug. 1953 issue of Popular Science. Oil pressure was used to drive a piston up and down in the cylinder depending on load to vary compression from 6-1/2 to 1 to 14 to 1.
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Old 03-31-2011, 11:47 PM   #14 (permalink)
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...the GM-Allison XM-1 "tank" that went up against the Chrysler "turbine" XM-1 tank used a variable compression ratio diesel engine.

...both got about 1 MPG or 1GPM (take your pick).
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Old 03-31-2011, 11:56 PM   #15 (permalink)
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Quote:
Originally Posted by janvos39 View Post
An engine developped by Lotus for mixed fuel ,variable compression, two stroke, high efficiency.

Run the engine

Lotus Cars
Updated link

Lotus Engineering - omnivore interactive demo
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Old 04-01-2011, 09:37 AM   #16 (permalink)
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It appears all the VCR solutions I've read involve varying the combustion chamber volume by applying a force normal to a flat structure parallel to the piston head which necessitates the use of very high pressure specification, high force actuators. On the other hand a sliding profiled plate that slides parallel to the combustion pressure forces would require a far lower specification actuator. Remember the volume of the combustion chamber does not have to vary by much to have a large effect on compression ratio. The displacement profile of the slider plate would be optimized such as to preserve symmetry and avoid pockets of uneven combustion. Optimizing the profile for the part load condition would be the priority as that is where the majority of the engine operation time would be spent. I hope this technology becomes mainstream soon as it would enable an optimum use of E85 which needs a high compression ratio to get the most out of it.

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