variable compression engines

[legion]

Originally Posted by pavulon

Seems prone to catastrophic failure...but would imagine that was accounted for in the R&D.

This is my thought.

[Nickshu]

Originally Posted by wdfifteen

The Saab system seems so simple. I assume it hasn't been adopted is that moving all that mass gives a slow response time.

I agree the Saab system seems so less complicated. The Infinity system seems like a nightmare for long term reliability. I'd guess GM ended up with the patent on the Saab system.

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[Bill Douglas]

At first I thought it sounded like my SC engine with broken head studs. But after having read the details I love the sound of it. A high compression engine for running around town, then drops the compression to handle the turbo on boost.

[svandamme]

Originally Posted by Bill Douglas

At first I thought it sounded like my SC engine with broken head studs. But after having read the details I love the sound of it. A high compression engine for running around town, then drops the compression to handle the turbo on boost.

I would think that if you do have variable compression and boost, you would not program it based on user mode, but simply tune it over in combination of a wide variation of parameters.


Just like Variocam and ram and ignition is now varied across the rev range.
Think High compression at low revs for low end power then the turbo kicks in and the compression is dropped accordingly.

You can fit 1 bigger turbo instead of ninnying about with a smaller one for less turbo lag. and a bigger one for top end boost.

You could even opt to
turn on HC for initial spool up,
then turn it off & use the boost to accelerate,
once on cruising speed at the highway, turn boost off in favor for HC for reduced fuel cost at cruise.

To be honest the amount of variables now become so complicated that they are probably going to look at Self learning engine DME's running off Big Data.

Eg all the engines send their feedback to the DME,
the DME will still work closed loop off some basic programming,
but the DME's will then send their data to the cloud
Big Data will send back optimisations to the DME

[Bill Douglas]

Yes.

And it would be a good idea to avoid the new technology for a couple of years until it got some maturity and reliability (limp home mode )

[fastfredracing]

[beepbeep]

hmm, this would be perfect for HCCI engine. Currently, Mazda needs to use low-boost supercharger and spark plug in order to keep combustion in line across whole range. With variable compression they could probably get rid of supercharger.


https://en.wikipedia.org/wiki/Homogeneous_charge_compression_ignition

[RKDinOKC]

Not sure, but Mazda seems to be claiming variable compression with their SkyActive technology. I think it is just a variable cam based on engine loading though.

[beepbeep]

Originally Posted by RKDinOKC

Not sure, but Mazda seems to be claiming variable compression with their SkyActive technology. I think it is just a variable cam based on engine loading though.

Yupp. It is amazingly clever but still needs low boost supplied by Roots SC to cover certain marginal areas of ignition map.

With fully variable geometrical compression ratio, HCCI would be the death of small diesel.

[stevej37]

To me, the simplest system is the one shown in post #13
The idea of raising and lowering the whole cyl head..seems way too bulky.

[daepp]

The Infiniti gets pretty darn near diesel compression at full efficiency - wow!