Variable Compression Ratio Engine

[float_6969]

Pretty cool! The narration is kinda dry, but stick with it. It's a good watch.
[youtube]http://www.youtube.com/watch?v=DdM2VbbdtB4[/youtube]

[PapaSmurf2k3]

Nifty. I wonder why they went supercharger instead of turbo.
"We made this awesome efficient engine, and then pissed some of that away by putting a supercharger on it"

[asoomal]

What's wrong with a supercharger?

[WDRacing]

What's wrong with a supercharger?

It's a parasite. Anything belt driven robs power. It's referred to as parasitic loss.

But they didn't use a supercharger, they used a turbo. They just make a couple verbal errors during the video. They even show the turbo early on in the video at the 57 second point.

[gwoods]

Supercharger is better less plumbing, runs cooler, more organic feel to power delivery.

Turbo's only advantage I'm aware of is the FREE power of exhaust gas, takes power to turn the pump on the supercharger.

[sx moneypit]

Saab had one years ago(don't remember exactly when).

Edit:Here it is http://en.wikipedia.org/wiki/Saab_Varia ... ion_engine

[Hijacker]

Supercharger is better less plumbing, runs cooler, more organic feel to power delivery.

Turbo's only advantage I'm aware of is the FREE power of exhaust gas, takes power to turn the pump on the supercharger.

Turbos also operate in peak efficiency longer. Superchargers are slaves to the drive RPM, so they can't self sustain their air pump independent of driving forces. This tends to leave them producing optimum power for less time than a turbo.

The only honest benefit I have ever seen from using a supercharger is packaging considerations and cost.

[float_6969]

Yea, it had a turbo on it. I really like the video that was the "in car" with the graph on top showing the comparison of CR to vac/boost.

I know this isn't the first VCR engine, and I have heard of Saab's attempt, but this is the first one I've seen implemented in this manner that allows for individual cylinder CR's to be different from each other. I also like that the piston/connecting shaft move perfectly up and down in the bore with no chance for side loading.

I'm also curious about the actuators for the CR change. I'm assuming they run off of oil pressure? They didn't go into the specifics of that in the video and I haven't found much more than what was in the video out.

[Looneybomber]

And I thought the W16 engines looked like an engineering mess...

[the converted]

Does look pretty spiffy. I'm not sure that having individual cr adjustability would really be of that much benefit when the additional manufacturing costs are taken into account. I'm also curious how much the added inertia of all of the pieces will effect the longevity and rev range of the engine. The lack of side loading does seem nice at first, but the machining tolerances are going to have to be incredible to keep the piston from chattering in the bore without the stabilizing effects of side loading.

Don't mean to seem negative about it, I do think it's a rather clever implementation of the concept. I'm just pointing out what I see as drawbacks to the design. They have people much smarter than myself working on it, who I'm sure have it under control.

[WDRacing]

Supercharger is better less plumbing, runs cooler, more organic feel to power delivery.

Turbo's only advantage I'm aware of is the FREE power of exhaust gas, takes power to turn the pump on the supercharger.

A supercharger does heat the air. Not to the extent that a turbo does, but that's only because it's not compressing the air charge. The air charge still gets quite hot and the supercharger suffers from heat soak as well. Most require an intercooler to run any sort of sustained boost. This only applies to positive displacement superchargers though. The centrifugal is just poor in every facet and not really worth mentioning.

The roots blower only has the benefit of immediate boost. However it suffers from parasitic loss and a total lack of boost control. I wouldn't call less plumbing any sort of bonus, only because you can't simply add a roots blower to most modern cars. They either come with one from the factory or require lots of custom fabrication.

I'm pretty sure that any supercharged engine will make much more power if it were turbocharged instead.

As far as linear feel goes, that's been solved for the most part by the wide array of sizing for turbo's, as well as variable vane technology.

[MinisterofDOOM]

Variable compression has always been a cool idea that is too hard to practically pull off. Every few years someone announces a breakthrough variable compression tech that's going to revolutionize engines as we know them. None of them are in production now.

I think this tech is the PERFECT compliment for a turbo. The whole theory of "power on boost, economy off" actually becomes feasible when you can drop compression on demand. Imagine being able to crank up compression to spool up the turbo faster (higher compression=more exhaust air at higher temp=faster spooling). Then, when under "idle" loads (cruising, not actually idling) you could pull way back on compression and either bypass the turbo or drop boost to basically nothing. Not adding extra air means no need for extra fuel. You could vary within that range dynamically. Cruising effortlessly at highway speeds? Drop back to 7:1. Need boost and fast? Crank way up to 9:1 or 10:1 briefly until spooled and then drop off to something suited to the intake charge temp/density that won't detonate.

The other cool part about this is the fuel flexibility. No longer would we be dealing with engines designed to run well on one fuel or merely okay on two. Of course variable compression doesn't solve ALL the problems, but coupled with a VVEL/Valvetronic-style infinitely-variable valve control system, you could get damn close to being ideal for a lot of fuels. Ethanol blends of all kinds. Propane. CNG and LNG. Diesel. Biofuels. Everything could be adapted by altering compression and adapting valve event.

Unfortunately, I just can't see this design matching traditional engine longevity. The whole oscilating pinion gear thing looks like a mechanical failure waiting to happen, and the stresses on the cantilever system that adjusts compression would be pretty intense. Keeping all that going over 250,000+ miles would probably be pretty tough. How do you effectively lubricate a cylinder like that?! And cooling and such. It's also BIG. They say it's no bigger than a normal engine, but look at the shots of the block with the head off. It's easily 30%-50% wider than the same block would need to be without variable compression. So a couple of the biggest bonuses of small-displacement engines are sacrificed.

I really think (yes, I'm sure you saw this coming) that a TT V8 with this tech would be amazing. With a V8, you're already not worried about enginebay space or you'd have gone with a different format. Combine this tech with cylinder deactivation and you'd have a superbly versatile engine. Go from low-comp off boost on four cylinders to high-comp on boost with eight. You can't lose. I imagine there's even a way to vary compression to combat pumping losses for disabled cylinders (increase compression on downstroke, decrease on upstroke or something like that).

I'd love to see someone come up with a workable variable compression setup, but nobody has yet. And this one just looks too fragile for performance use. Might be good for flex-fuel econoboxes, though. fill her up with whatever's cheap and the engine compensates, or toss in some diesel for a long trip to maximize distance between stops. Of course as 1980s GM can tell you, any engine that's doing double duty as gasoline and diesel needs to be built for the job. Which means no aluminum. Which means added weight.

What's wrong with a supercharger?

I look at S/C vs Turbo like this:
S/C is using power from the engine that could go to the drivetrain.
Turbo is using waste heat that wouldn't be used for anything anyway.
Of course it's not REALLY that simple, but that's basically it.

Oh, also:

[asoomal]

What's wrong with a supercharger?

It's a parasite. Anything belt driven robs power. It's referred to as parasitic loss.

But they didn't use a supercharger, they used a turbo. They just make a couple verbal errors during the video. They even show the turbo early on in the video at the 57 second point.

But at the same time, doesn't the pressurized air help push the piston down on the intake stroke, therefore reducing parasitic losses?

With a turbocharger setup, the same thing happens but then the piston has to push the exhaust out and spin the turbine wheel, which also slightly increases exhaust back pressure.

Or am I wrong?

[WDRacing]

Well...

It's not the air pressure that helps push the piston back down. It's the fact that forced induction engines are cramming in more air, and the according amount of fuel, into the combustion chamber for ignition. More air and more fuel = bigger bang. Bigger bang = more power to move the rotating assembly.

A parasite is something that puts a load on the rotating assembly, like the AC compressor or alternator. The supercharger is a large parasite because of the rotors inside the blower, they're heavy. The supercharger also loses efficiency as the rpms increase. A slow spinning supercharger isn't heating the air very much but as the rpms increase the charge air is heated. This is the reason behind the newer water/air intercoolers.

The turbo requires an air/air intercooler for any sort of decent boost level. Porsche ran without an intercooler for awhile, but they used a turbo that was larger that optimum to do so. The larger turbo didn't have to compress the air as much to produce the same volume of air as a smaller turbo. So the charge was cooler, but there was more lag.

Today's turbo's have eliminated lag almost entirely while at the same time producing much more efficient charge air temps. The addition of the intercooler allows for more boost and higher static compression ratio's.

The back pressure that a turbo places on the exhaust system is very minor when it comes to actual power loss and it's almost totally negated by choosing the proper sized turbo.

The only thing a roots style blower does better than a turbo is provide immediate boost at throttle tip in. The turbo will always have some sort of lag.

[PapaSmurf2k3]

I think he's talking about pumping efficiencies.

It takes work for the engine to suck all that air in, and then to push it back out of the combustion chamber. The turbo (and supercharger), even when it isn't "under boost" is helping to push that air along so the engine doesn't have to work as hard to "suck" the air in. This is sort of the idea behind today's smaller turbo engines replacing larger NA engines for better fuel economy. The problem is, people never seem to be able to stay out of boost, so your fuel economy goes to s*** haha (the air fuel ratio richens under boost to protect against detonation).

Like Brian mentioned, the backpressure you get from the turbo is pretty negligible compared to the parasitic loss you get from the supercharger.

[float_6969]

Compared to other VCR designs, I think this is one of the most robust. There does appear to be some weaknesses, but nothing that I don't think could be easily improved upon.

I'm sure this engine isn't designed strictly for performance, but any time you bring high compression ratio's and turbochargers into the mix, there HAS to be strength considerations taken into account.

I don't know if you caught it, but they're also talking about compression ignition capabilities. Imagine the even fuel distribution associated with a spark ignition engine combined with the fuel efficiency associated with a compression ignition engine. You also have the ability to delay when TDC of the piston occurs in relation to crankshaft angle to some extent. This would also allow for timing peak cylinder pressure to occur during the ideal crank angle independent of when the spark plug fires.

[RCA]

Combine VCR tech with free valve actuation (instead of camshafts and springs) and the internal combustion engine's efficiency will be as good as it will ever get.



Starts around 0:54
[youtube]http://www.youtube.com/watch?v=Bch5B23_pu0[/youtube]

[asoomal]

I think he's talking about pumping efficiencies.

It takes work for the engine to suck all that air in, and then to push it back out of the combustion chamber. The turbo (and supercharger), even when it isn't "under boost" is helping to push that air along so the engine doesn't have to work as hard to "suck" the air in. This is sort of the idea behind today's smaller turbo engines replacing larger NA engines for better fuel economy. The problem is, people never seem to be able to stay out of boost, so your fuel economy goes to s*** haha (the air fuel ratio richens under boost to protect against detonation).

Like Brian mentioned, the backpressure you get from the turbo is pretty negligible compared to the parasitic loss you get from the supercharger.

derp.

Yes, I meant to say pumping loss.

[float_6969]

Combine VCR tech with free valve actuation (instead of camshafts and springs) and the internal combustion engine's efficiency will be as good as it will ever get.

Thanks for that vid! The last info I had was Bosch was working on a purely electronic actuator (think electromagnet wrapped around the valve stem where the spring would normally set). They had a running vehicle, but were having issues with longevity because the heat from the cylinder head was melting the insulation on the windings. That was a few years ago and I hadn't heard anything else since.

I find it interesting that they're using a hybrid hydro-pneumatic actuation scheme. In the paper I read, Bosch had dismissed these options due to slow reaction time for hydraulic actuation and complexity (have to add an air pump, air tank, etc) for pneumatic actuation.

[Looneybomber]

Add in variable length intake runners along with independently controlled valves and you will have an engine management system so complex it'll take decrease the overall reliability, but maximize efficency.

[RCA]

Thanks for that vid!

No problem. I haven't been following the history of this tech so that was interesting to read. Not sure what the guys and gals at Koenigsegg are doing differently than those at Bosch but it seems like promising tech for Koenigsegg.

Add in variable length intake runners along with independently controlled valves and you will have an engine management system so complex it'll take decrease the overall reliability, but maximize efficency.

I am pretty sure the video was about independently controlled valves.

But I'm with you, engine management is going to be a nightmare once you're able to control individual cylinder compression ratio, timings, openings etc. They might a require Intel Xeon in order to handle all of those variables.

[Looneybomber]

I just couldn't imagine all the sensors and the coding required to make it happen. Now you have to worry about the longevity of sensors since everything is dependent upon them. That's the direction cars are headed (more complex), but with performance vs. cost and reliability, where is the point of diminishing returns? IMO it's right before VCR and maybe right at independently controlled valves.

[MinisterofDOOM]

One HUGE obstacle with that kind of advanced engine management is that modern exhaust-analysis is still extremely crude. We can really measure oxygen in exhaust overall, and that's it. There's no per-cylinder measurement and there's no metering of anything other than oxygen. No watching NOx to see where we're running lean, no regulating exhaust gas recirculation with intelligent analysis. We sort of just watch for a "clean" oxygen content level, and then recirc some of the exhaust gases based on a general all-encompassing set of criteria.

If we could measure exhaust gas temp, oxygen, nitrogen, carbon monoxide and dioxide, all per-cylinder, we could do some really cool stuff. Especially with modern multi-stage direct injection and variable valve lift...you could switch from otto to atkinson/miller cycles and back again, maximize scavenging, tune injection to regulate combustion chamber temperatures, determine individual cylinders that aren't burning efficiently and then tune accordingly (and identifying individual injector/plug/coil issues and even valve, seal, and carbon deposit issues). You could get extremely precise with all of this, in a way we just can't do today. It's kind of funny to me that the EPA makes a big deal about emissions but we still only bother to measure the bulk of what comes out of our tailpipes once a year. Don't get me wrong: I hate emissions testing and misguided selfrighteousness of putting the onus on the consumer in that regard offends me to the core. But how can we be doing so much on the pre-ignition side of our engine management while completely ignoring the post-ignition side?

[Dattebayo]

In order to test for certain chemicals on that kind of level, wouldn't there need to be some sort of heat-and gunk-resistant optical or spectral analyzing sensor?

That sounds like a job for NASA to me. Also, the sensor would probably cost more than the engine would at that point, right?

[PapaSmurf2k3]

Not really, it would be like an emissions test for each cylinder.

One can "extrapolate" some of that type of stuff from your O2 sensors, A/F sensors, and EGT. They can also use timing to tell which cylinder its coming off of, to an extent.