Last month we told about Ricardo's 2-Stroke/4-Stroke breakthrough, a very promising technology for sure, but one that is still just a series of gleams in a bunch of engineers' eyes. Much closer to prime time is the Scuderi Group's Split-Cycle engine. How close? Motor Authority is citing Automotive News who's claiming Scuderi's tech will be for sale within 12 months. This is big news, as the Split-Cycle internal combustion engine will be 40% efficient, compared to regular 4-cycle mills which are only 33% efficient. Scuderi is also promising lower emissions of NOx. So, how's it work? Just like it sounds, actually. The four-strokes of the Otto-cycle are split across two cylinders. One cylinder is used to compress the fuel and then "gas passages" move the compressed mixture into the detonation or power cylinder. The fun comes when you start playing with the bore and stroke of the various cylinders. For instance, you can make the power stroke longer than the compression stroke to take advantage of the Miller Effect (less energy is used by the compression cycle than the power cycle). Or you can increase the size of the compression piston to in effect supercharge the fuel mixture. We say not a moment too soon, as clean alternatives continue to (not) sputter along.
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More news along these lines, please :D
I’m kind of surprised that as old as the ICE is, there is still room for serious innovation.
Why not use what Mazda did with it’s miller cycle engines – use a supercharger to gain that effect.
I’ve been thinking about this all morning. First, wouldn’t frictional losses from the compressor piston offset a fair amount of the efficientcy gain? Second, if you need to double the piston count, you’re adding both size and weight and I really can’t see that being acceptable these days.
Finally, if you’re going to compress the air, why not just use some sort of totally external compressor? I could imagine having a turbine compressor to supply a constant volume of pressurized air to an accumulator tank. I’m sure there are a lot of reasons why this would be impractical (cost would be one of them), but it would be great to have a source of bleed air to run accessories.
Here’s a link to the animation that shows how it works …
http://www.scuderigroup.com/technology/animations/split_sideview.html
bunkie:
Great questions and I wish I knew more about it.
I’ll assume the answer to the added size and weight and friction is that the engine is so much more powerful/efficient that those losses are covered and there are still gains.
Now, combine this split-cycle with elctro-magnetic valves and… ICE hey day!
# bunkie :
April 18th, 2008 at 1:44 pm
I’ve been thinking about this all morning. First, wouldn’t frictional losses from the compressor piston offset a fair amount of the efficientcy gain?
Finally, if you’re going to compress the air, why not just use some sort of totally external compressor?
I don’t know too much about this, but from what I understand computer models have still shown a net gain in efficiency even with the 2nd set of pistons. The reason not to use an external compressor is because piston technology is very mature and the Scuderi engine could be manufactured on existing equipment.
An external compressor is exactly what’s used by a Miller cycle engine, with a supercharger.
As far as weight, note that this is techically a two-stroke motor with double set of pistons, so in effect your extra piston weight is offset by the fact that each one of them does twice the work of a 4-stroke.
I’m pretty sure that this requires FAST direct injection in order to work efficiently, in order to prevent fuel from leaving through the exhaust. Also, it would be a nightmare to do closed loop emissions control on.
Speaking of fast direct injection, a plain old Wankel would be a better recepient here.
I second Joshvar. Send more news long these lines.
bfg9k-
Thanks. I’m thinking that a typical piston compresses air much more than any turbo or supercharger, which is why I was wildly fantasizing about a turbine compressor.
The crazy picture that came to mind was the opposite of the 1930s Italian attempt to create a jet engine by using a piston engine to drive a compressor whose compressed air was fed into typical jet combustor. Can’t remember the name at the moment, but it did actually work in that they built a flying prototype, but weight, perfomance and fuel consumption were all too poor for the idea to really take off.
In any case, it’s fun to speculate!
Yes, please more news on this. Also link of the manufacturer would be nice.
Thanks
Not sure if it’s been mentioned before but I like the idea of this six stroke engine …
http://en.wikipedia.org/wiki/Crower_six_stroke
The thought of seeing a Chevy Tahoe hissing steam from its wheel wells like some old locomotive seems somehow apt.
This would NOT have the weight advantages of a 2 stroke engine. Simply because you still have 2 cylinders for every power stroke. Weight would be roughly the same as a traditional 4 stroke because you still get the same number of power strokes per revolution.
I think one problem with this would be vibration. With a traditional 4 stroke or 2 stroke, the cylinders (either inline or V) generally cancel out the primary vibrations of the other but with an engine with unequal pistons would have unequal forces from the accelerations of the pistons and thus greater vibrations.
“Motor Authority is citing Automotive News who’s claiming Scuderi’s tech will be for sale within 12 months.”
No way production worthy engines will be ready in that time frame. Based on what I could find on the Scuderi website, no physical prototype has been built yet. All of the efficiency improvement claims are based on computer models. Computer modeling works best when the underlying technology is well understood and the appropriate equations can be devised, constants understood, etc. In my years as a engineer I have yet to see the final result of a prototype effort outperform the computer models, yet often the opposite has been true. Losses and issues which were not foreseen often come up once you get to the physical stage.
Computer models said the Boeing 787 would be in the air by now, but it isn’t.
There have been many, many alternative ICE designs over these past 100+ years, and only a few of the promising ideas actually work out.
Third the motion…keep these type of stories coming!! Ingenuity can stretch the laws of physics..just look at a 911…
Message received.
I must say that I am skeptical about this.
Ultimate thermodynamic efficiency of *any* heat engine is dependent upon the difference between maximum and minimum operating temperatures:
http://en.wikipedia.org/wiki/Thermodynamic_efficiency#Carnot_efficiency
So Scuderi’s claim that increasing the *speed* of air-fuel mixture burn produces a 5% increase in thermal efficiency doesn’t ring true:
http://www.scuderigroup.com/technology/theory_of_operation/summary_of_gains.html
As for the other claimed efficiency improvements…
—Use of ceramics: They don’t explain why ceramics would benefit a Scuderi design more than a conventional ICE.
—Lean-burn: lean A/F ratios increase combustion temperatures (hence NOx emissions) regardless of when the mixture is ignited, so the claim that the engine wouldn’t need a NOx catalyst is dubious.
—Advanced piston motion: It is unclear why these piston/rod design criteria couldn’t be applied to a conventional ICE.
Finally, I don’t see anything that this engine does that couldn’t be accomplished by judicious application of variable valve timing, direct fuel injection, piston/head/combustion chamber optimization, and conventional supercharging/turbocharging.
My suspicion is that the computer modeling assumes “perfectly smooth” engine operation, so that effects of hot spots, misfires, non-homogeneous air/fuel charge, etc. are ignored, but would be problematic in the real world.
I’m with Eric here; it smells a little fishy, and I’ve yet to see a Rube Goldberg adaptation of an existing technology that gains efficiency with seemingly more parts, friction and mass.
The only real gain would be using ceramic components, allowing greater levels of temperature difference.
That said, the older I get, the smarter I think I am, so to be pleasantly surprised by some new tech would be wonderful…
Why not rotary valves?
http://www.coatesengine.com/
Ah, I think you need to reread the article. It will be available for licensing to a manufacturer in 12 months, and prototypes will be available in ‘by next year’. That puts it at about 5 years from production, if there are no major problems.
I actually think it makes sense!
Why – because of the “Miller effect” – conventionally the expanding hot gases are not allowed to give their full “umph” to the power piston, hence the “pop” and rush of hot exhaust gases out the exhaust valves, and the energy remaining causes the manifold to get broiling hot, and the upper pipes. This way, the full piston travel is possible, getting the best work use out of the hot gases. It just seems logical – we should be able to get more than 1/3 of the energy out of an IC engine, and perhaps other methods add complexities or components with lower reliability. If the other methods are better, why are they not more widely accepted?
If the combustion chamber were ceramic lined, the lining may be insulated/heat reflective, and prevent energy on the hot side escaping to the surrounding metal, thereby increasing efficiency. And if the combustion temperature and compression were increased, this may be worth it, even if NOx emissions are an issue – they’re high-energy compounds, so a catalyst should be able to handle them easily.
But looking broadly at mileage, the low-hanging fruit are engine efficiency, aerodynamics, vehicle weight, and braking, about in that order, give or take the type of vehicle. Improve all four, and we can achieve 120 mpg – seems like we should be there already!
An interesting concept, but without a working prototype, it is impossible to compare efficiency with conventional engines. Also, the compressor means more maintenance and a high efficiency air filtration system. The cost for manufacturing this engine will also be a major factor.