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Scuderi Group Unveils Cutaway Model of First Production Prototype of Split Cycle Engine

Model of the working prototype. The engine is packaged as a research engine, with easy access for instrumentation, a balancer shaft, etc., not as a production unit. Click to enlarge.

The Scuderi Group unveiled a cutaway model of the first proof-of-concept prototype for its Scuderi Split-Cycle Engine (earlier post) at the SAE World Congress in Detroit. The engine cutaway is an exact duplicate of the prototype undergoing testing and analysis by SwRI in San Antonio, Texas. First firing of the working prototype is slated for May, according to President Sal Scuderi.

The prototype is of the naturally-aspirated Split Cycle gasoline engine, and is intended to be a proof of the basic technology of the split cycle with firing after Top Dead Center (one of the key attributes of the engine and cycle). Subsequent implementation of the Split Cycle will be a turbocharged split cycle unit, an air hybrid version of the engine, and a diesel-fueled version.

“Our efficiencies right now are running higher than anything that is on the market .”
—Sal Scuderi

The one-liter, naturally-aspirated gasoline prototype is expected to produce up to 80% fewer criteria pollutants than a typical internal combustion engine. When fully developed with its turbocharged and air-hybrid components, the engine is expected to achieve significant gains in fuel efficiency.

The Scuderi Engine is a split-cycle design that divides the four strokes of a conventional combustion cycle over two paired cylinders: one intake/compression cylinder and one power/exhaust cylinder. By firing after top-dead center (TDC), it produces highly efficient, cleaner combustion with one cylinder and compressed air in the other.

The Scuderi engine achieves compression ratios in excess of 100:1 in its compression cylinder, Sal Scuderi said. The high pressure air flows into the crossover chamber, where it receives its fuel load from two direct-injection injectors, and then flows into the combustion chamber with a great deal of turbulence and concomitant rapid mixing of the fuel air charge. As a result, Scuderi said, combustion is four times faster than in a conventional engine.

The Scuderi engine also uses the high pressure air generated on the compression side to run accessories of the engine. The inlet and outlet valves are all pneumatically actuated valves. There is no throttle on the engine to control the load, rather “we control load with the intake and exhaust valves that are being fed from the compression side of the engine,” Scuderi said. The engine uses air springs to return the high speed valves in the crossover; those are also fed by the compression side of the engine.

Combustion starts 15 degrees after TDC and ends 23 degrees after ignition. This results in higher average temperatures but lower peak temperatures than conventional engines—one unanticipated benefit of this is low NOx formation.

The Scuderi engines offer high power density—the turbocharged split-cycle engine is projected to deliver 140 hp/liter.

Unlike conventional engines that require two crankshaft revolutions to complete a single combustion cycle, the Scuderi Engine requires just one. Besides the improvements in efficiency and emissions, studies show that the Scuderi Engine is capable of producing more torque than conventional gasoline and diesel engines. (Earlier post.)

With the assembly of the naturally aspirated Scuderi Engine now complete, the Scuderi Group and its independent laboratory continue to work on the next prototypes. Completion of the turbocharged Scuderi Engine and the Scuderi Air-Hybrid are expected in 2010.

Select Attributes of First Two Scuderi Prototypes
 Naturally Aspirated
Split Cycle Engine
Split Cycle Engine
Engine speed Up to 6,000 rpm Up to 6,000 rpm
Power Similar to conventional engine Up to 140 hp/L
Efficiency (full load) Similar to conventional engine 10-15% higher than conventional engine
Emissions Up to 80% less NOx than conventional engine Up to 80% less NOx than conventional engine
Air pressure levels 50-60 bar 110-130 bar
Fuel injection pressure Up to 200 bar Up to 200 bar
BMEP 9 bar/L displacement 22 bar/L displacement
Compression ratio 100:1 100:1
Displacement (approx. 1 liter) .58: compression side
.52: power side
.48: compression side
.52: power side

The company intends to license its technology to engine manufacturers. The Scuderi Group expects further advancement of the technology once the greater engineering community begins working with the engine, making their own modifications that will most likely take the efficiency to even higher levels. According to Scuderi, the company is in discussions with 14 of the largest 20 engine manufacturers in the world.



Very misleading when they say that one combustion cycle per 360 degrees. In a two cylinder engine (absolute minimum because a cylinder is required for intake/compression), one cylinder fires once every 360 degrees while the other fires zero times every 360 degrees. That averages out to .5 times every 360 degrees or once every 720 degrees... the exact same as a conventional 4 stroke ICE. Reductions in frictional losses will probably be minimal, IMO.

Also, what is the point of having 100:1 compression ratio if you are going to wait until 15 DEGREES AFTER TDC to fire? By that time the effective CR will be more like ~80:1.

And how, pray tell, is the combustion cylinder going to survive all without periodically being exposed to ambient air?

The concept of over-expansion is nice, indeed novel and well thought out, but the problems that this particular engine faces just seem too large to overcome.

Henry Gibson

Scuderi made a big mistake by taking long enough to develop the engine to the point where no car company could afford to buy it, but at least a few people got fed for a few years at scuderi.

The later arrival of their air hybrid design may make the engine worth something, but efficient european diesels are long since available. The steam diesel hybrid was invented over a hundred years ago, but has found its way to only one locomotive a few ships and an experimental car or two.

I guess that the money is running out so they actually have to finaly produce a prototype. It is too bad that their simulator did not predict the demise of GM and others along with the slightly increased engine efficiency. But even the lastest electric car adds emphasize acceleration over efficiency. Small low acceleration engines always had better efficiency. It was not wanted by most. ..HG..



They have taken way too much time to show something, and to me they haven't shown anything yet, only simulations, but no real results. The 10-15% better efficiency they claim over any commercial product doesn't make it any better than advnaced diesel concept, HHC, Direct injection or Variable compression ratio. Lower emission maybe but so far this calim is not backed by real data so, even if it works it may come too late, since automaker will have already make their choice for their next ICE architecture as a bridge to hybrid plug-in or fully electric

Randolph Toom

Congratulations to the Scuderi team. This is a major milestone in bringing your product to the market and I wish you success in the work still to be done.

I am also looking forward to see you again at Engine Expo in Stuttgart in June.

Best regards,

Randolph Toom
Managing director of heat2power



Thank you for your link. I have long thought that heat recovery from engines was a good way to improve efficiency.


I just read an article in the Wall Street Journal April 21st, it said executives at Daimler, Fiat, Peugeot and Honda confirmed they were closely looking at the Scuderi Design, and all have signed NDA's. This engine is for real, please stop being critical as it serves no purpose, and the results are forthcoming in the very near future. Thanks



Sorry sir, but can you tell me what purpose it serves for Scuderi to keep claiming promises for years that they haven't backed by ANY real data, I maintain ANY. Only simulation. I was very enthusiastic when they introduced their concept few years ago and have visited their site regularly waiting for some REAL data, but I lost heart and I got convinced that these people don't want to develop prototypes, they only want to "prove" the concept through simultions then to sell licences to big groups to make money with, their approach is purely marketing. Teams working on MUSIC concept or Variables compression ratio or others have shown real data, but these guys : none! and they will not because they have no intention of doing so. But I would be happy to be proven wrong. To me EESTOR and SCUDERI are the same type of hype.


Sal Scuderi said at the 2009 SAE Tech.Show that the engine will be actually running around the middle of May. Hopefully you will have all the data necessary to change your opinion sometime this summer. There must be something there because most of the major OEM's have been expressing interest in this technology. A Daimler
engineer was quoted in the Wall Street Journal stating
"there is realistic potential here" Sounds good enough to me.

Randolph Toom

Simulating can take a long time to a mature engine design if the concept is new and that is the case here. But during that time there is no money wasted on useless prototypes that would have had mistakes, because made too early and with too little understanding of the processes that go on in a geometry that is quite different from normal engines. Their valve control is furthermore quite tricky because the valves have very short open times. However from the photographs I assume they have solved it. The valve springs should be quite stiff to cope with those cams.

The water injection as shown on their website also looks interesting. It would only be feasible and durable with the appropriate control system so that corrosion is avoided. This engine looks very promising. I am not surprised they are in contact with various companies out there.

I wish them good luck with testing now.

Randolph Toom
Managing director of heat2power

Roger Pham

Please prove me wrong, but I don't think that compression ratio of 100:1 is possible in a functional, production engines. Unless it's a very long stroke engine, tolerance must be provided for difference in thermal expansion of the piston and the cylinder, and that usually reduces geometric compression ratio to below 30:1, using current materials. And then, there will be leaks through the piston rings and thru the valves...and you'll be down to a realistic 20-25:1 ratio as a practical,real-life limit.

But, the real limitation of this engine concept will be heat...too much heat in the power cylinders that will limit real-life power output for proper cooling, and too much heat in the valves of the transfer passage way that will affect durability. A big and under-powered engine will be a no-go in modern automobiles.

And then, after going thru all the troubles, the full-load efficiency of this engine in the NA form is now listed as "similar to conventional engine."

The air-hybrid mode will severely be limited by the very low energy storage ability of compressed air. Thus, it cannot replace the HEV-size energy-storage battery and electric motor if you wanna make it into a hybrid car of sort.



ha ok , because one engineer in Daimler sais it has "realistic potential" is good enough to you, well if I was a venture capitalistic fund, I would hire you as a board member or even as a consultant.


if simulation takes time and early prototypes are useless, then I would have had a poor carrer as a developper of lasers. That's not the case so my experience against yours, I stick to mine. And if you are right then they should spend less time claiming and communicating and more in simulating, right ?

I am pretty sure this concept will not make it trough, if it requires so much simulation to even show any tangible results then it won't work


"In the battle of life it is not the critic that counts;
not the man who points out how the strong man stumbled,or where the doer of a deed could have done better. The credit belongs to the man who is actually in the arena; who strives valiantly; who errs and comes up short again and again because there is no effort without error and shortcoming; who does actually strive to do the deeds; who knows the great enthusiasms, the great devotion, spends himself in a worthy cause; who at best knows in the end the triumph of high achievement; and who at the worst, if he fails, at least fails while daring greatly, so that his place shall never be withn those cold and timid souls who have tasted neither victory nor defeat.

Maybe you should or can suggest a solution to your apparent problems with the Scuderi Engine design rather than being a basher with limit knowledge of what is actually going on.


TH seems to be suggesting the solution to his problem with Scuderi would be to commit and make their first prototype.

This way they can progress from baseless claims for the simulation to endless claims for their "useless" prototype.

And it is Scuderi that is responsible for the knowledge being limited .


Am I missing something or are you two not doing your homework??? The proto-type is completed, Sal Scuderi said it would be firing by the middle of May. (refer to the website: Why don't you call the Scuderi Group, ask for Sal Scuderi, sign an NDA, fly down to Southwest Research at your cost of course, to see the engine actually running. Maybe then you will stop bashing this incredible technology which has the potential to replace the otto for the next 15 to 20 years. If there was nothing to the Scuderi Engine Technology, ask yourself why are so many OEM's interested. I have to go with the major OEM's Top Powertrain Engineers over your unreliable assumptions.


Yes pfb, you are missing something.

"According to Scuderi"
the company is in discussions with 14 of
the largest 20 engine manufacturers in the world.

"According to the Scudari website:"
The proto-type is completed

"According to Sal Scuderi" First firing of the working prototype is slated for May.
Does it take months of cranking before it fires.
The prototype can hardly by completed or it would be running NOW.

All that's running is their PR machine; for 7 years now and with the potential to operate efficiently for the next 15 to 20 years.



I am not bashing anything, I am passionate about innovations, but after 25 years of carreer in R&D I am more and more impressed by real achievements and less and less by simulations and claims or oversold potential not backed by data, you seems to be a bit young and tender in the job, but take no offense i was just reacting as you do when I was your age. This "interest of big groups" is just hype, I know from experience that big groups are always interested in innovations in their field, and then ?

Scuderi Group is just words so far, so many words for little results. You know I had an old teacher who liked to opine : when we know everything about a science area, the litterature on the whole thing is a thin book. When we know nothing about a science area then there is ton of books about it...

But again I would be happy to be proven wrong, I am just tired of waiting and listening their blabla


I think the Scuderi Group has been managing this new technology with extreme caution. Having technology that might change the automotive industry for the next 15 to 20 years, who would want to put it out there for everybody to see prior to protecting it. (they now have more than 200 world wide patents). The Scuderi group also hired a very respected engineering organization(Southwest Research) to develope the technology. Evidently the engineering community has alot of confidence in the software and Southwest Research reflected by the undisputed interest they have expressed. As mentioned before, your wait for data and results is just around the corner, most likely around the middle of June. I look foward to your comments on this matter when the data is made available as your interest is in the Scuderi Split Cycle Technology is evident and your knowledge vast. Thanks

Roger Pham


Your enthusiasm is admirable, but please consider the following:

Compression ratio (CR) of 100:1 is not achievable in a single stage piston compressor with a dead volume of 1%, as Scuderi claimed in their website. This is because by the time the pressure got to near 100 bars, the volumetric efficiency of the compressor approaches ZERO. To get to a CR of 33:1, the volumetric efficiency of the compressor with 1% dead volume will drop to 66%. This is to ignore the tremendous heat and pressure generated to get to this level of compression. A heavy-duty diesel engine with CR of 25:1 has to be built heavily, with very beefy cranksshaft and block to withstand the large forces involved.

Unable to achieve this kind of CR in an engine that fires 15 degrees after TDC mean that you cannot achieve rpm's competitive with an Otto-cycle engine, and hence your power density (power to mass and weight ratio) will be severely compromise to the point that you'll no longer be competitive.

Heat concentration in the power cylinders that fire every downward stroke without exposure to cool intake air is yet another limiting factor in specific power capability of the Scuderi Engine. Two-sroke engines suffers a lot from heat-related engine failures in larger size. High-output Otto-cycle engines have to be richen the mixture enough to obtain sufficient cooling at high output, (cooling by fuel) meaning that even firing every other stroke still is not able to cool the engine down enough to prevent engine damage. WWII aircraft engines may also use water-methanol injection to produce WEP (War Emergency Power). This practice is too impractical and wasteful for use in a lean engine for Green car congress. This means that the Scuderi engine must have its power severely restricted to prevent engine meltdown, meaning it must be much larger in size for a given peak output...

From the above, there will be little room left in the hood for air-pressure storage tank for the pneumatic hybrid mode...Compress air stores very little energy in comparison to an NiMh battery...

Please address those major concerns before investing further in this technology...Perhaps these concerns have been addressed by Scuderi to the major OEM's without yet releasing the info to the public...we will see!!!

Roger Pham

Look into the new Honda VCR (variable compression ratio) mechanism. Enabling this VCR engine with HCCI and ATkinson cycle operation and variable valve timing means that you will have a HOT ROD engine with output of 100 hp/liter yet capable of over 45% BTE (efficiency) at peak. Mate this engine with the new Honda electric hybrid technology that is cost competitive with conventional, non-hybrid vehicle drive train and you'll have mid-size cars with 60-70 mpg potential.



No my knowledge is very restricted, but I have been successful in my area though I am not that strong on "theory and simulation" because I stick to simple but powerful rules that very often avoid a lot of lost of time, in my compagny I keep wining awards for achievment in development (and believe me I am not competing for it, I don't care). All the idea of Scuderi engine is on the massive turbulence you create when you inject the compressed air front the 1st cylinder to the 2nd one then improving combustion then reducing emission and to a lesser extand improving efficiency. I like the idea because if it works you will be able to run gazoline engine like diesel with improved efficiency. The only problem is that there is nothing to day to prove that it really works. Simulation of turbulent combustion is beyond what simulatation can predict with a reasonable amount of confidence(sorry for that) so you can not be sure that this effect could not be offset by other undesirable effect. Sorry to lecture on you, but they could have build a bench to demonstrate specifically this highly turbulent mode that is supposed to improve the combustion, you don't need to built the whole engine for that, just a bench. Did they ? no they didn't, blabla instead.



I spoke to Scuderi people at the SAE show. I don't feel like getting into minute details, but I can clear up some blatant misconceptions.

The effective compression ratio is lower than 100:1 because the valve in the compression cylinder opens.

Peak temperature in the expansion cylinder is much lower than in Otto cycle engines.

The air storage tank cannot store as much energy as a battery with the same displacement. However, in this application it won't have to because the energy is expected to be used relatively shortly after being stored.

Peter Hill

It won't ever achieve the claimed efficiency.

They make claims to having 100:1 compression ratio for compression cylinder but this just proves they are stupid. The compression ratio is (swept volume + chamber volume) / chamber volume. For the compression cylinder the chamber is the transfer port or receiver vessel between the 2 cylinders. They don't actually have any more than 5:1 CR, add on the receiver vessel and it will be down to 1:1.

Then they open the inlet to the power chamber and reduce it still more.

Only way to fix this is to make the compressor 10x the size and then they will find they have 4% or maybe 5% overall efficiency - about 1/10 of current best such as Rolls-Royce Bergen K series.



If you're going to result to calling someone "stupid" (which I do not condone) you should probably make sure you know what you're talking about first.

(swept volume + chamber volume) / chamber volume is not the conventional definition of a compression ratio. The compression ratio of an engine is the ratio of the volume between the cylinder head and the piston before and after the compression stroke. What you're talking about is the effective compression ratio.

In the case of this engine the crossover acts like a queue for compressed air. They can control the effective compression ratio by the timing of the valves. According to Scuderi, the effective compression ratio is about 50:1, which is easily believable.

Maybe this design will live up to the hype or maybe it won't, but please stop spewing nonsense.

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