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SwRI Full-Load Study of Scuderi Split-Cycle Engine Indicates Higher Power, Torque and Efficiency Than Conventional Engines of Equal Displacement

The first independent laboratory study of the Scuderi Split-Cycle Engine (earlier post) under full-load conditions indicates that a gasoline-fueled version of the engine will have higher power, torque and efficiency ratings than the current state-of-the-art turbocharged gasoline engines of equal displacement on the road today.

The Full Load (FL) Study by Southwest Research Institute (SwRI) is the first of three reports to be published by the laboratory prior to the assembly of the first prototype, which is scheduled for completion later this year. A Part Load Study and an Air-Hybrid Study will be published in early and mid-2008 respectively.

The air hybrid study will incorporate the results of full load and part load studies, and add to that the compressed air storage tank used in the hybrid implementation. The air-hybrid study will compare the Scuderi air-hybrid efficiency levels to those of an electric hybrid.

The patented Scuderi Split-Cycle Engine divides the four strokes of the Otto cycle over a paired combination of one compression cylinder and one power cylinder. Intake air is compressed in the compression cylinder and transferred via a high-pressure gas passage to the power cylinder for combustion. The full-load study was made using a single paired combination of 1-liter displacement.

The SwRI study concluded that at full load, the efficiency of the gasoline-fueled split-cycle engine would be around 37.5%, versus approximately 33% for conventional Otto cycle engines, according to Sal Scuderi, president of the Scuderi Group and co-inventor of the split-cycle engine. Torque levels would be about 50% higher than those of gasoline engines, taking the split-cycle engine into diesel territory in terms of torque.

Additionally, the predicted NOx emissions are 50% to 80% less than that of a conventional engine, which will mean an even greater advantage in diesel applications.

The NOx reduction was an unanticipated result of the engine design, said Scuderi in a 2006 presentation. One of the design features of the engine—“the biggest breakthrough,” he said—is that it fires after top dead center in the combustion cylinder.

The compressed air charge pours into the combustion cylinder at 50 bar pressure with massive turbulence, rapidly atomizing the fuel charge, which is injected only into the combustion cylinder. By firing after top dead center, the piston is already pulling away from the combustion, enhancing the full air motion. Combustion is very rapid—10 crank angle degrees, two times faster than anything else the company had found, according to Scuderi.

With the very fast flame chasing the piston, rather than piston crashing into the flame, the flame front, where most of the NOx usually is formed, doesn't reach temperatures high enough for the same amount of NOx formation as in a conventional engine. This, Scuderi said, could turn out to be one of key features of engine, especially for diesel applications.

The company will begin ramping up its work on a diesel-fueled application of the split-cycle engine this quarter, said Scuderi, who noted that it looks like the split cycle engine may be able to address both NOx reduction and PM reduction without the same level of aftertreatment systems required by current diesel engines.

The combination of lower engine-out emissions along with the reduced cost of the split-cycle engine compared to a conventional diesel (no turbocharger, half the fuel injectors, reduced aftertreatment system) has piqued the interest of light-duty vehicle OEMs, Scuderi said.

At this point, the Scuderi Group is only releasing the complete data from the full-load report to OEMs who have signed a non-disclosure agreement. The data will eventually be made public after the company’s patent applications have been published. The company will again appear at the upcoming SAE World Congress in April.



The flame front chases instead of crashing into the piston. Yes and there are some interesting charge cooling and mixing possibilities. Sadly these early results show a lower than hoped for efficiency.
It would seem though much of the advantage is gained through the inherent design advantages rather than the sophistication of engine management which will always be inherently less reliable. IE a sensor malfunction , wiring, silicon failure.
I wonder how much space \weight penalty applies?
By comparison a single piston cylinder arrangement can now have multi event injection to provide the 'piston chasing flame front'. The ability of variable valve timing to manage over high compression ratios through reducing charge volumes. Should be able to achieve the same results in single cylinders. Also offsetting the crankshaft asymmetric to the cylinders gives a longer power stroke.
This may be a way to achieve efficiencies and reliabilities with servicing advantages at a 'village' or unskilled level.


One thing that still alludes me about the Scuderi design is how the firing cylinder will survive multiple events without access to a fresh air charge (or significant scavenging) available to traditional two and four stroke designs.

One possibility I see is an adaptation of the "Crower" cycle. Whereby steam is injected after combustion. A single intake/compression cylinder would serve two firing cylinders. Ceramic coatings could be used inside the cylinder walls to prevent heat loss.

The downsides to such a design would be
-lower specific power
-need for an on board water tank
-rpm restricted (has something to do with piston velocity and the rate at which steam expands
-probably issues with lubrication

The advantages would be
-increased torque
-well suited to diesel engine's rpm restricted nature
-increases thermal efficiency
-further reduction of NoX and PM emissions.

Notice: I'm not an ME so forgive me if I butchered any terms/concepts in the preceding post.


This is really not all that great. An Atkinson cycle Prius engine already has a peak thermal efficiency of 37% without needing to go to an unproven technology with undoubtedly large licensing fees. The beauty of the Atkinson cycle coupled with hybrid drive is that it approaches diesel efficiency without the huge initial costs of a diesel.

I think the real gains in efficiency will be from multistage turbine engines (possibly external combustion) where overall thermal efficiencies already exceed 50%. At that kind of thermal efficiency, we can justify the initial cost of retooling. Hybrid drive would allow the engine to be powered on electricity for a few miles until the turbine reaches peak efficiency.


Not much detail mentioned from the actual report, it's still mostly Scuderi predictions so I'm going to still be taking this with a large grain of salt. The only real number mentioned was the 37.5% vs. 33% efficency number which equates to a 4.5% fuel efficeny gain (against a theoretical gasoline maximum I presume) or a gain of approx 15% in overall efficency verses an Otto cycle if I am doing my maths right. This was at the low end of the promised range being trumpeted originally. Further this is all still based on theroretical calculations rather then actual measurements of a working engine. I'll think I'll wait for something other then smoke and theory before I start considering buying stock.


I think their approach is of limited interest for gazoline engine but might be interesting for diesel if it can speed up the front flame and reduce the emissions, could make diesel cheapper since will require half injector and possibly no turbo (still to be demonstrated). The increase in torque they obtained is interesting but is not enough to justify a new developement, stratified direct injection gazoline can improve effiency by 20% (an atkinson with direct injection would improve by 25%) when they can only report 10% (37.5/33), so not so good


Ralph, SI engines have always been near CI engines in terms of peak efficiency, and while the 1NZ-FXE is an improvement, it still isn't as efficient across the same power range as the TDI built a half decade earlier, which is why the hybrid system is used.

Rafael Seidl

It's not surprising that the engine should produce very high torque, 50 bar is roughly the pressure the fresh air reaches in a sequential turbo diesel with a geometric compression ratio of ~17 (e.g. BMW 3-liter). However, diesels feature intercoolers that reduce intake temperature and increase air mass in the cylinders, boosting specific power.

By contrast, the Scuderi engine relies on extreme geometric compression alone and features no intercooler. As a result, the air entering the combustion cylinder is already very hot. The directly injected fuel therefore vaporizes very rapidly, avoiding excessive PM formation. At full power, it may not even be necessary to fire the spark plug. Peak combustion pressures are reduced by firing after TDC, but so is efficiency - the thermodynamics are closer to the Diesel than the theoretical Otto cycle. At low power levels, that may not be the case.

The Achilles heel of the design is that the combustion chamber must be cooled vigorously to ensure adequate life expectancy, as it is never exposed to cool gas. Relatively small cylinder volumes are easier to cool, at the expense of efficiency, but the challenge is still much greater than in a conventional four-stroke design. Note that the compression cylinder in the Scuderi engine may well feature a larger displacement than the combustion cylinder. The piston crowns will need to be cooled aggressively using oil jets from below.

Note that temperature-related low life expectancy is the main reason why two-stroke opposed piston engines remain something of an engineering curiosity. However, one company in Germany has come up with a new carbon-magnesium matrix composite material for the pistons. It has a low coefficient of expansion and reaches maximum strength at 900 degC.

Rafael Seidl

@ Larry -

a) the efficiency numbers given here almost certainly reflect indicated work at the piston crown, not effective shaft work at the flywheel. At full power, the difference isn't all that great because internal friction and parasitic losses are small relative to the the amount of indicated work. At low power levels, the difference can be quite large, especially in high-displacement engines.

b) Engine efficiency gains are not numerically equal to fuel economy gains. This is because effective efficiency reflects the instantaneous amount of work delivered to the flywheel per unit of chemical input energy. Fuel economy reflects the amount of chemical input energy required to support traversing a standardized transient duty cycle for the whole vehicle.

Engine developers do produce diagrams showing brake specific fuel consumption in the engine speed-torque diagram as series of isoclines. If eta1 is the effective efficiency of a reference engine and eta2 that of a competing design, the gain in BSFC in that particular operating point can be computed as

delta BSFC = (1/eta2 - 1/eta1)/(1/eta1) * 100%

Engineers can predict vehicle fuel economy with the help of the BSFC map, a model for the downstream mechanical losses in the transmission, differential and tires and, data on the vehicle's weight and aerodynamics.



Thanks for your comments! Reading input from a real ME (I assume) is one of the reasons I keep coming back to GCC.

Joe Blow

It is incredible that Scuderi has been unable to produce even a proof-of-concept engine after 5 years or so of hyping their engine. The innovation of their engine relies on the design, operation and longevity of the valve that is situated between the compression and combustion cylinders. It would make most sense to design and build a few iterations of this valve for cold bench studies before adding the complexity of combustion. The fact that they have been unable or unwilling to do this raises concerns. Perhaps they realize that this particular Achille's Heel requires unobtanium to operate correctly.
I am sure that SwRI is quite happy to continue to take their money and to produce a series of reports showing that the theoretical efficiency is comparable to the current state of the art of both SI and CI (they missed out on the Idle Study, and the Low Speed, High Torque Study etc.), but the proof of the pudding is always in the eating. A crude analysis will not get the design done.


Remember that the separation of the intake and power cycles allows an engine manufacturer to tune the engine better. It would be interesting to see if the study used a model that overexpanded the gases - similar to an Atkinson cycle. If they omitted the overexpansion and changed the parameters in the Scuderi model closer to that of a regular SI engine to make the study comparable that would explain the lower efficiency rating. It would make sense that you could tune the Scuderi engine one way to deliver more power and torque or tune it the other way to extract more energy out of the combustion. I wouldn't make any conclusions until a paper is released that reports the efficiencies and power ratings.

If you use conventional engine materials in the power cylinder I'd think you'd have to overexpand the gas to keep the temperatures down. And how cool would the engine be after you apply ceramic coatings to the combustion cylinder(s)? If someone produces these engines I'd be suprised if they didn't add coatings to it - the cost of doing so would be half as much as the cost of coating a normal 4-cycle engine.


To me, a turbo does this nicely and has done it well for a long time. It is not 2 cycle, but then again you do not have the problems that come with that either.

There are lots of unique engine designs out there that claim lots of things. As long as they are based on combustion, I look at them as smog pumps.


And what if they really built one ?

Note that the compression cylinder in the Scuderi engine may well feature a larger displacement than the combustion cylinder.
This would essentially be the opposite of an Atkinson cycle, and would simply waste energy in the blowdown of the exhaust.
Henry Gibson

Why make an engine that the car companies would not install for 20 years. Just get investor and research money to pay for breakfast and lunch for ten years.

There are some good ideas in the engine. The air-hybrid is the best. No more starting motor is needed. They could have made 10,000 portable generators by now.

Brahmaiah Ganoj

I am very interested about knowing the CAE.Given information in the sites is fine,but i want information on the process of engine.It means that for complete the process how many cycles it requried.What are those cycles how it will be done.plz send infomation to my mail

Peter Hill

Where to start?

Lets start with Patent US7121236 by Mr Salvatore C. Scuderi (B.S., J.D) and Mr David P. Branyon. How to describe this? Well it can be summed up by one word.


Yes it's a crackpot crank. Mr Scuderi is supposed to be an Engineer. They can produce a displacement diagram in Fig 15 on sheet 14 and then demonstrate they can produce a Velocity diagram for this cam in Fig 16 on sheet 15. A layman would have left it at the displacement diagram, only an engineer would take the step of producing a velocity diagram. Anyone worthy of the title "Engineer" would then use the same method to obtain Acceleration diagrams. Mr Scuderi and Mr Branyon have for some reason chosen not to.

No matter, the destruction of this device is readily apparent from the Velocity diagram in Fig 16. There are sudden changes in velocity, labeled 254, 255, 257 and 258. These apparently instant changes in velocity require infinite acceleration. Force = mass x acceleration so infinite forces will be produced that hammer the cams guiding the big end pin to bits in a very few revolutions of the crank - possibly while dry cranking. (It will be the fault of the people that made the test engine, law suits will fly or it will demonstrate the huge uncontainable excess of power the engine made)

A brief google for "SVAJ cam" gives a good primer on cam design from Western Michigan University and why the work presented in US7121236 is not a viable design.
Fundamental Law of Cam Design
1 The cam function MUST be continuous through the first and second derivatives of displacement across the entire 360° interval
2 The jerk function MUST be finite across the entire 360° interval

Analysis of the REAL thermodynamic cycle that the Scuderi Air Hybrid engine can achieve will show large departures from the ideal Brayton cycle, resulting in losses that render it completely unworkable. The prime losses will be down to supersonic flow though the power cylinder inlet valve. Incomplete power cylinder fill due to restricted valve lift at TDC and short duration of transfer. I very much doubt a single stage compressor without inter cooler can deliver the required pressure.

I can only suspect that the staff of The Scuderi Group are well aware of the deficiency or they wouldn't be engaged in the wild and desperate measures seen in US7121236 to extend the duration of the transfer phase to the power cylinder.

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