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Scuderi Releases Video Footage of Running Split-Cycle 1L Prototype

Simplified pressure-volume curve for the Scuderi Engine. Source: Scuderi Group. Click to enlarge.

Scuderi Group, LLC has released the first video footage (with sound) of its split-cycle Scuderi Engine prototype running, on its own, in the laboratory test cell. The two-minute video, the first to show the naturally-aspirated one-liter gasoline prototype engine in operation, provides a view of the engine as it undergoes testing, proving the concept of Firing After Top Dead Center.

In September at the Frankfurt show, the Scuderi Group announced that it had proven the concept of Firing After Top Dead Center and that the naturally aspirated, 1-liter prototype was running. Preliminary test results have matched earlier computer simulation projections. (Earlier post.)

P-V curve for the Scuderi Engine. Source: Scuderi. Click to enlarge.

Split-cycle engines separate the four strokes of intake, compression, power, and exhaust into two separate but paired cylinders. The first cylinder is used for intake and compression. The compressed air is then transferred through a crossover passage from the compression cylinder into the second cylinder, where combustion and exhaust occur. A split-cycle engine is essentially an air compressor on one side with a combustion chamber on the other.

The Scuderi engine is expected to produce up to 80% fewer toxins than a typical internal combustion engine. The current naturally aspirated gasoline prototype is expected to reach efficiency gains of 5-10% more than any conventional engine on the road today. When fully developed with its turbocharged and Air-Hybrid components, the engine is expected to achieve efficiency levels of 25-50% higher.


The Scuderi Engine. Source: Scuderi. Click to enlarge.



Would be good for plug-in range extender. For conventional application would take long time to get into mainstream.


Would a compressed air engine be less complex, more convient, smaller, and greener? An Australian group seems to have a good one.


When one talks about a 10% increase in efficiency it is a multiple of the root number. For example: a 30% efficient engine increased by 10% is a 3% gain not a 10% gain. In any case a 25%-50% gain in efficiency would increase an engine from 30% to 37.5% or 45% efficiency...darn good!


Does a 2-minute movie of "Running on its own" prove the concept of Firing After Top Dead Center?

"Is expected" is a bit vague.

"efficiency gains of 5-10% more than" apparently means an increase from 30% to 31.5% or 33%, as Lad says (Since they later claim up to 50% increase).
And typically means "it's in the noise".


Toppa Tom,
I don't think Southwest Research a worldwide organization with an excellent reputation, would release anything, especially a video of the engine running, if it was not firing "after top dead center" as they claim it to be. Why is it that you are always so negative on this great invention??
Where is Roger Pharm??? At least he has constructive opinions on the Scuderi Split Cycle Engine.


I wonder if these engines might be better suited for stationary CHP applications.


The only things that concern me regarding this engine are:
-durability of the crossover valve
-engine balance
-frictional losses when the compressed air crosses over

Roger Pham

Hi, pfb.
The engine runs impressively smooth for something with two reciprocating pistons running together in the same direction. Excellent balancing shaft design. Sound level is quite pleasant even without muffler. Perhaps over-expansion thermodynamic cycle helps reducing noise and increasing efficiency.

Frictional losses of air in the cross-over passage is more than made up for by the much lower side-wall piston-cylinder friction losses in both the compression stroke and expansion stroke, for having a single crankshaft placed in the middle of the two cylinders.

The 25-50% gain in efficiency in the turbo-charged airhybrid mode is due to the use of load-leveling of the compressed-air storage tank. This is functionally equivalent to that of an Atkinson-cycle 4-stroke engine with a mild electric hybrid set up like the Honda IMA scheme. I'm open to further data from this running prototype. Best of wishes.


Regarding "frictional losses when the compressed air crosses over" some back of the envelope calculation would help understand.

Assuming no energy get added (no combustion), relative to losses during air intake:

1. Assume compression ratio is 10:1 (rho_c = 10 x rho_i)

2. Assume Intake and crossover flow cross section area are equal.


3. Mdot_i = rho_i x V_i x A

4. Mdot_c = rho_i x 10 x V_c x A

5. Assume crossover time is 5x faster than intake. ... Mdot_c = 5 x Mdot_i

=> rho_i x 10 x V_c x A = 5 x rho_i x V_i x A => V_c/V_i = 1/2

6. Drag loss is related to rho x V^2 (assuming all else equal)

Loss_c / Loss_i = (rho_i x 10 x (1/2)^2) / (rho_i x 1^2) = 10/4 = 2.5

So Loss_c / Loss_i ~= 2.5

But it is inversely related to the square of crossover time, so if that is 3X faster than intake instead of 5X faster, the losses are nearly equal.

Anyhow, I believe intake losses are pretty minimal as long as no throttle is present.


There are better simpler solution that deliver higher efficiency.
Look on an engine develop in Greece by Pattacon. This oppose piston diesel two struck engine promise to deliver 40% higher power density then conventional diesel engine (more then 134HP/L - no turbo charger). The engine is base on old Junkers diesel engine develop for airplanes in 1930s. Pattacon make significant improvement to that original design.
This engine look much simpler and lighter then Skuderi design.


I have worked with the Southwest Research Institute and indeed they do have and deserve an excellent reputation.

They would never refuse to release a video of a client's engine running, if the client so desired.

I have no reason to doubt that the engine was firing "after top dead center" as they claim.

But we're all still waiting for ANY real data from this Rube Goldberg engine.


I always hated the ATDC' settings on those horrid pollution controlled carbureted engines that sucked the juice and were 'mostly broken' so the exhaust was worse than no pollution control.

The devices hoses were a great source of ball bearings though ( often full of them.)

the aussie one was a design comp winner for Ford international as a university team light design contest , nothing real.I think two people could have pushed it further and faster.


TT and Roger
I'm sure Southwest Research is collecting data for the various OEM's who signed NDA's, however for some reason they won't release the details to the public. Is there anybody who can shed some light on why this information is only being made available to the OEM"s that signed NDA's? My opinion is if the results were outstanding news why wouldn't they want the entire world to know the results? Wouldn't this help their cause both commercially and politically?? What do I know anyway,
Have a nice day!!!

Ole Grampa

Pardon me if I'm wrong, but that engine really sounds like it is merely running on compressed air.


JT-It's definetly running on petro;
From the compression chamber, highly volitale air is moving towards the combustion chamber via the "cross over passage", this is a new invention, wih patents received, yata, yata. Bosch Engineering fabricated the fuel injection and timing systems along with several other important components for the engine. The fuel is then being injected at the top of the combustion chamber with perfect timing, on the down stroke with highly volitale air and the combustion process is now completed. This is what we call firing "after top dead center" a cleaner burning fuel with better efficiency and torque. I think it's pretty impressive that JT and others thought it was running on just air.


A bunch of "compressed air" engines use liquid fuels directly or indirectly.
Its just heat expanded with the heat from fuel one way or another.
You could say there is no such animal as a compressed air FUELED engine any more than a 'Hydraulic hybrid runs on fluid.'

An air engine running on wave power is powered by wave energy.
If we say air pump that is better.
Now we should know that an I.C.E. engine is also an Air Pump. Engines and pumps are different end of the same engineers will see them as interchangeable some may require no or small "small?" modifications to the

"JT-It's definitely running on petro;",
" The fuel is then being injected at the top of the combustion chamber with perfect timing"


"Is there anybody who can shed some light on why this information is only being made available to the OEM"s that signed NDA's?"

If you are implying that Scuderi does not utilize a NDA and allows SwRI to release any/all information you could not be more wrong.

Scuderi itself releases all this non-information that may or may not relate to anything real.

Roger Pham

Your calculation is valid for a non-compressible fluid, in which the cross-over flow is momentarily 5x faster than intake flow, then stays idle for the 4/5 of the time. However, since air is quite a compressible fluid, the calculation would be far more complex than a simple formula, due to the existence of turbulence as the flow passes thru the poppet valve, and pressure wave produced by every compression stroke. Certainly, the friction losses via the cross-over passage and even thru the cross-over inlet valve and exit valve are quite negligible, considering the fact that the density of the air in the cross-over passage is 10x that of ambient, assuming CR of 10, hence the average flow velocity is but 1/10th that of intake air, assuming equal cross section area as the intake runner, if we really want to over-simplifly the issue.

I think that the piston-cylinder friction saved due to the crankshaft arrangement in the Scuderi design will more than make up for the small losses from air flow thru the cross-over passage and the two valves.

Account Deleted

There are also other solutions than Scuderi engine to achieve same performances but using the the Carnot cycle. To see more consult: .
This technology opens the perspective to achieve small-size engines with half the number of cylinders reported to the same power as a classic four-stroke engine. The high power density recommends this engine for automotive, aircraft and navy applications as well as for stationary construction. When it is used in the automotive powertrains, the engine can have a hybrid operation option that attains the partial recovery of the braking energy (in city) and the exhaust gases energy (in highway). Compared with an electric hybrid system, the proposed solution eliminates the electric generator, motor and battery components which are additional to the engine. This reduces cost, complexity, weight and bulk while providing similar function and benefits. In case of the hydrogen utilization, the engine configuration largely compensates the low energy density per unit volume specific of this fuel without any supplementary adaptation. A spark ignition variant supplied with hydrogen can reach an efficiency superior to 40%. This invention was obtained a medal at International Invention Exhibition Geneva 2009.


Just where is piston-cylinder friction saved?
If the engine is of the “radial” or “Harley” side-by-side layout the piston side loads are lower on compression and expansion but higher on intake and exhaust.
The exhaust stroke might be a problem
- the angle is bad AND
- the direction is bad (rod pushing piston) AND
- lubrication is bad (there is always heat in this cylinder and always pressure pushing oil down).
But the photos imply the engine is an “in-line”. . In which case the side loading is exactly the same as any typical “in-line” engine except for the always-hot power cylinder.

Maybe Carmelo did not have time between patent filing in July 2001 and his death in Sept 2002 to solve all these problems.
Maybe company president Salvatore Scuderi, (degrees in engineering and law), Stephen Scuderi (patent attorney) Nick Scuderi (marketing) and Deborah Scuderi (accounting) are better at press releases, private “demos” and movies.

Roger Pham

You've said it: "...piston side loads are lower on compression and expansion and higher on intake and exhaust." Please be reminded that at 2000 rpm typical cruising at high load, the inertial loads on the pistons are quite low in comparison to the force of the power stroke and of the compression stroke, hence substantial reduction in side loading on the piston. At higher rpm's such as at 5000 rpm at low load, then, piston inertial force from reciprocal motion become much stronger to become the dominant force on the piston side loads, and in this case, Scuderi arrangement is of no advantage to conventional design.

Conventional splash lubrication should be sufficient, albeit a lot more oil cooling may be required in the absent of the cooling intake stroke in the power cylinder, and they may have to set the coolant at lower temperatures to bring get cooling down to par with conventional Otto engines. Furthermore, firing after TDC should significantly lower the combustion temperatures. We shall see how the heat problem will be solved. As the last resort, water injection may be employed for a brief moments when high power output is required, since an auto engine runs most of the time at much lower power than its rated output. The load-leveling feature of the Scuderi engine will greatly reduce the frequent needs for higher power output, so, water injection, if necessary at all, will rarely be needed.

The considerable efforts of the Scuderi family in developing this concept is very methodical and are very commendable. They've covered all the bases as far as R&D is concerned.


"Furthermore, firing after TDC should significantly lower the combustion temperatures."

But also increases the heat transfer to cylinder wall.

If the water were injected on its own Crower? 5th stroke whereby the steam drives the piston, cooling is achieved along with useful power?.


1. The side loads during exhaust, when the rod must push the piston up look very severe. More so because the cylinder will be hot and dry and the rod angle (on a radial arrangement) is so large.

2. The pictures and the movie seem to show an in-line engine, where crankshaft offset would provide no more benefit than in a normal engine (which is like, none).

3. An engine that is limited to anywhere near 2000 rpm will suffer a severe weight penalty. The bad con rod angles, the crossover flow and the ATDC firing do seem to imply a much lower rpm limit than a normal engine.

4. Firing after TDC should significantly lower the overall effective compression ratio (and BMEP).

5. The 10 year efforts of the Scuderi family in developing this concept could have been duplicated by a team of PR hacks and one person with a drill press.

Roger Pham

Thanks for pointed out to me that, indeed, the prototype is an in-line two cylinder instead of being a radial offset like in the original Scuderi's patent.

Firing after TDC requires faster combustion rate for high rpm operation, in order to maintain BMEP. Scuderi's strategy here is to increase the compression ratio, hence the charge concentration, and denser charge burns faster. N-octane would burn faster than iso-octane, and so will H2.

Don't discount the expertise of SWRI in this 10-year effort: much more than just "a team of PR hacks and one person with a drill press." The prototype appears to be expertly designed and built, and it runs silky smooth. So far, they have said that the actual prototype data is on par with computer simulation data.


This is a 10 year effort by Scuderi - NOT SwRI.

And it is Scuderi that says the actual prototype data confirms their claims.

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