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Bosch Engineering to Assist Scuderi Group in Developing Injection Timing System for Air-Hybrid Engine Prototypes

Early rendering of the Scuderi air-hybrid showing the compressed air tank attached to the compression cylinders. The engine depicted has two paired combinations of compression and power cylinders. Click to enlarge.

The Scuderi Group, developer of the Scuderi Split-Cycle Engine (earlier post), has engaged Bosch Engineering GmbH to assist in the prototype development of air-hybrid implementations of that engine.  Bosch Engineering will apply its expertise to the development of the timing system for the gasoline and diesel prototypes.

Specifically, Bosch will assist the Scuderi Group and Southwest Research Institute (SwRI) in defining the technical requirements, and supplying component specifications such as for the fuel injection system itself. The team will focus first on the Otto (spark ignition combustion) cycle and then address the diesel cycle.

A recent report from Southwest Research Institute (SwRI) has predicted that the Scuderi Split-Cycle Engine under full-load (FL) conditions provides higher power, torque, and efficiency ratings than are currently attainable by the conventional turbocharged engines used in vehicles today. (Earlier post.)

The 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 gas passage to the power cylinder for combustion. The gas passage includes a set of uniquely timed valves, which maintain a pre-charged pressure through all four strokes of the cycle.

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. With firing timed for after top dead center, the piston is already pulling away from the combustion, enhancing the full air motion.

Modeling of the basic split-cycle engine indicates fuel efficiency 25-50% higher and NOx emissions up to 80% lower than in today’s gasoline and diesel engines, according to the group.

Through the addition of a small compressed air storage tank with only a few control elements costing only a few hundred dollars, the Scuderi engine can recover the energy that is normally lost when a vehicle is decelerated in the form of compressed air.



This is starting to sound more and more promising every time I read something about it. I have a question for the engineers out there - could HCCI be employed in the combustion pistons, further increasing the efficiency and reducing the potential for the thermal problems in those cylinders? It would seem this design would give you more control over the combustion. Couldn't the compression ratio effectively be altered by careful control of the passage valves? You also have to like the cost savings from only needing half as many direct fuel injectors. They need to get this thing going!


You should visit what this french company is doing will pobably revolutionnize the gazoline car industry and also answer your question since their website is very rich in details of their technology. They are now working with PSA for the next step od development.


The Scuderi cycle requires that only air be compressed in the compression cylinder, so HCCI is incompatible.

The energy-storage air tank is a neat twist, though; it looks like it would allow hybrid-like operation without any need for an electric drive system.  It may not store very much energy, but if it can substitute for wheel brakes from 30 MPH to a stop and add to acceleration on takeoff by eliminating the need for compression strokes, it could add to both economy and performance in city cycles.


The main interest of this engine is that it can potentially reduces NOx on diesel engines and also reduce the cost of diesel engines because you need only half injectors. If this happen to be true then it can have a wide range of applications. It can tbe a multifuel diesel engine capable of burning cleanly everything including ethanol, gazoline, fuel, oil as long as the high pressure pump is designed for it and that you can adjust the timing. Could then be a nice efficient engine in a serie PHEV where it could be more efficient than a gazoline Otto engine and cleaner than a classical diesel engine.

But they still have to prove that it is really cleaner thanks to faster combustion day they have only performed simulation no real test, so that is very speculative.

I am still dubious about the air compressed storage for regenerative braking, it won't be easy to reuse that stored air during the braking, but anyway will see.


"The Scuderi cycle requires that only air be compressed in the compression cylinder, so HCCI is incompatible."

Maybe saying, "combustion pistons" was a bit confusing. I absolutely meant the power cylinders only. Why couldn't HCCI be used there?

Rafael Seidl

@ Engineer-Poet, Angelo,

the common feature of all HCCI strategies - regardless of fuel type - is that they require the entire charge to momentarily be in a state of nearly constant volume. In a conventional engine, the moment is long enough only up to ~3000 RPM.

In other words, the combustion must be nearly isochoric, thermodynamically a close approximation of the Otto cycle. This is efficient but also exposes the engine to very high mechanical and thermal stresses. Combustion noise levels are also very high. To tame the beast, the fresh charge with high levels (up to 50%) of inert recirculated exhaust gas. This delays the compression ignition and slows down the combustion process. On the other hand, apply too much EGR and you end up with a quick succession of misfires and/or partial combustion events.

Ergo, sustained HCCI relies on walking a very fine line between blowing your engine up and bringing it to a shuddering halt. This balancing act is only possible in low part load and very difficult to execute during load transients and mode shifts to and from conventional ignition.

With regard to the Scuderi engine, a key feature is that the fresh charge is only admitted to the combustion cylinder after it passes top dead center. The exhaust valve needs to close completely first, or fresh air at 50 bar would enter the exhaust system and cause damage to catalytic converters and mufflers.

This means the gas in the combustion cylinder of a Scuderi engine is never in a state of nearly constant volume, making controlled HCCI there impossible. Injecting fuel into and inducing ignition inside the feeder pipe connecting the compression and combustion cylinders would very quickly wear out the valves there.


It seems like the ICE will be with us in some form for quite a while. Considering all the parts that go into one, it is a marvel of mass production that they are truly affordable. I keep coming back to simplicity. If we can make a device do the job better in a simpler way, I tend to favor that.


Thanks, Rafael. That makes perfect sense.

I'm also curious about something else. Does this Scuderi design lend itself to a particular cylinder configuration (inline, V, flat boxer), or can any be used?



As we all value your expertise here, could you please have look on and tell us what you think of their approach to rethink the gazoline engine ?

It looks pretty innovative and serious to me, their website gives a lot of technical details which makes it quite credible. And I know that PSA is now engaged with them to developp a full prototype.

Roger Pham

I have similar concern with Rafael regarding the longevity of the valve connecting the transfer pipe to the combustion chamber. Compressing air at 300 K adiabatically to 50 bars will raise the temperature above 900 K, or 630 C. This means that the high pressure air in the transfer pipe will constantly transfer this kind of heat to the valve stem of this valve, making lubrication with conventional oil difficult. By contrast, the exhaust valve of an Otto engine is only briefly exposed to exhaust gas during the exhaust stroke, and the exhaust gas is so low in density and expanding, in comparison to the 50-bar pressure, that heat transfer is much poorer than the dense and hot compressed air.

Split-cycle piston engines like the piston version of the Ericsson or Brayton cycle have not been practical in real life due to the same technical problem. These cycles were conceived for piston engines initially, but were not able to be put to practice due to the heat involved and the need for proper lubrication of parts sliding past one another.

By contrast, the turbine version of the Brayton cycle (jet and turbine engines) works well due to the lack of valves and the lack of high-speed sliding parts in direct contact and constantly exposed to high heat.

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