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Scuderi working on turbocharged variant of split-cycle engine; smaller, more powerful, and more fuel efficient

Cartoon of the proposed turbocharged split-cycle engine. Note the reduction in size of the intake/compression cylinder. Click to enlarge.

The Scuderi Group announced at the SAE 2011 World Congress in Detroit that boosting one of its air-hybrid split-cycle engines (earlier post) with a turbocharger to 3.2 bar decreases the BSFC (brake specific fuel consumption) up to 14% compared to the air-hybrid engine, while resulting in a simultaneous increase in the engine’s power BMEP (brake mean effective pressure) by 140%. At the same time, the engine can be reduced in size by roughly 29%, according to recent modeling results.

The basic Scuderi engine divides the four strokes of a combustion cycle among two paired cylinders—the left cylinder functions as an air compressor, handling intake and compression, while the right cylinder handles combustion and exhaust. Key to Scuderi’s split-cycle design is that it fires after top dead center. An air-hybrid configuration of the engine adds a compressed air storage tank. (Earlier post.)

A naturally aspirated Scuderi Air-Hybrid configuration consumes 30-36% less fuel under similar drive conditions, according to preliminary results from simulations released earlier this year. (Earlier post.)

Rendering of the turbocharged split-cycle engine. Click to enlarge.

Consistent with conventional four-stroke engine designs, the combustion cycle of the Scuderi Engine has two high-pressure strokes—compression and power, and two low-pressure strokes—intake and exhaust. The power stroke is positive work, or the energy that is produced by the expanding gases to create mechanical work. The intake, compression and exhaust strokes are all negative work, or the energy that the engine consumes to create mechanical work.

With the compression cylinder separated from the power cylinder, the use of a standard turbocharger to convert recovered exhaust-gas energy into compressed air energy supports the downsizing of the compression cylinder to achieve substantial reductions in negative compression work.

The amount that ends up on the crankshaft is the difference between the negative work and the positive work. And when you split the cycles like this you can now try to figure out ways to reduce that negative side without impacting the power side.

We determined that if you put a simple standard turbocharger onto the engine, and you feed more air into the compression side—now it’s coming in at higher mass flow and high pressure—when you do that on a normal engine, what happens is that the pressures in that compression stroke goes up. Your power goes up, but you’ve pushed more mass into the cylinder and when you squeeze it you’re getting a higher pressure. Now, when you fire, you’ve got more air at a higher pressure, you’ll get more power out, but the efficiency doesn’t go up. In other words, you’ve got more power, but you’ve also have more negative work going in.

If we control the pressures of the engine internally so that you are not causing more pressure to occur, what happens is you cause less work of compression to come off the crank. If I boost it to say 2 bar, I have twice the mass of air. Now when I compress to get to my naturally aspirated compression levels, I only have to boost halfway, because we normalize. We don’s let the pressures go up to where they would normally be. So you literally do less compression work for the crank. In other words, the energy off the exhaust is actually doing some of the compression work for us.

By doing that, the volumetric efficiency of the compression side goes way up. When you turboboost to 2 bar and you only compress to a naturally aspirated level, the flow of air is twice what you need. You can either feed [two expansion cylinders] or the logical, more simple approach is that you downsize the compression cylinder. Even though it is downsized, it’s still feeding the amount of air you need. The net effect is the compression work goes down, the engine gets smaller and the efficiency gets better.

—Sal Scuderi, President of Scuderi Group

Simulated power and fuel consumption at 1400 and 4000 rpm. 40% turbo efficiency. Click to enlarge.

Scuderi said the that company is just beginning to explore the potential of the turbo design. The Group is in discussions with 15-16 OEMs so far, Scuderi said, and is under non-disclosure with 11. Scuderi is performing simulations in vehicle for three OEMs. Scuderi expects its first license by the end of the year.



The problem is that you have to accept low compression ratio at low load when the turbo doesn't do much. Ideally you want the CR to be higher at low load , but that might not apply for the Scuderi engine where the highly turbulent combustion can allows ignition of very lean mixture.

Anyway I am still waiting a demonstration in real of all the promises they keep claiming with, so far, little facts to support it.


I wonder about one of these for a range extender. All kinds of designs may not make it in a conventional transmission drive line setup, but range extension opens up whole new possibilities.


I dont get how the big piston which is power/exhaust is supposed to be acting like Im assuming a two-stroke if there is an exhaust valve at the top of the cylinder. Shouldnt it be a port at the bottom?? so when the piston passes, exhaust gasses exhaust, on the up stroke, the inlet opens for a split-second, allowing high-pressure air in, and is now ready for another combustion??


This story comes out every few months but no such engines are made.


This is sort of two stage forced induction, the turbo is the first and the air piston is the second. Combine that with "MAHLE Powertrain’s Turbulent Jet Ignition (TJI) spark-initiated pre-chamber combustion system" and who knows?

Nick Lyons

There's no point in speculating about this technology until Scuderi produces some real-world, in-vehicle test results.


"operating in a 2004 Chevrolet Cavalier" January 2011

It sounds like they have a working engine that they can compare with the stock engine in the same car.


The 2004 chevrolet Cavalier is certainly the perfect reference to compare with when it come to fuel economy...

I think the Scuderi engine is mainly interesting for diesel since it can reduce NOx emissions, the problem is that automakers might no need to use a Scuderi architecture to improve fuel economy.


Toyota, which I presume to be far more reputable than Scuderi, has already promised a new engine for 2014 which is around 45% peak thermal efficiency. The current generation Atkinson cycle 1.8L Prius engine returns 38% peak thermal efficiency.

If Toyota hits their number, then Scuderi has to be 50% or higher to even stand a prayer of being successful in the marketplace.

I think ideally we should aim for around 70% peak thermal efficiency -- which would probably involve multiple stages -- because once the design is mass-produced the fuel saving benefits transfer quickly around the world and without the need of hybrid technology.




To try and answer your question, since no one else will, as far as I see it the exhaust is blown out, not pushed out of the combustion chamber. Then the exhaust valve is closed and air is captured and fuel is injected.

Roger Pham

"I think ideally we should aim for around 70% peak thermal efficiency ..."

How do you go about achieving that? 70% efficiency is real close to Carnot's efficiency...meaning not even friction loss nor gas leakage nor cooling loss nor exhaust heat loss is allowed! Carnot efficiency means that only compression heat loss is allowed during the isothermal compression phase of the Carnot cycle! The most efficient combine-cycle large-scale power plant can only manage 60% thermal efficiency!

Meanwhile, major auto mfg's have promised to crank out mass-produced FCV's (Fuel Cell Vehicles) that can achieve ~70% efficiency by 2015! They will be squeaky clean without any air pollution issue, nor noise issue, nor any more oil stain in the garage or parking lot. They will require much less maintenance.
Best of all, they will be able to run on renewable H2 if and when H2 will be produced from solar and wind energy.


Daimler is aiming for a fuel cell that costs no more than a diesel engine by 2015. IF they can achieve that, a whole new way of looking at personal transport will be at hand.


The Scuderi engine and the Toyota engine have one thing in common; they do not (yet) exist as commercial products. At best, we could say that both companies have showed “proof of concept”. Between this state and a commercial product, we have a period, which we tend to call the “development phase”. For a conventional engine, this is a period of 3-5 years. It is difficult to shorten too much (<3 years), since endurance testing per definition takes time, cannot be accelerated at will and must be conducted at the end of the development period. For new concepts, it is likely that the development phase is at the longer end of the mentioned period (5 years), or even longer, depending on the difficult encountered with a new revolutionary concept.

According to Toyota they have achieved a 42.4% thermal efficiency with concept 1 and 43.7% with concept 2. A “good” automotive diesel engine today achieves an efficiency of ~43%, so Toyota’s concept engines would be on pair with that level. However, diesel engines are available at the dealers today (not in the USA, of course…) in contrast to concepts engines in the laboratories. Scuderi shows BSFC of ~232 g/kWh at 1400 rpm and ~250 g/kWh 4000 rpm. Presumably, BSFC could be marginally lower at the most favorable engine speed, presumably close to 2000 rpm. A BSFC level of 230 g/kWh is equal to ~36.6% efficiency. It appears to me that Scuderi has not tested a “full-size” multicylinder engine with a turbocharger but a “single cylinder” (albeit that you have two cylinders of each kind in this case) and a “simulated” turbocharger, i.e. charge pressure and back pressure are simulated with other means. The pressure difference corresponds to a turbocharger efficiency of 40%. This is common practice for prototype engines but it does not, of course, give the exact efficiency of a multi cylinder engine. The turbocharger efficiency might be somewhat conservative, so we could say that they have demonstrated an efficiency of 37%. It might also be that the Scuderi engine has additional advantages at low load (e.g. the “air hybrid”). Still, the results are not that impressive. During a period of more than a decade from the introduction in Japan, Toyota has increased the efficiency from 37% to 38%. The latter is about the highest figure we have seen for a commercial gasoline engine. We should also be realistic about what features from their Concept 1 and Concept 2 engines that could be realized in a commercial product. We will certainly not have a 45% efficient Toyota engine in 2014! Not even in our dreams (recall that it took about 10 years to improve from 37 to 38%)… It is more realistic to foresee something in the range of ~40% on a 5-year timeframe. It will be interesting to see if Scuderi can compete on that level for their first commercial product on a similar timeframe.


The Scuderi engine advancements are really incredible when you take into consideration the limited resources they have compared to OEM's who are sinking billions into their R&D programs. Once the OEM's start using this technology with their own resources, the effciency gains will be much higher than now being published. The Scuderi's have many interested OEM's today and this technology is being taken very seriously.


"So far a proof-of-concept, one-liter prototype has been built and tested."

So far, they have spent more than $50 million on developing the engine, which could explain why there may be many patents, but few working engines.


$50 million is quite a lot for a proof-of-concept engine, even at Toyota’s standards. However, it is difficult to develop something completely new and it will cost a lot more to make a commercial product. I am not that impressed with the results so far and I am not convinced about that this is the best solution but I am glad that someone is willing to fund R&D on this idea. We have to try new ideas. Eventually, Scuderi must get a partner from the motor industry to succeed. The motor industry will conduct own assessments and step in if they are interested. I think we can forget about the conspiracy theory involving oil and motor industry, who always want to kill any idea. An engine manufacturer who believes in this will gladly spend money to beat the competition. If it is not a good idea, it will be dropped… Still, there might be better ideas out there that will never get $50 million.


They have car makers interested under NDA and are waiting for more of the patents to be issued. Honda sent people to look at the engine and they stayed a while to look in more detail.


The Southwest Research is working on more than a few special projects, requested by various OEM's, who have signed NDA's. These are the more interested parties who have been following the technology since it's inception.
The Nissan Sentra/Scuderi Engine results will be made public in the near future, all other projects are strictly confidential.


@Roger: "How do you go about achieving that? 70% efficiency is real close to Carnot's efficiency..."

First of all, I said that 70% should be the aim. Second, you presuppose I'm talking about gasoline as the only possible fuel. The Carnot efficency can either be raised by increasing the fuel combustion temperature or reducing the ambient temperature. The key to hitting 70% without resorting to exotic fuel cells is to either burn hotter fuels or reduce the ambient temperature.



There are "tricks" for reducing the "apparent" ambient air temperature, i.e. to increase the temperature difference, without increasung the maximum temperature. However, I would put the target at 60%; 70% seems too ambitious for me.


While the 2015 date for affordable and reliable fuel cells may slip a bit, they are the most promising. M100 can run them without high pressure tanks, Daimler proved that over more than a decade with NECAR. Once they operate PEMs above 212F, the balance of system goes down and efficiency goes up. Reduce the platinum content and bring the cost down even more.

The problem is that you have to accept low compression ratio at low load when the turbo doesn't do much.
The claimed static compression ratio is on the order of 70:1, so that's not the problem it might appear to be at first blush.

Don't forget that the air hybrid also has a reservoir of air held at the pressure of the crossover passage. This air can be tapped at any time, allowing instantaneous power plus a surge of exhaust gas to spool up the turbocharger.

The things I would add to this are a split turbocharger (electric compressor plus TIGERS) coupled to GM's BAS II system.  The electric compressor allows full air charge to be pumped into storage during regenerative braking when there is no combustion going on (and no exhaust flow), the exhaust-gas turbine allows better energy recovery and feeding energy back to the crankshaft through the BAS, and the battery of the BAS allows accessory loads to be driven while the engine is off.

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