Scuderi Files Patent For 'Split-Cycle' Engine

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Scuderi twin-cycle Miller gasoline engine

Scuderi twin-cycle Miller gasoline engine

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Real revolutions in engine technology are rare.

By and large, the internal combustion engine has remained much the same for well over a century, with just general, incremental improvements in all areas separating today's engines from those in the very first automobiles.

Scuderi's patented split-cycle engine is a little different, and if not revolutionary, it's certainly a significant evolution of the engines we know and love.

Most gasoline engines today, with a few exceptions, run on the 'Otto' four-stroke cycle: induction, compression, ignition and exhaust. Fuel and air comes into the cylinder, it's compressed by the piston, the spark ignites the mixture, pushing the piston down in the power stroke, and as the piston makes its way back up again, the exhaust valve opens and the gases are pushed out.

It's simple to understand and the process has become quite refined these days, but it's still relatively inefficient.

The split-cycle engine

The split-cycle engine cuts this four-stroke cycle into two parts. It uses 'paired' cylinders, with each cylinder in the pair doing half the work. We first covered the concept a few years back, after Scuderi completed a prototype.

In the first cylinder, air is drawn through an intake valve, where it mixes with fuel injected into the cylinder. As the piston returns, a different valve opens into a special port. The mixture is pushed through, where it's drawn into the second cylinder through another intake valve.

The valve then closes, the mixture is compressed by the second piston, and ignited in the power stroke. As the piston returns again, the mixture exits through the exhaust valve as it would normally.

It sounds more complicated than it is, but what it means is that for every crankshaft revolution, the engine is doing more work--while one piston is drawing in fuel and air, the other is already combusting the mixture that's just been sent through.

No more cylinders than normal would be required--so you could still have four, six, eight or more cylinders--but those cylinders are paired so only half of them would actually be combusting mixture. That also means half the spark plugs and half the injectors of a regular engine.

The engine runs on a Miller-cycle principle. This is similar to the Atkinson-cycle used in several hybrids. That normally means less power, but Miller-cycle engines use forced induction--in this case a turbocharger--to make up the power deficit.


Scuderi says its split-cycle engine is 25 percent more efficient than a regular "high economy" engine found in efficient European cars, and 13 percent more efficient than best-in-class vehicles.

Emissions are reduced, and Scuderi predicts up to 65 mpg would be possible from a small-capacity unit.

Combine those figures with a hybrid drivetrain and the numbers would start looking very impressive indeed.

So is the Scuderi engine evolutionary, or revolutionary? Until it hits the market it's hard to say, but it could certainly breathe new life into combustion engines.
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Comments (28)
  1. So the second cylinder of the pair fires every revolution like a two stroke?

  2. Yes, the firing cylinder works like a two stroke, while the compression cylinder works like a compressor and does not fire.

  3. It does fire on each revolution, wasting energy pushing the slave intake cylinders along.... unlike the 2 stroke.

  4. There are no slave intake cylinders. Each cylinder has its appropriate intake and output valves. The cylinder pairs do not operate in tandem and overall less energy is wasted than with a four-stroke Otto cycle. The power and compression cylinders are timed with a corresponding crankshaft. The compression cylinder converts some mechanical power into air pressure, which is used to enhance combustion. A good question to ask is what is the efficiency improvement over a turbocharger, perhaps that is the 13% mentioned. Also, the differences in dynamic performance vs. a turbo are not explained.

  5. The intake cylinders work is drug around by the exhaust cylinders - hence they are slave to their efficency.
    Timed to a corresponding crankshaft? - they are tied to one crankshaft that has both lands clocked identically or it would not be timed. So if we are wasting energy from the exhaust cylinder to compress air only to put it into the next cylinder... isn't this the same exact pricipal as using a turbocharger and surge tank?? I don't suspect you have much in-the-shop experience except for at the cashier! There can't be much increase in performance over a turbo-aspirated motor - since they suggest AND Show a turbo in the diagram to make up for the loss in energy from the extra parts and their weight being thrown around...

  6. Lets see... twice as many parts.. twice as much friction... twice the chances for failure, twice the cost or more to repair. Heat it all up with a super or turbo charger (which auto ups the octane requirements and cost for the fuel AND the amount of fuel needed to spin the darn turbo - it turns because of unburnt fuel still expanding... Doesn't sound very promising... Having 2 sets of rings only allows for twice the fuel to get past the rings and into your oil.... which will shorten it's life. To get any "power" the turbo will need to spool up - which means it's already moving... so it's a slow poke till you get a chance for boost... And I doubt it gets 65! Unless you put it in an old GEO metro???

  7. Your critique appears misplaced. Friction when lubricated is negligible, otherwise any engine would seize. Besides, the Scuderi design has the same number of cylinders as a comparable four-stroke, but splits the compression and firing into cylinder pairs. The compression cylinder is not exposed to fuel and does not fire. The increase in efficiency is achieved by maintaining a pressurized air chamber that enhances combustion.

  8. So the oil pump would not have to work that much harder to pressurize all those extra bearing journals and surface areas created; and not make any extra heat in the process?? How about all the extra friction and heat created by the extra compression (compression creates heat! and that turbo will be a secondary heat pump thanks to a third source of compression! All the "extra" parts would not create any extra heat because, magically, somehow, friction is negated you state; even though we are scraping extra piston rings to create a seal for an extra cylinder? Do you have any hands-on real world engine building experience?? Duh, compression cyl does not fire!! Does the net result really differ any from turbo compression in any other surgetank

  9. OK – we see that the cylinder on the right in the diagram will make a power stroke on every crankshaft revolution. If this was an ordinary V-twin engine, one or the other of those two cylinders would make power each revolution too. What is the patented benefit? The fuel injectors operate without being subjected to the explosive force of ignition. Moreover, a V-twin might have eight valves but perhaps this machine needs only seven to function as well. I see some benefit but wonder how this engine can be tuned (optimized) with such an arrangement.

  10. A patent claim does not need to have any benefit, such as an improvement in efficiency. A patent claim must simply be directed to statutory subject matter that is novel and non-obvious over the prior art, both of which have specific legal definitions.

  11. Well now - I didn't mean that the BENEFIT could be patented - just that I wondered what benefit there really was. As other comments say, we wonder about the increase in efficiency. Even if the fuel consumption was equal or better perhaps there is a saving to the manufacturer - or not.

  12. Unless it's a diesel with compression-injection ignition (which this engine is not; this design is incompatible with compression ignition principals) a fuel injector is never subject to the "explosive force of ignition" in any gasoline motor. The air and fuel must be mixed before it is compressed and ignited. Most often the FI sprays on the back of the intake valve because it is hot and will help atomize the liquid fuel so it can ignite.

    This motor is more like a European vehicle - overengineered from simple stolen ideas, utilizing way too many parts to accomplish far little result - and is generally all assembled with inferior metals and materals.... with Marketing left to figure it all out... which marketing does very well!

  13. I agree that until recently your comment is correct. However, now there is a big move to direct-injection for gasoline fueled engines. That has to require super-duper injector technology.

  14. I'll agree with that; but basing experience with direct-injection diesel; they need to improve the technology greatly. The injector is one of the most unreliable components of the diesel motor and they have had over a decade to get it right, and if GM and the euro manufacturers are engineering and pushing this... don't hold your breath!

  15. I always am entertained by engineers that can determine the mileage of their engines or fuel components when there is no drivetrain / gearing attached...... Gallons per hour @ RPM would at least be honest. This engine sounds like an "Investment money" trap and no one who pays in gets anything in the end....

  16. Sounds fascinating and promising. Some skepticism arises from long-term unknowns and hidden detriments that are not evident from the initial presentation. Since Otto-cycle engines are very well understood, there is a reluctance to give them up. Also, all aspects of engine performance, power, torque, dynamic range, must be compared and better understood. Finally, my suggestion to Scuderi is to build a 12 or 18 cylinder version with simply stunning performance at lower fuel consumption, because market entry in the automotive space almost always starts at the high end, where there is greater emotional cover for risk and higher margins to provide service and support.

  17. Gaurav - you sound like you have an engineering or scientific background, as I do, too. IMHO the Scuderi air-hybrid will be their "killer app". A fiber-glass wrapped compressed-air tank will be a lot safer in a crash than any electric battery. Don't expect Scuderi to go the Bugatti Veyron route!

  18. Go to the Scuderi site and see their air-gasoline hybrid system. That sure beats the electric-gasoline hybrid. I have a crash-testing background. You can be certain that any electric storage system is dangerous. A crushed battery will explode as if lightening struck it. Look at

  19. Not to mention that compressed air is lighter than a battery cell and will have improved hysteresis during loading/unloading. It will be interesting to see the overall energy density and performance comparison to other types of hybrids.

  20. Added friction? Not necessarily. Since a typical 4 stroke has 3 strokes that don't create power, this is essentially the same as far as friction goes. The intake piston has a considerably smaller bore and stroke, if the model is correctly drawn, so maybe there is reduced friction. That is debatable, and testable. The issue I see is added weight, which could be detrimental. The turbo can be run through and intercooler, keeping closer to ambient temperatures. Essentially, this engine looks to be very comparable to a regular Otto, but with reduced rotating mass. Since the slave cylinders are smaller, with less bore, the effective rotating mass is reduced per firing cylinder. I believe that the claims must be true. I wonder how it sounds?

  21. I misspoke, I meant since the slave cylinders are of smaller bore and shorter stroke, the rotating mass is reduced per firing cylinder. Another question is whether a four cylinder model will produce the same power as an Otto four cylinder of the same displacement.

  22. How many people remember when it was predicted that we would all be driving turbine engine powered cars by this time?

  23. We would be if the oil companies hadn't stepped in. THe Chrysler turbines continued into the 80's with increasing efficiency and with a modern fuel management system, they could have run on about any flammable liquid or gas with fairly good fuel economy. A small turbine running a generator would make an efficient hybrid as both turbines and generators like high speed contiuous running.

  24. In my experience working with turbine engines, they are considerably less efficient. They have much more potential as far as power from a certain amount of fuel, however while they are running without a load, they still require much more fuel than say a diesel or an Otto. For example, I work on two different generators. One is powered by a turbine engine to have a maximum load of 72 kW, and a turbo diesel four cylinder four stroke powered generator with a max load of 72 kW. The turbine set will run a max of 6 hours loaded having 150 gallon tank. The diesel will run 24 hours on a 50 gallon tank. Same fuel, JP8. Not loaded, the turbine runs around 10 hours, and the diesel will run around 50 hours. Estimated.

  25. Let's say friction is negligible, but what about the increase in inertia or the moment thereof because of the extra-non-active-parts? Efficiency is about work delivered per heat energy received. The mechanical energy produced by the cylinders that ignite is split into a larger number of parts that will use this energy therefore it will not be sent to the wheels. It is simple energy conservation: IMO this engine should perform worse than a similar one without the extra "passive" parts...and I am a physicist, and a mechanical engineer wannabe... ;-)

  26. Since the Scuderi firing cylinders fire every cycle, instead of every other cycle as in a four-stroke engine, the energy dissipation into rotational mass of the engine averages out to be similar as in an Otto cycle.

  27. @Guarav: Energy comes from the active pistons whether it happens every cycle or every other cycle. You need to put energy into the non active parts to make them work, and there is a simple physical principle that states that you will never get more in return that you put into it; otherwise you will be creating enrgy in the process, which violates the 1st Law of Thermodynamics. In fact and at best you will get the same in return, which is unlikely to happen due to friction, though small is always there and heat will be lost to the atmosphere (cold temperature source or Third Object).

  28. Contrary to what many people believe, heat engine's efficiency has nothing to do with engine's fuel consumption or the amount of miles to the gallon it makes. I see a turbo coupled to the split-cycle-engine perhaps in an effort to recycling some of the heat to better assist the passive parts. But turbos produce more more heat than do they produce usable work so turbos may increase power but they reduce efficiency...I do not expect to see this engine in a high performance vehicle, but in a water pump or an electric generator. This engine is a theoretical attraction...indeed

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