Over the last couple of years I’ve been following the development of the Scuderi Split-Cycle engine with skeptical interest. The four-stroke internal combustion engine, first perfected by Nicolaus Otto 120 years ago, is a study in simplicity and, because of that, has proven to be a design on which it’s difficult to improve; though many, including Rudolph Diesel, have tried. Whether or not the effort put forth by the Scuderi Group will succeed is yet to be seen but, to say the least, it’s certainly interesting.

According to some recently concluded theoretical testing – all indications are that the Scuderi Split-Cycle engine, which can be configured for either diesel or gas operation, is as much as 30% more efficient than current designs and produces 50% to 80% fewer NOx emissions.

Scuderi Split-Cycle Engine
Update: 1/25/08

I’ve been offered an opportunity to interview the President of the Scuderi Group for the next Trucker Tech Podcast. Details are still being worked out so there’s no guarantee it’ll happen but, just in case it does, I thought I’d offer Life on the Road readers, contributors and authors the opportunity to submit questions. If you’re interested, just leave your questions in the “Comments section” along with the way you’d like to be credited if your question is used (i.e., Phil from Life on the Road).

Sooo…How does it work?

The Split-Cycle design is a variation on both 2- and 4-stroke engines. One cylinder provides compression while the adjoining cylinder provides the power stroke. When I first saw this design my initial reaction was along the lines of “hmmm, this’ll never fly ’cause only half the cylinders are producing power”. But as I thought about it, I realized that a conventional 4-stroke engine only produces power 25% of the time anyway. So I dug deeper.

It was clear to me that three cylinders producing power on every down-stroke were, at least, the equivalent of six cylinders producing power on every other down-stoke. As it turns out, because of other advantages inherent in a design in which the compression strokes are completed in a cylinder separate from the power cylinder, less power is consumed in compression and more energy is converted into rotational force.

Additionally, if a compressed-air tank is included in the equation, much of the momentum and braking energy that’s generally wasted can be recovered and used in the generation of power.

The engine has been described “as a Miller-cycle engine that uses half of the engine’s cylinders to provide mechanical supercharging.” That’s an approximation but a Miller-cycle engine leaves the intake valve open during part of the compression stroke, so that the engine is compressing against the pressure of the supercharger rather than the pressure of the cylinder walls. This seems counter-intuitive but Miller-cycle engines are about 15% more efficient than Otto-cycle engines.

Miller-cycle engines are in use today, most notably by Mazda and Subaru, and the efficiency is attributed to the fact that less power is lost in compression when the compression doesn’t really start until the connecting rod and wrist pin have rotated out of alignment with the crankshaft journal.

Along those same lines, the air-fuel mixture in the Split-Cycle engine isn’t ignited until after top-dead center rather than before TDC. That way, there’s no loss of mechanical leverage due to the wrist pin, connecting rod, and crankshaft being in direct alignment during ignition.

In case my explanation has resulted in your complete and utter confusion maybe it would be better if you visited the web site and saw an animation or went through the “Theory of Operation“; don’t forget to view the video. Scuderi also has several videos available on YouTube.

What are it’s advantages when configured as a diesel?

According to the Scuderi web site

The Scuderi Technology drastically reduces the cost of diesel systems by eliminating or dramatically reducing three of the most expensive and complex parts of a diesel system: turbocharging, injectors, and exhaust treatment.

Let’s look at those one item at a time:

  • Turbocharger: Because of mechanical supercharging the turbocharger can be eliminated reducing both the weight and cost of the engine.
  • Injectors: Because only half the cylinders provide power only half the number of injectors are needed. Additionally, “the Scuderi Diesel Engine will be able to use low pressure, low cost injectors instead of the expensive high-pressure injectors.”
  • Exhaust Treatment Systems: Because the Scuderi engine burns fuel more completely than current 4-stroke designs; the two biggest emission problems, NOx and soot, are all but eliminated. This could mean that the soon to be upon us urea-based Selective Catalytic Reduction systems that will, reportedly, increase engine costs by $10,000 or more might not be required at all.

And there’s another interesting factor. Since the compression cylinder is separate from the power cylinder and, therefore, not subject to violent explosions, it can be made of lighter materials to further enhance efficiency. The compression cylinder can also be built to utilize different volumes and/or ratios to enhance the supercharging effect; resulting in even greater power and efficiency.

In Conclusion

I don’t know if this engine will ever be built, let alone change the face of trucking. The Department of Defense has contracted with Scuderi to provide research and development funds and, while that does lend some credibility to the engine’s feasibility, I’m reminded of all the previous boondoggles that gained DoD support. A prototype is under construction and should be completed in time for testing some time this year. One way or another, it’s an interesting concept.