SwRI Full-Load Study of Scuderi Split-Cycle Engine Indicates Higher Power, Torque and Efficiency Than Conventional Engines of Equal Displacement
The first independent laboratory study of the Scuderi Split-Cycle Engine (earlier post) under full-load conditions indicates that a gasoline-fueled version of the engine will have higher power, torque and efficiency ratings than the current state-of-the-art turbocharged gasoline engines of equal displacement on the road today.
The Full Load (FL) Study by Southwest Research Institute (SwRI) is the first of three reports to be published by the laboratory prior to the assembly of the first prototype, which is scheduled for completion later this year. A Part Load Study and an Air-Hybrid Study will be published in early and mid-2008 respectively.
The air hybrid study will incorporate the results of full load and part load studies, and add to that the compressed air storage tank used in the hybrid implementation. The air-hybrid study will compare the Scuderi air-hybrid efficiency levels to those of an electric hybrid.
The patented 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 high-pressure gas passage to the power cylinder for combustion. The full-load study was made using a single paired combination of 1-liter displacement.
The SwRI study concluded that at full load, the efficiency of the gasoline-fueled split-cycle engine would be around 37.5%, versus approximately 33% for conventional Otto cycle engines, according to Sal Scuderi, president of the Scuderi Group and co-inventor of the split-cycle engine. Torque levels would be about 50% higher than those of gasoline engines, taking the split-cycle engine into diesel territory in terms of torque.
Additionally, the predicted NOx emissions are 50% to 80% less than that of a conventional engine, which will mean an even greater advantage in diesel applications.
The NOx reduction was an unanticipated result of the engine design, said Scuderi in a 2006 presentation. One of the design features of the engine—“the biggest breakthrough,” he said—is that it fires after top dead center in the combustion cylinder.
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. By firing after top dead center, the piston is already pulling away from the combustion, enhancing the full air motion. Combustion is very rapid—10 crank angle degrees, two times faster than anything else the company had found, according to Scuderi.
With the very fast flame chasing the piston, rather than piston crashing into the flame, the flame front, where most of the NOx usually is formed, doesn't reach temperatures high enough for the same amount of NOx formation as in a conventional engine. This, Scuderi said, could turn out to be one of key features of engine, especially for diesel applications.
The company will begin ramping up its work on a diesel-fueled application of the split-cycle engine this quarter, said Scuderi, who noted that it looks like the split cycle engine may be able to address both NOx reduction and PM reduction without the same level of aftertreatment systems required by current diesel engines.
The combination of lower engine-out emissions along with the reduced cost of the split-cycle engine compared to a conventional diesel (no turbocharger, half the fuel injectors, reduced aftertreatment system) has piqued the interest of light-duty vehicle OEMs, Scuderi said.
At this point, the Scuderi Group is only releasing the complete data from the full-load report to OEMs who have signed a non-disclosure agreement. The data will eventually be made public after the company’s patent applications have been published. The company will again appear at the upcoming SAE World Congress in April.