Intent on showing the industry continued progress in its split-cycle engine development program, as well as some new technology paths, Scuderi Group returns to the SAE World Congress where its floor display drew daily crowds last year. At the 2011 event, executives of the West Springfield, MA, company are expected to provide updates on their advanced-engine development enterprise.
The ongoing test program and control-map development is being conducted with a 1.0-L testbed engine at Southwest Research Institute (SwRI). This will be discussed, along with a new full-vehicle-simulation program that replicates a 2.0-L version of the Scuderi engine in a 2011 Nissan Sentra, according to company Vice President Nick Scuderi.
The Nissan simulation follows modeling conducted late last year on the "virtual" 2.0-L engine installed in a 2004 Chevrolet Cavalier. Data from that program show the engine capable of delivering 25 to 36% fuel-efficiency improvements, depending on whether the base split-cycle engine or the Air Hybrid variant is installed, claimed Scuderi. He said engine-out NOx emissions are reduced by up to 80% compared to a contemporary naturally aspirated gasoline engine, due to the combustion system firing after top-dead center.
Results of the first vehicle simulation program will be presented during the World Congress along with two technical papers: “Scuderi Split-Cycle Research Engine: Overview, Architecture, and Operation” and “Scuderi Split-Cycle Fast Acting Valvetrain: Architecture and Development.”
In a recent interview with AEI, Scuderi said development of a next-generation V-type engine is under way. The new design better optimizes the combustion system for turbocharging and vehicle packaging. The Vee layout provides improved access to the crossover, which connects each pair of compression and combustion cylinders, as well as better access to the compressed-air tank that is essential to the Air Hybrid version.
“It also gives us some nice control features such as control of predetonation using different cooling circuits for part- and high-load operating conditions,” he noted. “We want the ability to cool and not cool depending on operating conditions.”
He added that ongoing work with turbocharging has shown the design team that the existing Air Hybrid variant of the split-cycle engine can be “dramatically downsized” while delivering greater thermodynamic efficiencies and torque.
Company President Sal Scuderi noted in a separate interview that “with turbocharging, we’re able to downsize [the compression cylinder] and in the process our engine now is exceeding torque levels of a diesel engine. We think this could be one of the biggest advantages of the engine itself.” He said brake mean effective pressure (BMEP) has approached turbocharged automotive diesel levels (typically 14-18 bar) in testing.
The Scuderi engine's basic operating concept divides the four strokes of the combustion cycle among two paired cylinders. One handles intake and compression, essentially functioning as an air compressor, while the other is responsible for power and exhaust. The compressed air is transferred through a crossover passage from the compression cylinder into the combustion/exhaust cylinder.
In the Air Hybrid version, a 30-L pressure tank is fitted parallel to the crossover path. The tank serves as an energy storage system for the compressed air. When the air in the tank reaches a predetermined pressure, the controls (developed in collaboration with Bosch Engineering in Abstatt, Germany, and SwRI) shut down the compression side of the engine. It’s then operating in its high-efficiency mode, using the stored air rather than the compression cylinder’s work to charge the combustion cylinder.
The time to charge the air tank is 10-15 seconds; it releases into the combustion cylinder over about a 45-second period. “About 70 to 75% of the time you’re operating out of the air tank in this very high-efficiency mode,” Scuderi said.
The engine requires just one crankshaft revolution to complete a single combustion cycle. Ignition is timed to occur between 11 and 15 degrees after top-dead center—what the company claims is key to the engine’s thermodynamic and combustion efficiencies. To enable the ATDC ignition, Scuderi uses a combination of high air pressure in the crossover passage, extremely high mixture turbulence in the power cylinder, and fast flame speeds. The result is a combustion rate that is four times faster than that of a conventional four-stroke, company engineers claim.
Because the engine’s cylinders are independent of each other, compression ratio in the compression cylinder is not limited by the combustion process, the Scuderi brothers claim. The engine runs effective ratios of approximately 100:1. Cylinder pressures on the compression side are equal to that of a conventional engine during combustion. The pressures in the compression cylinder and the crossover passage reach over 50 bar (735 psi) on the naturally aspirated prototype.
Exceptionally long valve opening duration during combustion is also a key to the engine’s “excellent” turbulence characteristics, Sal Scuderi said, which results in very rapid atomization of the fuel/air mixture.
He pointed to the engine’s coefficient of variance—how the pressure profiles vary from one combustion cycle to the next—in comparing its current state of development to a baseline spark-ignition engine of similar size. At its sweet spot of operation, the typical gasoline engine and the Scuderi split-cycle each run 2 to 4% variance, he claimed. And in idle conditions where the baseline engine runs from 5 to 10% variance, the Scuderi is claimed to run about 1.4% variance.
The Scuderi brothers say their expanding development program is on track, and they’re confident of landing the company’s first licensee later this year. “We expect the efficiencies to continue to climb as modifications are made and new simulations are conducted,” said Sal.