The first proof-of-concept prototype of the Scuderi Split-Cycle engine was unveiled by Massachusetts-based Scuderi Group Monday at the 2009 SAE World Congress in Detroit.
The prototype, shown in cutaway form with fully operating internals, is an exact duplicate of the actual bench-test engine that will begin testing and analysis at Southwest Research Institute’s (SWRi) San Antonio facility next month. The 1.0-L twin-cylinder, naturally aspirated, indirect-injection gasoline prototype is expected to produce up to 80% less toxic emissions than a typical gasoline internal-combustion engine, said company Chairman Sal Scuderi.
The Scuderi engine was designed by company founder Carmelo Scuderi. His engineer sons Sal and Stephen (Stephen serves as Vice President and Patent Attorney) have moved development forward steadily and methodically since their father’s death in 2002. They believe the engine and its novel combustion process offer significant efficiency, emissions, and torque benefits compared with conventional Otto cycle engines. According to Stephen Scuderi, a number of OEMs have shown interest, and Scuderi Group is looking to license the technology.
The operating concept divides the four strokes of the combustion cycle over two paired cylinders (the prototype resembles a large parallel-twin motorcycle engine). The left cylinder handles intake and compression—essentially it functions as an air compressor—while the right cylinder is responsible for power and exhaust. The compressed air is transferred through a crossover passage from the compression cylinder into the combustion/exhaust cylinder.
Previous split-cycle engines (the concept dates to 1914) suffered two major problems— poor volumetric efficiency and low thermal efficiency. Scuderi’s engine solves the breathing problem on the compression side by using a pair of pneumatically actuated valves that open outwardly, enabling a very close (<1.0 mm) piston-to-cylinder head clearance without valve interference.
Sal Scuderi claims this effectively pushes nearly 100% of the compressed air from the compression cylinder into the crossover passage, eliminating the breathing problems of previous split-cycle designs.
The engine requires just one crankshaft revolution to complete a single combustion cycle. Ignition is timed to occur between 11º and 15º after top-dead center (ATDC), which Scuderi claims is key to the engine’s thermodynamic efficiency and cleaner combustion. 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, Stephen Scuderi said.
Because the engine’s cylinders are independent of each other, compression ratio in the compression cylinder is not limited by the combustion process. Stephen Scuderi said that the engine runs effective compression ratios of approximately 100:1 and that 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 and over 130 bar (1900 psi) on the turbocharged prototype.
Exceptionally long valve opening duration during combustion is also a key to the engine’s excellent turbulence characteristics, Sal Scuderi said. The result is very rapid atomization of the fuel/air mixture.
After tests of the base naturally aspirated unit are completed at SWRi, Scuderi will continue developing a turbocharged version; it is expected to be completed by 2010. “We believe we can achieve 140 hp/L specific output,” Stephen Scuderi told AEI.
Scuderi Group engineers are committed to using as much conventional hardware in the prototype engines as possible, to help minimize cost. Bosch is a development partner, supplying two fuel injectors per cylinder pair, as well as fuel and oil pumps and ECU. “We share some of the control software and IP with Bosch; our IP and patents are primarily in base engine architecture,” said Stephen Scuderi.
The Scuderi Group’s global patent portfolio contains more than 200 patents, including 72 issued in more than 50 countries.