Split-cycle engine
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The Scuderi Split Cycle Engine is a design of internal combustion engine invented by Carmelo J. Scuderi. The Scuderi group who own the patents on the design, claim that computer simulations of the engine show promising gains in efficiency and reduced toxic emissions over conventional four-stroke Otto cycle designs. The group also claim it could be used as part of an air hybrid system.
As of April 2007 no working prototypes of the engine exist.
Design
In a conventional Otto cycle engine, each cylinder performs four strokes per cycle: intake, compression, power, and exhaust. This means that two revolutions of the crankshaft are required for each power stroke. The Scuderi split-cycle engine divides these four strokes between two paired cylinders: one for intake/compression and another for power/exhaust. Compressed air is transferred from the compression cylinder to the power cylinder through a crossover passage. Fuel is then injected and fired to produce the power stroke. In a standard Otto cycle engine, the pistons fire every other revolution. However, the Scuderi engine fires every revolution.
In the Scuderi cycle, the power cylinder fires just after the piston has begun its downward motion (after top dead center, or ATDC). This is in contrast to Otto cycle design convention, which calls for combustion just before top dead center (BTDC) in order to allow combustion pressure to build.
Scuderi group claims
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The separation of the intake/compression and power/exhasut cycles allows for a unique "boosting" effect to the power cylinder. The compression cylinder can be made with a larger bore and/or stroke than the power cylinder, thus the volume of air compressed into the power cylinder is greater than if the bore and stroke is uniform across the cylinders. In addition, since the compression cylinder is not required to withstand the violence of combustion, it can be made of lighter materials, thus reducing the overall weight of the crankshaft and piston assembly [citation needed].
The Scuderi-cycle engine can get away with firing ATDC because its burn rate is three times faster, and so is able to build pressure more quickly [citation needed]. This property of firing ATDC is a key feature of the design, as it enables the engine's higher efficiency and lower emissions [citation needed]. In an Otto cycle engine, ignition BTDC implies that the engine is momentarily fighting against the combustion flame front, while in the Scuderi engine the piston is moving with the flame front [citation needed]. Another feature offered by the Scuderi engine is the Miller effect [citation needed]. Finally, the Scuderi-cycle engine shares a similar infrastructure with a conventional internal combustion engine, so it can be packaged similarly in an automobile.
Air-hybrid Capability
The addition of an air storage tank and some controls would allow the Scuderi engine to function as an air hybrid. According to the Scuderi Group[1], the engine can produce and utilize compressed air by cycling through four separate modes:
- Regenerative Braking This mode disables the power cylinder while leaving the engine connected to the wheels. The compression cylinder continues to operate, filling the air storage tank with compressed air. In this way, the engine is able to recover energy from the momentum of the car as it brakes.
- High-efficiency mode This mode disables the compression cylinder, feeding the power cylinder with compressed air from the storage tank. The work of compression is eliminated, allowing more of the engine's power to be used to drive the car (thus reducing fuel consumption).
- Cruising Mode While cruising, not all of the compressed charge that the compression cylinder provides is needed by the power cylinder. This excess compressed air is utilized to refill the storage tank. When the tank is full, the engine enters high-efficiency mode.
- Turbocharged Mode A turbocharger can be placed in the exhaust stream to recover heat energy that would otherwise go to waste. The turbo would be used to feed compressed air to the compression cylinder, reducing the amount of work necessary to compress the charge. This mode is well suited to stationary applications such as electric generators.
The Scuderi group estimates that their engine could achieve 60% greater fuel efficiency by operating as an air hybrid.