Scuderi Split Cycle Engine
Encyclopedia : S : SC : SCU : Scuderi Split Cycle Engine
The Scuderi Split Cycle Engine design is a rethink of the conventional four-stroke Otto cycle internal combustion engine conceived by Carmelo J. Scuderi (1925-2002). While as of this writing no working prototype of the engine exists, computer simulations carried out by the [Scuderi Group] and the Southwest Research Institute showed promising gains in efficiency and toxic emissions. It also has the innate capacity to power an air hybrid system.
The 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 transfered from the compression cylinder to the power cylinder through a crossover passage. Fuel is then injected and fired to produce the power stroke. Because the engine produces one power stroke per crankshaft rotation, a Scuderi-cycle engine has the same total engine size (number of cylinders and displacement) as a comparable Otto-cycle engine.
The power cylinder fires just after the piston has begun its downward motion (after top dead center, or ATC). This is in contrast to engine design convention, which calls for combustion just before top dead center (BTC) in order to allow combustion pressure to build. The Scuderi-cycle engine can get away with firing ATC because its burn rate is faster, and so is able to build pressure more quickly. This property of firing ATC is a key feature of the design, as it enables the engine's higher efficiency and lower emissions.
Potential advantages
- Reduced NOx emissions The engine could produce 80% less nitrous oxides (NOx). Most of the NOx is produced at the high peak temperatures reached during combustion. Since a conventional engine fires BTC, it further compresses the combusting gas, raising its temperature. By firing ATC, the Scuderi cycle produces lower peak temperatures and thus, lower toxic emissions.
- Increased efficiency; from 33% to 40% Several factors contribute to the engine's efficiency, including:
- *Increased burn rates The rapid transfer of compressed air to the power cylinder creates a great deal of turbulence, facilitating a faster burn. Whereas conventional engines require 22-24 degrees of crankshaft rotation for the charge to fully combust, the Scuderi engine requires only 10.
- *Ability to run lean Increasing the air:fuel ratio in an engine increases operating efficiency. However, conventional engines are limited in this regard by the need for a catalytic converter, which requires specific stoichiometry in the exhaust stream in order to function. Given its lower emissions, the Scuderi engine should not suffer from this limitation.
- *Geometric optimization Each of the two cylinders may be offset at different angles that reduce the friction inherent in their specialized tasks.
- *Longer power stroke The power stroke can be lengthened, over-expanding the combusted gas and increasing thermal efficiency by the Miller effect.
Potential drawbacks
- Cooling and lubrication Due to the fact that cool air never enters the power cylinder, heat would quickly build up causing lubrication oils to break down and components to fail. It may be necessary to use expensive exotic materials to line the cylinder walls, or otherwise provide special cooling, to address this issue.
- Valve-train durability Given the high accelerations experienced by the crossover valve, durability could be an issue. New valve designs could address this.
- Auto-ignition and/or flame propagation into crossover passage Auto-ignition occurs when the temperature of the compressed air becomes sufficient to ignite the fuel before a spark is fired; this causes knocking/pinging and is harmful to the engine. The Scuderi Group hopes to address this with proper placement and timing of fuel injection, and also proper crossover valve timing.
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[link], the engine can produce and utilize compressed air by cycling through four separate modes:
- Regenerative Breaking 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.
References
- [Scuderi Group pages] on the engine's technology, particularly the [theory of operation] section.
- [Theory of Operation (PDF)]
- [Green Car Congress article]
External links
- [Company website]
- [U.S. Patents]
- [Motor Trend article]
- [Wards Auto article]
- [Gizmag article]
From Wikipedia, the Free Encyclopedia. Original article here. Support Wikipedia by contributing or donating.
All text is available under the terms of the GNU Free Documentation License See Wikipedia Copyrights for details.