DETROIT – The Scuderi Group, proprietors of advanced engine technology and developers of the Scuderi split-cycle engine, takes the wraps off its new Air-Hybrid split-cycle powerplant here at a recent industry conference here.
Touted as the “first hybrid system that makes sense,” the air hybrid concept uses the West Springfield, MA-based company’s advanced engine design to compress and store excess engine intake air in much the same fashion a hybrid/electric vehicle (HEV) stores energy in batteries.
At the heart of the Air-Hybrid is Scuderi’s patented split-cycle engine, a unique design concept dating back to 1914 that divides a 4-cycle internal combustion engine’s individual strokes of operation into opposing cylinders – one side for intake and compression, the other for power and exhaust.
Connecting the cylinders is a pressurized crossover passage that transfers the compressed intake air from the compression cylinder to the power cylinder. Unique disc-type check valves, adapted from air-compressor design, control the airflow from the compression cylinder, allowing nearly all of the pressurized gas to be utilized before the next intake cycle begins.
Camshaft-driven poppet valves control airflow in and out of the power cylinder and prevent the combustion process from “backtracking” into the crossover chamber, the company says.
The hybrid element of the engine begins in this crossover chamber, where a separate valve controls the flow of excess air into an external storage tank. The tank is pressurized to a similar degree as the combustion chamber gases – about 735 psi (50 bar) – and has a volume of about 1L per each of the engine’s cylinders, says company President Sal Scuderi.
Once the tank is charged, the air supply can be used in several ways.
In low-load situations, the compression cylinder can be disabled, allowing the power side of the engine to be fed with stored compressed air from the tank. The company says this greatly enhances efficiency by eliminating the power losses of the engine’s compression cylinder.
Conversely, the power cylinder can be switched off during coasting and braking, thereby allowing the compression cylinder to act as a built-in engine brake. Regenerative braking also occurs, as the compression cylinder’s intake air is routed into the storage tank to replenish any compressed air that has been depleted.
During regular cruising, the system also can vary the distribution of the intake air to both supply the power cylinder and fill the storage tank.
An added benefit of the design, Scuderi says, is the on-board supply of compressed air itself. The charged air could be used to start the engine if the battery runs low, operate air brakes, inflate tires and operate air tools – features that would have considerable value for commercial trucking and military applications.
In addition, the compressed air could be used to power a pneumatic valve system for the power cylinder, enabling a completely camless design and further improving efficiency.
The company says adding the Air-Hybrid feature to the split-cycle engine requires only a “few hundred dollars” of additional investment, compared with thousands for typical hybrid-electric powertrains.
Currently, the split-cycle engine exists only in the computer modeling stage at the Southwest Research Institute (SwRI), a San Antonio-based nonprofit engineering lab that is working with Scuderi on thermodynamic development of the engine.
The program has been funded by about $8 million from various private investors, including a $1.2 million grant from the U.S. Dept. of Defense’s Appropriations Bill passed earlier this year.
Along with computer modeling and fluid-dynamics evaluations, Scuderi also has tasked SwRI with development of two working prototypes of the split-cycle engine, which it plans to unveil next year – a 2-cyl. gasoline-powered model and a 6-cyl. diesel variant.
The compatibility with various types of fuel, including gasoline, diesel, biofuels and natural gas, is just one of the many benefits the company touts.
Because of the split-cycle design’s similarities to conventional 4-stroke engines, the technology can be scaled to apply to any piston-driven engine, large or small.
The similarities to conventional internal-combustion engines also necessitate a minimal amount of retooling to manufacture the split-cycle unit, an aspect that dramatically improves the concept’s prospects for mainstream production applications, Scuderi says.
However, the real benefits of the engine concept, with or without the Air-Hybrid feature, may be the potential dramatic improvements in efficiency and emissions it makes over traditional IC engines.
Scuderi claims the split-cycle technology can produce significantly more power than a conventional engine of equal size; nearly double a vehicle’s fuel economy; improve the efficiency of current engines by 24%; and exceed the efficiency of modern HEVs without using a costly and complex electrical system.
The concept also emits about 80% less oxides of nitrogen (NOx), primarily due to its ability to ignite the intake charge after the piston has reached top dead center (ATDC), a unique feature that Scuderi says is key to the engine’s success.
Firing ATDC, along with the development of the check valves in the crossover passage, were the major hurdles the company had to overcome in making the split-cycle engine workable, the company says.
Due to the massive turbulence created by the pressurized air entering the combustion chamber from the crossover passage, the fuel/air charge vaporizes much faster than in a conventional engine, Scuderi explains. The faster fuel atomization also creates a much quicker combustion flame speed inside the chamber when ignited, making it easier to burn all the fuel in a shorter amount of time.
Even though firing ATDC means the piston is moving away from the charge when it is ignited, reducing the pressure inside the chamber and limiting its power potential, the greater flame speed is said to compensate.
In addition, because of the lower pressures and the more efficient burn, peak temperatures inside the combustion chamber are reduced, which is largely responsible for the large NOx reduction, Scuderi says.
The inherent design of the split-cycle engine – with different components handling individual parts of the engine cycle – also allows for mechanical advantages that would be impossible to obtain in a conventional engine.
By making the compression cylinder larger than the power cylinder, a natural supercharging effect is generated as the greater volume of air on the compression side is crammed into the smaller space of the power cylinder. The pistons also can be offset in relation to the centerline of the crankshaft in order to reduce the internal friction of the engine’s components – a design seen in some contemporary production engines.
These intrinsic features, along with the benefits of the Air-Hybrid system, play an even greater role in diesel engine applications, as they reduce reliance on turbocharger, fuel injection and exhaust aftertreatment systems.
The split-cycle’s built-in supercharging effect eliminates the need for a turbocharger, Scuderi developers say, while the reduced engine-out NOx emissions allows for the use of less complex and expensive aftertreatment systems, Scuderi says.
Because the engine fires on only half of its cylinders, half as many fuel injectors are needed to produce an equivalent amount of power. Furthermore, the turbulent, high-pressure gas entering from the crossover passage means that less-expensive, lower-pressure injectors can be used with no degradation in performance.
The Scuderi Group currently has six patents filed in 45 countries for the split-cycle engine, with several more recently filed and pending.
Although he declines to specify potential customers and partners due to the engine’s early stage of development, Scuderi says the concept has been well received, with several auto makers showing interest in the technology.
However, the company has no plans to become an engine manufacturer. Once development is complete and the prototypes prove viable for mainstream production, Scuderi plans to license the design to various companies.
“These technology enhancements, and the subsequent patents, come at an important time as we as a nation look to be more efficient in our use of petroleum products and while the automobile industry struggles to increase the value of their vehicles,” Scuderi says.
“Once these advancements are incorporated into our internal combustion engine, the industry will have available the fuel efficiency, power, and impact on the environment that consumers are looking for and at a cost that makes sense.”