T. KORAKIANITIS Nutating-disk internal-combustion engine	"Korakianitis" is pronounced phonetically
email: tk@mecf.wustl.edu	link: [ 183 kB audio wav]

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Simple cycle gas-turbine engines have high specific power (power per engine volume and weight) because of their large swallowing capacity. As engine power is reduced below approximately 1,000 kW gas turbine passages become smaller, and centrifugal components are being used. Below about 500 kW turbomachinery flow passages become small and component efficiencies drop. In that power range piston engines with smaller swallowing capacity are more efficient than simple-cycle gas turbines, but they have lower specific power.

In the following we present the concept for a high specific power internal combustion engine (L. Meyer, 1993, US patent no. 5,251,594, Nutating internal combustion engine). At present commercial applications (perhaps with the exception of car racing) do not have an economic impetus to bear the substantial cost of developing a new engine. Even though the proposed concept has potential for emissions reduction, it is likely that its initial development will be funded by military applications.

In order to use one fuel in military applications engines are required to burn what is commonly called "heavy diesel" fuel (which is much "lighter" than marine heavy diesel fuel). The flame propagation speed in diesel is much slower than that in gasoline, and small military piston engines can not burn diesel. This poses a fuel compatibility problem for some applications such as portable power generation, uninhabited aerial vehicles (UAV) and others. The military has a need for a high-power-density engine that can burn heavy diesel in the 2 kW to 500 kW power range for power generation and/or propulsion.

The concept engine has a few analogies with piston-engine operation, but like gas turbines it has dedicated spaces and devices for compression, burning and expansion. The engine operates on a modified limited-pressure thermodynamic cycle, and it has distinct advantages over piston engines, and over gas turbines in low power ranges. The core of the engine is a nutating non-rotating disk, with the center of its hub mounted in the middle of a Z-shaped shaft. The two ends of the shaft rotate, while the disk nutates. The motion of the disk circumference prescribes a portion of a sphere. A portion of the surface area of the disk is used for intake and compression, a portion is used to seal against a center casing, and the remaining portion is used for expansion and exhaust. The compressed air is admitted to an external accumulator, and then into an external combustion chamber before it is admitted to the power side of the disk. The accumulator and combustion chamber are kept at constant pressures. For every two shaft revolutions we obtain four intake, four compression, four power and four exhaust disk sweeps, each 270 degrees crank angle rotation, because both sides of the disk are in use.

325 kb avi movie (23 seconds)

For the same engine volume and weight, this engine produces less specific power than a simple-cycle gas turbine, but approximately twice the power of a two-stroke engine and four times the power of a four-stroke engine. The thermal efficiency is similar to that of comparably-sized simple-cycle gas turbines and piston engines. The computed sea-level engine performance in the 2 kW to 500 kW power range for a 15 inch diameter disk with engine shaft rotating at 2,400 rpm is presented below.

where each point on the graph represents an engine with different specifications (compression ratio, maximum temperature of products of combustion, pressure losses, heat losses, fuel-injection rate etc).

TOP 10 ADVANTAGES OVER OTHER INTERNAL COMBUSTION ENGINES

1. Two power strokes per crank revolution.
2. Inherently balanced.
3. Fewer moving parts; less friction; higher reliability.
4. Reduced seal (perimeter ring) velocities compared to piston rings; permits higher shaft speeds for increased power, or lower seal friction for comparable shaft speed.
5. Variable compression ratio (accumulator valve pressure).
6. Expansion volume can be greater than intake volume for increased power and efficiency (sea-level applications).
7. Compression volume can be greater than expansion volume for "self-supercharging" high-altitude applications.
8. External combustion pre-chamber permits better arrangements for emission control.
9. External combustion pre-chamber increases length of flame travel, providing fuel flexibility; for example it permitting use of diesel fuel in small-size engines.
10. Flexibility: two disks in series displaced 180 degrees along the shaft axis minimize axial-thrust bearing; one disk may be dedicated to compression, the other to expansion, improving heat-transfer flows.

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