Eco Sustainable Village
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Eco Sustainable Village |
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Three Cylinder Stirling/HydraLink Animation
and Description
The displacer skirt serves to support the regenerator matrix within the displacer, and also to move it when appropriate by means of differential pressure on the annular Ringbom "piston" created by the skirt (see How Does it Work? below). The skirt is coated inside and out with a low friction, dry lubricated surface. Gas flow past the skirt is minimized, but the same helium exists above and below the skirt and a small leakage exists. This leakage equalizes over the full cycle.
How Does It Work? The stirling cycle is easy to explain to kids, more difficult to explain to adults because it is unexpectedly simple. Heated gas expands, this expansion is translated to crankshaft torque, the gas is cooled which causes it to contract, and the crankshaft returns to its original position. That's it. The same working gas, such as helium, is cycled over and over just as freon is cycled around and around in a refrigerator. Gas molecules do not wear out and the same gas continues to work indefinitely. The gas is heated by moving it to a hot space. This space includes the heater, and the gas movement is accomplished by the displacer. The gas is displaced to the hot end as the displacer moves to the cold end of the working chamber. Thermal energy is added to the body of gas in the heater, raising the gas temperature and therefore its pressure. Later, the displacer strokes to the hot end and the gas is forced to move to the cold end of the engine. But there is a more subtle action going on at the same time. As the displacer moves the hot gas to the cold space, a large portion of the thermal energy in the gas is transferred to the regenerative matrix. When the gas reaches the cooler it is already most of the way cool and the cooler only has to remove a fraction of the energy that otherwise would have been required. An instant later, as the gas returns to the hot space it retrieves the energy from the regenerator. So, when the gas reaches the hot space, only a fraction of the energy is needed to finish heating the gas compared with what would be required without regeneration. This is the secret of the excellent fuel efficiency of the stirling cycle, fuel is only needed to supply the shaft output and make up for losses. Compare this with a common spark ignition engine, where each cycle takes new air and new fuel and begins the process from scratch without saving anything from cycles that have gone before. To follow the stirling cycle through one crankshaft rotation, let us focus on the upper cylinder, beginning when the crankshaft is at top dead center. The displacer is in the process of moving down toward the piston. It contacts the piston and the two travel together through the downward stroke. Since the displacer is at the cold end of the gas chamber, the gas is at the hot end. Thermal energy is transferred to the gas, raising its temperature and pressure. This pressure exists not only in the hot chamber, but throughout the gas chamber and also the hydraulic oil underneath the piston. Since the piston is free to move at any time, there is no difference between gas pressure and oil pressure. The oil pressure increases as the gas heats, and the pressure is exerted on the vanes of the HydraLink mechanism which in turn cause the crankshaft to rotate. Oil volume of a HydraLink chamber is a function of crank position, with minimum volume near TDC and maximum near BDC. As the crank rotates and the power piston descends, the working gas expands and pressure decreases. Very near bottom dead center of the crankshaft, gas pressure reaches a value slightly below the buffer space pressure which exists between the inner and outer cases. Therefore, pressure on the annular displacer skirt area is higher below than above, forcing the displacer to travel to the hot end of the gas space. As the regenerative displacer strokes through the hot gas it absorbs much of the thermal energy. Thus the gas emerges from the bottom side of the regenerator at a lower temperature and the energy is stored momentarily in the regenerator matrix. The gas is now in contact with the cool power piston. Again, the proprietary means of providing large surface area and efficient energy transfer from gas to hydraulic oil is not shown. The gas becomes fully cool, gas pressure is at a minimum, and the power piston begins to travel back toward the top. As the piston nears top dead center, gas pressure rises until it slightly exceeds the constant buffer space pressure and the difference in pressure forces the regenerator back through the gas to rest against the piston. This action allows the gas to pick up much of the energy left in the regenerator from the previous cycle, and the process is ready to begin anew. Cylinders #2 and #3 operate in the same way, with 120 degree separation which provides smooth output torque. But What Makes it Go? The force that makes the crankshaft rotate is the difference between oil pressure in the three chambers. Oil pressure is equal to gas pressure in each cylinder since the pistons are free to move at all times. When the pressure is higher in one HydraLink chamber than the next, the crank is forced to rotate. The hinge-like action of the HydraLink naturally resists bending, and transmits force to the crank without any substantial bending moment.
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Send mail to
ghazi@wavepowerplant.com with
questions or comments about this web site.
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The purpose of the Heater is
to conduct high temperature thermal energy from the burner into the working gas
(helium). It is incorrectly shown as a simple crown shape, in reality it is a
proprietary design that provides the surface area necessary to achieve highly
efficient movement of the heat energy into the hot chamber. Surrounding the
heater crown is the serpentine cylinder wall. This design allows the engine to
be "short and fat" from an internal aerodynamic perspective while being longer
from a thermal conductivity perspective. The increased metallic length also
minimizes thermally induced stresses. Insulation within the folds of the
serpentine impede radiant and convective losses. The insulation also occupies
space within the serpentine that would otherwise be dead volume.
The Regenerative
Displacer consists of two parts, the gray color displacer matrix itself and the
light blue cylindrical skirt. Like the heater, this illustration does not show
the true shape of the displacer. During the portion of the cycle when the gas is
cool, this displacer resides virtually in contact with the heater, minimizing
hot space "dead volume" at that time. During the hot phase of the cycle, the
displacer rests on the surface of the power piston, minimizing dead volume in
the cold space. Dead volume is only "dead" during the portion of the cycle when
it is counterproductive, and the QRMC design permits the hot and cold spaces to
be used to their full advantage.
The Power Piston is located
within the displacer skirt, and serves as a barrier between the gas above and
the hydraulic fluid below. There is no pressure difference across the piston, it
is free to move up and down at any time. Since the piston does not have to
withstand any pressure differences it can be very low mass.
The Roll Sock Seal
serves to completely isolate the helium working gas from the hydraulic medium.
It is composed of back-to-back seals with an incompressible liquid contained
within. This seal is located between the power piston and the inner case. Roll
sock seals are very low friction devices and by operating them in an opposed
fluid filled configuration each seal is limited to positive pressure excursions
only.
The Inner Case contains the
hydraulic fluid (not shown). Outside this case the helium buffer space is
pressurized to the average working pressure. The inner case only has to
withstand positive and negative excursions from the average pressure. Not shown
in this animation is the cooling exchanger which is part of the inner case. This
exchanger serves to remove the low quality heat energy from the hydraulic oil.
The Crankshaft exists in
the center of the engine, totally bathed in hydraulic oil. It is pictured in a
single ended configuration, the crank throw is not subjected to the bending
loads of the usual crankshaft/connecting rod configuration. The crank can rotate
in either direction.
In this design, six Links make
up the patented HydraLink (tm) mechanism,
