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« Quasiturbine Stirling and Short Steam Circuit »
Hot Air Engine

From a Reversible « Quasiturbine Heat Pump »


First QT option - Stirling engine turns from heat flowing from a hot sink to a cold one.
The hot sink can be kept hot by fuel external clean combustion.
High theoretical efficiency results from absence of intake and no exhaust,
but inside pressure differential is lower than boiler steam supply,
and consequently the Stirling specific power density is not impressive...

Second QT option - « QT Rankin Short Steam Circuit Stirling » improves both
high and low pressure, and speed pressure transition without heat regeneration:
Flash steam is a very fast process that produces a much higher pressure
that heating a gas. Furthermore, steam condensation is also a fast process
producing a much deeper vacuum that the surface cooling of a gas.

Third QT option -  « QT Brayton Short Gas Circuit Stirling »
On a QT internal combustion engine, just replace the spark plug
by a hot stator area heated from an external source. In such a configuration,
ambient air will be compressed in a cold area of the QT,
then heated in the dead top center and expansion area,
and then exhausted without cold sink (ambient air acting as it).

Such a configuration is not possible with piston engine,
because intake and expansion occurs in the same physical location.


Mechanical Conversion of Low Heat

From looking at the USA energy flow chart at

https://flowcharts.llnl.gov/

The amount of Low temperature heat discarded is quite impressive. This waste energy has a tremendous potential for energy recovery, and the Quasiturbine offers more ways to tackle the challenge through Brayton, Ranking and Stirling cycles!

Historically, to avoid feed pumps, the steam boiler was over-designed to hold sufficient water for a full operating cycle. This is still of interest for the solar steam systems (or geothermal), ou il est avantageux d'avoir une citerne d'eau pressurisé en marge du circuit vapeur suffisante pour l'alimentation la journée entière (remplissage la nuit), justement pour ne pas avoir à injecter les condensats contre la pression de vapeur. Une seconde citerne peut accumuler les condensats à la sortie de la turbine à pression atmosphérique, et le transvasage peut se faire la nuit sans soleil... Ici, la pulsation quotidienne est obligatoire de toute façon.

Coté puissance spécifique, la pulsation du cycle à haute fréquence impose l'arrêt du circuit vapeur et la chûte de pression de la chaudière (et son refroidissement en pure perte), un inconvénient majeur qui fait baisser à la fois la puissance moyenne et l'efficacité thermique. Voilà pourquoi on revient à la pompe de remplisage en phase liquide et continue! Many think that the feed pump in a steam (Rankin cycle) is a system waste of energy, while in fact, most of the feed pump energy is recovered by the turbine. It is like the compression energy in a piston engine which is almost all recovered at relaxation, or the energy of the compressor turbine in a Brayton cycle (jet engine), recovered in the hot turbine.

La pression d'un circuit vapeur est déterminer par le point le plus froid (condensation),
alors que l'éfficacité est donné par la température de la vapeur (les surchauffeurs font une chauffe à pression constante - celle du point froid, souvent la chaudière elle-même). L'efficacité optimum requiert souvent un surchauffeur distinct de la bouilloir, laquelle fixe la pression. Coté efficacité du cycle lui-même, la basse pression de vapeur réduit la demande de puissance de la pompe d'alimentation en phase liquide, ce qui est pratique mais pas critique, parce que du point de vue globale, l'addition d'énergie au système par la pompe est presque totalement récupérée par la turbine...
Mise à part la chaleur latente, l'énergie est essentiellement dans les débits volumiques, et les débits en phase liquide sont typiquement 600 fois moindre qu'en phase vapeur.

Souvent, l'optimum est d'utiliser les thermies basses températures comme préchauffe d'un cycle à plus haute température, au quel cas l'efficacité différentielle du carburant utiliser pour la haute température est bonifiée... La QT favorise un cycle vapeur basse pression aussi pour une raison réglementaire, car les hautes pressions sont dangeureuses et bien exigentes. Dans le cas de la QT, nous préconisons pour le solaire, de supprimer la chaudière, et de chauffer le bloc moteur de la QT lui-même, et d'injecter de la vapeur gardée en phase liquide dans un injecteur pour vapeur éclaire (flash steam). Pratique aussi pour les unités mobiles qui craignent les réservoirs d'eau bouillante.


Principle

Heating a gas makes pressure, while cooling it makes vacuum. Contrary to piston where heat and cooling occurs at the same physical location, in a Quasiturbine the pressure and vacuum occurs at different angular sectors of the QT engine block, which provide an interesting Stirling characteristic. In principle, providing heat and cold will make the rotor to turn, making the most compact QT Stirling engine without much hardware.

The principle is very simple. A fix amount of gas (work better with helium) is kept in the chambers of a positive displacement machine. This gas is heated just after TDC and cooled just after BDC. The speed and the level at which the gas can be heated and cooled is the limitation of this concept, which is generally limited to low power and low rpm, and has poor power to weight ratio. However because it has no intake and no exhaust, not only the piston gets a push from high pressure, but it gets a pull from the cold gas, which is in part responsible for the higher efficiency.

You have a thermodynamic cycle (Brayton or Rankin), with proper selection of temperature and pressure, you are likely to be able to run this cycle within a Quasiturbine without any boiler, reservoir, pipe, pump, expander or motor!

General advantages are efficiency and low noise, and ability to turn on any external heat source. A Stirling will always be Stirling, and the Quasiturbine objective is not to compete with other types of engine, but with current Stirling engines. It has its own environmental benefits in specific applications.


Quasiturbine Brayton Short Gas Circuit Stirling

On a QT internal combustion engine, just replace the spark plug by a hot stator area heated from an external source. In such a configuration, ambient air will be compressed in a cold area of the QT, then heated in the dead top center and expansion area, and then exhausted without cold sink (ambient air acting as it). Such a configuration is not possible with piston engine, because intake and expansion occurs in the same physical location.

It is all about transforming heat into usable pressure. As an introduction to heat engine, let consider a pneumatic Quasiturbine where the engine block is kept hot by an external heat source, and into which relatively low pressure cold air is introduced through checkvalves at intake ports (it could alternatively be water flash steam - see QT Type Steam). Cold air will adsorbs heat from the Quasiturbine chamber walls and expand, making the rotor to turn (intake checkvalves prevent the pressure increase to flow back into the feed line). The rotor must spent part of its energy (partly recovered when air pressure is feedback) to drive a small (Quasiturbine) compressor to provide the low pressure cold air needed, but overall efficiency could be fairly good. This is an open Brayton cycle very similar to the complex one used in turboshaft jet engine, and it is usable in numerous applications, not to exclude cogeneration and conventional engine exhaust heat recovery. Stirling cycle does almost de same, but without any intake or exhaust, using rather a captured gas volume going alternatively into hot and cold areas.


Primary Heat Sources

The Stirling heat engine principle apply well to primary heat source like solar, wood stove, co-generation... However, making heat specifically for a Stirling engine from a quality liquid or gaseous fuel is generally not a good idea, because of the down grading of a valuable potential fuel pressure. In an internal combustion engine, part of the internal pressure is due to heat, but an even more important part of this pressure comes from state change (a vapor occupied in the order of 600 times the volume of the liquid phase). If you burn fuel in open air, this pressure is released in turbulent motion and is transformed into heat in the flame, which heat has to be harvested back into mechanical energy. Because fuel internal pressure has an higher quality than heat energy, it is best suitable to use quality fuels in an internal combustion engine (extracting pressure energy), and to use a Stirling as a complementary machine to recover exhaust heat losses. Of course, there are exceptions...


Piston Stirling Limits

Gas to cylinder-piston heat exchanging surface geometry is very limited and does not favor sufficiently violent gas temperature variation, mainly because the cylinder wall is common to the heating and the cooling cycle. Pressurized gas leak is an other problem, because the whole crankshaft can not be encapsulated. Regenerator slows down the rate of temperature variation, reduces the specific power and offers little (or no) overall efficiency gain.


Quasiturbine Made Stirling Engine

Consider a Quasiturbine without any intake or exhaust port, where all the chambers are filled with the same quantity of a compressible gas, and suppose that two opposed quadrants are kept at high temperature, while the two others opposed quadrants are kept cooled. The rotor surface could be thermally insulated. Since there is a lag time in the gas temperature variation, it is in fact desirable to apply the heat with some advance on their respective quadrants. Like for the piston, the Quasiturbine Stirling is not self-starting, and has a preferential direction of rotation.

Initiating the rotation will move the cool gas into the hot area where it will expand and produce a torque, until it get cooled again in the following quadrants and so on. This rotation is provided by two simultaneous opposed closed gas circuits, each one working on the Stirling thermal engine principle (mechanical work produced by a close fluid circuit simply from a constant heat flow between two hot and cold poles, by opposition to hot-air-engines which are hot-monopole devices, since they generally intake fresh air at ambient temperature and exhaust their hot residual gas).

The 4 poles Quasiturbine Stirling cylindrical concept

The figure is showing arbitrary angular lengths
and positions of the hot and cold zones.

An alternate flat geometric arrangement would be to use one lateral enlarged flat side engine cover as a cold plate linked to the corresponding cold radial zone, and the other lateral enlarged flat side engine cover as a hot plate linked to the corresponding hot radial zone. This would give a sandwich like compact disk engine with wide flat head exchanger surfaces particularly appropriate for solar free space applications (with cold shadow side).


QT Stirling Advantages

In the Quasiturbine Stirling, all the engine shell is pressurized with helium, so that the inter-chambers leaks are automatically recycled by the central region, and required only sealing of a turning shaft (comparatively to the sealing of the back and forth piston connecting rods, unless sealed machines, which the Quasiturbine also can be).

No regenerator. Since the gas is moved sequentially rather that alternately from the zones of different temperatures, the Quasiturbine Stirling is exempted from the need of a regenerator without efficiency lost, which increases its power output through an increase in RPM. The Quasiturbine has no need either for a "gas displacer".

More torque. Instantaneous resulting torque on the rotor is more constant than in internal combustion mode (but less powerful) because it has 2 positive contributions by revolution about 90 to 120 degrees in duration each, that is one push and one pull. For each revolution of the Quasiturbine rotor, each one of the four pivoting blades receives a push at the top and at the bottom hot plate (approximate angular location), and a pull at the left and the right cold plate, that is 8 pushes and 8 pulls, for a total of 16 torque impulses per rotation, which levels out the instantaneous torque fluctuations, increases the power density, and removes the need for a flywheel (further reducing substantially the engine weight and size).

Faster rotation. Because each Quasiturbine pivoting blade goes through 2 pushes per revolution compare to 1 for the piston, the same time constant would means that the Quasiturbine rotor RPM would be half of the piston equivalent machine. However, time constants in the Quasiturbine are anticipated to be quite shorter, so that about the same RPM can fairly be expected. Consequently, based on equal chamber volume, a Quasiturbine rotor will produce up to 16 times more power than a piston (8 times due to the geometrical frequency, and 2 times due to the RPM), and hopefully with less than 16 times the heat flow...

More power per pound. The Stirling Piston engines are known to be large and heavy, which the Quasiturbine-Stirling concept should solve, because there is no pipe or external accessory or heat exchanger required. Conventional Piston Stirling engines need inter-chamber connecting pipes to carry the gas to and from the cold and hot areas (displacer side spacing plays the same role). Those pipes are passive extension of the compression chambers, and since they are kept at a near constant intermediary temperature, their gas content does not actively participate to the pushing effort, but rather attenuates them. The Quasiturbine Stirling concept suppresses the need for such interconnecting pipes, and allows for higher peak pressure in the chambers, and consequently higher specific power density. Quasiturbine offers up to 16 times more power than a piston with a comparable chamber volume! The Quasiturbine-Stirling is further vibration free.


Stirling from 2 Quasiturbines

A dual-Quasiturbine Stirling engine? One hot and one cold? Side by side? On the same shaft? After all, Quasiturbine chambers are analog to piston chambers, but are making 2 compression-expansion per revolution. Instead of cooling the hot gas into a cold quadrant, move it from the hot-BDC into the cold-BDC chamber of a cold Quasiturbine located nearby, and when the gas has cooled to cold-TDC, move it back to the hot-TDC Quasiturbine. This will work, and the back and forth flows could be one way, which is again not appropriate for "regenerators". However this dual-Quasiturbine configuration is not likely to raise the power density, neither the efficiency(?), because it will introduce holes and may be pipes as passive volume extending from the chambers. On the other hand, the rotor itself could now have an active role being either cold or hot, instead of thermally insulated.


QT Rankin Short Steam Circuit Stirling

Flash steam is a very fast process that produces a much higher pressure that heating a gas. Furthermore, steam condensation is also a fast process producing a much deeper vacuum that the cooling of a gas. « QT Short Steam Circuit Stirling » simultaneously improves both high and low pressure, and speed pressure transition without heat regeneration device!

Stirling is a gas-gas (no phase change) machine by opposition to Ranking cycle, which is a phase change machine with liquid and gas. Quasiturbine further allows for a phases change mode? To increase the heat flow transfer rate, the Quasiturbine-Stirling engines can be operated in Ranking cycle with fluid like water or alcohol, where steam is produced in the hot zones and condensed in the cold zones. It is not a Stirling any more, but a short Steam Circuit all self packaged in Ranking cycle. This requires only a small quantity of liquid water, which the centrifugal force of the Quasiturbine rotation can maintain permanently in contact with the perimeter for an optimum heat transfer. Ultimately, this option could also be considered as an attractive combo Quasiturbine-Stirling-Steam engine.

This Quasiturbine Ranking cycle concept has one advantage over the Stirling, which results form vapor condensation. Vapor droplets on the cold housing are scraped and accumulated by the contour seal and violently flash-steamed while getting on the hot area. This provides the very violent pressure variation needed to produce high power at high efficiency.

You have a thermodynamic cycle (Brayton or Rankin), with proper selection of temperature and pressure, you are likely to be able to run this cycle within a Quasiturbine without any boiler, reservoir, pipe, pump, expander or motor!


No Fuel 4-Stroke Thermal

In 4-stroke combustion mode, combustion heat is given to the Quasiturbine always in the same geometric sector. Providing heat to this sector by conduction or solar concentrator will make the engine running, without having to bother with the cooling aspect of the Stirling, since the hot gas is simply exhausted.


Applications

Quasiturbine provides a new powerful compact gas or liquid Stirling Engine, Heat Pump & Cryocooler for use in submarine, in free space thermal gradients, in vehicle... in cogeneration, in solar heat device... Non-stop nuclear Quasiturbine-Stirling for vehicle could drive a several HP generator continuously for many years, based on a small hot nuclear pellet...

Engine Exhaust Heat Recovery: By placing a Stirling or short steam circuit Quasiturbine into or around an engine exhaust pipe, some heat can be recovered into mechanical energy!

Electricity production generator with magnets can be incorporated into the Quasiturbine core to make the system a seal unit. Furthermore, due to the high torque continuity resulting from the 16 pulses per revolution, the Quasiturbine Stirling can provide optimum no-controller-sine-wave electrical output, without risking over harmonics, or the risk to stop the engine rotation by a surge peak power.


Stirling Engine Made Heat Pump

Forcing the Quasiturbine shaft to turn reverses the thermal process and the Quasiturbine becomes a Heat Pump! Driving this device with an external motor will also move heat from one quadrant to the next. The hot compressed gas will give its heat to a quadrant, while the following gas expansion will take heat (cold) from the next one. In reverse cycle, this device is a complete loop and an integrated "Quasiturbine Heat Pump" with heat exchangers. (Such a compact device is not possible with piston, because both compression and expansion occur at the same physical location, which is not the case with the Quasiturbine) Furthermore, no polluting gas or liquid is required. The air or liquid-cooled component can be as needed hot or cold. Please visit the page:

Quasiturbine Heat Pump

www.quasiturbine.com/ETypeHeatPump.htm
From an Hot Air Engine Reversible
« Quasiturbine Stirling and Short Steam Circuit »


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