PISTON STEAM ENGINE HAVING INTERNAL FLASH VAPORIZATION OF
A WORKING MEDIUM
Existing piston steam engines operate with steam that is produced by a steam generator.
The steam is routed through inlet valves and exhaust valves in such a way that it passes at
high pressure into the cylinder chamber, moves the piston within the cylinder chamber,
when its pressure is released, after which it is forced out of the cylinder chamber by the
piston.
In most instances, the steam generators that are required for a piston steam engine consist
of a heat transfer device within which the working medium, for example water, is
vaporized at the desired operating pressure. The heat that is required for the vaporization
process is generated by a thermal-transfer medium, for example smoke gases. Within the
steam generator, the thermal transfer medium is cooled to a temperature within the range
of the vaporization temperature of the working medium.
In another approach, the attempt is made to bring about so-called flash vaporization in a
screw-type machine. Here, reference is made to the work of Professor Kauder of the
University of Dortmund. The principle disadvantages of a screw-type machine are
numerous.
In a screw-type machine, the compression or expansion ratios (subsequently referred to
as the volume ratio) are between approximately 4 and a maximum of 8. In a piston steam
engine, volume ratios of greater than 100 can be achieved.
The convective heat exchange that takes place between the working medium and the
walls of the screw-type machine is extremely large because there exists a fully formed
two-phase flow, besides which the heat-transferring surface is very large.

By virtue of its construction, the degree of efficiency of a screw-type machine is
relatively low, and the leakage losses cannot be reduced by seals or piston rings, as is the
case with piston steam engines.
In the case of other known combustion engines that are on the market, for example
conventional piston steam engines, ORC engines that operate according to the organic
Rankine cycle, Rankine engines, or steam turbines, only a relatively low mechanical
performance can be achieved from them, particularly if the heat source is at a relatively
low temperature, for example 200°C.
In order to make the best possible use of the energy contained in the heat of the working
medium, the heat-transfer medium of the heat source should be cooled to ambient
temperature in a process that is as reversible as possible.
In general, however, in the steam generators of known combustion engines, the thermal
transfer of the heat source is cooled only to a temperature that is close to the vaporization
or condensation temperature. For example, the thermal transfer medium is cooled only
from 200°C to 140°C and not to ambient temperature. In particular, if only heat at a
relatively low temperature level is available, and only a small amount of it is convertible
into mechanical energy, then this relatively high end temperature of the thermal transfer
medium of the heat source and the associated low exergonic efficiency has a particularly
deleterious effect on the performance and the economics of the combustion engine.
In addition, partially toxic or injurious working media are used in many of the
combustion engines referred to above.
It is the objective of the present invention to describe a combustion engine that
eliminates, at least in part, the above described disadvantages that are found in
combustion engines that are found in the prior art. In addition, using the combustion
engine according to the present invention, the greatest possible proportion of the
available heat is converted into mechanical work.

According to the present invention, this objective is achieved with a piston steam engine
as defined in the preamble to Patent Claim 1, in that the working medium is introduced at
least indirectly into the working chamber of the piston steam engine in liquid form when
the piston is at top dead centre, too. This means that it is possible that in the piston steam
engine according to the present invention the liquid phase and the vapor phase of the
working medium are separated, so that the liquid phase comes into contact with the walls
of the piston steam engine to a very slight extent. In a test model, for example, only 2%
of the surface of the working chamber was wetted by the liquid phase of the working
medium. This greatly reduces thermal losses.
In the piston steam engine according to the present invention, hot working medium that is
under pressure is introduced directly or indirectly into the working chamber in liquid
form. Because of the pressures and temperatures within the piston steam engine, the
working medium begins to vaporize as soon as it is introduced into the piston steam
engine. The resulting vapor pressure drives the piston.
As the piston moves, the volume of the cylinder also increases and more of the working
medium can vaporize. The liquid fraction of the working medium cools during
vaporization. As the pressure decreases, the vapor fraction of the working medium also
cools. Because of these processes, the efficiency—especially the exergonic efficiency
and the power of the piston steam engine according to the present invention increases
greatly as compared to other combustion engines.
In one advantageous version of the present invention there is at least one prechamber that
is connected to the working chamber; it is preferred that the working medium be
introduced into the prechamber and more preferably by way of a circular path. The
circular path of the liquid phase generates centrifugal forces that accelerate the liquid
phase forcefully radially outward because of its high density. The vapor that results
during the flash vaporization of the working medium is considerably less dense than the
liquid phase and can flow into the cylinder chamber since the connection between the
prechamber and the working chamber opens out into the centre of the working chamber.

The radial acceleration means that the liquid phase cannot escape from the prechamber.
This forms a very simple and at the same time effective phase separation. The volume of
the prechamber should be as small as possible.
In another version of the present invention, there is a plurality of prechambers and/or a
plurality of injectors for each cylinder, and each of these is connected to the working
chamber. Thus, it is possible to introduce the working medium into the prechambers
and/or into the working chamber at different temperatures, depending on the pressure
prevailing within the working chamber during the power stroke, and/or the prevailing
temperature within the working chamber one after the other, and/or position of the piston,
Thus working medium at different temperatures can be coupled into the piston steam
engine according to the present invention without exergonic losses because of the mixing
processes.
If a plurality of injector valves inject into a prechamber or the working chamber one after
another, it must be ensured that the working medium that is already within the cyclone is
not vaporized or sprayed by the injection process.
Alternatively, it is also possible to introduce the working medium directly into the
working chamber either completely or partially. When this is done, the liquid working
medium can be vaporized during the injection process and be divided between the
working chamber and, if there is one, the prechamber, in the form of small droplets.
Direct contact between the droplets and the surfaces of the piston steam engine is avoided
because of the friction between the droplets and the gaseous phase of the working
medium. As a result, the undesirable transfer of heat between the droplets and the
surfaces of the piston steam engine is also greatly reduced.
The injectors that are used can be the same as those that are used in the fuel injection
systems of conventional Otto or Diesel engines. These commercially available injectors
will, of course, have to be adapted to the special working conditions, in particular the
very high temperatures and corrosive working media.

If the heat transfer medium is at a temperature of approximately 200 degrees C to 359
degrees C, water has been found to be particularly suitable.
If the heat or waste heat is at a temperature of approximately 150 degrees C to 200
degrees C, methanol has been found to be particularly suitable.
If the heat or waste heat is at a temperature of approximately 100 degrees C to 150
degrees C, pentane has been found to be particularly suitable.
If the heat or waste heat is at a temperature of approximately 100 degrees C, R134a has
been found to be particularly suitable.
For the remainder, it has been found to be advantageous to provide internal and/or
external thermal insulation on those surfaces of the piston steam engine that come into
contact with the liquid working medium.
The internal thermal insulation is particularly important to prevent the liquid working
medium that is cooling down picking up convective heat from the cyclone walls or other
surfaces of the piston steam engine. This coating that is arranged on the working
chamber or on the inside walls of the cyclone can be of Teflon, enamel, or ceramic.
As an alternative, or in addition, the surfaces of the piston steam engine that come into
contact with the working medium can be heated in order to prevent the working medium
condensing on these surfaces. If a gaseous phase is formed by the flash process, the parts
of the machine that are accessible to the gaseous phase must be at a temperature that is
greater than the condensation temperature of the working medium at that particular and
prevailing gas pressure. Were these parts colder, part of the resulting gaseous phase
would condense instantaneously on these surfaces and the condensed phase would no
longer be available to power the machine and the machines power and efficiency would
decrease.

Other advantages and advantageous versions of the present invention are set out in the
drawings, the description and the patent claims. All of the features that are disclosed, can
be considered essential to the present invention, either singly or in combination.
The drawings appended hereto show the following:
Figures 1 & 2: Embodiments of a piston steam engine according to the present
invention, with a cyclone;
Figure 3: A prechamber of a piston steam engine according to the present
invention;
Figure 4: An embodiment of a piston steam engine according to the present
invention, with an injector that sprays into the working chamber.
Figure 1 shows an example of the construction of a first embodiment of a piston steam
engine according to the present invention, with a prechamber 13, a piston 3, a cylinder 5,
a connecting rod 7, and a crankshaft 9, which can be connected to a generator (not shown
herein).
The piston 3 and the cylinder 5 define a working chamber 11. A prechamber 13 is
connected to the working chamber 11. A feed line 15 and a drain line 17 for the working
medium open out into the prechamber 13. The drain line 17 for the working medium can
also open out directly into the working chamber 11.
A switchable inlet valve 19 for the liquid working medium is arranged in the feed line 15.
With the help of this inlet valve (which can be configured as an injector) it is possible to
spray liquid working medium into the prechamber 13. It is preferred that this spraying
take place when the piston 3 is at or close to TDC.

Since, at the time of injection, the pressure within the prechamber 13 is lower than the
pressure of the working medium in the feed line 15, immediately after the injection of the
working medium, so-called flash vaporization takes place within the prechamber 13 and
in the working chamber 11 connected with the prechamber 13. As a result of this, the
pressure within the prechamber 13 rises so that the piston 3 is moved towards bottom
dead centre, thereby imparting work to the crankshaft 9.
When the piston 3 is in the area of BDC , a switchable outlet valve that is incorporated in
the drain line 17 for the working medium is opened and during its next movement the
piston moves the towards TDC and moves the remaining liquid phase and the working
medium that has become vapor in the direction of top dead centre and out of the working
chamber.
Among other things, the drain line 17 removes the liquid phase that is remaining in the
prechamber 13. The working medium that has become vapor can also be removed
through the drain line 17. As an alternative, it is also possible to incorporate an
additional vapor valve 22 within the working chamber 11 and the working medium that
has become vapor drains off through this. The vapor valve 22 can be a poppet valve and
configured and operated by a cam shaft (not shown herein) in the same way as a gas-
exchange valve in an internal combustion engine.
If the working medium in routed in a closed circuit, the drain line 17.1 for the working
medium opens out into a condenser 23. The working medium that is drained off through
the vapor valve 23 can be routed into the condenser 23 through a drain line 17.3, where
the working medium is again liquefied and then passed to a heat exchanger 27 by a pump
25. From there, the working medium moves into the prechamber 13 by way of the feed
line 15.

Figure 2 shows the construction of a piston steam engine according to the present
invention with two prechambers 13.1 and 13.2, two feed lines 15.1 and 15.2 for the
working medium. Two switchable inlet valves 19.1 and 19.2 are arranged within the feed
lines 15.1 and 15.2.
The remaining parts of the piston steam engine and its periphery can be the same as in the
first embodiment as shown in Figure 1, to which reference is made herein. The working
medium within the first feed line 15.1 is at a higher temperature than the working
medium within the second feed line 15.2. For thin reason, a specific quantity of the
working medium within the first feed line 15.1 is first introduced into the first
prechamber 13.1, where it vaporizes and imparts work to the piston 3. When this takes
place, the temperature and the pressure of the working medium within the working
chamber 11 and the prechambers 13.1 and 13.2 grow less. As soon as the temperature of
the working medium within the working chamber 11 and the prechambers 13.1 and 13.2
approximates the temperature of the working medium within the second feed line 15.2,
working medium from the second feed line 15.2 is introduced into the second prechamber
13.2 through the briefly opened second inlet valve 19.2, in the same stroke of the piston
3. Once introduced into the prechamber 15.2, this working medium also vaporizes
immediately and imparts work to the piston 3.
Using this embodiment of the piston steam engine according to the present invention it is
possible to utilize heat that is at two levels. As a result, for example, in an internal
combustion engine the waste heat can be used in an optimal manner since in an internal
combustion engine the exhaust gases are at a temperature of greater than 200°C, whereas
the cooling agent ant the oil are at a temperature of 120°C. In order to bring the working
medium to two different temperatures it is necessary to have a first heat exchanger (not
shown herein) that operates on the waste heat of the exhaust gases, and a second heat
exchanger (not shown herein) that is heated with the waste heat of the cooling water and
of the oil.

First, the hotter working medium is injected at a temperature of 200°C. Once this has
cooled to 120°C, working medium at approximately 120°C is injected. The efficiency of
an internal combustion engine, which is related to combustion heat, can be increased by
approximately 10% with such a piston steam engine.
The piston steam engine according to the present invention is a two-cycle engine that has
neither an induction nor a compression stroke. The inlet valve(s) 21 are closed when the
piston 3 is within the area of TDC, and the working medium is injected through the inlet
valve 19. As the piston 3 moves from TDC to BDC, part of the working medium
vaporizes, as has been described. The outlet valve 21 opens in the area of BDC. As the
piston 3 moves from BDC to TDC, the remaining liquid phase and the gaseous phase that
has formed are expelled through the outlet valve 21. The liquid and the gaseous phase
can pass through the same outlet valve 21, or separate valves can be provided
Hot, liquid working medium is injected under pressure into a prechamber of the piston
steam engine according to the present invention. The working medium can be harmless
water.
Figure 3 shows the construction of a prechamber 13 for a piston steam engine according
to the present invention. The prechamber 13 is constructed in the same way as a cyclone
separator. The drawing shows the feed line 15, the drain line 17, and the valves 19 and
21.
The liquid working medium is essentially introduced tangentially into the prechamber 13
and follows a circular path that lies radially to the outside. Because of its low density, the
vapor that results from the flash vaporization is forced to the middle of the prechamber
13 so that separation of the liquid and the gaseous working medium takes place within
the working chamber 11. A connection 29 that opens out into the working chamber 11 is
arranged in the middle of the prechamber 13, and the gaseous working medium moves
from the prechamber into the working chamber 11 by way of this connection.

If the prechamber 13 is located below the connection 29 and below the working chamber
11 (not shown in Figure 3), gravity will also assist in the separation of the liquid and the
gaseous phases.
It order that the resulting vapor does not condense on surfaces within the working
chamber, the particular surfaces of the piston 3, cylinder 5, and prechamber 13 must be
heated and/or thermally insulated. Two additional steps can be taken in order to ensure
that no heat is transferred from the heated surfaces to the liquid phase of the working
medium.
Geometrically, the prechamber 13 is formed in such a way that the liquid phase of the
working medium that is injected can move in a stable fashion on a circular path. In this
case, the prechamber 13 is designated as a cyclone. The centrifugal forces that are
generated along the circular path ensure that the resulting vapor—on which smaller
centrifugal forces act because of lesser density—can escape into the cylinder space of the
piston steam engine and the liquid heat-carrier medium—on which greater centrifugal
forces act because of greater density—remain in the circuit. Tests have shown that phase
separation can be achieved in this way during the vaporization process.
Calculations have shown that despite the friction of the liquid on the walls of the
prechamber 13, the rotational speed of the liquid working medium remains at a level that
is sufficient for phase separation to take place, and that the thermal exchange of the liquid
working medium with the walls of the cyclone does not lead to any noteworthy
impairment of the process, given suitable dimensioning of the machine and coating of the
prechamber walls.
Tests have also shown that phase separation is successful: the liquid phase remains in the
cyclone during phase separation, whereas the gaseous phase escapes into the cylinder
chamber.

In addition, it could be shown that the convection of the liquid phase with the wall of the
prechamber 13 is not considerable. In the test, after the flash process, essentially the
calculated quantity of liquid phase is present. Convection did not lead to an essential
additional vaporization.
Finally, tests also showed that the flash process takes place at very high speed in the
prechamber 13 and the working chamber 11, which is important for the performance of
the machine.
Figure 4 shows an additional embodiment of a piston steam engine according to the
present invention. This embodiment has no prechamber 13 and the liquid working
medium in injected directly into the working chamber 11. This can be done with the help
of an injector known in the prior art.
During the injection process, the working medium is reduced to small droplets in much
the same way as when diesel fuel is injected into the combustion chamber of in internal
combustion engine. The droplets are kept is suspension because of friction in the gas
phase. In this way, the droplets can come into contact with the hot surfaces only to a
slight extent and thermal exchange between the liquid phase and the hot surfaces is kept
at a low level and thermal exchange between liquid phase and the hot surface is kept low.
With a piston steam engine according to the present invention, given an available heat
source it is possible to obtain approximately double the mechanical efficiency as
compared to current machines that are based on an ORC or a Kalina process. In addition,
a non-hazardous working medium, for example water, is used.

Patent Claims:
1. Piston steam engine with at least one cylinder (5), a piston (3) oscillating within
the at least one cylinder (5), with a working chamber (11), said working chamber
(11) being defined by the cylinder (5) and the piston (3), with at least one inlet
valve (19), the working medium being routable into the working chamber (11)
through the at least one inlet valve (19), with at least one outlet valve (21), the
working medium being routable out of the working chamber (11) through the at
least one outlet valve (21), characterized in that the working medium is
introduced into the working chamber in liquid form, at least indirectly, when the
piston (3) is in the area of TDC or during the power stroke.
2. Piston steam engine an defined in Claim 1, characterized in that at least one
prechamber (13) is provided; in that the working chamber (11) and the
prechamber (13) are connected (29) to each other; and in that the working
medium in liquid form is so introduced into the prechamber (13) that the greater
part of the liquid phase of the working medium remains within the prechamber
(13), whereas the vapor phase of the working medium flows into the working
chamber (11).
3. Piston steam engine as defined in Claim 2, characterized in that the working
medium is introduced essentially tangentially into the prechamber (13).
4. Piston steam engine as defined in Claim 2 or Claim 3, characterized in that the
connection (29) between the working chamber (11) and the prechamber (13)
opens out in the middle of the prechamber (13).

5. Piston steam engine an defined in one of the Claims 2 to 4, characterized in that a
plurality of prechambers (13.1, 13.2) is arranged for each cylinder (5); in that the
prechambers (13.1, 13.2) are connected to the working chamber (11); and in that
working medium at different temperatures is introduced into the prechambers
(13.1, 13.2) or into the working chamber (11) depending on the prevailing
pressure within the working chamber (11) or the prevailing temperature within the
working chamber (11).
6. Piston steam engine as defined in one of the preceding Claims, characterized in
that a plurality of inlet valves (19.1, 19.2) is provided for each cylinder (5).
7. Piston steam engine an defined in one of the preceding Claims, characterized in
that the liquid working medium that is injected from the various inlet valves or
injectors (19.1, 19.2) is at different temperatures; and in that the liquid working
medium that is injected out of the various injectors (19) is injected in sequence
from the warmest to the coldest and the next working medium in turn is injected
when the working medium that is already in the prechamber (13) or the working
chamber (11) has reached the temperature of the next coldest working medium.
8. Piston steam engine as defined in one of the preceding Claims, characterized in
that the liquid working medium is injected into the working chamber (11) or into
the at least one prechamber (13) with the help of an injector (19).
9. Piston steam engine as defined in one of the preceding Claims, characterized in
that during the injection process, the liquid working medium is reduced to small
droplets of liquid.

10. Piston steam engine as defined in one of the preceding Claims, characterized in
that water, methanol, pentane, and/or R 134a is used as the working medium.
11. Piston steam engine as defined in one of the preceding Claims, characterized in
that the cylinder (5), the piston (3) and/or the at least one prechamber (13) are
thermally insulated internally and/or externally.
12. Piston steam engine as defined in Claimll, characterized in that the interior
thermal insulation is of Teflon, enamel, and/or ceramic.
13. Piston steam engine as defined in one of the preceding Claims, characterized in
that the cylinder (5), the piston (3) and/or the at least one prechamber (13) can be
heated.
14. Piston steam engine as defined in one of the preceding Claims, characterized in
that a vapor valve (22) is provided; and in that the vaporized working medium
can be expelled from the working chamber by means of the vapor valve (22).
15. Piston steam engine as defined in one of the preceding Claims, characterized in
that the outlet valve(s) (21) and the vapor valve (22) are closed in the area of
TDC; in that liquid working medium is next introduced into the prechamber (13)
or into the working chamber (11); and in that the outlet valve(s) (21) are opened
in the area of BDC.

The invention relates to a piston steam engine having flash
vaporization. Said inventive piston steam engine has a simple
constructions, a very good exergetic degree of efficiency and can be
operated with various working mediums and at different
temperatures. Also, the inventive piston steam machine can reach
very high power density.