US3798908A

US3798908A - External combustion power producing system

Info

Publication number: US3798908A
Application number: US00226206A
Authority: US
Inventors: J Davoud; J Burke
Original assignee: Cox Edwin Associates
Current assignee: EDWIN COX ASS US; Cox Edwin Associates
Priority date: 1972-02-14
Filing date: 1972-02-14
Publication date: 1974-03-26
Anticipated expiration: 1991-03-26

Abstract

An external combustion power producing cycle is provided in which a condensable fluid is heated to the vapor state and the heated vapor is expanded isentropically. After expansion, the expanded fluid is separated into at least two portions without substantially changing the state of the expanded fluid such as temperature, pressure, entropy, enthalpy, or its specific volume. After the expanded fluid has been separated into portions, one of the portions is condensed, and the weight equivalent of the condensed portion is added, in liquid form, to the other portion of the expanded fluid. Thereafter, the mixture, now having substantially lower entropy than the fluid prior to addition of liquid, is compressed to the desired operating pressure. In a variant of the power producing cycle, after the expanded fluid has been separated into portions, one of the portions is allowed to continue expansion, in such a way as to do further useful work, before being condensed as described above.

Description

Davoud et a1.

[ Mar. 26, 1974 I EXTERNAL COMBUSTION POWER PRODUCING SYSTEM [75] Inventors: John Gordon Davoud; Jerry A,

Burke, Jr., both of Richmond, Va.

[73] Assignee: Edwin Cox Associates, Richmond,

[22] Filed: Feb. 14, 1972 [21] Appl. No.: 226,206

Related US. Application Data [63] Continuation of Ser. No. 58,099, July 24, I970,

abandoned.

511 int. Cl .roiiq qe 51 Int. Cl. E01ki7/09 [58] Field of Search 60/1, 36-38, 60/39, 40, 69, 73, 93, 92, 94, 97, 95

[56] References Cited UNITED STATES PATENTS 2,939,286 6/1960 Pavlecka 60/92 X FOREIGN PATENTS OR APPLICATIONS 931,889 7/1949 Germany 60/94 100% OF STEAM AT 2500 PSIA AT 250 PSI A EXTRACTION FLOW r" R I55 r" L rinse a" |s7 I? l CONDENSER 4'62 ll\wATER CONSTANT l PRESSURE M F DE-SUPERHEATERWO HOT WELL I I65 3 I64 30% OF STEAM 1 WATER HEATER I l kiss RE- HEATER I58 Primary Examiner-Martin P. Schwadron Assistant Examiner-Allen M. Ostrager Attorney, Agent, or Firm-Harold L. Stowell [5 7] ABSTRACT An external combustion power producing cycle is provided in which a condensable fluid is heated to the vapor state and the heated vapor is expanded isentropically. After expansion, the expanded fluid is separated into at least two portions without substantially changing the state of the expanded fluid such as temperature, pressure, entropy, enthalpy, or its specific volume. After the expanded fluid has been separated into portions, one of the portions is condensed, and the weight equivalent of the condensed portion is added, in liquid form, to the other portion of the expanded fluid. Thereafter, the mixture, now having substantially lower entropy than the fluid prior to addition of liquid, is compressed to the desired operating pressure.

In a variant of the power producing cycle, after the expanded fluid has been separated into portions, one of the portions is allowed to continue expansion, in such a way as to do further useful work, before being condensed as described above.

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P M IN MUM ENTHALPY I T, T

WATER INJECTION TMAXIMUM F/G suPERHEATER HP INLET LINES OF CONSTANT TEMPE RATURE PISTON INVENTORS JOHN GORDON DAVOUD 8\ O JERRY A. BURKE, Jr.

BY M m A \J I ATTORNEYS 1 EXTERNAL COMBUSTION POWER PRODUCING SYSTEM This is a continuation, of application Ser. No. 58,099, filed July 24, 1970, now abandoned.

Considerable effort and money have been and are continuing to be spent to introduce the Rankine steam cycle to ground traveling vehicles as a replacement for engines operating on the conventional Otto and Diesel cycles, particularly in view of the reduced air pollution from the external combustion system used for heat input in the Rankine cycle.

Also, it is desirable to increase the thermal efficiency of the steam power system in electric power generation, and thereby reduce both air and thermal pollution, while at the same time saving fuel.

It is a particular object of the present invention to provide a technically feasible and commercially adaptable external combustion power producing cycle which may be used as the power producing cycle for vehicular and stationary engines, and electric power generation, which would have improved air pollution abatement and substantially greater efficiency than the known Rankine cycle and in addition, would have the following advantages:

A. A cycle that may be applied to all known combinations of reciprocating, turbine, and positive displacement rotary engines and compressors;

B. A cycle which has a significant improvement in thermal efficiency and therefore corresponding reduction in fuel usage compared with gasoline fuel internal combustion spark ignition engines and conventional Rankine cycle steam engines;

C. A cycle which will function with large reduction, in condenser load and proportionate reduction in condenser dimensions and weight, compared with Rankine system of similar power;

D. A cycle which would be readily adapted to automotive propulsion systems, having increased efficiency and reduced pollution; in addition, a system which would be amenable to mass production, and have acceleration and driving response comparable to present automotive pleasure cars, together with high reliability, low maintenance costs, reasonable life expectance and acceptable start-up time.

E. A cycle which is adaptable to electric power generation in thermal stations, and which would result in more efficient use of fuel, decreased thermal pollution and, where fossil fuels are the heat source, reduced air pollution.

These and other objects and advantages will become more apparent to those skilled in the art from the following detailed description of the present invention which may be defined in general terms as comprising an external combustion power producing cycle including the steps:

1. Heating a condensable fluid to the vapor state;

2. Expanding isentropically the vapor;

3. Separating the expanded fluid into at least two portions without substantially changing the state thereof (such as temperature, pressure, entropy, enthalpy, or specific volume);

4. Condensing one of the said portions;

5. Adding in liquid form the weight equivalent of the condensed portion of the fluid to the other portion of the fluid; and

6. Thereafter or simultaneously compressing isentropically the mixture to the. operating pressure.

The invention may also be defined as providing an external combustion power producing cycle comprismg:

1. Heating a condensable fluid to the vapor state;

2. Expanding isentropically the vapor;

4. Allowing one of the portions to continue furtherexpansion, thereby doing useful work;

5. Condensing said portion;

6. Adding in liquid form the weight equivalent of the condensed portion of the fluid to the other portion of the fluid; and

7. Thereafter or simultaneously compressing isentropically the mixture to the operating pressure.

l. Superheating the vapor of a condensable fluid from a dry saturated state at a predetermined pressure to a predetermined temperature;

2. Expanding isentropically the superheated vapor toa state such that the expanded vapor is dry saturated, superheated, or lies within the region of mixtures;

3. Separating the expanded fluid into at least two portions without substantially changing the state thereof (such as temperature, pressure, entrophy, enthalpy, or specific volume);

4. Condensing one of the portions of expanded fluid;

5. Adding in liquid formthe weight equivalent of the condensed portion of the fluid to the other portion of the fluid; and

6. Compressing isentropically the mixture to the dry saturated state.

1. Superheating the vapor of a condensable fluid from a dry saturated state at a predetermined pressure to a predetermined temperature;

2. Expanding isentropically the superheated vapor to a state such'that the expanded vapor is dry saturated, superheated, or lies within the region of mixtures;

4. Allowing one of the portions to continue further expansion, thereby doing useful work;

5. Condensing said portion;

7. Compressing isentropically the mixture to the dry saturated state.

The invention will be more fully described with reference to the following drawingwhereln:

FIG. 1 is a diagram of pressure of the working fluid plotted as Y-axis against the heat content or enthalpy along the X-axis of a cycle functionable in accordance with the teachings of the present invention; 7

FIG. 2 is a similar diagram illustrating a specific embodiment of the present invention;

FIG. 3 is a diagram of temperature plotted as Y-axis against entropy along the X-axis, of the same embodiment of the cycle depicted in FIG. 2.

FIG. 4 is a schematic diagram illustrating the use of the system of the present invention in a turbine;

FIG. 5 is a schematic diagram illustrating another aspect of the system of the present invention applied to a turbine;

FIGS. 6A through 66 illustrate the operation of the external combustion power producing cycle in conjunction with a single acting reciprocating engine;

FIG. 7 is a diagrammatic sectional view of a reciprocating engine of a modified form operable with the cycle of the present invention;

FIG. 8 illustrates the use of the cycle of the invention in a double acting reciprocating engine; and

FIGS. 9A through 9G are similar to the diagrammatic views shown in FIGS. 6A through 6G with the valving mechanism for the reciprocating piston located to reflect a slightly modified method of separating steam into portions in controlled ratio.

FIG. 10 has the same coordinates as FIGS. 1 and 2, of pressure and enthalpy, and shows, for steam, lines of constant entropy; and lines of constant temperature in the region of superheat.

FIG. 11 is a schematic diagram showing a valve mechanism which can remove, from a cylinder, to atmosphere or condenser a controlled portion of steam without altering the state of the portion remaining.

As hereinbefore set forth, the present invention is directed to a method for greatly increasing the thermodynamic efficiency of an external combustion power system employing steam or other condensable vapor as the working fluid. While a number of condensable vapor type working fluids may be employed in the cycle of the present invention, the detailed description of the improved cycle will be in reference to steam. The thermodynamic properties of steam as applied to its use in heat engines can be most simply understood by reference to a phase diagram for water, wet and superheated steam, in which the pressure of the steam is plotted as Y-axis against the heat content or enthalpy along the X-axis of a diagram. Such a diagram, not shown to scale, is illustrated in FIG. 1 of the drawings. While the diagram FIG. 1 is for water, it will be appreciated by those skilled in the art that it will be similar for other fluids containing polar groups, of relatively low molecular weight, such as ammonia, carbon dioxide, methanol, ethanol, and trifluorethanol.

In order to appreciate the novel characteristics of the present invention, comparison therewith can be made with the well known Rankine cycle which on a pressure-enthalpy diagram such as illustrated in FIG. 1 would comprise:

AB Heat water from condensing temperature T to T the temperature corresponding to saturation pressure P. Heat input equals length AB.

BC Evaporate water in boiler at constant temperature T and constant pressure P. Heat input corresponds to length BC.

C-D Superheat saturated steam at constant pressure P to maximum operating temperature T Heat 4 input is given by length CD LG. Total heat input AB BC CD distance AD.

D-E Expand superheated steam through engine, to condensing temperature T, and pressure p. Work out" is given by length KG. The point B can lie in the region of superheat (E on the saturated vapor line (E), or in the region of mixtures (E as shown in FIG. 1.

E-F Condense at temperature T and pressure p. Condensate at point F is returned to the boiler at point A, by the boiler feedwater pump, thereby completing the cycle.

Rankine Efficiency is Work out/Heat in KG/AD The heat represented by distance EF is lost to the condenser.

In heat engines of the type we are considering, both expansion and compression of the working fluid take place, theoretically, at constant entropy. Thus the course of an expansion between two pressures P and p can be shown by a line of constant entropy, such as DE, D E D E or C], in FIG. 1. The Work out, or work done by the expansion, is given by the length of the projection of the line of constant entropy, for example DE, between P and p, on the xaxis,-shown by KG in the diagram.

Similarly, compression from E to D would take place in the reverse direction along the same isentropic line, and the intercept KG would in this case be the work done on the system or work in, or compressor work.

On p-H diagram as in FIG. 1, the entropy at any given pressure decreases with decreasing enthalpy. Thus any point on the constant entropy line .lC will have a lower entropy than any point on the constant entropy line DE, D E or D E Between any given pressure, P and p, the slope of the isentropic line is given by (P p)/(Imercept an X -axis), i.e., in FIG. I, the slope of isentropic line JC is P -p/IL; of the isentropic line DE is P p/KG Thus, between any given pressures, the slope of the isentropic line is a reciprocal measure of work done by the system in expansion, or of work done on the system in compression; that is, the greater the slope, the less the work out in expansion, or work in during compression.

One aspect of this invention relates to the fact that there is a progressive increase in the slopes of the lines of constant entropy of steam with decreasing entropy. Thus, more work can be gained, for example, by ex panding a given weight of superheated vapor from a higher pressure P to a lower pressure p, at high entropy, (DE, D E D E than is required to compress the same weight of (liquid plus vapor) back from p to P at lower entropy (JC). From FIG. 1 it will be seen that conditions can be found where the difference in slope between two pressures P and p approaches 2; i.e., almost twice as much work is theoretically released by expanding altogether, largely or partially, in the superheat region between two given pressures, as is required to compress the same weight of (vapor plus liquid) in the region of mixtures, from lower to higher pressure.

On the diagram in FIG. I, this can be seen as the difference between KG (expansion work along the isentropic line DE) and IL (work of compression along the isentropic .IC).

On the diagram, FIG. 1, the point C corresponds to saturated steam at the working pressure. In the Rankine cycle, this point is reached in practice by condensing from point E to point F, all the vaporfrom the engine at the end of the expansion; (and losing all the energy FE to the condenser); pumping the liquid into the boiler against operating pressure P, heating the water to temperature corresponding to P, and boiling water, the heat required being AB BC in the diagram, rather more than has been entirely lost in the condenser.

In one aspect of the invention, a method for bringing the working fluid to point C on the diagram is to compress a mixture of vapor plus liquid corresponding to point J, to point C. The point C is such that the dotted line .l-C of constant entropy which passes through it also passes through point .I. This is accomplished by removing only a part (in the case shown, about onefourth) of the vapor from the engine or expander at the end of expansion, which removed amount would be passed to the condenser. The amount of vapor removed would be made up by an equal weight of liquid at the condenser'temperature; and the misture of water and saturated vapor is then compressed along the lime of constant entropy from point J on the diagram to point C.

The heat input or heat in is then confined to superheat C-D.

Net work is work out KG minus compression work IL.

Efficiency KG IL/CD or KG IL/LG Heat lost to the condenser is JE, approximately FE/4.

Some numerical examples for water-steam, will serve to illustrate the extent of the increase in efficiency which this invention permits, and the inherent reduction in condenser size which can be attained by the practice of the present invention.

Before turning to the numerical examples, reference should be had to FIGS. 2 and 3. FIG. 2, which again is a pressure-enthalpy diagram similar to that illustrated in FIG. 1, illustrates the cycle of the present invention when expansion starts from the saturated vapor line and no superheat is applied to the vapor. This same cycle, when plotted on the temperature-entropy diagram, is rectangular in form as illustrated in FIG. 3 since the heat is put in at constant temperature T rejected at constant temperature T and the expansion and compression operations are isentropic; that is, take place at constant entropy.

The theoretical thermal efficiency of this version of the cycle, is equal to that of the Carnot cycle between the same temperature limits, i.e., it is the maximum obtainable.

It is not necessary that point D in this example should lie exactly on the saturated vapor line. Maximum theoretical efficiency results if it lies on the line, or within the region of mixtures, as shown.

The following four working examples representative of the cycle of the present invention have been selected to show respectively:

1. Expansion of superheated steam, with expansion ending in the region of mixtures, such as is shown by isentropic expansion line D E in FIG. 1.

2. Expansion entirely within the region of superheat,

(D E FIG. 1).

3. Expansion taking place entirely within the region of mixtures, (D, E,, FIG. 2)

4. Expansion with'reheat. (Typical of modern thermal power station practice). First or high pressure expansion takes place entirely within the region of superheat. The superheated and expanded steam is re-heated at constant pressure, and expanded to a point within the region of mixtures.

In each example, thermal efficiency of the present cycle is calculated on two bases.

A. The smaller portion of steam separated at the end of expansion is carried to a condenser with no further expansion being allowed to take place; and

B. The smaller portion of steam separated is allowed to continue expanding to some lower pressure, thus doing added useful work, before being passed to a condenser.

EXAMPLE 1 Expansion of superheated steam into the region of mixtures (FIG. 1)

P (at start of expansion): 1000 psia T (at start of expansion): 1000F.

p (at end of main expansion): 40 psia T (at end of main expansion): 276F.

A. Separated portion of steam is carried to condenser without further expansion Heat in=CD =3 l 3 BTU/lb.

Work ouFKG=353 BTU/lb.

Compressor work=IL=230 BTU/1b.,

Net work out=3532 30=123 BTU/lb.

Efficiency e=123/313=39.3% v

Efficiency (Rankine cycle) e=353/(27.8%

At point E, 0.208 pounds of steam per pound of total steam expanded is removed and condensed. Pounds of steam condensed per horse-power/hour for the cycle 2,545/123 0.208 4.30 lbs/hour for Rankine cycle 2,545/353 7.22 lbs/hour (Note: There are 2,545 BTU per horse-power hour).

B. Steam separated at E is allowed to continue expansion.

At the point where compression of the main portion of steam starts, the remainder (0.208 of the total in the cylinder) is at a pressure of 40 psia, and has entropy 1.6525. This steam continues to expand, and the expansion ratio for the continued expansion is 1/0.208 4.80 to l. Specific'volume v for 40 psia is 10.498. As the steam at this point has a quality of 0.98, the specific volume at the end of the further expansion will therefore be 0.98 X 10.498 X 4.80 49.5. The pressure will be 7.65 psia; the extra work done by this expansion is:

(1,152 1,038) X 0.208 23.7 BTU/lb. 0.208 pounds of steam at this pressure (754 psia) and saturation temperature (181F) is condensed, and must be heated to the saturation temperature of the steam at the end of the expansion and before separation into two portions. (40 psia, T 267). Heat required is 0.208 (236 149) 181 BTU. Net work then becomes (353 23.7) 230= 147.4 Heat in is 313 18.1 331.1 Efficiency e 147/331= 44.3 percent This corriparesiv ith Rankine efficiency of 27.8 percent Amount of steam condensed per horsepower per hour is 2545/1474 X 2.08 3.60 pounds.

EXAMPLE 2 Expansion entirely within the region of superheat (F 1G. 1

P (at start of expansion): 500 psia T (at start of expansion): 1000F p (at end of main expansion): 20 psia T (at end of main expansion): 243.1 At the end of main expansion, remove 0.193 of steam; replace with 0.193 of water, at 234.

Pressure will fall slightly, to about 19.8 psia on addition of water to superheated steam.

A. Separated portion of steam carried to condenser without further expansion.

Efficiency e 41.0 percent Pounds of steam condensed per horsepower per hour 4.37 B. Separated portion of steam is allowed to continue expansion toa lower pressure P 2.4 psia.

Efficiencye 47.1 percent Pounds of steam condensed per horsepower per hour 3.60. For Rankine Cycle: Efficiencye (Rankine) 27.2 percent Pounds of steam condensed per horsepower per hour I EXAMPLE 3 Expansion entirely within region of mixtures (FIG. 2)

P (at start of expansion): 1,500 psia (on saturated vapor line) T (at start of expansion): 596F.

p (at end of expansion): 1 psia T (at end of expansion): 102F.

A. Portion of steam (27.7 percent) removed at end of expansion is condensed.

Efficiency e 46.2 percent Amount of steam condensed per kilowatt-hour 5.86

lbs. B. The main expansion is stopped at psia. 33 percent of steam is removed, and allowed to continue further expansion to l psia, doing further useful work. The remainder is compressed, together with injected water.

Efficiency e 42.3 percent Amount of steam condensed per kilowatt per hour is 7.0 lbs.

For Rankine cycle, working between highest and lowest pressure and temperature limits Efficiency e (Rankine) 38.4 percent Amount of steam condensed per kilowatt per hour is 8.1 lbs.

EXAMPLE 4 Expansion with Re-heat (Typical for electric power generation) High pressure expansion P=2,500 psia superheated steam T,=|.000F.

Expand to P,-600 psia superheated steam T,-593F.

Reheat at 600 pain to 1000F.

Expand to P-lrfi" mercury, 0.74 psia Expansion with Re-heat (Typical for electric power-Continued generation) in region of mixtures T =92F.

A. At end of expansion to 0.74 psia, remove 0.306 of steam; replace with same weight of water; compress to 2,500 psia.

Efiiciency e 156.2 percent Amount of steam condensed per kilowatt hour 3.1 1 lbs. B. Stop main low-pressure expansion stage at 10 psia.

Amount of steam condensed per kilowatt-hour i 4.56 lbs.

it will be noted that in Examples 1 and 2 (reciprocating engines) efficiency of Case Bis greater than that for Case A; whereas in 3 and 4, the reverse is true.

The reason is that in reciprocating engines, in Case B, the pressure of the main portion of steam at the end of its expansion is the same as in case A, and the separated portion continues expanding to some lower pressure doing additional useful work; whereas in Examples 3 and 4 (applicable to turbines) the outlet pressure of the main portion of steam is higher in the Case B than in Case A; and the final outlet pressure of the separated portion of steam in Case B, is the same as that for all steam in Case A.

The advantage for turbines of the type of procedure described in Examples 38 and 4B lies in the possibility which it confers of reduced capital cost, particularly of large thermal power plants, while retaining acceptable thermal efficiency, and in reducing the work of compression.

The pressure range over which compression takes place can with great advantage be made a relatively small portion of the total pressure range used in the cycle. Thereby compression work is reduced, and the difference between (work out) and (work of compression) is increased. This in turn renders the cycle less affected by departure from theoretical isentropic expansion and compression; and maximizes realizable effi- Work out compressor work/work out compressor work By way of example, if compressor work is one-half (work out), the above ratio is (1 0.05 )/1 5 3.0;

if compression work is reduced to one-tenth of (work out), the ratio is reduced to 1 0.1/1 0.1 1.23

The effect on capital cost can be seen from the above.

Such a'cycle, suitable for electric power generation, in which compressor work is a relatively small portion of work out, is described herewith as Example 4 C.

EXAMPLE 4 C.

Expansion with Re-heat. High realizable efficiency, and small compressor work High pressure expansion P=2,500 psia superheated steam T =l,000F.

Expand to P =l,S psia superheated steam T =838F Remove 0.244 of steam;

Reheat portion removed at 1,500 psia to 1,000F.

Expand to 0.7 psia In region of mixtures T =90F and condense.

Add 0.244 of condensate at 90 to remaining superheated steam (0.756) from high pressure expansion, in constant pressure de-superheater at 1,500 psia. Compress resultant wet steam to 2,500 lbs.

Efficiency e 48.9 percent Ratio of compressor work to work out 0.123

Ratio of rotating horse-power to that .of Rankine cycle of same net power 1 +0.123/1 0.123 1.28

lt will be clear from the foregoing Examples 1A, 1B, 2A, and 2B, 3A and B, and 4, A, B and C that, for a given power output, .a system workingon the disclosed principle, making use of condenser, expander, compressor and with the main external heat input confined to the working fluid after attainment of the rated working pressure, compared with the usual arrangement of engine, condenser, boiler feed pump, boiler, and superheater, will:

1. Require a larger engine, because of the loss of mechanical work in compression, of steam, or steam plus water.

2. Require a smaller condenser.

3. Restrict the main input to the working fluid, after attainment of maximum operating pressure, thus doing away with the need for a boiler and boiler feed pump, except for start-up purposes.

The cycle is sensitive to the condition of steam at the end of expansion; to the amount of steam removed and replaced by water; and (for mechanical reasons, especially in turbine operation) to the way in which the water is added. From FIG. 1 it will be appreciated by those skilled in the art that the difference in slope of isentropic lines becomes significant, for practical purposes, when expansion takes place partially, largely or altogether in the subsequent and compression takes place effectively in the region of mixtures. This suggests that the best operating mode to work the cycle is to expand altogether in the region of superheat. Other factors, however, must be taken into consideration.

The effect of these factors can be seen by reference to FIG. 10, which shows a Pressure P Enthalpy H phase diagram similar to FIG. 1, with lines of constant temperature drawn in the superheat region.

For any practical application, there will be restrictions on two important parameters, maximum temperature, and pressure at the end of expansion. Maximum temperature is usually set by engineering, not thermodynamic limits; minimum pressure is determined, for example by temperature of the cooling medium; and by, engine and condenser dimensions, and condensing efficiency in reciprocating engines, and by practicable condenser and turbine dimensions in electric power generation.

In the diagram DE, D E D E are isentropic lines. D, D and D lie on the line of maximum practicable temperature. E, E and E lie on the line of minimum practicable pressure, P and E and E, are at minimum temperature, T E is at a somewhat higher temperature than T but for practical purposes all three expansions De, D E D E takes place between T and T Other things equal, the larger T T the better, for this quantity is a direct measure of maximum (Carnot) efficiency.

From the diagram, it is obvious that to restrict the expansion to the superheat, for a given temperature difference T T and a given minimum pressure P we are restricted in choice of maximum operating pressures to the pressure P If on the other hand a higher operating pressure such as P or P, is desirable, confining expansion to the superheat, DF or D F means that the temperature difference T T or T T is smaller than T T and the pressure at the end of expansion increases to P or P For a maximum operating pressure of 1,000 psia at 1,000, minimum exhaust pressure is liminted to 50 psia and operating temperature range is limited to l,-000 28 l= 729F.

With higher initial pressure, the operating temperature range is further reduced. For 1,500 psia and 1,000F the operating temperature range is (1,000 330) 670F. Exhaust pressure is raised further, to psia.

If, on the other hand, a lower exhaust pressure is selected, maximum operating pressure is greatly reduced. For example, with a 20 psia exhaust pressure the maximum pressure is limited to about 500 psia. Reduced maximum pressure means increased specific volume; and this in turn results in generally poorer heat transfer in the superheater and increased superheater dimensions; substantial disadvantages.

Examples 2A and 2B herein have been based on expanding in the superheat but right up to the saturated vapor line. If, at the end of expansion, substantial superheat actually remained, the above restrictions on limits of operating conditions would be further tight-, ened.

Expansion ending with significant superheat has a further disadvantage, as when water is added at constant volume to superheated steam, there is a fall in pressure until the saturated vapor line is reached.

For example, a practical engine may be developed with maximum steam conditions 300 psia and l,000, expanding entirely in the superheat to 20 psia, (Enthalpy H approximately 1,210 BTU/1b., Entropy S 1.805). Upon addition of enough water (at the temperature of dry saturated steam at 20 psia) to remove all the superheat the pressure would decrease to about 18 psia. Such a cycle is disclosed in US. Pat. No. 742,888, J. Missong. The fall in pressure during removal of steam and addition of water as in the Missong cycle has a very deleterious effect on the thermal efficiency of the cycle, and is completely eliminated the present invention.

As hereinbefore set forth, a feature of this invention is that expansion may take place to the saturated vapor line, or preferably into the region of mixtures, before the removal of steam and addition of water. Addition of water at substantially the same temperature as the expanded steam will result in no change of temperature, and completely negligible change in pressure and volume. Therefore, it is a feature of this invention that no cooling and substantially no pressure or specific volume change should accompany removal of a portion of steam from the power system, and its replacement by water.

It follows that a system in accordance with this invention must remove a portion of steam from an engine reciprocating, or positive displacement rotary or turbine without allowing the pressure to decrease and rules out any device which simply allows a portion of steam to escape to the atmosphere or to a condenser and which results in an increase in the specific volume of steam remaining in the cylinder, or in the case of turbines, of the steam prior to compression. Devices of the kind required for reciprocating and positive displacement rotary engines are described hereinafter. For turbines in which a separate compressor is required, a different method embodying, however, the same principle is also described.

The effect of a pressure drop is to increase the compressor work. The net work, which is thedifference between work out work of compression" is usually between 30 and 40 percent of work out." A relatively small increase in compression work therefore has a disproportionate effect on thermal efficiency.

Applied to piston engines, a further advantage of the present system for withdrawal of steam is that it results in removal of a constant proportion of the expanded in the cycle of steam regardless of the pressure changes at the end of expansion resulting from changes in cut-off. It is thus possible by varying the amount of water injected to always bring the steam at the end of compression to or close to the desired state of entropy. This is, for example, the entropy of steam on the saturated vapor line, and at the maximum operating pressure.

Since expansion ratio decreases with increasing cutoff the pressure at the end of expansion increases with increasing cut-off. Compression ratio can remain constant; or it can be varied. When cut-off increases, more steam is removed at the end of expansion; more water is injected to bring the entropy to or close to design line, and the pressure at the end of compression will increase, nearly in proportion to the increase in cut-off ratio. This is undesirable because it increases compression work without any counterbalancing advantage. A valve system sensitive to pressure is therefore required to maintain (when this is desired) a constant maximum operating pressure. The effect of increasing cut-off under these circumstances will be to increase the mean effective pressure, power, and torque, nearly in proportion to the ratio of increased to normal" cut-off.

It is also possible to raise the operating pressure. This can be done with or without changing the cut-off, by injecting slightly more water per stroke than is removed as steam. The net result will be, within a very short time framework to increase the operating pressure to some controlled higher value. Doubling the cut-offratio, and doubling the operating pressure, would yield close to a four-fold increase in mean effective pressure, power and torque.

Only a very small difference between amount of water injected and amount of steam removed can be used; otherwise the work of compression becomes too great.

To return the system to normal maximum design pressure it is only necessary to add slightly less water per stroke than is removed as steam.

Controlled increase of both cut-ofi ratio and maximum pressure is particularly useful in a vehicle, operating in the superheat range, where sudden and large variations in load are normal. The increase in maximum pressure also increases the density of the now superheated steam from the compressor and this is useful in providing increased thermal transfer in the superheater, precisely when it is needed.

In vehicle application, the cycle of the present invention can participate in deceleration by changing the timing of water injection; that is:

l. Inject water during expansion. This will decrease expander work.

2. Compress dry steam. This will increase compressor work.

To accomodate these operating modes, it is necessary to have, in piston engines, a system which:

1. Allows separation of expanded steam into at least two portions, in controlled ratio, without sensible alteration to the state of either portion.

2. Permits one portion to be compressed in the same cylinder in which it expanded, or in another cylinder or compressor.

3. Allows the portion so compressed (as in (2) above) to pass to a superheater, through a valve sensitive to pressure, which pressure can be variably controlled.

4. Allows injection into the steam while being compressed as in (2) above of an amount of water variably controllable, either the same, less than, or more than, the amount of steam (by weight) separated in (1) above.

Ways in which this can be done are described below in Examples 5A, 6A, and 68. Example 5B shows a method of separation of steam without altering its state.

The system can be further improved by allowing one of the separated portions to continue expansion to some lower pressure; doing further useful work, as described in examples 5A, 6A, and 6B, and FIGS. 6A through G, 7, and 8.

EXAMPLE 5A. SEPARATION OF STEAM IN PISTON ENGINES By way of illustration, the diagrams in FIGS. 9A 9E show the principle by which in a piston engine steam after expansion can be separated into two portions, without sensible alteration of the state of either portion. The method employs a passage, containing a valve, and connecting the two ends of the cylinder.

The ratio of the separated portions will be constant if the valve is operated at a pre-determined crank angle, by, for example, a cam, in the way common to the art.

The conduit can be external to the cylinder, as shown, or it can be within the cylinder wall; or the valve can be within the piston itself, and self-actuated at the required crank angle by suitable mechanism.

The diagrams 9A to 9E show the operation of a single cylinder, in which:

I is the inlet valve 2' is an exhaust valve leading to a condenser 3 is an injection system for water or other liquid 4 is an exhaust valve leading to a superheater is a mechanically operated valve in a conduit communicating with either end of the cylinder Start of Power Stroke FIG. 9A; Piston Is Just Past Top Dead Center.

Valve 1' (inlet) open Valve 2' (exhaust to condenser) closed Valve 3' (inlet for liquid) opening Valve 4' (exhaust to superheater) closed.

Valve 5 (in conduit connecting two ends of cylinder) closed.

Power Piston About One-Quarter of Power Stroke FIG. 98

Valve 1 closed. Normal cut-off would be about 5 percent.

7 Valve 1 would in the majority of operations be closed at this point. Valve 2' (exhaust to condenser) closed. Valve 3' (inlet for water or other liquid) open.

Valve 4' (exhaust to superheater) closed. Valve 5 (in conduit connecting two ends of cylinder) closed.

Power Piston at One-Half of Power Stroke FIG. 9C.

Valve 1 (inlet) Closed.

Valve 2' (exhaust to condenser) closed.

Valve 3 (inlet for water or other liquid) starting to close.

Valve 4' (exhaust to superheater) starting to open.

Valve 5 (in conduit connecting two ends of cylinder) starting to open.

When the piston reaches dead center, Valve 5' (in conduit connecting two ends of cylinder) opens, FIG. 9D, and remains open for the greater part of the return stroke, thus equalizing the pressure on both sides of the piston; this pressure is that attained by nearly isentropic expansion, and depends on the expansion ratio corresponding to the conditions chosen, i.e., inlet temperature and pressure and cut-off.

Start of Return Stroke FIG. 9D

Valve 1' (inlet) closed. Valve 2 (exhaust to condenser) closed. Valve 3' (inlet for water or other liquid) closed.

Valve 4 (exhaust to superheater) closing Valve 5 (in conduit connecting two ends of cylinder) open.

Power Piston About One Half of Return Stroke FIG. 9E

Valve 1' (inlet) closed Valve 2' (exhaust to condenser) opening. Valve 3' (inlet for water) closed.

Valve 4' (outlet to superheater) closed.

Valve 5' (in conduit connecting two ends of cylinder) starting to close.

Power Piston About Three Quarters of Return Stroke FIG. 9F.

Valve 1' (inlet) closed.

Valve 2 (exhaust to condenser) open.

Valve 3 (inlet for water) closed.

Valve 4 (outlet to superheater) closed.

Valve 5 (in conduit connecting two ends of cylinder) closed.

Power Piston at Top Dead Center FIG. 9G

Valve 1' (inlet) opening.

Valve 2' (exhaust to condenser) closing.

Valve 3' (inlet for water) closed.

Valve 4' (exhaust to superheater) closed.

Valve 5' (in conduit connecting two ends of cylinder) closed.

By altering the relative position of valves of FIG. 9, it is possible to increase the efficiency of the cycle by allowing a portion of steam after separation to continue further expansion. A method of doing this is shown in FIG. 7, and designated as Example 6A.

EXAMPLE 6A CAM-OPERATED VALVE IN CYLINDER WALL OR EXTERNAL TO CYLINDER The two ends of each of the power cylinders may be directly connected through passages in the cylinder walls or external passages containing valve means operable by a suitable cam connected to the driving mechanism of the reciprocating engine. Such a structure is illustrated in FIG. 7 wherein the power cylinder 10 is provided with an internal passage 12 having communication at 14 at the inlet end 16 of the cylinder 10 and communication at 18 with the opposite end of cylinder 10. The passage 12 is provided with a valve 20 which corresponds to the self actuating valve 5 of the forms of the invention shown in FIG. 6. The system also includes

valves

22, 24, 26 and 28, which correspond to

valves

1, 2, 3 and 4 of the forms of the invention shown in FIG. 6, and function in the same manner.

Another method of carrying out the function described in 6A and FIG. 7 is by use of a self-actuated valve in the piston, described below as Example 58.

EXAMPLE 5B. SELF ACTUATED VALVE IN PISTON The diagram in FIGS. 6A 6G show the operation of a single cylinder, in which:

1 is the inlet valve 2 is an exhaust valve leading to a condenser 3 is an injection system for water or other liquid 4 is an exhaust valve leading to a superheater 5 is a piston operated valve in the piston, communicating with either side of the piston.

Start of Power Stroke FIG. 6A; Piston Is Just Past Top Dead Center Valve 1 (inlet) open.

Valve 2 (exhaust to condenser) open, allowing exhaust steam from previous stroke to pass to the condenser.

Valve 3 (inlet for liquid) closed.

Valve 4 (exhaust to superheater) closed.

Power Piston One-Third of Power Stroke FIG. 6B

Valve 1 closed. Normal cut-off would be about 5 percent.

Valve 1 would in the majority of operations be closed at this point. Valve 2 (exhaust to condenser) open. Valve 3 (inlet for water or other liquid) closed.

Valve 4 (exhaust to superheater) closed. Valve 5 (connecting two sides of power piston) closed.

Power Piston Approaching End of Power Stroke FIG. 6C

Valve 1 (inlet) closed. Valve 2 (exhaust to condenser) starting to close.

Valve 3 (inlet for water or other liquid) closed.

Valve 4 (exhaust to superheater) closed.

Valve 5 (connecting two sides of power piston) starting to open.

When the piston reaches dead center, Valve 5 (connecting two sides of power piston) opens, FIG. 6D, and remains open for part of the return stroke, thus equalizing the pressure on both sides of the piston; this pressure is that attained by nearly isentropic expansion; and depends on the expansion ratio corresponding to the conditions chosen, i.e., inlet temperature and pressure and cut-off.

Start of Return Stroke FIG. 6D

Valve 1 (inlet) closed Valve 2 (exhaust to condenser) closed. Valve 3 (inlet for water or other liquid) closed.

Valve 4 (exhaust to superheater) closed.

Valve 5 (connecting two sides of power piston) open.

These conditions continue until the portion of exhaust steam which is to be replaced by water, is in the end of the cylinder remote from the steam inlet Valve Start of Compression FIG. 6B

Nearing End of Compression FIG. 6F

Valve 1 (inlet) closed.

Valve 2 (exhaust to condenser) closed. Valve 3 (inlet for water) open.

Valve 4 (outlet to superheater) opening.

Valve 5 (connecting two sides of power piston) closed.

Top Dead Center FIG. 6G

Valve 1 (inlet) opening.

Valve 2 (exhaust to condenser) opening.

Valve 3 (inlet for water) closed.

Valve 4 (outlet for superheater) closing.

Valve 5 (connecting two sides of power piston) closed.

In general, the system embodied in the devices as shown in FIGS. 6, 7 and 9 are limited to single acting engines. Two of them (FIGS. 6 and 7) have the advantage of obtaining work from the portion of the steam removed before compression by allowing further expansion. The effect on the net work and efficiency is notable because net work is a difference, that is, increasing work out is as beneficial as a decrease in compressor work. Applied to the system shown in FIGS. 6 and 7, this effect can be numerically evaluated as follows: at the start of compression, the amount of steam to the right of thepistonis 0,208 of the total in the cylinder at, for example, a pressure of 40 psia and entropy 1.6525. When

valves

5 or 20 close this steam will continue to expand and the expansion ratio will be l/0.208 which is equal to 4.80 to I when the piston reaches top dead center. The specific volume for 40 psia is 10.498; the specific volume at the end of expansion will be 0.98 X 4.8 X 10.498 49.5 (The steam has guality 0.98) and the corresponding pressure will be 7.65 psia. Thus, the extra work done by this expansion is l ,15 2 1,038) X 0.208 23.7 BTU per pound of steam originally admitted to the cylinder.

Thus, it will be seen that the single acting systems wherein the withdrawn steam is further expanded have highly desirable characteristics; however, as hereinbefore set forth, these particular systems cannot be employed with a double acting engine.

Where the system of the present invention is employed with double action and means are provided for withdrawing a portion of the expanded steam without change in temperature, pressure or specific volume is described in reference to FIG. 8 of the application and designated Example 6B.

Referring to FIG. 8, each double acting cylinder 30 having a double acting piston 32 has a separate extraction cylinder 34 of identical internal dimension and its own work piston 36. Each end of the extraction cylinder 34 is connected via a

valve

38 and 38 to a condenser which valves correspond to valve 2 of the previously described apparatus shown in FIG. 6, and valve 24 in FIG. 8. Further, each end of the cylinder 34 is 0 connected via a

conduit

40 and 40 to opposite ends of the power piston cylinder 30 and each of the

conduits

40, 40 is provided with a cam actuated valve 42-42, which valves 42 and 42' correspond to valve 5 of the forms of the invention shown in FIG. 6 and valve 20 in FIG. 7. Further, one end of the power piston 30 is connected to inlet steam via conduit 44 and valve 46 while the opposite end is similarly connected thereto via conduit 44' and valve 46'. Each respective end of the cylinder 30 is also connected to the superheater and to water injection via

conduits

48, 48', 50, 50' provided with

valves

52 and 52 and 54 and 54' respectively.

In operation of the apparatus illustrated in FIG. 8 in which the various valves function in a manner similar to those described in the previous systems shown in cylinder 30 with the extraction cylinder 34 are open and

pistons

32 and 36 are moving at the same speed and in the direction of their respective directional arrows with the result that expanded steam in the power cylinder 30 is moved into the extraction cylinder 34 until the valve 42 is closed. At this point, compression of the remaining steam in the power cylinder 30 commences together with injection of water via conduit 50 and valve 54, while the steam in the extraction cylinder 34 continues to expand doing positive work to the end of the stroke of the piston 36 while discharging exhaust steam from the previous stroke through valve 38' to the condenser of the system.

The method described in Example 6B, and FIG. 8, can be applied in such a way that a single extraction cylinder can serve two or more power cylinders. By way of example, if 25 percent of steam were extracted from the power cylinder, one extraction cylinder could serve two double acting power cylinders and allow expansion of the extracted steam to some lower pressure, doing useful work. The expansion ratio of the extracted steam would be somewhat reduced compared with the case described in Example 6B. With 25 percent extraction, a single extraction cylinder could serve up to four double acting power cylinders, though in this case no further expansion work could be gained from the extracted steam.

All the above examples referring to operation of piston engines, separate steam by moving a portion from one part to another of the same cylinder, or in another cylinder, without changing volume while the separation is taking place. All require a cylinder and piston.

ln Example 9, and FIG. 11, are described, and shown diagrammatically a valve assembly which allows transfer of a given portion of steam after expansion from a cylinder directly to a condenser or to the atmosphere, without sensibly altering the state of the portion remaining in the cylinder. The valve can be applied to a single acting cylinder and piston as shown, or to a double acting cylinder.

Valves

209 and 210 are cam operated from the engine crank. In operation, valve 210 remains open through the expansion stroke equalizing the pressure between the chamber 211 and the cylinder chamber 201. At bottom dead center (BDC) 210 closes, and the pressure in 211, working on the face 207 of the valve stem 204 is that of the fully expanded steam, plus the pressure from the spring, 208.

At BDC the valve 209 opens; and as the piston rises, the pressure of the steam in the cylinder rises until the force on the face 207 of the valve stem 204 is just suffcient to move the stem, and allow steam to pass into conduit 206. In this way, steam is removed at substantially constant pressure; and the specific volume of the steam remaining in the cylinder remains substantially the same as at the end of the expansion. When the required amount of steam has been removed, valve 210 is opened, and valve 209 is closed, by cam action.

In FIGS. 9 (A-G), 6 (A-G), 7, 8, and 11 are shown in each case a valve or valves connecting a cylinder to a superheater.

Such valves can be ordinary check valves.

The methods described in reference to FIGS. 6, 7 and 8 having the following common features:

1. Each allows separation of a precise portion of expanded steam without appreciable change in pressure, temperature or specific volume; i.e., of state;

2. Each allows expansion of one portion of the steam separated in or from the power cylinder continuously down to condensing pressure thereby doing further useful work; and

3. Water can be admitted throughout most of the compression stroke of each engine.

Further, each of the three mechanical methods for removing steam is equally applicable to positive displacement rotary engines, and the principle is applicable to turbines. With respect to operation of the improved cycle with turbines reference is had to FIG. 4, designated Example 7, and wherein 152 is a superheater and steam from the superheater 152 is connected to a high pressure turbine 154, through conduit 153, where it expands for example from a pressure of 2,500 psia to 250 psia; thence through an extraction flow divider, 155, where it is divided into two portions. The greater portion which can be about percent, is passed directly to the low pressure end of a compressor, 156, in which it is compressed to maximum operating pressure, together with water injected during compression through conduit 166.

The extraction flow divider in FIG. 4 and 112 in FIG. 5, consists of concentric inner and outer ducts of circular cross-section as shown in FIG. 4. The ratio in which the steam divides is determined by the ratio:

Cross Sectional Area of Inner Duct (Cross sectional area of outer duct)--(Cross sectional area of inner duct) The lesser portion of steam separated at 155 is passed via conduit 157 to a reheater 158, where it is heated at constant pressure to 1,000; thence through conduit 159 to low pressure turbine 160, where it expands and exhausts at about 1 psia; thence via conduit 161 to condenser 162, hot well 163, and through conduit 164, to water heater, 165, and via conduit 166, is injected into the main portion of the steam in compressor 156. The compressed steam from the high-pressure end of the compressor is passed to the super-heater 152, via conduit 167, and the cycle repeats.

In an alternative mode of operating the cycle the water heater 165 can be by-passed as shown by the dotted line in FIG. 4. Water at condensing temperature is added to superheated steam from the high pressure turbine, in a constant pressure de-superheater 170, and the wet steam so formed is returned to the low pressure end of the compressor 156 via conduit 172.

These modes of operation have the advantage of reducing the ratio of compressor work to total work of expansion which has great practical importance.

The method of addition of water is important. A preferred method is to add water continuously throughout the compression. Water is added down the shaft of an axial flow compressor, which is made hollow for this purpose, and introduced continuously into the compressor space through appropriate orifices located between compression stages.

Another form of turbine assembly which can yield higher theoretical efficiency than the method in Example 7, and operable with the system of the present invention is illustrated in FIG. 5 and designated Example 8, wherein superheated steam from superheater 100 is passed to a high pressure turbine 102 via conduit 104. The exhaust from the high pressure turbine 102 is directed to a reheater 106 via a line 108. Steam from the reheater 106 passes to the main turbine 1 l and at the exhaust end an annular flow divider generally designated 1 12 extracts, for example a 30 percent portion of the exhaust steam at for example, psia while 70 percent of the exhaust steam flows directly to a low, intermediate and high pressure axial flow compressor 114 within which the low'pressure steam is recompressed to operating pressure and directed to the superheater 100 via conduit 116 together with the recompressed fluid added from the condenser'hot well 118 via conduit 120 which feeds the fluid during the various stages of compression in the compressor 114. Prior to passing to the condenser and hot well 118, the 30 percent of the low pressure steam extracted by flow divider 112 passes to a low pressure turbine 120 which, like turbine 110 and high pressure turbine 102, may be mounted on a common power shaft, together with the axial flow compressor 114. The exhaust from the low pressure turbine flows to the condenser via conduit 122. In broken lines at 124 is a valved branch line whereby the low pressure turbine may be bypassed in whole or in part by the 30 percent low psia steam extracted by the flow divider 112. Extracted steam does not have to be further expanded as shown, in FIGS. 4 and 5, but can be passed directly to a condenser as shown by the dotted line 124 in FIG. 5.

In the examples hereinbefore set forth in reference to FIGS. 4 and 5 of the drawings, the

flow dividers

155 and 112 are illustrated as splitting the low pressure steam into portions 30 percent and 70 percent. This split is by way of example only and greater or lesser portions may be divided at the flow dividers or extractors.

From the foregoing description considered in respect to the illustrative embodiments thereof, it will be seen that an improved system for external combustion power production is provided which has very high efficiency and may be used in operation of land. vehicles, sea going vehicles, and stationary power producing plants of the conventional fuel or atomic fuel types.

The amount of expanded fluid withdrawn, condensed and injected into the fluid being compressed generally has an optimum range when efficiency of a particular power producing engine is considered. The amount may be varied substantially for other reasons as hereinbefore set forth. In general, with turbine type expanders withdrawals of about 25 to about 35 percent have been found to provide very satisfactory results with a preferred range of from about 28 to about 32 percent. With reciprocating engines withdrawals of from to about 30 percent provide satisfactory results, with a preferred range of from about 19 to about 22 percent.

it is also recognized that various modifications may be made in the system and the illustrated examples are by way of example and not by way of limitation.

We claim: 1. An external combustion power producing cycle comprising:

a. heating a condensable fluid to the vapor state; b. expanding the vapor isentropically; c. separating the expanded fluid into at least two portions without substantially changing the state thereof;

d. permitting one of the said portions to continue expanding to some lower pressure; thereby doing further useful work;

e. condensing the said portion described in (d);

f. adding in liquid form the weight equivalent of the condensed portion of the liquid to the other portion of the fluid, wherein at least a part of said condensed portion is added to said other portion during the compression of said other portion whereby the mixture of said condensed portion and said other portion is isentropically compressed to a desirable operating pressure,

g. reheating the resulting compressed working fluid in the vapor state; and

h. re-expanding the vapor isentropically.

2. An external combustion power producing cycle comprising:

a. superheating the vapor of a condensable fluid from a dry saturated state at a predetermined temperature;

b. expanding isentropically the superheated vapor to a state such that the expanded vapor is dry saturated or within the region of mixtures;

c. separating the expanded fluid into at least two portions without substantially changing the state thereof;

d. condensing one of said portions;

e. adding in liquid form the weight equivalent of the condensed portion of the liquid to the other portion of the fluid, wherein at least a part of said condensed portion is added to said other portion during the compression of said other portion whereby the mixture of said condensed portion and said other portion is isentropically compressed to a dry saturated state,

f. resuperheating the resulting compressed vapor of the condensable fluid from said dry saturated state the a predetermined temperature; and

re-expanding isentropically the resuperheated vapor to a state such that the expanded vapor is dry saturated or within the region of mixtures.

3. An external combustion power producing cycle comprising:

a. superheating the vapor of a condensable fluid from a dry saturated state at a predetermined pressure to a predetermined temperature; I

b. expanding isentropically the superheated vapor to a state such that the expanded vapor is still superheated, or dry saturated or within the region of mixtures;

e. condensing the said portion described in (d);

f. adding in liquid form the weight equivalent of the condensed portion of the liquid to the other portion of the fluid, wherein at least a part of said condensed portion is added to said other portion during the compression of said condensed portion whereby the mixture of said condensed portion and said other portion is isentropically compressed to the dry saturated state;

g. resuperheating the resulting compressed vapor of the condensable fluid from said dry saturated state at a predetermined pressure to a predetermined temperature; and

h. re-expanding isentropically the resuperheated vapor to a state such that the expanded vapor is still superheated or dry saturated or within the region of mixtures.

4. The method defined in claim 2 wherein the isentropic expansion takes place to the saturated vapor line.

5. The method defined in claim 2 wherein the isentropic expansion takes place into the region of mixtures.

6. The method defined in claim 2 wherein the isentropic expansion takes place entirely within the region of mixtures.

7. The method defined in claim 2 wherein the liquid added in step (1) is at the same temperature as the expanded vapor before compression.

8. The method defined in claim 2wherein the isentropic expansion takes place in a single acting reciprocating engine.

9. The method defined in claim 2 wherein the isentropic expansion takes place in a double acting reciprocating engine.

10. The method defined in claim 2 wherein the isentropic expansion takes place in a positive displacement rotary expansion engine.

11. The method defined in claim 2 wherein the expansion takes place in at least one turbine, and compression takes place in at least one turbo-compressor.

12. The invention defined in claim 2 wherein the condensable fluid comprises steam.

13. The invention defined in claim 2 wherein compressing in a turbo-compressor the liquid is added continuously through apertures in the compressor shaft, which is made in tubular form for the purpose.

14. An external combustion power producing system comprising:

a. means for heating a condensable fluid to the vapor state;

b. means for expanding the vapor isentropically;

0. means separating the expanded fluid into at least two portions without substantially changing the state of at least one of the portions;

d. means for adding liquid to the at least one portion wherein at least a part of said liquid is added during the compression of said at least one portion whereby the resulting mixture is isentropically compressed to a desirable operating pressure,

e. means for reheating the resulting compressed vapor.

15. An external combustion power producing system as defined in claim 14 wherein the means for separating the expanded fluid into at least two portions comprises valved passage means connecting opposite ends of a cylinder of a reciprocating piston-cylinder power producing engine.

16. The invention defined in claim 15 wherein the valved passage is contained in a wall of the cylinder.

17. An external combustion power producing system as defined in claim 14 wherein the power is produced in a main double acting piston-cylinder engine and the means for separating the expanded fluid into at least two portions comprises an auxiliary piston-cylinder unit and valved passages separately connecting the Zones adjacent the cylinder heads of the auxiliary piston-cylinder unit to the cylinder zones adjacent the pair of cylinder heads of the main piston-cylinder engine.

18. An external combustion power producing system as defined in claim 14 wherein the means for separating the expanded fluid into at least two portions comprises automatic pressure responsive valve means communicating with the means for expanding the vapor isentropically.

Claims

1. An external combustion power producing cycle comprising: a. heating a condensable fluid to the vapor state; b. expanding the vapor isentropically; c. separating the expanded fluid into at least two portions without substantially changing the state thereof; d. permitting one of the said portions to continue expanding to some lower pressure; thereby doing further useful work; e. condensing the said portion described in (d); f. adding in liquid form the weight equivalent of the condensed portion of the liquid to the other portion of the fluid, wherein at least a part of said condensed portion is added to said other portion during the compression of said other portion whereby the mixture of said condensed portion and said other portion is isentropically compressed to a desirable operating pressure, g. reheating the resulting compressed working fluid in the vapor state; and h. re-expanding the vapor isentropically.

2. An external combustion power producing cycle comprising: a. superheating the vapor of a condensable fluid from a dry saturated state at a predetermined temperature; b. expanding isentropically the superheated vapor to a state such that the expanded vapor is dry saturated or within the region of mixtures; c. separating the expanded fluid into aT least two portions without substantially changing the state thereof; d. condensing one of said portions; e. adding in liquid form the weight equivalent of the condensed portion of the liquid to the other portion of the fluid, wherein at least a part of said condensed portion is added to said other portion during the compression of said other portion whereby the mixture of said condensed portion and said other portion is isentropically compressed to a dry saturated state, f. resuperheating the resulting compressed vapor of the condensable fluid from said dry saturated state the a predetermined temperature; and g. re-expanding isentropically the resuperheated vapor to a state such that the expanded vapor is dry saturated or within the region of mixtures.

3. An external combustion power producing cycle comprising: a. superheating the vapor of a condensable fluid from a dry saturated state at a predetermined pressure to a predetermined temperature; b. expanding isentropically the superheated vapor to a state such that the expanded vapor is still superheated, or dry saturated or within the region of mixtures; c. separating the expanded fluid into at least two portions without substantially changing the state thereof; d. permitting one of the said portions to continue expanding to some lower pressure; thereby doing further useful work; e. condensing the said portion described in (d); f. adding in liquid form the weight equivalent of the condensed portion of the liquid to the other portion of the fluid, wherein at least a part of said condensed portion is added to said other portion during the compression of said condensed portion whereby the mixture of said condensed portion and said other portion is isentropically compressed to the dry saturated state; g. resuperheating the resulting compressed vapor of the condensable fluid from said dry saturated state at a predetermined pressure to a predetermined temperature; and h. re-expanding isentropically the resuperheated vapor to a state such that the expanded vapor is still superheated or dry saturated or within the region of mixtures.

7. The method defined in claim 2 wherein the liquid added in step (f) is at the same temperature as the expanded vapor before compression.

8. The method defined in claim 2 wherein the isentropic expansion takes place in a single acting reciprocating engine.

14. An external combustion power producing system comprising: a. means for heating a condensable fluid to the vapor state; b. means for expanding the vapor isentropically; c. means separating the expanded fluid into at least two portions without substantially changing the state of at least one of the portions; d. means for adding liquid to the at least one portion wherein at least a part of said liquid is added during the compression of said at least one portion whereby the resulting mixture is isentropically compressed to a Desirable operating pressure, e. means for reheating the resulting compressed vapor.