Compact Steam Generator And System

Abstract

An ultra-compact flash steam generator is provided for driving various types of steam engines such as turbines, rotary positive displacement and reciprocating piston engines. Water or other liquid medium is injected against one side of a heat transfer boundary and premixed air-fuel fluid is injected against the opposite side of the boundary where combustion becomes self-sustaining. Sub-systems and controls are provided for a complete, operational prime mover functioning on the generated steam.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to steam driven prime movers and more particularly is directed towards a new and improved ultracompact steam generator along with a steam driven engine including a closed loop steam system with accessory equipment and controls.

2. Description of the Prior Art

Considerable effort has been applied towards the development of steam engines and especially towards one that is competitive with the internal combustion engines. Most steam engines currently in use are associated with installations having large power requirements such as electric generating plants, ocean-going vessels and the like. This is due primarily to the fact that steam turbines are efficient under continuous high speed operation but at low speed or intermittent operation, become inefficient. While reciprocating steam engines have long been built for use in large plants as well as in smaller units, such as for self-propelled vehicles, the bulk, weight and complexity of such engines have sharply limited their widespread adoption for use where efficiency and compactness are of prime importance. More recent efforts have been made towards developing small, efficient steam generators and engines to replace the internal combustion engines for automobiles as a means for reducing atmospheric pollution. Results to date have been only marginally successful, the engines still lacking the combination of performance, efficiency, compactness and lightness in weight necessary to be competitive with internal combustion engines.

Accordingly, it is a general object of the present invention to provide improvements in steam generators and steam engines. A more specific object of this invention is to provide a steam generator and engine of efficient, compact design, having a minimum number of parts and one which is easily controlled for rapid, flexible operation.

SUMMARY OF THE INVENTION

This invention features an ultra-compact, highly efficient steam generator, including a wall serving as a heat transfer boundary, means for injecting water or other liquid medium against one side of said wall where it is flashed into steam and means for injecting a combustible fluid against the opposite side of said wall where combustion becomes self-sustaining. The flash boiler may be formed integral with an engine for a compact prime mover. Accessory equipment and controls include a high efficiency feed water preheater, an electronic control system for a reciprocating engine, injectors and other components.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view in side elevation of a flash steam generator made according to the invention,

FIG. 2 is a top plan view of a portion of the inner face of the heat transfer barrier of FIG. 1,

FIG. 3 is a cross-sectional view somewhat enlarged, of a water injection spray tube employed in FIG. 1,

FIG. 4 is a schematic diagram of a water injection system employed in FIG. 1,

FIG. 5 is a detail sectional view in side elevation of a fuel nozzle made according to the invention,

FIG. 6 is a schematic diagram of a closed loop steam prime mover system made according to the invention and applied to a reciprocating engine,

FIG. 7 is a sectional view in front elevation of a reciprocating steam engine made according to the invention,

FIG. 8 is a cross-sectional view taken along the line 8--8 of FIG. 7,

FIG. 9 is a top plan view of a feed water preheater made according to the invention,

FIG. 10 is a cross-sectional view taken along the line 10--10 of FIG. 9,

FIG. 11 is a cross-sectional view taken along the line 11-11 of FIG. 10,

FIG. 12 is a detail sectional view of the commutator assembly employed in the system of FIG. 6,

FIG. 13 is a detail perspective view of a portion of the FIG. 12 assembly,

FIG. 14 is a sectional view in side elevation of a feed water injector employed in the invention,

FIG. 15 is a sectional view in side elevation of a flash steam generator embodied in a turbine engine,

FIG. 16 is a sectional view of a steam driven rotary piston engine made according to the invention,

FIG. 17 is a cross-sectional view taken along the line 17--17 of FIG. 16, and,

FIG. 18 is a detail sectional view in side elevation of a thin film spray nozzle made according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

1. flash Steam Generator

Referring now to the drawings and to FIG. 1-5 in particular, there is illustrated a flash steam generator 10 that adds the heat of vaporization to saturated liquid water. Its basic elements include a reaction chamber 12, a heat transfer boundary wall 14 and a water injector system 16. The heat transfer boundary doubles in function as part of a pressure container preferably being integral with an engine as will presently appear. In order to achieve extreme compactness, both the rate of heat release and rate of heat transfer must be unusually high.

The chamber 12 functions on the principle of impingement surface combustion in order to achieve high rates of heat release and heat transfer. Surface combustion is used both to concentrate the combustion reaction and to eliminate the stagnant laminar sublayer that usually reduces the heat transfer rate of a heated surface. Impingement is used to accelerate the rate of bringing fresh reactants to the surface and moving products of combustion away from the reaction zone.

The material of the wall 14 preferably is a solid, thermally conductive, refactory material such as a nickel-base or cobalt base super alloy with good high temperature oxidation resistance, e.g., Hasteloy or Haynes Alloy 188. The reaction temperature may be lowered by the use of a catalyst added to the wall material. Nickel oxide or platinum, for example, may be surface-coated onto or diffused into the wall material.

The chamber includes a number of nozzles 18 (FIG. 5) that direct jets of premixed fuel and air against the hot heat transfer boundary 14, the heat input with respect to heat extraction is controlled so that the impingement surface operates above the ignition temperature of the fuel-air mixture.

The fuel-air nozzles 18 heat the impingement surface to the ignition temperature and then serve to stabilize the combustion process. In order to help the combustion process to transfer to the impingement surface, to stabilize combustion and increase heat transfer, the impingement surface is extended with many small projections 20 like a miniature "waffle iron" pattern as best shown in FIGS. 1 and 2. As the flow from each jet radiates out along the impingement surface, it passes these small projections and generates vortices. Accordingly, these projections serve as miniature flameholders that stabilize the flame over the whole area washed by each fuel-air jet. The fuel-air nozzles 18 that direct the jets are also high intensity pilot burners that provide stable flameholding over a large turndown ratio. These burner nozzles feature a swirling "splash pilot" design that produces strong recirculation and turbulence.

When the flames, stabilized by the small projections 20, have heated the surface of the wall 14 to ignition temperatures, the reaction condenses onto the surface so that the visible flames disappear. At this stage, the combustion reaction is consuming the stagnant laminar sublayer of absorbed gases that usually limits the rate of heat transfer.

Preferably the boundary wall 14 is concave as shown to enhance and control the flow of gases applied thereto. The configuration may be hemispherical for certain applications or annular for other applications to be described more fully below.

The fuel-air nozzles 18 are mounted on a concave inner wall 22 defining a plenum chamber 24 that distributes premixed fuel and air, introduced through a port 26, to the jets so that one surface of the plenum chamber forms one wall of the reaction chamber 12. Therefore, the plenum chamber and burner nozzles constitute an air preheater which not only reduces fuel consumption but also recovers heat that would otherwise leak out through the plenum chamber. The incoming fuel-air mixture also serves to prevent the plenum chamber from reaching ignition temperatures and supporting surface combustion. Metal screen or perforated metal plates (not shown) may be located inside the plenum chamber to block radiant heat losses, protect against flashback and improve air preheating.

Premixed propane gas and air is supplied to the plenum chamber through a venturi proportional mixer 30 (FIG. 6) with a pressure regulator 32 that provides the correct fuel-air mixture over a large turndown ratio. Air is supplied by a centrifugal blower 34 and the rate of reaction chamber heat input is modulated by a throttle valve 36 located at the blower air intake.

The reaction chamber heat input throttle 36 is controlled by a thermostat 38 (FIG. 6) so as to maintain the desired temperature of the heat transfer boundary. A standby flame maintains the design temperature when the engine is not operating so that it is always ready to generate steam when the operator calls for power. The device 38 used to sense temperature could be a photoelectric cell that measures radiation intensity from the incandescent surface of the heat transfer boundary and actuates the throttling valve electrically. A back-up device shuts off the gas supply if the temperature exceeds safe limits.

Ignition is achieved by utilizing a high-energy sparkplug 40. A flame-proving and air purging system is used to insure safe operation. The burner can be adapted to any other gaseous or liquid fuels.

The outer or steam generating side of the heat transfer boundary wall 14 is designed to achieve flash boiling with the highest possible rate of heat extraction. This is achieved by using a heat transfer surface temperature that is several hundred degrees higher than the boiling temperature of the water. Ordinarily, this would result in stable film boiling; however, this condition is avoided by the use of needle jets impinging on the hot surface or a disc type nozzle to be described below for forming a thin film. Using a high velocity stream of water insures that liquid water reaches the surface and spreads out for a short distance; steam is able to escape between the jets so that the flows of liquid and vapor do not interfere with each other.

In order to distribute the injected water uniformly over the surface, maintain water in a liquid state until impingement and insure high-velocity needle jets throughout the injection period, a specially designed injector 16 system, organized about an elongated spray tube 42 (FIG. 3), is used and helically disposed in closely spaced relation with respect to the convex side of the wall 14. Other requirements are that all spray orifices 44 open simultaneously and quickly, that feedwater be subject to negligible heating or cooling during its passage through the spray tubes and that the tubes take up a minimum of space.

In the spray tubes of FIG. 3, the spray orifices 44 are closed by a hydraulic valve consisting of two flexible tubes 46 and 48, perhaps made of teflon or the like and contained in a rigid tube 50 that is drilled to let water in on one side and out to the spray orifices 44 on the other side. These flexible tubes 46 and 48 are connected by a conduit 51 to the pressure side of a circulation pump 52 so that they are filled with water or other liquid at a pressure of 500 psi, for example. This forces the tubes 46 and 48 tightly together so that water cannot pass between them.

When the injection cycle begins in a particular cylinder for a multi-cylinder reciprocating engine, for example, a solenoid 54 that lets the heated injection water enter the spray tube also closes a valve in the line 51 between the pump and the flexible tubes 46 and 48; this traps the water in the tubes 46 and 48 so it cannot escape back toward the pump. The other ends of the flexible tubes 46 and 48 are closed by a pressure relief valve 56 set for 3000 psi or higher, for example.

As the heated water is pumped through a line 58 into the spray tube 42 by an injector pump 60, it elastically displaces a core 62 of resilient material that fills the tube. This resilient material is preloaded to a pressure of 500 psi, for example, and, as the volume of water in the spray tube increases, the pressure level of the heated water increases and the trapped water in the flexible tubes 46 and 48 also increases. The flexible tubes 46 and 48 try to take on a minimum energy cross-section; therefore as the pressure increases, the seal is formed more tightly and resists leakage between their opposing faces.

When the pressure level inside the flexible tubes 46 and 48 reaches 3000 psi, for example, the pressure relief valve 56 opens and lets the trapped water escape back through return lines 64 and 66 to the suction side of the pump 52. The flexible tubes 46 and 48 then collapse and quickly and simultaneously open all the spray orifices 44. Typically the relief valve 56 is set not to close until the pressure drops to 1000 psi.

The elastic energy stored in the resilient material then forces the water through the spray orifices 44. When the solenoid 54 closes, it simultaneously connects the flexible tubes 46 and 48 to pump pressure. However, the flexible tubes 46 and 48 cannot close the orifices 44 until the pressure in the tube 42 drops to 500 psi, at which point all the water has been injected.

The valve system works with the speed of sound in water which should be adequately fast for a reciprocating engine or the like.

The resilient core material 62 may consist of gas-filled microballoons bonded together with silicone rubber or similar material. The surface would be folded to allow it to spread out when the core material is compressed.

The unheated water in the flexible tubes 46 and 48 helps prevent the spray tube 42 from overheating. When the engine is not running, a small built-in leak insures that this water will not overheat.

The water jets from the orifices 44 impinge on the outer convex side of the cylinder head heat transfer boundary wall 14 and spread out radially on the surface. Each spray orifice 44 may be extended by a short tube 68 so that it leaves only a thin annular outlet between the heat transfer surface and itself. This maintains the high pressure to prevent vaporization of the water until the heat is added. It also turns the water flow radially under high pressure and prevents rebound or splashing of liquid water.

To minimize rebound and splashing plus extend the heat transfer area, wire bristles 70 may be silver brazed or stud welded to the steam generating surface. The projections would serve to trap the liquid water by capillary attraction until its conversion into steam; this effect could be augmented by providing small heads on the ends of the wires.

For use with steam generators that require intermittent, short bursts of steam, it is desirable to apply a layer 72 of material having high thermal conductivity to the steam generating surface. This layer acts as a heat reservoir that is filled slowly between injection periods and drained quickly when heat is extracted by flash steam generation. In addition to high thermal conductivity the steam generating surface must resist corrosion and scaling at 1200.degree.- 1400.degree. F and not weaken the superalloy by diffusion migration of its atoms. Possible materials for this layer would be silver, silver-copper alloy, silver-nickel composite or silver-tungsten composite.

It is desirable that the water mass flow for each jet be small. At high pressures, this would result in extremely small orifices which may be subject to clogging. This condition may be avoided by the use of swirl type nozzles.

The objective of the water injection system is to create a thin liquid film against the hot surface. In FIG. 18 there is illustrated a device for producing a thin film, which device includes a spray tube 42" with a nozzle 68' extending towards the steam side of a heat transfer boundary wall 14'. The nozzle is formed with a relatively wide range or disc 71 having a concave lower face with the peripheral outer edge bearing against the surface of the wall 14' and close to surrounding abutments 73. Spiral grooves 75 are formed in the wall 14' opposite each nozzle and serve to enhance the transfer of heat from the wall 14' to the thin film of water or other liquid formed between the disc 71 and the wall. A diaphragm 77 with a central opening is mounted across the bottom of the disc 71 and serves to form a very thin film of water when the water is injected through the nozzle. Wires 79 may be mounted on top of the abutments 73 for super-heating the steam generated by the device.

Alternatively, in order to generate and maintain a stable liquid film, several small wires 74 (FIG. 3) radiate out from each water nozzle for a distance equal to half the spacing between nozzles. These wires spread water droplets into a thin film, the wires should spiral in the swirl direction and possibly touch the heat transfer surface lightly. An additional device that may be used to prevent the escape of liquid water before it is converted to steam is a wire mesh or screen 76 that contains clearance holes for the water nozzles and overlays the wires 74 radiating from the water nozzles. It may prove desirable to design this wire screen with projections that can be silver soldered to the heat transfer surface so as to extend the heat transfer surface and add additional heat to the steam and possibly, to superheat the steam.

2. The System

Referring now to FIG. 6 of the drawings, the overall system embodying the foregoing steam generator will be described followed by detailed descriptions of the various components and sub-systems.

The system of FIG. 6 is organized about a reciprocating steam engine embodiment indicated generally by the reference character 78 and comprised of a piston 80 mounted for reciprocation in a cylinder 82, the piston being drivingly connected to a crank shaft as will be described more fully below. The engine is provided with a combination cylinder head and integral flash steam boiler 10 whereby water or other liquid injected into the cylinder will convert to steam to drive the piston. The combination cylinder head and steam generator 10 is heated by the ignition of combustible fluids fed from a fuel tank 84 via a conduit 86, through the gas pressure and mixture regulator 32, thence via a conduit 88 to mix with air delivered from the combustion blower 34 through a conduit 90. The fuel and air mix with one another just before entering the flash steam generator 10 to heat the injected water. The exhausted combustion gases then discharge through a line 92 and pass through a feed water preheater 94 to the atmosphere.

The steam-water system essentially is a closed loop and includes the feed water pump 52 taking suction from a condensing section including a jet ejector 96, a water cooler 98 and an ejector pump 100 connected via conduits 102, 104 and 106 respectively. The feed water pump 52 draws condensate from the conduit 104 and delivers it under pressure, unheated, through a conduit 110 to a three-way valve 111 operating a booster 112 for the feed water injector 60. A single injector 60 is connected to all of the spray tubes 42 with a solenoid actuated valve 54 provided for each cylinder. The feed water entering the cylinder converts to steam and is then exhausted through a conduit 114 to the ejector 96 to be condensed. An injector return switch 116 serves to open the timing circuit after each pulse as will appear more fully below.

The operation of the reciprocating engine is under control of an electronic system including an operator control device 120 connected to an engine condition feed back unit 122 which, in turn, connects to coils 236 and 236', used only in the starting mode, to a series of Hall effect commutator segments 126, 128, 130 and 132. Each of the commutator segments controls a related SCR 134, 136, 138 and 140, respectively. Each SCR, in turn, controls a related solenoid actuated valve 54, 54', 54", and 54'", it being understood that a solenoid 54 will be provided for each cylinder of an engine with the illustrated system serving a four-cylinder engine.

3. The Engine

In the illustrated embodiment of FIGS. 7 and 8, the engine 78 is comprised of four cylinders 82, 82', 82", 82'" arranged radially in the same plane and oriented 90.degree. from one another. Each cylinder is provided with an associated piston 80 having a concave outer end, with the pistons of opposing cylinders connected by rigid piston rods 142 and 144. The rod 144 is formed with a transverse slot 146 to accommodate the rod 142 extending therethrough so that their reciprocating motions are not restricted by their intersections with one another. Each piston rod includes an eccentric 148 at their mid-points, these eccentrics being joined to each other and to a crank shaft 150 through pivot pins 152. The eccentricity of each eccentric 148 is equal to one-fourth of the piston stroke length. The mechanism of eccentrics and crank pins is enclosed in a crank case 154 to facilitate lubrication without contaminating the steam and also to shield the mechanism from the hot pistons. While the interaction between the piston rods introduces a side thrust, this thrust is reduced insofar as it is divided between two cylinders.

The configuration of the engine may be classified as a single-acting uniflow design wherein the water injected to the cylinder head is expanded to drive the piston and exhausted through ports 156 and 158 that are uncovered when the piston reaches the end of the power stroke. This design eliminates intake and exhaust valves as well as eliminating gland seals around the piston rods. As a result, the clearance volume is at a minimum, heat transfer surface is maximized and steam leakage is practically eliminated. Further, the configuration also will avoid mechanical complexity of valve gear and crossheads.

The engine requires a good seal against leakage plus minimum friction for the reciprocating piston. These requirements may be met by using a cylinder liner made of isotropic or pyrolitic graphite shrunk into a steel cylinder and employing piston rings faced with a material such as "Teflon" or the like. Pyrolitic graphite is characterized by a hard surface and serves as a good insulator. Furthermore, water on graphite provides a very low coefficient of friction.

Uniflow engines, because they exhaust steam at the end of the expansion stroke, always contain come residual steam during the compression stroke. This is true even for engines that exhaust to a condenser. Since this characteristic can reduce power during normal operation or can even damage the engine if the condenser should fail or be overloaded, it is desirable to provide an auxiliary exhaust valve 160 in the piston itself. This valve permits any residual steam to pass through the piston and out through the cylinder exhaust ports to the condenser. This valve may be actuated by means of a push rod timed to close before each injection of water takes place.

A further advantage of this design is that both sides of the piston are evacuated so that condenser vacuum does not retard the pistons.

The power output and thermal efficiency of the engine may be improved by higher steam pressures and temperatures and higher RPM. This may be brought about by a higher rate of heat flow into each cylinder. One way to achieve this would be to heat the face of the piston so that the flash boiler area would be doubled. For this purpose, a heat pipe (not shown) may be employed to transmit heat into reciprocating pistons. The heat pipe may extend between two connected pistons at each end of a connecting rod. At the point where the pipe passes through the crank case, the heat pipe may be enveloped by a stationary heat jacket with hot combustion gases flowing through it. Seals and insulation may be used to limit gas leakage and heat losses. The heat transfer would take place whether or not the piston was moving so that flash boiler temperatures may be maintained. The heat pipe is light in weight since it is hollow and contains only vapor, therefore, reciprocating masses are not greatly increased. Also, the heat pipe need not be a stressed member.

The convective heat transfer into the heat pipe may be improved by utilizing its reciprocating motion to create turbulence. It is also possible to again use surface combustion to add heat directly and eliminate any stagnant gas films.

4. Feed Water Preheater And Water Temperature Control

The function of the feed water preheater unit 94 is to heat the pressurized water supplied by the feed water pump 52 to a temperature slightly below the saturated liquid condition. The heat is provided by the combustion gases exhausting from the combination cylinder head flash steam generators of the engine. This also extracts the low temperature heat energy from the combustion gases and minimizes heat rejected with exhaust gases.

Insofar as it is desirable that the power plant respond instantly to any change in power demand, particularly where used for a prime mover, the reaction time of the preheater must be extremely quick. This will also shorten start-up time for a cold engine. In addition, compact size is desirable for obvious reasons and a minimum mass of metal to avoid a fly wheel effect. These requirements dictate a high rate of heat transfer per unit of water mass flow and per unit of preheater volume.

Referring now particularly to FIGS. 9, 10 and 11, there is illustrated a feed water preheater having the desirable characteristics of compactness and a high rate of heat transfer. The unit includes an outer casing 162 in the form of a thermally insulated pressure vessel formed from two concentric hemispheres joined at their maximum diameters to provide a hemispherical annular cavity 164. The use of hemispheres makes possible a stronger pressure vessel. The pressurized feed water flows through this cavity, entering through a hub 166 at the smaller diameter and leaving at the large diameter through a conduit 168 to the cylinder water injector 60.

Suspended inside the hemispherical cavity 164 is a structure comprised of an array of angularly spaced tubes 170, typically copper, extending along the length of the hemispherical arc. Hot combustion gases flow through these tubes from an axial inlet 172. In practice, half of the tubes carry entering gases while alternate tubes carry leaving gases. At the large end of the hemispherical cavities these tubes are connected by bent tubes 174 so that both the entrances and exits of the hot gas tubes are located at the small diameter hub of the structure. This structure is supported at the hub by an elastic seal 176 that prevents leakage and simultaneously permits small angular displacements in either direction of rotation. The seal preferably is made of a synthetic rubber or silicon rubber and is bonded between two conical surfaces in such a way that water pressure compresses the seal and helps prevent leakage. The proximity of the cold water entrance is used to keep the seal cool.

Two mechanisms may be employed to accelerate conductive heat transfer. For heat transfer between the water and the hot gas tubes the entire tube assembly is given a periodic angular oscillation within the cavity. This motion produces torsional shearing forces in the water which generates turbulent vortices. This eliminates the stagnant boundary layer which otherwise acts as a large resistance to conductive heat transfer. The oscillation may be powered by a rotating cam 178 bearing against a lever 180 extending from the hub or the tube assembly.

The second heat transfer accelerative mechanism relates to conduction between the hot gases and the tube walls. Each tube 170 contains a concentric core 182 (FIG. 11) constructed from a steel foil tube filled with magnesia powder. These cores match the contour of the copper tubes and leave an annular flow passage for the hot gases. The cores do not continue around the return bends. When the tube assembly is at rest, the cores move to the inside. Therefore the cores should be suspended from small leaf springs 184 that return the cores to the inside. As the tube oscillates the cores move in and out and displace the hot gas so that they circulate rapidly back and forth around the periphery. This generates turbulence which increases the conductive heat transfer.

In any power plant it is a desirable characteristic that the system be able to respond instantly to a demand for power. This is particularly true for vehicle engines and the like. A minimum amount of stored energy, therefore, should be made readily available to cover the reaction time or lag of the feed water pump and the preheater. This stored energy can be provided by an accumulator 186 located at the outlet of the preheater for the purpose of storing heated, pressurized, injection water. The accumulator may be located on the concave side of the hemispherical preheater. The quantity of stored energy should be kept to a minimum so that the accumulator itself will be compact in addition to considerations of safety and cold starting. In addition to enhancing the responsiveness of the system, the accumulator also suppresses water hammer generated by the sharp initiation and termination of each water injection cycle.

As has been indicated, the rate of combustion of the fuel within each integral flash boiler 10 is controlled by the surface temperature in the combustion side of the heat transfer boundary. The exhaust combustion gases leaving the flash boilers are then used to heat the feed water to the proper temperature for injection. A temperature control unit 188 for the feed water preheater 94 senses the temperature of water as it leaves the preheater. If the water temperature exceeds the desired limit, the combustion gases are diverted by a valve 190 into a by-pass line 192 around the preheater in response to the temperature control unit 188. Since the temperature sensor and its associated valve should be both reliable and fast acting, a liquid or vapor filled bellows may be used to advantage for this purpose.

To insure that the injection water is held at the design temperature level, a temperature sensor 210 monitors the water in the injector valve and, when its temperature cools below the minimum limit, opens up a leakage path through a recirculating line 212 back to the suction side of the feedwater pump. The resulting circulation pulls in freshly heated water from the preheater and returns the cooled water so it can be reheated. When water temperature in the injector pump reaches the maximum limit, the leakage stops. This controlled circulation insures that the injection water is maintained at the required condition.

Where there is no water flowing thru the feedwater preheater and the temperature exceeds the desired limit, the flow of hot gases through the preheater is diverted and also the oscillatory motion of the heating elements within the preheater is stopped.

5. Feed Water Pump & Pressure Control

The feed water pump 52 serves to maintain a designed pressure head in the feed water system and also provides the necessary rate of circulation. While various types of pumps may be employed for this purpose, a rotary vane, variable displacement pump is preferred. Such a pump automatically varies its displacement in response to a pressure-sensing device 194 and the pump typically is powered by an electric motor 196 or other means independent of the prime mover.

6. Governor & Overspeed Protection for The Engine

The power developed by the engine is controlled by varying the quantity of water injected This has the same effect as a cut-off type of control.

As engine having a falling torque characteristic could overspeed if the load were removed with the throttle open. In order to protect the engine, its speed may be regulated by means of a governor operating off the crank shaft, for example, or, alternatively, a speed sensing device 198 may be utilized to de-energize the motor 196 for the feed water pump in addition to stopping the burner blower 34 and shutting off the fuel supply.

7. Condenser System

A steam condensing loop is utilized in the system for two specific reasons. First, the large expansion ratio requires a low steam exhaust pressure. Secondly, it is desirable to recover and re-use the working fluid medium so that it need not be continually replenished.

Like the remaining part of the system, the condenser is also designed for compactness. By using the ejector jet condenser 96 in conjunction with the air-cooled water cooler 98 and the ejector pump 100, all condenser requirements can be met for the compact unit. The primary savings is in the elimination of the large surface tube condenser common to this type of system which surface condensers normally must be made large because they must handle vapor. The water cooler 98, however, handles the fluid medium only in the liquid state. Another reason for the reduced size is greater heat transfer effectiveness by means of forced convection. The water cooler 98 operates at approximately atmospheric pressure so that leaks are easily avoided. Furthermore, since the injector outlet is at atmospheric pressure, any entrained air can easily be removed. An electrically driven fan 200 blows ambient air over the tubes of the water cooler 98.

8. Water Injection Pump

The function of the injector pump 60 is to inject the correct amount of water into each cylinder at the proper instant. The single injector pump serves all four cylinders since the complete injection cycle for one cylinder requires less than a quarter of one crankshaft revolution.

As best shown in FIG. 14, the injector pump consists of a cylinder 202 with a reciprocating plunger 204 which is driven by a booster piston 206 in an integral booster cylinder 208. Since the booster piston area exceeds that of the injector plunger 204, the injector is actuated when the booster cylinder is connected to feedwater pump pressure.

The booster piston 206 is single-acting and uses a return spring 210. The pressure end of the booster cylinder 208 is connected to either feedwater pump pressure or suction through the solenoid-operated, 3-way valve 111. Each water injection cycle is initiated by the injection timing control which simultaneously actuates the booster cylinder 208 and opens the solenoid valve 111 that admits water to the proper cylinder. However, closing of the three-way valve and return of the injector to its initial position is carried out by an automatic switching system that is independent of the main control and is described below in connection with injection timing control.

In order to conserve heat energy, only the water supplied to the injector pump is passed through the feedwater preheater; however, water supplied to the booster cylinder is unheated.

The power output of this engine is governed by the quantity of water injected. The injector pump meters the quantity of water injected during each power stroke; as in diesel engine fuel injector, this is controlled by rotating the injector pump plunger 204 so that a helical passage 214 in its surface will by-pass water through a spill port when the desired quantity has been injected. The amount of plunger rotation is controlled by the operator demand lever typically employing a gear 216 connected to the plunger. It bears noting that this type of power control is in effect a cut-off type control which is more efficient than a throttle type of control.

Since water has low viscosity it is necessary to augment its lubricating qualities by treating the sliding surfaces of both injector pump and booster cylinder with Teflon or other solid lubricant and possibly using a stellite or a ceramic such as silicon carbide to provide a hard surface with good thermal conductivity.

9. Water Injection Timing Control

The timing of the water injection into each cylinder is optimum when the pressure build up timing is most effective in aiding the desired direction of rotation.

In addition to the normal operating modes for either forward or rearward rotation, there are two other types of situations which must be handled by the control; one is initiation of rotation when the engine is stationary, and the other is reversal of the engine that is already rotating.

The control system employed is an all-electric, digital type. This control uses the input of an operator demand lever 220 plus feedback information about engine rotation to select the proper injection timing. Each of the available timing settings are programmed in the form of commutators. The commutator segments 126-130 are "Hall effect" devices which are activated by a rotating magnet 222 (FIGS. 12 and 13). Together, the commutator and the rotating magnet select the cylinder which is ready for injection and simultaneously initiate the injection process. This type of control is simple, fast and reliable. Furthermore, it can initiate water injection even when the engine is stationary.

When the operator wants the engine to continue turning in either the forward or rearward direction, water injection is timed to occur when piston is close to top dead center. When the operator wishes to reverse the rotation of the engine, the control must advance the timing so that pressure builds up prior to TDC and reverses the piston direction. When the new direction is established the timing again switches to the optimum setting for that direction. When the operator wishes to start a stationary engine, the control must select the cylinder whose piston is in the best position for starting the engine and initiate water injection to that cylinder; when rotation is established, the timing switches to the optimum timing for that direction.

The complete control system comprises the operator demand lever 220, engine rotation feedback 224, commutator and rotating magnet 222, injector plunger return 116, SCR's 134-140 and solenoid valves 54.

The operator demand lever has three basic settings, namely, "forward", "stop" and "rearward". The "stop" setting corresponds to zero cut-off and if the lever is moved away from "stop" in either direction, the amount of cut-off (quantity of water injected) increases.

The engine rotation feedback signals direction and speed of rotation using a DC electric generator 226 which is geared up to magnify the speed. The magnitude of current reflects speed and the direction of current reflects direction of rotation. This signal actuates a three-position switch 228 to a "forward", "rearward" or "stationary" position.

The operator demand lever and the engine rotation feedback actuate electric switches which are in series with each other. The various combinations of switch positions provide a total of six different outputs each of which activates one particular water injection timing as programmed by a set of commutator segments; there being one segment for each steam cylinder.

The construction of the commutator consists of a stationary annular disk or sleeve 230 containing the solid state, "Hall effect" segments 126-130 at the desired angular positions. Each of the six sets of commutator segments is mounted in the same disc or sleeve 230. Instead of a carbon brush, this commutator features a rotating permanent magnet 222 plus two electromagnets 232 connected through slip rings 234. All of these magnets have a horse shoe configuration so that the pole faces face each other through the thickness of the annular disc or sleeve 230. The permanent magnet has a pole face that spans about the same arc as a single "Hall effect" segment 126, however, each of the electromagnets 232 span a 90.degree. arc which extends out in opposite directions from the center line of the permanent magnet face.

The control system selects the proper water injection timing by passing a current through the segments of the appropriate commutator. The current is led to that particular commutator by the combination of switch settings resulting from both the operator demand unit 120 and the engine condition unit 122.

The operation of the commutator is as follows: when one of the Hall effect segments is acted upon by magnetic flux, a small DC current is induced in that segment at right angles to the initial current direction. This induced current is used to fire an associated SCR 134-140 which then conducts current to the coil of one of the solenoid valves 54 that admits water injection to the selected corresponding engine cylinder and also energizes an associated coil for the three-way valve 111 thereby actuating the booster 112 and injector 60. Using a commutator provides a very direct way to determine which cylinder is in condition for water injection and, of course, a commutator can easily give the proper sequence of water injection for either direction of rotation.

The solenoid control valve 111 employed is a normally closed three-way poppet type valve. Using this combination valve eliminates the possibility of having both valves open at the same time and short circuiting the pump. This construction is not subject to external leakage, does not require lubrication and is easy to open with the solenoid.

An SCR has a characteristic that once its control electrode initiates conduction, the electrode no longer controls. Therefore, to stop conduction it is necessary to interrupt, momentarily, current flow through the SCR. In this control circuit, the SCR will continue to hold open the solenoid valves 54 and 111 until the end of the injection stroke when the injector plunger opens the switch 116 that interrupts the SCR current. When this happens, the normally closed three-way solenoid valve 111 closes and returns the booster piston to its initial position. The booster piston then closes the switch 116 that was opened by the injector plunger and the system is ready for the next water injection cycle. It should be noted here that the signal from the Hall effect commutator segments to the control electrode of the SCR is very short because of the narrow width of the permanent magnet pole face, therefore, even if the engine is rotating slowly, the control signal should have disappeared before the circuit is again completed.

When starting an engine that is stopped, there are also electromagnetic coils 236 and 236' in the circuit that extends the pole face to span a 90.degree. arc, and are used for starting a stopped engine, the crank of which may be at any angular position. One coil is for forward, the other for rearward rotation. The coils are arranged so that their leading edges have approximately the same angular position relative to the crank pin. This feature makes it possible to start a stopped engine because, even if the crank pin is not in the optimum position for water injection, the 90.degree. span will automatically initiate water injection in the next best cylinder.

10. Accessory Drive System

The powerplant accessories include the feedwater pump, jet condenser pump, radiator fan, burner blower, ignition system and oil pump. All these accessories may be driven by electric motors which may be energized by a storage battery and electric generator combination.

The electric generator may be driven by the steam expansion engine or by a separate small steam turbine.

11. Rotary Positive Displacement Engine With, Integral Flash Steam Generator

The Wankel configuration is used here merely to typify the positive-displacement, rotary engine. This type of engine offers high power output in a compact, lightweight package. In addition, it offers the advantages of a reciprocating steam engine such as high static torque and reversability.

The Wankel configuration FIGS. 16 and 17 includes a three-lobed rotor 238, rotating within an elliptical stator 240. Since a steam engine involves only the expansion process, it is possible to use two angular positions on the stator for water injectors 42' and heat all three faces of the rotor for steam generation. The engine can then deliver six power pulses during each revolution and is, in effect, a "uniflow" engine. By altering the positions of water injection and steam exhaust, this engine is also reversable. No valves are required except possibly to close unneeded exhaust ports 242 on a reversing engine.

Fuel-air mixture flows in through one end of a rotor shaft 244 and combustion products flow out the opposite end. The airflow into the shaft is supplied by a blower through an ejector nozzle 246 that matches the end of the shaft with a slight clearance. The ejector action entrains the gaseous fuel through the clearance. A rotating seal 246 on the shaft prevents leakage air from diluting the entrained gas flow. Power take-off is from the cool end of the shaft as by a gear 248.

Inside the rotor, there are plenum chambers 250 and combustion chambers 252 for each face of the rotor. The inside of each rotor face is heated by impingement surface combustion and steam is generated by injecting water against the outer surfaces of the rotor at the minimum volume position.

Only the lobes of the rotor contact the surface of the stator. These lobes are insulated from the hot faces and from the hot products of combustion and contain seals 254 that prevent leakage of steam between the expansion chambers. These seals slide against the relatively cool surface of the stator.

The control of water injection timing for this engine is closely similar to that for the reciprocating steam engine except that reversing the engine involves alteration of the angular positions for water injection and steam exhaust. This may be achieved by providing separate systems for forward and reverse and switching to the appropriate system.

In all other respects, this engine could utilize the same systems as used by the reciprocating engine configuration.

12. Turbine With Integral Flash Steam Generator

Referring now to FIG. 15, there is illustrated a further modification of the invention and in this embodiment a flash steam generator 10' is incorporated into a steam turbine 256.

A steam turbine provides a very compact expansion engine capable of utilizing a large expansion ratio. It also has a favorable torque characteristic except under static conditions. However, it rotor 258 usually turns at high speeds and requires a speed reducer for most applications. A turbine also requires a transmission for reversing operation.

A flash steam generator 10' can take a variety of forms. One that would be compatable with a steam turbine is an annulus shaped like a split torroid with steam generation on the convex side. The steam outlets through steam nozzle blades 260. Since water injection is continuous, water injector spray tubes 42' can be of very simple design and neither an injection metering pump nor a timing control system is required.

The feedwater supply system, condensing system and accessories drive would be quite similar to that for the reciprocating steam engine.

While the foregoing system and its components have been described for particular application in connection with a steam engine and steam system, obviously certain of the components have utility apart from the overall system such, for example, the feed water preheater, the timing system, etc. Also, the reciprocating engine itself in certain aspects, can be converted for use with a diesel engine, for example. Likewise the timing control and the hydraulic injector pump are adaptable to diesel engines.

Claims

Having thus described the invention what I claim and desire to obtain by Letters Patent of the United States is:

1. A flash steam generator, comprising

a. a wall of solid, refractory and thermally conductive material providing a heat transfer boundary,

b. means for directing a fluid medium in the form of a thin film against one side of said wall,

c. means for heating the other side of said wall to a temperature sufficient to initiate surface combustion, and,

d. means including at least one nozzle in close proximity to said other side for delivering a combustible fluid fuel in the form of a jet against said other side of said wall at a rate sufficient to maintain surface combustion on said other side,

e. said one side of said wall including means for producing capillary attraction of said medium.

2. A flash steam generator according to claim 1 in combination with an expansion prime mover.

3. A flash steam generator according to claim 1 wherein said one side of said wall is convex and the other side is concave.

4. A flash steam generator according to claim 1 wherein said means for directing a fluid medium includes a spray tube formed with a plurality of orifices in closely spaced relation to the one side of said wall and feed means connecting said tube to a source of pressurized liquid.

5. A flash steam generator according to claim 4 wherein said spray tube includes a pair of resilient parallel conduits extending lengthwise within said tube across said orifices, restraining means engaging said conduits, means connecting said conduits to a source of pressurized fluid for internally pressurizing said conduits and maintain a seal across said orifices until the pressure within said tube increases sufficiently to collapse said conduits and open said orifices.

6. A flash steam generator according to claim 1 wherein the fluid directing means includes a plurality of second nozzles each defining a narrow clearance with said one side to form a thin film of fluid medium therebetween.

7. A flash steam generator according to claim 6 wherein said one side of said wall is formed with spiral grooves opposite said second nozzles.

8. A flash steam generator according to claim 6 wherein each of said second nozzles is formed with a concave end opposite said wall and an apertured diaphragm is mounted across said concave end.

9. A flash steam generator according to claim 1 wherein said wall includes a catalyst for intensifying the combustion reaction.

10. A flash steam generator according to claim 2 wherein said prime mover is a reciprocating piston engine.

11. A flash steam generator according to claim 2 wherein said prime mover is a turbine.

12. A flash steam generator according to claim 2 wherein said prime mover is a rotary, positive displacement engine.

13. The method of generating steam from a fluid medium on one side of a heat transfer boundary, comprising the steps of

a. directing said fluid medium into the form of a thin film against said one side,

b. heating the other side of said wall to a temperature sufficient to produce surface combustion thereon, and,

c. directing a flow of combustible fluid fuel in the form of a jet against said other side at a rate sufficient to maintain surface combustion thereon.

14. The method of claim 13 including the step of catalyzing combustion at the surface of said other side.

15. The method of claim 13 including the step of forming said medium into a spiral path against said one side.