Duplex free-piston engine with enhanced cooling system

Abstract

A duplex free-piston engine with a cooling system comprises a free-piston linear generator (1) and has at least two cold cylinders (9, 10). These cylinders (9, 10) are connected via pipes (11, 12) to the right and the left coolers (13, 14), respectively. The coolers (13, 14) are connected to a duplex valve (16) located in a housing (15) between the coolers (13, 14). This duplex valve (16) is also connected to the left and the right regenerators (25, 26), each of which has a porous structure made of sintered thin metal meshes. Each regenerator (25, 26) is further connected to a heater (27) via a lower left manifold (28) and a lower right manifold (29). The heater (27) consists of left and right tubes (30, 31), which are connected to an upper manifold (32)..

Description

[0001] Title of the Invention

[0002] Duplex free-piston engine with enhanced cooling system.

[0003] Technical Field

[0004] The invention relates to external combustion engines, namely, to free-piston Stirling-like systems with valve-controlled working fluid and separate regenerators.

[0005] Prior Art

[0006] Traditional free-piston Stirling engines with one hot and one cold chamber are known to achieve a real efficiency level of 30-35%. However, the absence of a clear cut-off of the dead volume, a shared hot and cold zone without valves, and the impossibility of independent control over the hot and cold working fluid flows lead to additional thermal energy losses.

[0007] A Stirling engine is known, comprising at least one displacer cylinder, in which a displacer piston moves, separating the cylinder volume into hot and cold cavities. Herein, the heater, regenerator, and cooler are installed sequentially in the manifold connecting the hot and cold cavities. The cooler comprises a cylindrical cooling jacket filled with cooling fluid and enclosing the cylinder with the piston, with two annular collectors connected to the fluid inlet and outlet pipes. The cooler, designed as a "tubein-tube" type, contains annular channels formed by sleeves with internal apertures, evenly distributed along the cylinder diameter in the cooling jacket, through which the working fluid circulates. RUNo. 2100634, Published: 27.12.1997.

[0008] A disadvantage of this device is the insufficient heat exchange of the cylindrical walls of the cooler channels with the working medium, which reduces the engine's efficiency. A second disadvantage is that the displacer piston periodically enters the hot zone, which leads to additional requirements for seals and increases energy consumption due to friction.

[0009] A Stirling engine is known, comprising at least one cylinder with an upper cover¬ heater, facing an external heat source, a displacer piston and a power piston, which are placed in the cylinder and separate its volume into a hot cavity, a cold cavity, and a buffer cavity, a cooler, a regenerator, and a heater, installed sequentially in the manifold connecting the hot and cold cavities, wherein the heater is made in the form

[0010] Iof a disk with profiled channels placed therein, one part of which connects the hot cavity to the periphery of the disk, which is connected to another part of the channels connecting the periphery of the disk to the regenerator, wherein the heater channels are made in the form of a cylindrical tube truncated along its generatrix, with its larger surface facing the heat source. RU No. 2008489, Published: 28.02.1994.

[0011] A disadvantage of this engine is the necessity of using a disk with channels in the heater, which has great stiffness and thickness to withstand high pressure of the working fluid (gas) inside. A second disadvantage is that to ensure the necessary heat flow, it is necessary to use large dimensions for the heater disk, which complicates the use of this design in multi-piston engines. A third disadvantage is the low heat transfer efficiency in the cooler, which contains a channel where the working fluid is cooled by cooling the walls with an external cooler jacket with cold coolant circulating therein.

[0012] No technical solution analogous to the proposed one, solving the same problem and having the same structural features, has been identified from the prior art.

[0013] Definitions of Terms

[0014] Working fluid of the system is helium gas.

[0015] Bottom Dead Center (BDC).

[0016] Top Dead Center (TDC).

[0017] Internal Combustion Engine (ICE).

[0018] Disclosure of the Invention

[0019] The basis of this invention is the task of creating a reliable device with increased efficiency, capable of converting thermal energy into mechanical and electrical energy through the direct use of a modified thermodynamic Stirling-Ericsson cycle, the design of which would ensure the expansion of technological capabilities due to the reverse use of this cycle for creating cryogenic devices with high efficiency.

[0020] This objective is achieved in a duplex free-piston engine with an enhanced cooling system, which includes a free-piston linear generator, and has at least two cold cylinders, namely, the left and the right ones, each having its own pistons, and neodymium magnets fixedly located on the rod between the pistons with the possibility of moving conjointly with them inside a stator, on which coils with windings areplaced, and on the generator casing, Hall sensors are fixed, which determine the position of the magnets, wherein the right and left cold cylinders are connected by means of pipes to the right and left coolers, respectively, which are located inside a casing that has pipes for supplying cooling water, wherein the coolers are connected to a duplex valve system, which is located in the casing between the coolers and has a rod with two "plates" designed for two flows of working fluid from the left and right sides, has solenoid coils, a neodymium magnet for electrically driven rod movement, stepper motors for smooth adjustment of the rod's position, moreover, the valve is connected by means of pipes to the left and right regenerators, which have porous structures made of sintered thin metal meshes inside, and each regenerator is connected to the heater by the lower left manifold and the lower right manifold, wherein the heater consists of left and right tubes connected to the upper manifold 32.

[0021] The presence of coolers that remove heat from the cylinders, and additionally, the cylinders can have external air or water cooling up to 40-60 °C, allows for compressing gas at -40-60 °C that is close to an isothermal process.

[0022] The transfer of mechanical energy from piston oscillations without crank mechanisms, by simple variable induction of magnets in coils, as provided by this invention, allows for achieving higher efficiency. External air or water cooling of the piston cylinders to 40-60 °C allows the pistons to operate in the cold zone and, at the same time, to use various seals, for example, Teflon or rubber seals with low friction.

[0023] The presence of a duplex valve system prevents gas from "hanging" in intermediate volumes. During compression, the heater is cut off, minimizing dead volume and making compression in the cold zone almost isothermal. At maximum compression, the duplex valve switches, connecting the regenerator and heater to the cooler, and the cold gas, passing through the regenerator, collects part of the thermal energy accumulated in the regenerator meshes from the previous cycle. Later, when the gas returns from the heater to the cold chamber, it passes through the same regenerator, returning heat and thus reducing final losses.

[0024] Thus, the duplex free-piston engine with an enhanced cooling system, constructed under this invention, ensures a reduction in compression costs due to isothermalcompression via the presence of cooling and the design of the duplex valve system, as well as due to isobaric heating, which is close to Ericsson process, where gas is heated at almost constant pressure. Expansion in the heater reduces heat exchange losses. Furthermore, the presence of free-piston transmission, minimal mechanical friction, easy auto-oscillatory stabilization, as well as the use of multiple regenerators contribute to reducing these losses.

[0025] All this ensures an increased thermodynamic efficiency (COP) of 43-45% instead of the usual 30-35%, which will lead to an increase in overall electrical efficiency in the range of approximately 36-42%.

[0026] Another advantage of the claimed technical solution is its flexible scalability, allowing the use of two, four or eight cylinders with the same number of heat exchange units. Due to reduced friction losses, the engine operates without the use of lubricants. The aforementioned thermodynamic indicators, given a high-quality regenerator, minimal losses in mechanical components, and an efficient linear generator, are competitive - even in niches where standard ICE-electric generators typically have an overall electrical efficiency of 25-35%.

[0027] The proposed design has the capability to operate in a reverse cycle, i.e., as a refrigerator in cryogenic installations.

[0028] The technical result is an increased efficiency to 43-45%, due to isothermal compression in the cold zone and isobaric heating of the heater to high temperatures of ~850 °C, as well as the design of the cut-off duplex valve, which eliminates "dead" volume.

[0029] The system is designed for efficient conversion of the temperature difference of the working fluid between the heater and the cooler into mechanical and electrical energy through a modified Stirling-Ericsson cycle.

[0030] Thus, all of the above allows concluding that the claimed technical solution meets the criteria of "novelty" and "inventive step".

[0031] The proposed technical solution has a reliable and quite compact design, very convenient in operation.Below is a description of a specific embodiment of this invention with references to the appended drawings.

[0032] Brief Description of Drawings

[0033] Fig. 1 - schematically depicts a duplex free-piston engine with an enhanced cooling system, constructed under this invention, frontal cross-section.

[0034] Fig. 2 - shows a top view.

[0035] Fig. 3 - shows a side view.

[0036] Fig. 4 - shows a multi-block system (8 pistons) in a square layout.

[0037] Fig. 5 - shows a multi-block system (8 pistons) in a parallel layout, front view. Fig. 6 - shows a multi-block system (8 pistons) in a parallel layout, side view. Best Mode for Carrying Out the Invention

[0038] The free-piston engine with an enhanced cooling system, constructed under this invention, includes a free-piston linear generator 1 (Fig. 1), which comprises two pistons 2, 3 with neodymium magnets 4, located on rod 5 with the ability to move inside stator 6, where coils 7 are placed.

[0039] The position of the pistons is tracked by Hall sensors 8, located near the magnets 4.

[0040] The generator 1 has cold cylinders - the right one is number 9 and the left one is number 10 (Fig. 1), each with its own piston, respectively, 2 - the right one and 3 - the left one, which are connected to their respective cooler by means of pipes 11 (right pipe) and 12 (left pipe). Pipe 11 is connected to cooler 13, and pipe 12 is connected to cooler 14. Between coolers 13, 14, in the housing 15, the system of duplex valve 16 is located, which has rod number 17 with two "plates" 18, 19 for two flows of working fluid (gas), namely, from the left and right sides (Fig. 1). Solenoid coils 20 and a neodymium magnet 21 provide electrically driven movement of rod 17. Stepper motors 22 allow for precise adjustment of the rod 17 position for smooth opening and closing of the system of duplex valve 16. Pipes 23, 24 are connected to the system of duplex valve 16, connecting the valve 16 with two regenerators 25 (left) and 26 (right), which inside have porous structures made of sintered thin metal meshes that store heat from the hot gas of the first half-cycle and return it to the cold gas in the next half-cycle. Each regenerator 25, 26 is connected to the heater 27 by a lower left manifold 28 and a lower right manifold 29. The heater 27 consists of left tubes 30 and right tubes 3 1 , which are connected to the upper manifold 32. Due to the use of refractory material Inconel, the temperature of the heater 27 reaches -850 °C with external combustion, burner, solar concentrator, etc. Coolers 13, 14 are located inside the casing 33 with pipes 34, 35 for water supply to these coolers. The temperature of the coolers is maintained at 40-60 °C. The piston cylinders can have external air or water cooling up to 40-60 °C. The working fluid of the system - helium gas - is cooled to -40-60 °C.

[0041] When using four pairs of pistons, two variants of layout arrangement are possible: 1. In the square layout (Fig. 4) - where the cylinder and piston blocks are placed and rigidly connected at the vertices of the square, opposite blocks are in one phase, the other two are in anti-phase. Two coolers 13, 14, one system of duplex valve 16, two regenerators 25, 26, and one heater 27 remain. Minimum vibrations, high total power, and efficiency remain at 43-45%.

[0042] 2. All four blocks are rigidly connected in parallel in the form of a single structure tightly fitted to each other (Fig. 5), the movement of two pistons will be opposite to the movement of the other two pistons, i.e., opposite blocks are in one phase, the other two are in anti-phase. Two coolers 13, 14, one system of duplex valve 16, two regenerators 25, 26, and one heater 27 also remain, which significantly reduces vibration loads, provides high total power, and efficiency remains at 43—45%.

[0043] Operation of the Duplex Free-Piston Engine with Enhanced Cooling System Initial state.

[0044] Piston 2 in the right cold cylinder 9 and piston 3 in the left cold cylinder 10 are in a certain average position (Fig. 1). The working gas, helium, at a pressure of approximately 150 bar, is present throughout the system, particularly in coolers 14 and 13 at a temperature of 40-60 °C.

[0045] Pistons 2, 3 with neodymium magnets 4 are the moving masses of the free-piston linear generator inside the stator 1 , with coils 7. The entire assembly can move in a "left-right" direction within the cold cylinders 9, 10. The position of the pistons is tracked by Hall sensors 8, which transmit signals to the electronic control unit.Compression Phase.

[0046] In the first phase, the right cold cylinder 9 is blocked from the side of the right regenerator 26 by the duplex valve 16. The left cold cylinder 10 is open to the left regenerator 25. The piston cylinders can have external air or water cooling up to 40-60 °C. The gas in the right cold cylinder 9 is compressed by piston 2 from 150 to -165-170 bar, depending on the calculated volumes of the piston's working stroke, while the heat of compression is dissipated by the water cooler 13, that is, the water circulates through pipes 34 in the casing 33. Compression in the right cold cylinder 9 occurs almost isothermally, as the temperature is maintained at approximately 40-60 °C.

[0047] Expansion Phase

[0048] Simultaneously, in the left cold cylinder 10 (Fig. 1), the path is open through pipe 24 to the left regenerator 25 and further to the heater via tubes 30, 31, lower manifolds 28, 29, and upper manifold 32. High-pressure gas at a temperature of approximately 850 °C from the heater pushes piston 3, forcing it to move in its working stroke, i.e., expansion occurs, and mechanical energy is transferred to the generator with stator 6 and coils 7. Piston 3 moves to the bottom dead center (BDC). During the movement of pistons 2, 3 together with magnets 4, current is induced in coils 7.

[0049] Duplex Valve Switching

[0050] When piston 2 reaches the top dead center of the right cold cylinder 9, the pressure reaches 165-170 bar at 40-60 °C, thanks to the kinetic energy that the pistons with neodymium magnets received from the working stroke. Conversely, as piston 3 in the left cold cylinder 9 reaches the bottom dead center, the pressure drops to approximately 150 bar at 850 °C. The electronic control unit, based on signals from Hall sensors 8, sends an impulse to the solenoid coils 20 of the duplex valve 16 to close the left side and open the right side.

[0051] Further Thermodynamic Conversion

[0052] After switching valve 16, the gas in the left cold cylinder 10 is cut off and begins to be compressed by piston 3. The gas from the right cold cylinder 1, compressed to 165-170 bar and cooled to 40-60 °C, passes through pipe 23 into the right regenerator26, where first it is heated by the heat accumulated in the previous cycle, and then it enters the heater through tubes 31, 30, manifold 29, upper manifold 32, and is additionally heated by an external heat source to 850 °C.

[0053] The pressure in the heater can instantaneously rise to 180-200 bar in the heater, manifolds 29, 28, 32, and tubes 30, 31, as a result of which the pressure force is transmitted to the right piston 2 which is at BDC.

[0054] During the almost isobaric heating and expansion, the thermal energy of the gas is converted into the kinetic energy of the pistons 2, 3 with neodymium magnets 5, which induce current in coils 7. At the end of this phase, piston 2 is at BDC, and piston 3 is at TDC.

[0055] The next switching of valve 16 again changes the directions of the flows: the left cold cylinder 10 releases the compressed cold gas to the left regenerator 25 and heater 27, while the right cylinder 9 performs compression, and the process is repeated.

[0056] Thanks to the alternating cut-off of the dead volume in heater 27 and regenerators 25, 26, the compression of helium occurs isothermally in coolers 13, 14, and heating occurs almost isobarically. This corresponds to the modified Stirling-Ericsson cycle, which allows achieving an efficiency of 43-45% at a temperature difference between the cold and hot parts, for example, 40 °C and 850 °C.

[0057] The free-piston design of the engine does not require complex mechanical transmissions, namely, crankshafts, connecting rods, or bearings, which reduce friction losses. Since pistons 2 and 3 are in the "cold" parts, cylinders 9 and 10 with T-40-60 °C, Teflon rings can be used for sealing, and lubrication can be entirely avoided, minimizing friction losses.

[0058] Use of the Reverse Modified Stirling-Ericsson Cycle (Fig. 1)

[0059] If the reverse cycle, i.e., cooling, is applied, the working chamber of the heater 27, through expansion processes, can absorb heat from the cooled object and, during compression, transfer this heat to coolers 13, 14 and cylinders 2, 3. The latter, in turn, transfer heat through heat exchangers in coolers 11, 12 to water or another medium. The expansion of gas in the expansion chamber of the heater 27 causes a temperature drop to cryogenic levels depending on the design features.Thus, the operation of the duplex engine is reduced to alternating compression of helium in one cold cylinder 9 and its expansion in the heater 27 and the other cylinder 10 at high temperature, with flow control through the duplex valve 16, two regenerators 25 and 26, and one heater 27. Pistons 2 and 3 oscillate freely according to the compression / expansion phases, converting thermal energy into mechanical energy and further into electrical energy in the linear generator 1. Thanks to such an organization of processes, the engine can achieve a thermodynamic efficiency of 43-45% and an electrical efficiency in the range of approximately 36-42%, which is higher than in typical standard ICE- electric generators, which usually have an overall electrical efficiency at the level of 25-35%. Various engine configurations are possible: two-, four-, and eight-cylinder (the latter in a square layout (Fig. 4) and parallel layout (Fig.

[0060] 5) with opposed motion of some piston pairs relative to others, for best balancing and vibration reduction).

[0061] Due to their movement in cylinders 9, 10, compression and expansion processes are simultaneously realized. In addition, there are two cold cylinders 9, 10 and one heater 27, between which two regenerators 25, 26 are located. Between each regenerator 25, 26 and the cold cylinders 9, 10, system of duplex valve 16 with an electromagnetic solenoid or other drive is installed, controlling the flows of the working gas. The working gas, helium, is compressed in the cold cylinder at a temperature of approximately 40-60 °C. Simultaneously, the second piston performs an expansion working stroke under increased pressure. Phase change occurs alternately by switching the system of duplex valve 16, which ensures a modified Stirling-Ericsson cycle with isothermal compression and almost isobaric heating, thereby achieving increased efficiency. As a result of such organization, the engine operates in an auto-oscillating free-piston mode. In each half-cycle, one piston performs a working stroke, and the other performs compression. Auto-oscillations are stabilized due to the elastic properties of the gas, pressure difference, piston inertia, and controlled switching of the duplex valve 16. The mechanical energy of piston oscillations is directly transmitted, without crank mechanisms, to the kinetic motion of neodymium magnets, which move and excite EMF in the stator coils.Hall sensors 8, installed near the pistons, record the position of the magnets and transmit signals to the electronic control unit, which precisely switches the system of duplex valve 16, implementing the modified Stirling-Ericsson cycle. Due to minimized friction, through the absence of crankshafts, bearings, and connecting rods, the engine has higher efficiency.

[0062] Since the moving part of the pistons is in the cold section of the engine, seals in the form of Teflon rings can be used on each piston, which improves friction properties and reduces mechanical friction. Also, lubrication can be avoided, which reduces operating costs.

[0063] Thus, the enhanced cooling system reduces requirements for seals and lowers frictional energy costs and increases efficiency, due to all moving pistons, along with the linear generator, being located in the cold zone. The use of the original duplex valve leads to optimal control of the working fluid (helium gas) flows in thermodynamic phases, which implements the modified Stirling-Ericsson cycle and reduces "dead" volume in the cycle, which also significantly increases efficiency. The use of refractory material Inconel for the heater tubes and manifolds, which withstands a prolonged temperature of -850 °C at a pressure of up to 20 MPa, significantly increases the temperature difference between the heater and the cooler, which also increases the thermodynamic efficiency.

[0064] The proposed design has a thermodynamic efficiency of 43-45% and an electrical efficiency in the range of approximately 36-42%, which is higher than typical standard ICE-electric generators, which usually have an overall electrical efficiency at the level of 25-35%. Therefore, the claimed technical solution in the form of a duplex free-piston engine can be competitive in niches where ICE-electric generators are used.

[0065] Industrial Applicability

[0066] The proposed technical solution can be most successfully used as an autonomous power source, for heat utilization in industrial cogeneration systems, and in a reverse cycle in cryogenic coolers for infrared sensors, quantum computers, etc. There are also other areas of application where it is necessary to convert heat of various origins, forexample, solar, biofuel, waste into mechanical or electrical energy with an increased thermodynamic efficiency of 43—45% and electrical efficiency of 36-42%.

[0067] The proposed technical solution provides for the use of two cold cylinders and one heater, as well as the use of a duplex valve system, which makes it possible to synchronize the compression / expansion phases and control the working gas flow, minimizing energy losses. No technical solution analogous to the proposed one has been found in public sources that would simultaneously provide free-piston generation, valve cut-off, minimal dead volume, and the use of two cold cylinders and one heater with a possible efficiency of 43-45%.

[0068] This device can use various types of thermal energy, namely, solar, geothermal, from biofuels, industrial waste, and can be applied in industrial cogeneration systems, reducing harmful environmental impact by reducing emissions. This makes the device more environmentally friendly and sustainable compared to known analogues.

[0069] The application of the proposed technical solution makes it possible to create autonomous power sources that obtain electricity from various heat sources, namely, solar, geothermal, nuclear, biofuels, and waste. When using the reverse modified Stirling-Ericsson cycle, by connecting the device to electricity, it can be used as a cryogenic machine for cooling infrared sensors, quantum computers, etc. Also, a cryogenic device can be made in a reduced form, for example, micro-scale for portable use.

[0070] In addition, the use of the invention will contribute to reducing the negative impact on the environment by reducing harmful emissions, which makes it more environmentally friendly compared to existing analogues.

Claims

ClaimsA duplex free-piston engine with an enhanced cooling system, which includes a free-piston linear generator 1 (Fig. 1), and has at least two cold cylinders 9, 10, namely, the left one is number 10 and the right one is number 9, each having its own pistons 3, 2, respectively, and neodymium magnets 4 non-fixedly located on a rod 5 between the pistons 3, 2 with the possibility of moving conjointly with them inside a stator 6, on which coils 7 with windings are placed, and on the generator casing, Hall sensors 8 are fixed, which determine the position of the magnets, wherein the right 9 and left 10 cold cylinders are connected by means of pipes 11, 12 to the right 13 and left 14 coolers, respectively, which are located inside a casing 33 that has pipes 34, 35 for supplying cooling water, wherein the coolers 13, 14 are connected to the system of duplex valve 16, which is located in the casing 15 between the coolers 13, 14 and has a rod 17 with two "plates" 18, 19 designed for two flows of working fluid from the left and right sides, has solenoid coils 20, a neodymium magnet 21 for electrically driven rod movement 17, stepper motors 22 for smooth adjustment of the rod 17 position, moreover, by means of pipes 23, 24 the duplex valve system is connected to the left 25 and right 26 regenerators, which have porous structures made of sintered thin metal meshes inside, and each regenerator is connected to the heater 27 by a lower left manifold 28 and a lower right manifold 29, wherein the heater 27 consists of left 30 and right 31 tubes, which are connected to the upper manifold 32.

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