Two-stroke expansion engine for converting thermal energy into mechanical energy, and method for said conversion

Abstract

The present invention aims to convert thermal energy in general, and solar energy in particular, into mechanical and electrical energy by means of a closed circuit of water heated to below 100°C to act as a hot-water reservoir. A two-stroke expansion engine is disclosed, comprising a device for converting heat into work based on a two-stroke cycle. During said first stroke of the engine, hot water is sprayed through the feed duct (6) onto the air contained in a heat exchanger (10) by means of a hot-water pressurising valve (9), thereby promoting heat exchange between the hot water and the air. This process results in an increase in the air pressure within the heat exchanger (10), which is transmitted to a pressure cylinder (11), thereby driving a piston (18) while said air expands. During the second stroke of the engine, an air pressurising valve (8) introduces new air into the heat exchanger (10) through the air line (7), while the air and water used during the previous stroke are directed to a separator (14), wherein the air is released into the atmosphere and the water is returned to the closed heating circuit. The water used as the working fluid is heated in the heater (4) by capturing solar energy (heat may be supplied from other sources) and is stored in the hot-water reservoir (2). The mechanical energy produced by the piston (18) drives an electrical power generator (21).

Description

"TWO-STROKE EXPANSION ENGINE FOR CONVERTING THERMAL ENERGY INTO MECHANICAL ENERGY AND METHOD FOR SAID CONVERSION" FIELD OF THE INVENTION

[0001] The present invention falls within the technological field of energy generation from thermal sources, presenting innovative and efficient solutions for converting heat into usable energy. It relates to a two-stroke expansion engine that aims to transform thermal energy in general, and solar energy in particular, into mechanical and electrical energy from a closed circuit of water heated slightly below 100°C to act as a hot water reservoir. Furthermore, the present invention relates to a system and method for generating energy using said engine. FUNDAMENTALS OF THE INVENTION

[0002] Traditionally, the techniques available for converting heat into work and electricity involve the use of machines such as steam turbines; Stirling engines; Rankine organic cycle turbines; and / or Peltier-Seebeck effect plates.

[0003] However, steam engines and turbines require high temperatures (>100°C) and are therefore not suitable for the purpose described above, as they depend on a higher temperature of the hot water reservoir. Stirling engines heat and cool air through the respective hot and cold walls of the same container. Let T a and T b the temperatures of the walls of a Stirling engine, where T a represents the temperature of the hot wall and T b the one with the cold wall.

[0004] Heat transfer from walls to air occurs through two distinct processes: radiation and conduction. Radiation <p r It is governed by Stefan-Boltzmann law. <p r = a. (T - Tb ), where cr is Boltzmann's constant. The conduction <p c , on the other hand, is proportional to the temperature difference: (p c = C. (T a - T b ), where C is a constant that depends on the thermal conductivity of the materials involved. It follows from these two formulas that radiation is the process that prevails at high temperatures: < >

[0005] where AT = (T a - T b ~), while conduction is the process that prevails at low temperatures: B.C? c = C. AT

[0006] Consequently, to operate at low temperatures, a Stirling engine would fundamentally depend on thermal conduction. However, it is well known that air is a poor conductor of heat. This problem will be greater the larger the dimensions of the Stirling engine and therefore the greater the mass of air to be traversed by the heat. It follows that large Stirling engines are not suitable for working at low temperatures, typically below 100°C.

[0007] Rankine organic cycle turbines present a promising technology, but still face some challenges to their wider acceptance. The organic fluids used to drive the turbines, such as hydrocarbons or siloxanes, are often very expensive, toxic, or aggressive to the turbines themselves and the environment. The interaction between the organic fluids and other components must be carefully considered to avoid corrosion, degradation, and other problems that can compromise the safety and economic potential of the system, increasing operating costs and making the installation of these systems unfeasible in various types of power generation plants.

[0008] Peltier-Seebeck effect plates exhibit low efficiency, high cost, require a large temperature difference, and present challenges in thermal management, in addition to difficulties in adequately insulating the plate ends. This limits their viability for large-scale energy production.

[0009] These technical limitations create opportunities for innovations in the field of energy generation that prove to be more versatile, safe, and adapted to modern demands for practicality and sustainability. In this sense, some solutions and technologies have already been developed using these principles:

[0010] Document US2010218741 discloses a heat engine comprising a cylinder and a piston and an insulated heat battery including at least one thermal mass, such as the engine block itself, for storing and retaining heat in order to increase or cause the expansion of the fluid within the cylinder and actuate the piston, wherein the heat battery further comprises an electrolytic chamber containing a thermal electrolyte to function as a thermal electric battery, and the heat is stored in the heat battery, for example, by activating heating elements by electrical resistance in the heat battery; such that the stored heat causes the expansion of a non-combustible expanding fluid, such as water, or increases the expansion of a combustible expanding fluid, such as gasoline.

[0011] Furthermore, document W02008064418 discloses a method for operating a non-combustion piston engine comprising a cylinder with an upper and lower chamber separated by a partition including an opening with a valve, a first means of supplying air to at least one of the chambers; and a second means of supplying at least water vapor and hydrogen to the lower chamber, the method comprising supplying air to at least one of the chambers; compressing the air into the upper chamber and closing the valve to temporarily store the heated air; supplying at least water vapor and hydrogen to the lower chamber; and opening the valve when the lower chamber is at a minimum volume where the heated air is released into the lower chamber, causing the water vapor and / or hydrogen to expand and force the piston out of the cylinder.

[0012] In general, state-of-the-art thermal energy conversion systems operate under high thermal gradients in order to maximize their thermodynamic efficiency. However, a high thermal gradient also causes an inevitable increase in heat loss and a consequent decrease in overall efficiency.

[0013] Another problem for the efficient conversion of thermal energy into work concerns energy storage. This issue is an essential part of the operation of power plants, given that production according to availability and demand is a requirement for the convenient operation of a power plant. Thus, an effective and economical energy storage system must be an integral part of the design of a power generation unit and, particularly, of a solar power plant, due to the intermittent nature of its primary energy source.

[0014] Few proposed solar energy systems directly integrate energy storage into the overall design of a generator. In practice, in many state-of-the-art solar energy projects, energy generated during periods of high insolation is often stored in electric batteries so that this energy can be used during periods of higher consumption. However, the costs, environmental impacts, and limited storage capacity of currently available batteries have hindered the wider and more economical use of photovoltaic solar energy.

[0015] Systems that store heat in large tanks of molten salt at high temperatures for energy production are well known in the state of the art.

[0016] The undeniable fact is that heat loss will always be greater the larger the temperature gradient involved. Thus, these systems are, by their very nature, inefficient at conserving stored heat. This is precisely due to the high temperature of the heat reservoir. Molten sodium-based solar power plants aim to exploit more efficient regimes through operation at higher temperatures. However, the materials currently available for manufacturing the equipment where heat exchange takes place must be resistant to the strong corrosion of molten sodium, and therefore are very expensive and severely limit operating conditions. Many limitations related to heat loss, costs, and the thermal and mechanical resistance of the materials used still need to be resolved. Furthermore, all components of these plants are subject to significant physical degradation as a result of high and repetitive thermal shocks.In fact, maintenance and component replacement represent a significant portion of the total cost of a solar energy harvesting system stored in molten sodium tanks. Thermal stress shortens the lifespan of these elements due to their use under varying temperatures and subjection to large thermal gradients.

[0017] It therefore becomes clear that new methods and efficient facilities for heat storage and utilization are fundamental requirements for economically viable power plants. And this is particularly true for solar power plants.

[0018] The fact is that there is currently no device or method capable of converting a large amount of heat from small temperature differences into useful energy.

[0019] To solve the problems described, the present invention presents an expansion engine based on a two-stroke cycle, for transforming large amounts of heat from small temperature differences into mechanical work and electrical energy. The small temperature difference may originate from heat from geothermal sources, or from the temperature difference between surface and seabed water, or from water heated by solar thermal radiation. In any of these cases, the present invention aims to extract useful energy from a large amount of heat originating, however, from a small temperature difference.

[0020] For the application of the present invention in harnessing solar energy, the energy storage and conversion system can be sized so that the hot water reservoir, containing water heated by the sun, is large enough to store energy for consumption over many consecutive days without any sunshine. The combination of a large mass in the hot water reservoir with the high specific heat of water is what allows maximizing the thermodynamic use of the solar energy source. On the other hand, the relatively low temperature differences and the large volume of water involved drastically minimize heat losses by conduction. In short, the large heat storage capacity allows a solar energy system using the present invention to operate continuously and under conditions suitable to the demand and variability of the energy source.

[0021] It is therefore clear that there is no equivalent solution in the state of the art to that presented in the present invention that combines technical differences, economic advantages, reliability, and environmental safety. OBJECTIVES OF THE INVENTION

[0022] Thus, it is an objective of the present invention to provide a solution to the challenges and limitations listed above, presenting a two-stroke expansion engine for the production of energy from low-temperature heat sources such as: geothermal sources, or the temperature difference between surface water and seabed water, or water heated by solar thermal radiation.

[0023] It is also an objective of the present invention to provide a two-stroke expansion engine aimed at transforming heat into mechanical work and subsequently into electrical energy.

[0024] Another objective of the present invention is to provide an optimal method for heat exchange between a liquid medium such as water and a gaseous medium such as air.

[0025] Another objective of the present invention is to offer an efficient energy generation system capable of harnessing existing natural heat sources in a sustainable and environmentally friendly manner. SUMMARY OF THE INVENTION

[0026] The present invention achieves these and other objectives by means of a two-stroke expansion engine, which comprises a heat exchanger that is a compartment with the function of heating and renewing the air; the heat exchanger having its walls thermally insulated and connected to three valves controlled, electrically or mechanically, through a cam installed in an inertia disc. The three valves are: a hot water pressurizing valve, an air pressurizing valve, and an exhaust valve. The heat exchanger is further connected by a pressure line to a pressure cylinder delimited by a piston.

[0027] In more detail, the present invention comprises:

[0028] - a hot water pressure booster valve configured to spray hot water inside the heat exchanger;

[0029] - an air pressure booster valve that can include ambient temperature water mixed with air in the heat exchanger;

[0030] - An exhaust valve is connected to a separator via an air and water exhaust duct, in order to collect the water and discharge the air to the atmosphere through an air outlet line;

[0031] The pressure cylinder receives the pressure generated inside the heat exchanger through the pressure line and drives the piston.

[0032] The piston's motion is transmitted through a connecting rod to a flywheel.

[0033] The inertia disc is coupled to a generator in order to produce electrical energy.

[0034] - A heating circuit directs the water collected in the separator to a heater which, in a preferred version of the invention, could be a solar collector. The air received in the separator is discharged into the atmosphere through the air outlet line.

[0035] - The water heated in the heater is circulated by a thermal siphon, or by means of a mechanical valve (not shown) between the heater and the hot water tank through a water feedback pipe.

[0036] The hot water tank feeds hot water through a hot water supply duct into the heat exchanger during the spraying cycle.

[0037] The two-stroke expansion engine achieves its proposed objectives through a method of converting thermal energy into mechanical energy, which comprises two strokes:

[0038] - a first stage of the method in which the cam, installed in the inertia disc, acts to open the hot water pressurizing valve and keeps the other valves closed, so that the air contained inside the heat exchanger is heated, expands, and transmits, through the pressure line, the overpressure generated in the heat exchanger to the pressure cylinder. This overpressure in the pressure cylinder pulls the piston which, through the connecting rod, sets the inertia disc in motion and, finally, the generator;

[0039] - a second stage corresponding to the exhaust of the air and hot water used in the first stage, in which the machine acts to open the pressurizing valve for air combined with water at room temperature, and the exhaust valve. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] The present invention will be described based on the attached drawings, which illustrate: Figure 1 represents the schematic of a two-stroke expansion engine in a preferred embodiment. Figure 2 represents the behavior of the two-stroke expansion engine system, before and after the spray cycle and the renewal cycle, in a preferred embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0041] The present invention relates to a two-stroke expansion engine for transforming heat into mechanical work and subsequently into electrical energy. The present invention presents, through an innovative design, a system that aims to exploit extensive heat sources arising from small temperature differences, such as those available in geothermal sources, or in the temperature difference between surface and seabed water, or in water heated by solar thermal radiation. The objective is to extract useful energy from a large amount of heat resulting from small temperature differences.

[0042] Conventional piston engines operate by exploding fossil fuels, whereas the present two-stroke expansion engine uses the expansion of heated air to generate energy.

[0043] The present invention offers numerous technical and economic advantages when compared to the state of the art, some of which are listed below:

[0044] The present invention eliminates dependence on electrical power distribution networks because it allows for the production of energy where needed, on demand, and without interruptions.

[0045] The present invention takes advantage of renewable and naturally available energy sources and is more environmentally friendly and efficient when compared to other methods of energy production.

[0046] The present invention describes an efficient and economical system for storing and generating large quantities of energy as an integral part of the design of a power generation unit.

[0047] The two-stroke expansion engine comprises a heat exchanger (10) and a pressure cylinder (17) housing a piston (18). According to a preferred embodiment of the present invention, the heat exchanger (10) is thermally insulated on its outer part.

[0048] The two-stroke expansion engine comprises a hot water reservoir (2) which is also thermally insulated. Preferably, the hot water reservoir (2) can be one of: a mass of water heated by said heater (4) and / or by a geothermal source.

[0049] The two-stroke expansion engine further comprises a hot water pressure valve (9) and an air pressure valve (8) located at the top of said heat exchanger (10). The hot water pressure valve (9) is configured to spray hot water into the interior of the heat exchanger (10) through a hot water supply duct (6) during the spraying time, and the air pressure valve (8) is configured to admit air mixed with water at ambient temperature, in an adjustable proportion, into the heat exchanger (10) during the renewal time.

[0050] The two-stroke expansion engine further comprises a separator (14) disposed at the outlet of the heat exchanger (10) in order to separate, during the renewal time of the two-stroke expansion engine, the hot water from the air used in the previous spraying time.

[0051] According to the preferred embodiment of the present invention, an exhaust valve (11) communicates via an air and water exhaust duct (13) to the separator (14) which in turn is connected via a water recovery duct (12) to the heating circuit (5), the heater (4), and the hot water tank (2).

[0052] According to the present invention, the hot water pressure booster valve (9) contains a plurality of orifices through which hot water is sprayed onto the heat exchanger (10) in the form of jets. The jets turn into droplets that have a relatively small diameter and flow in the form of a shower, transferring the temperature of the hot water to the air contained inside the heat exchanger (10).

[0053] A first connection in the heat exchanger (10) is associated with the hot water pressure booster valve (9) for adding heat to the interior of the heat exchanger (10).

[0054] A second connection in the heat exchanger (10) is associated with an air inlet line (7) controlled by the air pressure valve (8) and configured to introduce air into said heat exchanger (10) or to introduce air and water at ambient temperature into said heat exchanger (10).

[0055] A third connection in the heat exchanger is associated with a pressure line (16) that communicates the pressure of the heat exchanger to the pressure cylinder in order to actuate a piston (18) and, through a connecting rod (19), move an inertia disc (20) and consequently a generator (21) connected to the motor.

[0056] A fourth connection in the heat exchanger (10) is associated with the exhaust valve (11) linked to the separator (14), said separator (14) being connected to an air outlet line (15) configured to discard air to the atmosphere and also connected, by means of the water recovery duct (12), to the hot water tank (2) and to the heater (4), so that the water in the separator (14) is recovered and reheated in the heater (4) for subsequent return to the heat exchanger (10) by means of the hot water pressurizing valve (9).

[0057] In a preferred embodiment, the heater (4) is fed back by a water feedback duct (3) connected to the heater (4), which may be a solar collector and, in that case, positioned to optimize its direct exposure to sunlight, wherein a heat storage fluid, which in a preferred version of the invention may be water, is circulated by means of a pump (not shown), or spontaneously by means of a thermal siphon, flows between the heater (4) and the hot water tank (2). Alternatively, the water, after being heated inside the heater (4), which may be a solar collector, is conveyed by pumping, or by thermal siphon, through the water feedback duct (3) to the hot water tank (2) after receiving the heat collected in the heater (4).

[0058] As the water passes through the heater (4), it is heated to a temperature at which it remains liquid. The heated water is then transferred through a hot water duct (1) to the hot water tank (2). The hot water tank (2) is thermally insulated to minimize heat loss by radiation and conduction through its walls. The hot water is circulated through the hot water duct (1) and the hot water feedback duct (3) by means of a thermal siphon between the heater (4) and the hot water tank (2). The hot water is conveyed at an appropriate rate, according to the production needs of the power plant, to the heat exchanger (10). This conduction of hot water from the hot water tank (2) is carried out through the hot water feed duct (6) and through the hot water pressure booster valve (9) to the heat exchanger (10).

[0059] It is important to highlight that a mass of water heated to approximately 60°C above room temperature contains a considerable amount of thermal energy. This is due to the fact that water has the highest specific heat among all available substances, 4.18 kJ / (°C).

[0060] According to the method presented here, the two-stroke expansion engine uses the pressure cylinder (17) delimited by the piston (18). The piston (18) performs an upward and downward movement as a function of, respectively, the expansion and exhaust of air in the pressure cylinder (17).

[0061] The two-stroke expansion engine described here converts heat into work in two strokes:

[0062] The first stage consists of spraying hot water in order to heat the air inside the heat exchanger (10) and increase the air pressure. In this first stage, the hot water pressure valve (9) is opened and the air pressure valve (8) and the exhaust valve (11) are closed.

[0063] The second stage consists of air renewal. During this second stage, the hot water pressure valve (9) is closed, the exhaust valve (11) is opened, and the air pressure valve (8) is opened.

[0064] Subsequently, the air contained in the heat exchanger (10) is again sprayed with hot water, thus increasing the air temperature once more. The resulting increase in pressure is transferred to the pressure cylinder (17) via the pressure line (16) and is used to drive the piston (18) and, via the connecting rod (19), to drive the inertia disc (20) and the generator (21).

[0065] According to the method presented here, heated water and air are admitted alternately in a controlled manner into the interior of the heat exchanger (10). The spraying of hot water causes the air to heat up, increase in pressure and expand. This expansion is used to drive the piston (18) which, through the connecting rod (19), drives the inertia disc (20). In the next cycle, the air in the exchanger is renewed for the next expansion.

[0066] The entire system is preferably configured so that the water and air come into intimate thermal contact with each other inside the heat exchanger (10). Thus, the inlets and outlets are arranged in the heat exchanger (10) in such a way that the air and water prolong the heat exchange.

[0067] The heat exchanger (10) has the function of transferring heat between the water and the air. Valves are provided to conduct and collect both water and air to and from the heat exchanger (10). The heat exchanger (10) includes means for transferring the temperature of the water to the air. The hot water reservoir (2) supplies both the heater (4) and the heat exchanger (10) of the two-stroke expansion engine.

[0068] Furthermore, the two-stroke expansion engine comprises the inertia disc (20) in which a cam (22) is installed with the function of switching on and off both the hot water spray and the air intake and exhaust, at the respective appropriate times.

[0069] The arrangement of the cam (22) is designed to ensure the correct operating time of the valves as the inertia disc (20) rotates.

[0070] In the energy conversion system described here, the dimensions of the hot water tank (2) and the heater (4) are selected to maintain a continuous energy production, and according to demand, during the necessary time period considering variations in the primary energy source.

[0071] The hot water tank (2) is constructed taking into account its physical and chemical stability in contact with water. Much relevant information for the design and construction of such tanks is available in the literature on cistern industry technology. Additionally, the walls of the hot water tank (2) can be constructed of a plurality of layers of insulating and heat-resistant materials.

[0072] Additionally, the possibility of replacing water with another liquid medium suitable for heat exchange in the system described by the present invention is foreseen. It is worth emphasizing that water is the most advantageous liquid because, among all available substances, it has the highest specific heat (4.18 Joules / °C.gr), as mentioned above. It is also worth pointing out that water is much more readily available than any of the other substances that could be used for energy storage. The solar collector, commonly found in the state of the art, can heat water to a temperature slightly below 100°C or 373K. This heated water can be stored in the appropriately thermally insulated hot water tank (2), allowing its use according to the needs of a solar power plant constructed in accordance with the present invention.The air heated by the hot water inside the heat exchanger (10) undergoes an expansion and this change in volume and pressure is used to drive the piston (18) inside the pressure cylinder (17) in order to drive, through the connecting rod (19), the inertia disc (20) and the generator (21).

[0073] The temperature of the hot water from the hot water tank (2) is transmitted to the air inside the heat exchanger (10). As jets of hot water pass through the heat exchanger (10), the hot water transmits its temperature to the air. The hot water from the jets released by the hot water pressure booster valve (9) is subsequently collected by the separator (14).

[0074] The air admitted by the air pressure valve (8) is responsible for renewing the air inside the heat exchanger (10).

[0075] The walls of the heat exchanger (10) of the two-stroke expansion engine may have their inner surface coated with a hydrophobic polymer material, such as a fluorocarbon, in order to restrict water retention by capillarity. This structure may be produced with a casing of thermally insulating material such as a plastic or a composite material and also with external coatings, also thermally insulating. The heat exchanger (10) of the engine may be constructed with insulating materials similar to that of the hot water tank lining (2).

[0076] The efficiency with which energy conversion and storage occurs is favorably reflected in the total cost of the solar energy conversion system. As explained here, more useful energy can be obtained by simply adding more solar collectors, which are particularly inexpensive. Furthermore, the low thermodynamic efficiency of the two-stroke expansion engine described here (~16%), a consequence of the small temperature difference between the hot source (~80°C) and the cold source (~20°C), is still sufficient to present itself as a viable option compared to the alternatives available today. Finally, the fact that the hot water spray is always carried out inside the heat exchanger (10) maximizes the thermal conduction potential between the heat exchange media and minimizes energy losses.

[0077] The said two-stroke expansion engine is the central component of the energy storage and conversion system presented here, where jets of hot water and fresh air are alternately launched through the hot water pressurizing valve (9) and the air pressurizing valve (8), respectively, inside the heat exchanger (10). SYSTEM OPERATION

[0078] According to the method presented here, heated water is sprayed onto the air contained within the heat exchanger (10), which, as a result, heats up, raising the air pressure in the heat exchanger (10) and in the pressure cylinder (17), so as to move the piston (18). The operation of the two-stroke expansion engine is achieved by the controlled opening and closing of the system's valves. Although there is a very high number of possible combinations of valve openings, the system and method of operation of the present invention provides for a finite and reduced number of system stages, each of which stages is defined by which valves are open and closed, enabling or preventing communication between the components of the two-stroke expansion engine in predetermined ways.

[0079] In the first stage, corresponding to the spraying, the cam (22) acts to open the hot water pressure valve (9) in order to raise the air temperature. The air inside the heat exchanger (10) is heated by thermal contact with the sprayed hot water, which results in an increase in pressure in the heat exchanger (10) and, through the pressure line (16), in the pressure cylinder (17), which leads to the expansion of the piston (18). Hot water is sprayed by the hot water pressure valve (9) in the quantity necessary to maintain the air temperature constant and just below the temperature of the hot water reservoir (2). During this stage, work is performed by the motor.

[0080] Ideally, it is desirable that the temperature during expansion be kept close to the temperature in the hot water tank (2).

[0081] In a second phase, the air renewal phase, the cam (22) acts to open the air pressurizing valve (8) and the exhaust valve (11). During this phase, the hot water pressurizing valve (9) is closed. During this phase, work is performed on the motor.

[0082] The cam (22) allows you to turn the three valves on and off at the appropriate times:

[0083] In the first stage, open the hot water pressure valve (9), and keep the air pressure valve (8) and the exhaust valve (11) closed.

[0084] In the second stage, you open the air pressure valve (8) and the exhaust valve (11), and keep the hot water pressure valve (9) closed.

[0085] Furthermore, in a preferred embodiment, the opening and closing commands of the valves of the two-stroke expansion engine are represented here by electrical contacts (23) actuated by the cam (22). Naturally, for the same purpose, other means of control can be used, such as, for example, mechanical controls involving rods and levers. In the representation of Figure 2, as the piston (18) of the two-stroke expansion engine rotates the inertia disc (20), the cam (22) closes and opens the circuits of the electrical contacts (23) sequentially, actuating or deactivating the valves. The electrical contacts (23) are connected to a power source (24) with the function of allowing the operation of the valves (8, 9 and 11).

[0086] The present invention describes a two-stroke expansion engine in which the heat exchanger (10) does not require materials capable of withstanding large mechanical stresses and thermal stresses. Therefore, the two-stroke expansion engine, constructed according to the present invention, is not exposed to the problems related to intense thermal and mechanical shocks, as is characteristic of the current technique of systems for converting thermal energy into mechanical energy.

[0087] The two-stroke expansion engine of the present invention is substantially immune to the problems associated with conventional energy converters, such as corrosion, wear, and low reliability due to the high thermal gradients and pressures used. The two-stroke expansion engine of the present invention also offers outstanding heat exchange performance due to the considerable heat transfer area provided by the large surface area of ​​the dense cloud of sprayed liquid droplets.

[0088] Furthermore, the reliability of the two-stroke expansion engine of the present invention is noteworthy due to the fact that it does not involve piping subjected to high pressure and which, therefore, poses a risk of rupture.

[0089] Another notable result of the energy conversion method presented in the present invention is the ability to store energy in quantities necessary for the operation of the two-stroke expansion engine for extended periods. By accumulating heat directly in the water, the energy storage is naturally integrated into the energy and power production cycle.

[0090] This aspect is of utmost importance for all intermittent energy sources and, more specifically, for solar energy. Ultimately, the integrated capacity for energy storage and production presents itself as one of the main advantages of the two-stroke expansion engine.

[0091] Thus, the limitation of low thermodynamic efficiency due to small temperature differences is largely compensated for by the considerable ease of energy collection, storage, and conversion. This allows for the utilization of energy stored in a large amount of heat resulting from small temperature differences.

[0092] In the case of harnessing solar energy captured by conventional solar collectors, the heated water must be stored in a substantially voluminous and thermally insulated hot water tank (2) to allow for a large accumulation of energy in water heated to a relatively low temperature, slightly below 100°C.

[0093] The use of a two-stroke expansion engine to harness solar energy has the remarkable characteristic of utilizing virtually the entire solar radiation spectrum: from infrared and visible light to ultraviolet. In other words, almost all available solar energy is captured, stored, and converted into heat. By comparison, photovoltaic panels collect only a fraction of the visible part of the solar spectrum.

[0094] However, due to the efficiency limitations imposed by thermodynamics regarding the temperature differences used in the two-stroke expansion engine, typically 80°C for heated water and 20°C for ambient temperature, only ~16.6% of this energy can be recovered. Even so, the solar radiation absorbed by the solar collector allows for the generation of a significant amount of useful energy, especially when compared to conventional solar energy production technologies, whether thermal, molten sodium-based, or photovoltaic.

[0095] Therefore, the method described in this invention offers an efficiency that can be compared to that of photovoltaic panels (~15%) and fossil fuel engines (~25% for gasoline and ~30% for diesel). Furthermore, it provides the significant advantage of harnessing ~16.6% of the energy from a free and inexhaustible source, such as the Sun, using an abundant resource like water in a renewable and closed-loop manner.

[0096] Having described some examples of preferred embodiments of the present invention, it should be understood that the inventive concept presented encompasses other possible variations, being limited only by the content of the claims, including possible equivalents.

Claims

CLAIMS 1. Two-stroke expansion engine for converting thermal energy into mechanical energy, characterized by comprising: - a heat exchanger (10) thermally insulated on its outer surface and connected to a hot water supply duct (6) configured to spray hot water onto said heat exchanger (10); - an air inlet line (7) configured to renew air in said heat exchanger (10); - a pressure line (16) configured to communicate the pressure of said heat exchanger (10) to a pressure cylinder (17); - an exhaust valve (11) connected to a separator (14) for air and water exhaust, said separator (14) being connected to an air outlet line (15) configured to conduct the discarded air to the atmosphere through an air and water exhaust duct (13) and further connected to a water recovery duct (12); - a heating circuit (5) receives recovered water through the water recovery duct (12) and comprises a heater (4) connected to a hot water tank (2) through a heated water duct (1), said hot water tank (2) being connected by a water feedback duct (3) to the water recovery duct (12) and further to a hot water pressure booster valve (9), said hot water pressure booster valve (9) being connected to said heat exchanger (10) by means of said hot water feed duct (6); and - a piston (18) that is driven by the pressure of said pressure cylinder (17) and is configured to, by means of a connecting rod (19), rotate an inertia disc (20) comprising a cam (22) that connects and disconnects electrical contacts (23) in order to switch on and off an air pressure valve (8), said hot water pressure valve (9) and said exhaust valve (11), said inertia disc (20) being configured to drive by rotation an electric generator (21).

2. Two-stroke expansion engine, according to claim 1, characterized in that said air pressurizing valve (8), said pressurizing valve (9) and said exhaust valve (11) are controlled by cam (22), and activated by means of an electrical contact (23) energized by an electrical power source (24).

3. Two-stroke expansion engine according to claim 1 characterized in that said air pressurizing valve (8), said pressurizing valve (9) and said exhaust valve (11) are controlled by the cam (22) by mechanical means.

4. Two-stroke expansion engine according to claim 1 characterized in that the heater (4) is configured to heat water by means of a geothermal source.

5. Two-stroke expansion engine according to claim 1 characterized in that the heater (4) is configured to heat water by means of a solar heater.

6. Two-stroke expansion engine according to claim 1 characterized in that the heater (4) is configured to heat water through a natural source.

7. Two-stroke expansion engine, according to claim 1, characterized in that the hot water reservoir (2) is one of: a mass of water heated by said heater (4) and / or by a geothermal source.

8. Two-stroke expansion engine, according to claim 1, characterized in that said air inlet line (7) is configured to introduce air into said heat exchanger (10).

9. Two-stroke expansion engine, according to claim 1, characterized in that said air inlet line (7) is configured to introduce air and water at ambient temperature into said heat exchanger (10).

10. Expansion motor, according to claim 1, characterized in that the expansion motor is connected to an electric generator (21).

11. A method for converting thermal energy into mechanical energy using an engine as defined in claims 1 to 10, characterized by comprising: - a first stage of the two-stroke expansion engine that begins with the piston (18) at bottom dead center, in which the air contained in the pressure cylinder (17) is contained in its smallest volume, and the air pressure valve (8) and the exhaust valve (11) are kept closed and when the spray of hot water through the hot water pressure valve (9) causes a rise in pressure inside the heat exchanger (10) which, through the pressure line (16), is transferred to the pressure cylinder (17) in order to propel the piston (18) to top dead center, and, during the movement of the piston (18) from bottom dead center to top dead center, the piston (18), through the connecting rod (19), sets in motion the inertia disc (20) and the generator (21) in order to produce electrical energy; - a second stage of the two-stroke expansion engine that begins with the piston (18) at top dead center, when the air contained in the pressure cylinder (17) is at its maximum volume, and when the hot water pressure valve (9) is kept closed, with the air pressure valve (8) and the exhaust valve (11) kept open in order to renew the air inside the heat exchanger (10), the movement of the piston (18) from top dead center to bottom dead center being driven by the inertia disc (20) through the connecting rod (19) and the inertial rotation of the inertia disc (20) maintaining the production of electrical energy from the generator (21).

12. Method according to claim 11, characterized in that the valves (8, 9 and 11) are mechanically controllable.

13. Method according to claim 11, characterized in that the valves (8, 9 and 11) are electrically controllable.

14. Method according to claim 11, characterized in that the hot water reservoir (2) is one of: a mass of water heated by said heater (4) or by a geothermal source.

15. Method according to claim 11, characterized in that the heater (4) uses the following means to heat a body of water: heat from natural sources, solar energy and / or geothermal sources.

16. Method according to claim 11, characterized in that the two-stroke expansion engine is connected to an electric generator (21).

17. Method according to claim 11, characterized in that said air inlet line (7) is characterized by introducing air into said heat exchanger (10).

18. Method according to claim 11, characterized in that said air inlet line (7) is characterized by introducing a mixture of air and water at ambient temperature into said heat exchanger (10).

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