A hot air engine and a method to operate the same

Abstract

A hot air engine (10) is disclosed The engine includes an expansion vessel (20) and a compression vessel (30) coupled together and placed at a differential height on a spring supported movable platform (40, 50). The expansion vessel is empty, and the compression vessel is filled with a liquid in its initial natural state. An air heater (120) coupled to the expansion vessels increases air pressure due to heat and pushes the liquid of expansion vessel to flow towards the compression vessel when air pressure is raised above a threshold. The liquid from vessel flows in reverse back to vessel when air pressure is released after exhaust port is opened by the cut off valve (100) from the top of the liquid level in vessel due to gravity head caused by the elevation difference of vessel and vessel.The filling and refilling results in conversion of heat energy into mechanical energy.

Description

[0001] A HOT AIR ENGINE AND A METHOD TO OPERATE THE SAME

[0002] EARLIEST PRIORITY DATE

[0003] This Application claims priority from a Complete patent application filed in India having Patent Application No. 202341084437 filed on 11th day of December 2023 and titled A HOT AIR ENGINE AND A METHOD TO OPERATE THE SAME

[0004] FIELD OF INVENTION

[0005] Embodiments of the present disclosure relates to a hot air engine and more particularly to a hot air engine to convert heat energy into mechanical energy.

[0006] BACKGROUND

[0007] Hot air engines such as Sterling and Ericson engines are engines that use the expansion and contraction of air under the influence of a temperature change to convert thermal energy into useful mechanical work. They are considered to be among the most efficient way of converting thermal energy into mechanical energy, however such engines with conventional reciprocating piston cylinder are seldom used in any real life applications. Further, such external combustion hot air engines have the potential for high theoretical efficiency. However, they tend to have lower practical efficiencies when used at lower temperature differential and slow speeds. This is mainly frictional losses and piston leakage loses within the engine due to the use of conventional reciprocating piton cylinder arrangement.

[0008] One of the main disadvantages is that such engines are not economical to scale up these engines to large capacities and sizes. It is even difficult or costly to make engines even with a capacity of 1 or 2 kilo watts. In order to make these engines economical, the engines need to be designed to work at high temperature differences which further require high metallurgy and complicated designs.

[0009] The engines cannot be practical or economical if they are designed at lower temperatures since it may require a very large piston-cylinder. The use of a large piston cylinder further increases frictional losses. Most of the problem arises due to the use of the reciprocating piston cylinder in these engines. Hence, there is a need for an improved air engine to address the aforementioned issue(s).

[0010] BRIEF DESCRIPTION

[0011] In accordance with an embodiment of the present disclosure, a hot air engine is provided. The hot air engine includes a fluid gravity piston arrangement comprising an expansion vessel and a compression vessel. The expansion vessel and the compression vessel are airtight vessels coupled to an up and down arrangement and placed at multiple elevations. The expansion vessel and the compression vessel accommodate a liquid suitable to a working temperature of a cycle. The compression vessel is empty or only contains fresh air taken from the atmosphere through an intake valve, and the expansion vessel is filled with the liquid in its initial due to gravity head caused by difference of the multiple elevations. The expansion vessel and the compression vessel are interconnected at the bottom using flexible hose pipes, wherein the flexible hose pipes allow transfer of the liquid from the expansion vessel to the compression vessel and vice versa, whilst allowing movement of the expansion vessel and the compression vessel. Further, restoration force is provided to the expansion vessel and compression vessel. Thus, the expansion vessel and the compression vessel are arranged in such a way that they can perform up and down motion under the restoration and gravity force of the liquid weight. Further, the vessels are coupled with a mechanism to convert the up and down movements of the expansion vessel and the compression vessel into useful work. The hot air engine further includes an air heater coupled at a top portion of the expansion vessel and the top part of compression vessel is connected to a receiver or storage tank and an intake valve using another flexible hose pipes via non-retum valves. Air heater increases air pressure due to heat and is applied on top of the liquid level of fully filled expansion vessel, the air pressure when raised above a threshold limit pushes the liquid of expansion vessel to flow towards the compression vessel via a hose pipe.

[0012] In accordance with an embodiment of the present disclosure, a method to operate an exemplary hot air engine is provided. The method includes applying, by heating inside an air heater, an increased air pressure on top of liquid in an expansion vessel when a compression vessel is empty, and the expansion vessel is filled with the liquid. The method also includes allowing, by hose pipes, the liquid to flow from the expansion vessel to the compression vessel, due to the air from the air heater pushing the liquid downwards when air pressure is raised above a threshold limit due to heating. The expansion vessel and the compression vessel are placed at a differential height on movable platforms on springs. Further, the method includes evacuating the expansion vessel and filling the compression vessel with the liquid by transferring working fluid from expansion vessel to the compression. Furthermore, the method includes decompressing and compressing of the first spring and a second spring placed beneath expansion and compression vessel respectively, to move the expansion vessel in upward direction and the compression vessel in downward direction, when the liquid of the expansion vessel moves to the compression vessel in a first half of the cycle. Moreover, the method includes releasing air pressure from the top of the liquid level of expansion vessel and subsequent reversal of working fluid from compression vessel to the expansion vessel due to the gravity head. The method includes decompressing the second spring and moving the compression vessel in upward direction and compressing the first spring and moving the expansion vessel in downward direction respectively when the liquid of the compression vessel starts refilling the expansion vessel in a second half of the cycle. The method includes alternate filling and refilling of the expansion vessel and the compression vessel according to the air pressure variation in the air heater causing the movement of the mechanism attached to the vessels to convert heat energy into mechanical energy.

[0013] To further clarify the advantages and features of the present disclosure, a more particular description of the disclosure will follow by reference to specific embodiments thereof, which are illustrated in the appended figures. It is to be appreciated that these figures depict only typical embodiments of the disclosure and are therefore not to be considered limiting in scope. The disclosure will be described and explained with additional specificity and detail with the appended figures.

[0014] BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The disclosure will be described and explained with additional specificity and detail with the accompanying figures in which: FIG. 1 is a schematic representation of a hot air engine in accordance with an embodiment of the present disclosure;

[0016] FIG. 2 is a schematic representation of one embodiment of the hot air engine of FIG. 1 in accordance with an embodiment of the present disclosure;

[0017] FIG. 3 is a schematic representation of another embodiment of the hot heat engine of FIG. 1 in accordance with an embodiment of the present disclosure;

[0018] FIG. 4 is a schematic representation of one embodiment of the hot air engine of FIG. 1 in accordance with an embodiment of the present disclosure;

[0019] FIG.5a and 5b is a schematic representation of an exemplary intermediate storage tank of one embodiment of the hot air engine of FIG.l in accordance with an embodiment of the present disclosure;

[0020] FIG. 6(a) and 6(b) is a schematic representation of an exemplary intermediate storage tank of another embodiment of the hot air engine of FIG.l in accordance with an embodiment of the present disclosure; and

[0021] FIG. 7a and FIG. 7b is a flow chart representing the steps involved in a method to operate the hot air engine in accordance with an embodiment of the present disclosure.

[0022] Further, those skilled in the art will appreciate that elements in the figures are illustrated for simplicity and may not have necessarily been drawn to scale. Furthermore, in terms of the construction of the device, one or more components of the device may have been represented in the figures by conventional symbols, and the figures may show only those specific details that are pertinent to understanding the embodiments of the present disclosure so as not to obscure the figures with details that will be readily apparent to those skilled in the art having the benefit of the description herein.

[0023] DETAILED DESCRIPTION

[0024] For the purpose of promoting an understanding of the principles of the disclosure, reference will now be made to the embodiment illustrated in the figures and specific language will be used to describe them. It will nevertheless be understood that no limitation of the scope of the disclosure is thereby intended. Such alterations and further modifications in the illustrated system, and such further applications of the principles of the disclosure as would normally occur to those skilled in the art are to be construed as being within the scope of the present disclosure.

[0025] The terms "comprises", "comprising", or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a process or method that comprises a list of steps does not include only those steps but may include other steps not expressly listed or inherent to such a process or method. Similarly, one or more devices or subsystems or elements or structures or components preceded by "comprises... a" does not, without more constraints, preclude the existence of other devices, sub-systems, elements, structures, components, additional devices, additional sub-systems, additional elements, additional structures or additional components. Appearances of the phrase "in an embodiment", "in another embodiment" and similar language throughout this specification may, but not necessarily do, all refer to the same embodiment.

[0026] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this disclosure belongs. The system, methods, and examples provided herein are only illustrative and not intended to be limiting.

[0027] In the following specification and the claims, reference will be made to a number of terms, which shall be defined to have the following meanings. The singular forms “a”, “an”, and “the” include plural references unless the context clearly dictates otherwise.

[0028] Embodiments of the present disclosure relates to, a hot air engine. The hot heat engine or a hot air engine is a heat engine that uses the expansion and contraction of air under the influence of a temperature change to convert thermal energy into mechanical work. Such engines may be based on a number of thermodynamic cycles encompassing both open cycle devices such as those of Sir George CayleyRand John EricssonRand the closed cycle engine of Robert StirlingR. The hot air engines are distinct from the better-known internal combustion-based engine and steam engine. In a typical implementation, air is repeatedly heated and cooled in a cylinder and the resulting expansion and contraction are used to move a piston and produce useful mechanical work. The hot air engine is further described in detail in FIG. 1 onwards.

[0029] FIG. 1 is schematic representation of a hot air engine (10) in accordance with an embodiment of the present disclosure. The engine (10) includes a fluid gravity piston system including a first vessel (20) and a second vessel (30) that replaces the sliding piston and cylinder of a conventional hot air engine. The first vessel (20) is equivalent to the expansion or working cylinder, while the second vessel (30) can be considered as the compression or supply cylinder in an Ericsson cycle engine. Henceforth, the first vessel (20) shall be referred to as the expansion vessel, and the second vessel (30) shall be referred to as the compression vessel. In one embodiment, the first vessel (20) and the second vessel (30) may be a cylindrical arrangement. The expansion vessel (20) and the compression vessel (30) are placed at a differential height on a spring supported movable platforms (40)(50). In a specific embodiment, the compression vessel (30) may be kept at a predefined height on a movable platform (50)and the expansion vessel (20) may be kept at lower height than the expansion vessel (20)on another movable platform (40). The expansion vessel (20) is filled with a liquid, and the compression vessel (30) is empty initially. As used herein, the liquid of suitable density is used according to pressure generated by an air heater (120). In a specific embodiment, the spring supported movable platform (40) may include a first spring (60) and second movable platform(50) include second spring (70) coupled to the expansion vessel (20) and the compression vessel (30) respectively. While theoretically any liquid can be used, the operating temperature must remain within the boiling point of the chosen fluid. The compactness of the system is influenced by the density of the chosen liquid. A higher liquid density results in a more compact system. Without an intermediate isolation tank, practical difficulties arise, such as preventing heat transfer between the expansion and compression vessels. Insulation oils with low specific heat and thermal conductivity are preferred in such cases. Alternatively, a combination of immiscible liquids can be used to achieve the desired outcome. Another challenge arises when using oil in the compression vessel, as moisture from atmospheric air can condense and mix with the oil, leading to emulsification in that case emulsion resistant oil can be used. Further, a restoration force is provided against the fluid gravity piston system by using springs(60) and (70) in the hot air engine illustrated in Fig-1. The restoration force acts against the gravitational force for acting on the vessel arrangement due to liquid weight. In other words, the expansion vessel (20) and the compression vessel (30) move downwards under gravitational force when the weight of the expansion vessel (20) and the compression vessel (30) increases when liquid fills inside the vessels (20) (30). Likewise, the expansion vessel (20) and the compression vessel (30) move upwards under restoration force when the weight of the expansion vessel (20) and the compression vessel (30) decreases when the vessels (20) (30) empties. The restoration force can be provided by several ways such as, but not limited to, by using springs to place the expansion vessel (20) and the compression vessel (30), connecting one or both vessels to a fulcrum mechanism with a counterweight and by linking both vessels to a single mechanism similar to a weighing balance so that both vessels counter act each other. Therefore, the motion of the vessels will be synchronous but out of phase. This out of phase motion can be implemented by addition of intermediate storage vessels and is further explained in FIG. 5(a), FIG. 5(b), FIG.6(a) and FIG.6(b).

[0030] Furthermore, within the engine (10), an air receiver tank (90) is incorporated, and at the outlet of this receiver tank (90), a four-way cut-off valve (100) is positioned. The cut of valve (100) can be electrically or mechanically actuated. Downstream of this cut-off valve (100), a regenerative heater (110) and an air heater (120) are provided. The air heater (120) can take various forms, such as a liquid-to-air shell and tube heat exchanger or an air-to-air heat exchanger, and it can utilize heat sources such as solar energy or waste heat, or heat from burning any fuel. Furthermore, the engine (10) incorporates two Non-Return Valves (NRVs) (170) and (180) to regulate air flow within the system. First Non-return valve (170) is positioned at the inlet of the compression vessel (30), Second Non-return valve (180) is positioned at the inlet of the receiver tank (90). These components together will act as a stationary air heating circuit that generates air pressure variation facilitating the transfer or lifting of the liquid between the lower and upper vessels achieved by applying and releasing air pressure on top of the liquid level inside the expansion vessel (20). The top part of the expansion vessel (20) is connected to the outlet of air heater (120) by a flexible hose pipe (150). The air intake line of the engine (10) includes the non-return valve (170), and this line is connected to the top part of compression vessel (30) by another flexible hose pipe (160). The bottom part of expansion vessel (20) and compression vessel (30) are interconnected by two other flexible hose pipes (130) and (140) respectively. The four flexible hose pipes (130) (140) (150) (160) thus will establish connection between the stationary parts of the engine (10) and the movable vessels (20) (30) without restricting the movement of the vessels (20) (30). An external filling line (80) is connected to the receiver tank for initial pressurized air filling and the Non-retum valve (180) will prevent pressurized air flow back to the compressor vessel (30) from receiver tank (90).

[0031] Further, the disclosed system operates through an expansion and compression stroke as usual as any hot air engine. The initial state of the system involves expansion vessel (20) being completely filled with the working fluid, resulting in the compression of the supporting spring (60) under the liquid weight. In contrast, compression vessel (30) remains empty, and its supporting spring (70) remains in a normal, decompressed state. In the described configuration, the expansion vessel (20) is in the lowest position, while the compression vessel (30) is positioned at the topmost point. This condition of expansion vessel (20) and compression vessel (30) resembles the configuration of position of a conventional piston cylinder where one piston is positioned at the top dead center and another piston is situated at the bottom dead center.

[0032] When cut of valve (100) is positioned to opened the output port of receiver tank (90), this allows release of the already stored compressed air from receiver tank (90), first to the regenerative heater (110) which preheats the air and then to the air heater (120). Up on further heating in the air heater (120) this pressurized air then will try to expand inside the expansion vessel (20), pushing the liquid downwards. In detail, the increase in air pressure due to heating inside the air heater (120) is applied on top of the liquid level in the expansion vessel (20). As soon as the pressure reaches the head required to overcome to lift, the liquid along the elevation difference of both the vessels (20) and (30), the air pushing on top of the liquid level in the expansion vessel (20) causes the liquid to flow from the expansion vessel (20) to the compression vessel (30) through the interconnected hose pipes (130) and (140). During this process the expansion vessel (20) is getting evacuated while the compression vessel (30) is getting filled. Or, During this process, the entire weight of the working fluid is now transferred from the expansion vessel (20) to the compression vessel (30).Without the liquid in it the net weight and hence the gravitational force acting on the expansion vessel (20) is reduced to minimum whereas the net weight of the compression vessel (30) is gradually increased to maximum as the liquid fills in it. Further, in this process the spring (70) supporting the compression vessel (30) will be compressed also the output shaft below the compression vessel (30) will move down under the weight of filling liquid. Whereas under the reduced liquid weight of the expansion vessel (20) will cause the output shaft below this vessel (20) to move up due the restoration force exerted by the spring (60). This is the expansion stroke of the cycle. During this stroke the expansion vessel (20) move up and the compression vessel (30) move down.

[0033] Additionally, before the completion of expansion stroke that is before the complete filling of liquid in the compression vessel (30), the cut of valve(100) is positioned to close the output port of receiver tank (90) at a particular cut-off ratio of the cycle. The air supply from the receiver tank(90) is stopped and heated air in the air heater (120) expansively completes the remaining stroke. Further, as the cut of valve(100) is closed the compression stroke of the cycle begins and the volume of air inside the compression vessel (30) at the time of closing the cut-off valve(100) is compressed and forced to fill inside the receiver tank(90)by the filling liquid. During the expansion-compression stroke the expansion vessel (20) move up and the compression vessel (30) move down. The non-return(170) valve will prevent airflow from the compression vessel(30) to escape back into the atmosphere during compression stroke.

[0034] In continuation, at the end of compression stroke, the four-way cut off valve (100) closes the output port of the receiver tank (90) and is also positioned to open the exhaust port, allowing the release of air pressure from the top of the fluid level in the expansion vessel (20). As a result, the air pressure in the expansion vessel (20), which holds the liquid along its height, is released. This causes the fluid from the compression vessel (30), which is at a higher elevation, to flow back into the expansion vessel (20) due to the gravity head caused by the height difference. As the expansion vessel (20) at the lower elevation is refilled during in this phase, its weight gradually increases again, leading to the downward movement of the platform (40) and the connected output shaft. Simultaneously, the spring (60) underneath the platform is compressed. Throughout this refilling process, the hot air inside the expansion vessel (20) is expelled to the atmosphere through the exhaust port. The exhausted hot air follows a flow path through the regenerative heater (110), transferring heat to the medium or heat exchange matrix within it. Simultaneously as the liquid level inside the compression vessel (30) decreases, suction pressure is created, allowing for the intake of fresh air for the next cycle. Further, as the compression vessel (30) empties, its net weight decreases, resulting in an upward movement of the movable platform (50) and the connected output shaft under the restoration force exerted by the spring (70). This completes the exhaust and intake stroke, with the expansion vessel (20) moving down and the compression vessel (30) moving up. The system has now returned to its initial condition, completing the cycle. During one complete cycle as the vessels (20) and (30) moves up and down, the mechanism attached to output shafts of each movable platforms (40) and (50) will also move up and down accordingly, producing useful work.

[0035] This out of phase up and down motion of the vessels (20) and (30) can be converted into useful work by the mechanism linked to fluid vessels. The mechanism can be of many forms-Vessels are arranged on spring supports or suspended on springs, and their movement is harnessed through crank lever mechanisms to generate useful shaft work. Alternatively, the output shaft of the spring-loaded vessels (20) and (30) can be directly connected to linear reciprocating current generators, eliminating the need for intermediate mechanisms. Another option is to connect the output shaft to a reciprocating piston of a hydraulic pump, generating pressurized liquid to drive a turbine's impeller. In a different configuration, only one vessel is movable mounted on a fulcrum mechanism and balanced by a counterweight instead of a spring. Lastly, both vessels (20) and (30) can be connected to a modified Roberval weighing balance mechanism, where their weights balance each other, and the shifting centre of gravity caused by the liquid movement causes the balance mechanism to move. This motion can be transmitted to a crankshaft to produce rotational motion. The above mentioned are only some examples , there are many other way up and down motion of vessels due to gravitational force generated due to the changes net weight of the vessels (20) and (30). FIG. 2 and 3 is a schematic representation of two specific embodiment of the hot heat engine of FIG. 1 in accordance with an embodiment of the present disclosure. This specific embodiment shows an engine where both the vessels (20) and (30) are connected to a common crank lever mechanism via a flywheel. Further, in this specific embodiment the for-way cut off valve (90) and the two non-retum valves(170) and (180) have been replaced with three independently actuated valves. With this arrangement the Otherwise, the principle of operation in this specific embodiment is in accordance with the present disclosure.

[0036] The specific embodiment illustrated in Fig.2 with method involves replacing the non-return valve (NRV) at the compression vessel inlet with a separately actuated valve to control the timing of opening and closing will allow the hot air engines to utilize vessels with different volumes for the expansion and compression processes. This allows for the creation of differential work between the expanding and compressing vessels. The flexibility of the approach enables adjustments to the vessel volumes to accommodate variations, such as in the Ericson / Jules / Bryton cycle where a smaller compression vessel is preferred. In the absence of an intermediate tank, complete transfer of liquid between vessels becomes necessary, necessitating equal volumes for both vessels under normal circumstances. However, it is possible to achieve different volumes of expanding and compressing air while keeping the vessels the same size. By replacing the non-return valve (NRV) at the compression vessel inlet with a separately actuated valve to control the timing of opening and closing.

[0037] This valve remains open during the intake phase until the level in the compression vessel reaches a certain point. During this period, the liquid fills inside the compression vessel, while the equivalent volume of air is expelled back to the atmosphere instead of being supplied to the receiver tank. Only after the valve is closed, the air inside is compressed and pushed into the receiver tank. Thus, the work of compression is expended by the expanding vessel only when this valve is closed. By carefully selecting the closing time of the intake valve, we can optimize the starting time of the compression process and the volume of air supplied to the receiver tank, even though the volume of both vessels remains the same. FIG. 4 is a schematic representation of one embodiment of the hot air engine of FIG. 1 in accordance with an embodiment of the present disclosure. In this embodiment of the present disclosure, one vessel is fixed and kept on ground and other vessel is kept at a height. In such an embodiment, the elevation of the compression vessel (30) may be according to the pressure generated by the air heater (50). In detail, the expansion vessel (20) is fixed at a ground position and the compression vessel (30) is placed at a predefined height on a weight balance mechanism. The movement of fluid from the expansion vessel (20) to the compression vessel (30) changes a centre of gravity of the system causing the crank-lever mechanism to move, thereby converting the heat energy into the mechanical energy. Such arrangement of the engine (10) replaces the piston in conventional piston vessel arrangement of the heat engine (10). The pressure increase in the isothermal expansion process of an air power cycle will be used to shift the liquid from the lower vessel to the higher one. Such caloric heat engine (10) which may convert heat into power, is primarily designed to work in reversible Ericsson cycle.

[0038] It must be noted that the illustrations in Fig.l,Fig.2and Fig.3 are exemplary, however, it is to be noted that the scope of the invention is not limited to the illustrations, but many such designs can be derived from the concept of this invention.

[0039] In one embodiment, the hot air engine is also designed to shift in centre of gravity when the liquid transfer from one vessel to another where at least one vessel is mounted on a fulcrum or balance mechanism, imparting motion to the mechanism connected to the vessels.

[0040] FIG. 5(a) and 5(b) is a schematic representation of an exemplary intermediate storage tank of one embodiment of the hot air engine of FIG.1 in accordance with an embodiment of the present disclosure. FIG. 5(a) represents an initial condition of the hot air engine (10) with the inclusion of the intermediate storage tanks (170) thereby increasing flexibility to the hot air engine. The storage tanks (170) are kept at a level intermediate to the levels between the expansion vessel and the compression vessel to avoid direct connection between the primary vessels. In one embodiment, the volume of the intermediate storage tanks (170) is double of the volume of the expansion vessel and the compression vessel to isolate the working fluid of the expansion vessel and compression vessel from each other.

[0041] FIG. 5(b) illustrates the hot air engine (10) in an expansion stroke. The vacant space (180) above the intermediate vessel acts as an isolation space between the working fluids thereby isolating and preventing mixing of the working fluids of the expansion vessel and the compression vessel.

[0042] FIG. 6(a) and 6(b) is a schematic representation of an exemplary intermediate storage tank of another embodiment of the hot air engine of FIG.l in accordance with an embodiment of the present disclosure. Specifically, FIG. 6(a) illustrates an initial condition of the hot air engine (10). Likewise, FIG. 6(b) illustrates a condition of the hot air engine (10) in an expansion stroke. It must be noted that the working fluids inside the expansion vessel and the compression vessel is different with the intermediate storage tanks (170).

[0043] By incorporating an intermediate storage tank with vacant space above, two different working fluids can be utilized. For instance, higher boiling point oil can be used in the expansion vessel, while an emulsion-resistant fluid or water itself can be employed in the compression vessel. A higher density liquid if in the compression vessel result a smaller compression vessel than expansion vessel, by this a differential volume work can be created.

[0044] FIG. 7(a) and 7(b) is a flow chart representing the steps involved in a method (200) for operating the hot air engine in accordance with an embodiment of the present disclosure. The method (200) includes applying an increased air pressure, due to heating inside an air heater, on top of liquid in an expansion vessel when the compression vessel is empty, and an expansion vessel is filled with the liquid in step 205. In one embodiment, the expansion vessel and the compression vessel may be a part of fluid gravity piston system. In a preferred embodiment, the air heater may be coupled at a top portion of the expansion vessel via flexible hose pipe.

[0045] The method (200) also includes flowing the liquid from the expansion vessel to the compression vessel, via a hose pipe, as the air from the air heater pushing on top of the liquid when air pressure is raised above a threshold limit in step 210. The expansion vessel and the compression vessel are placed at a differential height on a spring supported movable platform. In such an embodiment, the spring supported movable platform may include first spring and a second spring coupled to the expansion vessel and the compression vessel respectively.

[0046] During this process as the air filled inside compression vessel will undergo compression which will further pushed to fill the receiver tank. The liquid will return to the expansion vessel if this air pressure from the air heater is released from the top of liquid level in the expansion vessel. The admission and release of air pressure on top of liquid level of expansion vessel and hence the timing of expansion and compression strokes is controlled by a cut-off valve placed at the outlet of receiver tank. Unlike, a conventional hot air in the proposed engine, pressure of the hot expanding gases is used to transfer the liquid of lower elevation to higher elevation and back alternatively in a working cycle. During this process weight or gravitational force acting on vessels are changed, and a motive force is generated to move a mechanism whatsoever connected to the vessels producing useful work.

[0047] The method (200) further includes evacuating the expansion vessel and filling the compression vessel with the liquid by transferring liquid from one vessel to another in step 215. In one embodiment, the expansion vessel and the compression vessel are connected with a hose pipe at bottom.

[0048] The method (200) further includes decompress and compress the first spring and a second spring, to move the expansion vessel in upward direction and the compression vessel in downward direction respectively when the liquid of the expansion vessel moves to the compression vessel in a first half of the cycle in step (220).

[0049] The method further (200) includes releasing air pressure from the top of the liquid level of expansion vessel by positioning the cut-off valve to open the exhaust port and subsequent reversal of working fluid from compression vessel to the expansion vessel due to the gravity head in step (225).

[0050] In one embodiment, the method (200) further includes decompressing the second spring and moving the compression vessel in upward direction and compressing the first spring and moving the expansion vessel in downward direction respectively when the liquid of the compression vessel starts refilling the expansion vessel in a second half of the cycle in step (230). The method further includes expelling hot gas filled inside the expansion vessel as the liquid refills inside this vessel, through a path via regenerative heater to atmosphere, as well as simultaneously include intake of fresh air inside compression vessel through the intake valve as suction pressure is created inside the compression vessel due to descending liquid level inside the compression vessel. In some embodiment, the method include storing the heat from the hot exhaust air in the regenerator and using this stored heat to preheat the incoming fresh air from released from the receiver tank.

[0051] The method (200) further include filling and refilling the expansion vessel and the compression vessel alternatively according to the air pressure variation in the air heater causing the up and down movement of the mechanism attached to the vessels to convert heat energy into mechanical energy in step (235). In a specific embodiment, the method includes fixing the expansion vessel at a ground position and placing the compression vessel at a predefined height on a weight balance mechanism, wherein movement of liquid from the expansion vessel to the compression vessel changes a centre of gravity of the compression vessel causing the crank-lever system to move, and thereby converting the heat energy into the mechanical energy.

[0052] In one embodiment, a plurality of intermediate movable or fixed storage vessels is added to isolate the working fluids of primary vessels. With this intermediate storage vessel arrangement, the volume of primary vessels can be different by choosing liquids of different densities.

[0053] Various embodiments of the hot air engine as described above enables the caloric heat engine which converts heat into power, to use a fluid gravity piston engine unlike the conventional heat engines which uses reciprocating piston cylinder to extract work from an expanding gas. One of the vessels or both the vessels are placed on movable platforms or mechanism which may replace the piston conventional piston cylinder arrangement of a hot air engine. The engine design offers several advantages. It requires only small air pressure to lift liquids compare to moving a metallic piston, making it compatible with low temperature sources. By replacing metal pistons with air-tight tanks filled with liquid, the engines can be scaled up to large sizes and capacities. Since sliding pistons are omitted, the engine operates with low friction. The 100% piston sealing is achieved as liquids replace sliding pistons, eliminating the need for piston rings. This method of replacing conventional piston cylinders can be used to design many simple and cost-effective engine configurations. It can be easily augmented with heat storage devices.

[0054] It will be understood by those skilled in the art that the foregoing general description and the following detailed description are exemplary and explanatory of the disclosure and are not intended to be restrictive thereof.

[0055] While specific language has been used to describe the disclosure, any limitations arising on account of the same are not intended. As would be apparent to a person skilled in the art, various working modifications may be made to the method in order to implement the inventive concept as taught herein.

[0056] The figures and the foregoing description give examples of embodiments. Those skilled in the art will appreciate that one or more of the described elements may well be combined into a single functional element. Alternatively, certain elements may be split into multiple functional elements. Elements from one embodiment may be added to another embodiment. For example, the order of processes described herein may be changed and are not limited to the manner described herein. Moreover, the actions of any flow diagram need not be implemented in the order shown; nor do all of the acts need to be necessarily performed. Also, those acts that are not dependent on other acts may be performed in parallel with the other acts. The scope of embodiments is by no means limited by these specific examples.

Claims

I CLAIM:What is claimed is:

1. A hot air engine (10) comprising: a fluid gravity piston arrangement comprising: at least two vessels, wherein the at least two vessels is an expansion vessel (20) and a compression vessel (30), wherein the expansion vessel (20) and the compression vessel (30) are airtight vessels coupled to an up and down arrangement and placed at multiple elevations, wherein the expansion vessel (20) and the compression vessel (30) accommodate a liquid suitable to a working temperature of a cycle, wherein the compression vessel (30) is empty, and the expansion vessel (20) is filled with the liquid initially due to gravity head caused by difference of the multiple elevations, wherein the expansion vessel (20) and the compression vessel (30) are interconnected at the bottom using flexible hose pipes, wherein the flexible hose pipes allow transfer of the liquid from the expansion vessel (20) to the compression vessel (30) and vice versa, during the movement of the at least two vessels, wherein a restoration force is provided to the movable vessel; wherein the expansion vessel (20) and the compression vessel (30) are coupled with a mechanism to convert the up and down movements of the expansion vessel (20) and the compression vessel (30) into useful work; wherein the top part of the compression vessel is coupled to a storage tank and an intake valve using flexible horse pipes via non-retum valves;an air heater (120) coupled at a top portion of the expansion vessel (20))using a hose pipe (150) wherein the air heater (120) increases air pressure due to heat and pushes the liquid of expansion vessel (20) to flow towards the compression vessel (30) via a hose pipe (130) and (140), when air pressure is raised above a threshold limit; and wherein the cycle comprises an alternate filling and refilling of the expansion vessel (20) and the compression vessel (30) by transfer of liquid between the expansion vessel (20) and the compression vessel (30) according to the air pressure variation produced by the air heater (120), thereby causing the movement of the up and down arrangement of movable vessels and the mechanism whatsoever connected to the vessels producing useful work.

2. . The hot air engine (10) as claimed in claim 1, comprising: an air receiver tank (90) to receive compressed air from the compression vessel (30) when a fraction of air volume as per the cut of ratio is compressed by the rising liquid inside the compression vessel (30); a cut off valve fixed at an outlet of a receiver tank (90) wherein the cut off valve controls the air supply to the expansion vessel (20) as per the cut of ratio of the cycle; a non-return valve (170) adapted to open when the fluid level in the compression vessel (30) is descending, wherein the opening of the non-retum valve (170) due to suction pressure created inside the compression vessel (30) allows fresh air to be filled; and a regenerator (110) to store heat from the hot exhaust in hot condition before transferring to the cold incoming fresh air from the receiver tank (90).

3. The hot air engine (10) as claimed in claim 1, wherein the spring supported movable platform (40) comprises a first spring (60) and a second spring (70) coupled to the expansion vessel (20) and the compression vessel (30) respectively where the restoration force is provided by the springs, wherein the first spring (60) and the second spring (70) expands and compresses to move the expansion vessel (20) in upward direction and the compression vessel (30) indownward direction respectively when the liquid of the expansion vessel (30) moves to the compression vessel (20) in a first half of the cycle.

4. The hot air engine (10) as claimed in claim 1, wherein the restoration force is provided by connecting anyone or both expansion vessel (20) and the compression vessel (30) to different fulcrum mechanisms with counterweights on one end.

5. The hot air engine (10) as claimed in claim 1, wherein the restoration force to the Movable vessels may also be provided by linking by placing / linking both vessels to a single mechanism similar to a weighing balance. In this case the vessels will act as a counterweight to one another.

6. The hot air engine (10) as claimed in claim 1, wherein the movable vessels hang on a pully mechanism thereby maintaining the elevation difference.

7. The hot air engine (10) as claimed in claim 2, wherein the expansion vessel (20) and the compression vessel (30) are placed on the spring supported movable platform (40)and connected to one or more linear reciprocating current generators without intermediate mechanism.

8. The hot air engine (10) as claimed in claim 2, wherein the expansion vessel(20) and the compression vessel (30) are placed on the spring supported movable platform (40, 50)and connected to a reciprocating piston of a hydraulic pump to generate pressurized liquid to move impeller of a turbine.

9. The hot air engine (10) as claimed in claim 2, wherein the expansion vessel (20) and the compression vessel (30) placed on spring loaded movable platform are directly connected to crank liver mechanisms to make use of the movement of up and down movement of vessels to produce useful shaft work.

10. The hot air engine (10) as claimed in claim 1, comprises a plurality of intermediate storage tanks arranged at an elevation intermediate to the elevations of expansion vessel (20) and compression vessel (30), thereby isolating the working fluids of expansion vessels (20) and compression vessel (30).

11. The hot air engine (10) as claimed in claim 11, wherein the working fluids are unique with different densities properties in expansion vessel (20) and compression vessel (30).

12. The hot air engine (10) as claimed in claim 2, wherein the non-retum valve (170) at the compression vessel (30) inlet is replaced with an actuated valve, allowing for control over the timing of its opening and closing thereby allowing the hot air engine to utilize vessels with varying volumes for the expansion and compression processes, thereby creating differential work between the expansion vessel (20) and compressing vessel (30).

13. The hot air engine (10) as claimed in claim 13, wherein the actuated valve is adapted to remain open during the intake phase until the liquid level in the compression vessel (30) reaches a specific point and subsequently the liquid fills the compression vessel (30) while an equivalent volume of air is released back to the atmosphere instead of being supplied to the receiver tank.

14. A method (200) to operate a hot air engine comprising: applying, by heating inside an air heater, an increased air pressure on top of liquid in an expansion vessel when a compression vessel is empty, and the expansion vessel is filled with the liquid; (205) allowing, by a hose pipe, the liquid to flow from the expansion vessel to the compression vessel, due to the air from the air heater pushing the liquid upwards when air pressure is raised above a threshold limit, wherein the expansion vessel and the compression vessel are placed at a differential height on movable platform; (210) evacuating the expansion vessel and filling the compression vessel with the liquid; (215) decompressing and compressing, by a first spring and a second spring, to move the expansion vessel in upward direction and the compression vessel in downward direction respectively when the liquid of the expansion vessel moves to the compression vessel in a first half of the cycle; (220)releasing air pressure from the top of the liquid level of expansion vessel (20) and subsequent reversal of working fluid from compression vessel (30) to the expansion vessel due to the gravity head (30); ( 225) decompressing and moving the compression vessel in upward direction and compressing and moving the expansion vessel in downward direction respectively when the liquid of the compression vessel starts refilling the expansion vessel in a second half of the cycle; (230) filling and refilling of the expansion vessel and the compression vessel according to the air pressure variation in the air heater causing the movement of the mechanism attached to the vessels to convert heat energy into mechanical energy. (235)

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