Method and device for converting heat energy into mechanical energy

The invention relates to a method of converting thermal energy into mechanical energy by changing the volume, pressure and temperature of an operating medium, in particular gas, in several stages, as well as devices for carrying out this method.

Such a method and device are published e.g. in WO documents

03/102403 A and WO 03/012257 A.

Methods for converting thermal energy into mechanical energy are known, at which the pressure and temperature of the working medium in the working space along with the alternating volume change. With decreasing volume, pressure and temperature increase, both due to the aforementioned volume change, as well as - and especially - in the last phase of volume reduction, or in the first phase of increasing the volume again, as a result of additional heat input either from outside or as a result of heat generation, e.g. due to combustion, in the medium inside the working space. When the volume increases again, the pressure arising from the previous decrease in volume in a closed working space, after deducting losses, performs the work necessary for the subsequent reduction in volume, while the pressure, resulting from the additional supply of thermal energy, also performs after deduction losses, mechanical work. In a permanently closed working space, due to the additional heat input, the temperature of the medium at the end of each

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- 2 increase in volume, and thus also at the end of the subsequent decrease in volume, would always be higher than the temperature at the beginning of the previous increase in volume, hence when the heat is supplied from outside, the temperature of the medium would be equal to the temperature at which heat is supplied from outside, and the temperature difference, and hence the amount of heat input, would be zero, regardless of losses. The heat input through its generation in the refrigerant, in a permanently closed working space, would stop due to oxygen deficiency. Hence, it is necessary to open the work space for a specific time in order to drain the applied medium and bring fresh, both at the beginning of the volume reduction or before it, as well as at the end of the volume increase or after it. The working process of pressure and temperature changes while reducing and increasing pressure takes place in two strokes. If we add another two to these two strokes, i.e. increasing the volume to supply the factor used and reducing the volume to discharge the factor used, the process consists of four strokes of conversion of thermal energy into mechanical. If the supply and discharge of the refrigerant takes place at the beginning of one stroke, at the end of the second stroke, we are talking about a two-stroke process. All these processes take place in accordance with the known state of the art in one workspace, in exceptional cases divided into two parts.

According to the method of converting thermal energy into mechanical energy by changing the volume, pressure and temperature of the working medium according to the invention, the working medium is sucked into the first stage as the volume of this stage increases, and then during the decrease

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- 3 volumes of the first stage are transferred to the second stage as the volume of the second stage increases, after which, when the volume of the second stage decreases, it is transferred by the third stage while applying heat to the fourth stage as the volume of the fourth stage increases, then from the fourth stage when reducing the volume of the fourth stage is transferred to the fifth stage, and in the fifth stage as the volume increases, the fifth stage expands. Advantageously, during the reduction of the volume of the second stage, the working medium is transferred through the third stage, with simultaneous heating, directly to the fifth stage.

The working medium is cooled down advantageously during transfer from the first stage to the second stage. Advantageously, the working factor is transferred from the fifth stage while the volume of the fifth stage decreases, while cooling to the first stage while increasing the volume of the first stage. Advantageously, the working medium is transferred from the fifth stage when the volume of the fifth stage decreases to the third stage and is used in the heating process. Advantageously, the working medium is transferred from the fifth stage directly to the second stage as the second stage volume increases during the reduction of the fifth volume and / or with simultaneous cooling. In devices that perform a multi-stage conversion of thermal energy into mechanical energy by changing the volume, pressure and temperature of the working medium, the third stage is made, at least in accordance with the invention, as a working space with an unchanging volume, while the remaining stages are made as variable-volume work spaces, especially machines with a rotary piston, and are configured one after the other in the direction

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- 4 movements of the working medium, partly before and partly after the third stage. Advantageously, the largest volume of the first stage is larger than the largest volume of the second stage, where the largest volume of the fifth stage is larger than the largest volume of the fourth stage, and the largest volume of the fifth stage is larger than the largest volume of the first stage or as large as the maximum volume first degree. The fifth degree is connected with the first stage. The third stage is advantageously designed as a combustion chamber and / or as a heat exchanger. The fifth stage is equipped with a suction valve. There is a benefit between the first stage and the second stage as well as between the fifth stage and the first stage and between the combined stage and the second stage there is a cooler.

The invention is further illustrated in the attached technical drawing, where in fig. 1 the basic embodiment of the invention is shown, in fig. 2 the embodiment with the cooler between the first and second stage, as well as between the fifth and first stage, and in fig. 3 the implementation with the first stage connected to the fifth stage and to the cooler between the fifth and second stages.

The working medium is fed to the first stage 1 (Fig. 1) when the volume of the first stage 1 increases, and then, when the volume of the first stage 1 decreases, it is transferred to the second stage 2 when its volume increases. Then, when the volume of the second stage 2 decreases, it is transferred to the third stage 3. During passing through the third stage 3, heat is supplied to the working medium or

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- from the inside, by burning the fuel in the working medium, or from the outside, by heating the third stage, e.g. by external combustion. From the third stage 3, the working factor is transferred to the fourth stage 4, the volume of which increases simultaneously, then from the fourth stage 4 when its volume decreases, it is transferred to the fifth stage 5. In the fifth stage 5, during its volume increase, the working factor expands. After expansion, when the volume of the fifth stage 5 decreases, the working medium is discharged to the outside, or again to the first stage 1. When using air as the working medium and external combustion as a way of bringing heat to the third stage, it is preferable to use expanded, but hot air for external combustion. The method according to the invention is a five-stroke thermodynamic cycle. In selected cases, it may be advantageous to skip the fourth grade 4 and transfer the refrigerant directly to the fifth grade, where it will expand. It is beneficial to cool the medium during transfer from the first stage 1 to the second stage 2 in the intercooler 6 (fig. 2). In a closed circuit, in which the working medium is led from the fifth stage 5 back to the first stage 1, it is preferable to place another intercooler 7 between the fifth and first stages. In selected cases, it is preferred, according to a further embodiment of the invention, to combine the fifth and first stages into a combined stage 51 and to transfer the working medium, expanded during the increase in volume of the combined stage 51, while the volume of the combined stage is again reduced to the second stage 2, while increasing the second degree, which may take place either through a combined one

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- 6 intercooler 76. In this case, the basic five-stroke thermodynamic cycle is replaced by a three-stroke cycle.

The device for performing the described method of converting thermal energy into mechanical energy is configured in accordance with the invention so that the third stage 3 is made as at least one working space with an invariable volume, while the remaining stages 1, 2, 4, 5, 51 are made as spaces working volumes. It is preferred that all stages, except the third stage, be made as rotary piston machines, in which during the rotation of the piston over each surface connecting its edges cyclically increases and decreases the volume of space limited by this surface and the adjacent inner surface of the cylinder, in which the piston rotates. The largest volume of the first stage 1 is larger than the largest volume of the second stage 2, then the largest volume of the fifth stage 5 is larger than the largest volume of the fourth stage 4, and the largest volume of the fifth stage 5 is larger or the same as the largest volume of the first stage 1. The largest volume of the combined stage 51 is larger than the largest volume of the fourth stage 4 and than the largest volume of the second stage 2. The third stage 3 is made as a combustion chamber and / or as a heat exchanger. The working medium is first supplied, e.g. by suction, to the increasing volume of the first stage 1. After reaching the maximum, the volume of this stage begins to decrease, and the working medium is pushed into the increasing volume of the second stage 2. Because the highest volume of the second stage 2 is several times lower than the highest volume of the first degree 1, condition

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- the working medium 7 changes in such a way that when it is transferred from the first stage 1 to the second stage 2, the refrigerant has a higher pressure and a higher temperature. If an excessive temperature rise is undesirable, an intercooler 6 can be placed between the two stages, as shown in Fig. 2. When the volume of the second stage 2 decreases again, the working medium is transferred from it through the third stage 3 to the fourth stage 4 with increasing volume. In the third stage 3, heat is supplied to the working medium, either by external heating, where this stage will be made as a heat exchanger, or by internal combustion, as in turbine combustion chambers, although at a clearly higher pressure. Since the largest volume of the fourth stage 4 is usually equal to the largest volume of the second stage 2, the working medium in the final stage 4 after heating in the third stage 3 will have a higher pressure and temperature than in the initial stage in the second stage. From the decreasing volume of the fourth stage 4, the working medium expands to the increasing volume of the fifth stage 5, where it does the work. However, it is possible to modify the device according to the invention so that the largest volume of the fourth stage 4 is larger than the largest volume of the second stage 2, so that between both stages there will be a partial, isobaric to isothermal expansion, and the method according to the invention will be similar to the method according to Carnot. In an extreme case, the fourth stage can be completely ruled out and allow the working medium from the second stage 2 when heating in the third stage 3 to expand directly to the fifth stage 5. The third stage has a non-zero volume, and therefore, if no heat is supplied to it, the beginning of the transfer of the working medium will come to

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- 8 partial expansion, and when transferred through the third stage, the working medium in the fourth stage will have a lower pressure and temperature than in the second stage. As a result of said lower pressure, the fourth stage will take from the third stage proportionally less amount of the weight of the working medium than transferred from the second to the third stage, and the remaining quantity will generate, or increase the residual pressure in the third stage. In this way, depending on the size of the third stage, also without the introduction of heat, the pressure in the third stage will increase very quickly so that there is no expansion during the transfer of the working medium from the second to the fourth stage (through the third stage), and the heat can be supplied under pressure (given by compressing the working medium from the first stage to the second stage). Therefore, the third stage can be made both as a combustion chamber with a small external surface (so that there is no unnecessary heat loss), as well as a large surface heat exchanger (so that as much heat as possible can be supplied). In order for the third stage to be able to provide as much heat as possible and reduce the work necessary to perform the compression phase of the cycle, the temperature should be reduced as much as possible during the transfer from the first to the second stage. According to the invention, this is possible due to the intercooler 6 being placed between the first stage 1 and the second stage 2. With closed circulation, when the working medium is led from the fifth stage 5 back to the first stage 1, it is preferable to place another intercooler 7 between these stages. With the configuration according to the invention, it is possible to choose the value of the expansion stage, irrespective of the compression ratio, and so you can allow it to be compressed and heated

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- 9 working medium has expanded to ambient pressure, which will ensure high cycle efficiency. At a given expansion rate, the pressure at the end of the expansion depends on the pressure at the beginning of the expansion, therefore, with less heat, the pressure at the end of the expansion may drop below the ambient level. If this phenomenon is undesirable, another feature of the invention can be used, i.e. suction of the working medium at the end of expansion through the suction valve 8. The working cycle implemented in the manner and with the device according to the invention is then a five-stroke cycle. At a certain value of the fifth degree expansion, i.e. the ratio between the largest volumes of the fifth and fourth stages, not only the pressure, but also the temperature close to the ambient temperature will drop at the end of the expansion. Therefore, with a closed circuit and with external heating of the working medium in the third stage 3, according to another feature of the invention, it is possible to connect the fifth stage 5 to the first stage 1 (Fig. 3), and it is advantageous to lead the working medium after expansion through the intercooler 76, from Stage 51 to Stage 2 with compression simultaneously. Also in this case it is advantageous to equip the combined stage 51 with a suction valve 8. As part of the invention, it is therefore possible to modify the basic five-stroke cycle into a three-stroke cycle in selected cases.

The invention, as in accordance with embodiments, also in other embodiments arising from the claims, has the advantage compared to known heat engines (especially with a four-stroke cycle) that it allows higher operating pressures than turbine engines, as well as a longer heating time for compressed working factor and

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Lower pressures and temperatures at the end of expansion than previously known piston engines. The result is higher cycle efficiency, and when the working medium is heated by internal or external combustion also lower noise levels and lower emissions of carbon oxides and nitrogen. The invention can also be advantageously applied to the conversion of solar energy into mechanical energy.

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