CN110234863B

CN110234863B - Regenerative cooling system

Info

Publication number: CN110234863B
Application number: CN201880007916.6A
Authority: CN
Inventors: V·拉比
Original assignee: V labi
Current assignee: V labi
Priority date: 2017-02-27
Filing date: 2018-02-12
Publication date: 2022-03-18
Anticipated expiration: 2038-02-12
Also published as: JP2020509282A; EP3585993B1; AU2018225327B2; JP7065106B2; KR102525744B1; ES2874807T3; WO2018154214A1; FR3063311A1; EP3585993A1; CA3053015A1; AU2018225327A1; KR20190116275A; FR3063311B1; CN110234863A

Abstract

A regenerative cooling system (100) is provided for regenerating the heat engine (1) and comprises a cooling chamber (79) surrounding a gas expander (78), a gas circulation space (80) remaining between said chamber (79) and said expander (78), a working gas (81) discharged from the gas expander (78) circulating in said space (80) before returning to the regenerative heat exchanger (5) in which it is cooled, a majority of the heat of said gas (81) being reintroduced into the thermodynamic cycle of the regenerative heat engine (1).

Description

Regenerative cooling system

The present invention relates to a regenerative cooling system which constitutes in particular an improvement of a transfer-expansion and regenerative heat engine which is the subject of patent application No. fr 1551593 belonging to the applicant's 2015 year 2 month 25 and patent number US 2016/0252048 a1 also belonging to the applicant's 2016 year 9 month 1 publication.

Brayton regeneration cycles, which are typically implemented by means of centrifugal compressors and turbines, are familiar.

According to this mode of embodiment, the cycle results in the engine providing significantly higher efficiency than that of a controlled ignition engine. The efficiency is comparable to that of a fast diesel engine. However, it is still smaller than the very large displacement low speed two-stroke diesel engines found, for example, in marine propulsion or stationary power generation.

In addition to very modest overall efficiencies, centrifugal compressors and turbine engines using the brayton regeneration cycle provide optimal efficiencies over a relatively narrow range of power and rotational speeds. Furthermore, their response time in power modulation is long. For these various reasons, their field of application is limited and they are difficult to adapt to land transportation, in particular to cars and trucks.

The transfer-expansion and regenerative thermal engine of patent application No. fr 1551593 has been proposed to remedy these drawbacks. A special feature of said engine is that the regenerative brayton cycle is no longer carried out by means of a centrifugal compressor and a turbine, but by means of a positive-displacement machine or at least by means of a positive-displacement expander formed around an "expander cylinder".

In the drawings of patent application No. fr 1551593, it is noted that each end of the expander cylinder is closed by an expander cylinder head. In addition, the cylinder houses a double acting expander piston to form two variable volume transfer-expansion chambers. The piston may be displaced in an expander cylinder to transfer work to a power take-off shaft via a familiar connecting rod and crankshaft.

One of the advantages claimed by the invention, which is the subject of patent application No. fr 1551593, is the efficiency of the conversion of heat into work, which is much higher than that of any operating principle replacing a conventional internal combustion engine, which means that the same work provides a lower fuel consumption than said conventional engine and also reduces the associated carbon dioxide emissions.

In order to achieve these objectives, at least three conditions need to be satisfied, as is explicitly indicated in patent application FR 1551593.

The first is that the positive displacement expander is actually composed of a single cylinder, which is not a prior art teaching relating to such machines. As an example, the patent US2003/228237 a1, 12/11/2003, does include a compressor, a regenerative heat exchanger, a heat source and an expander, however the expander is not a cylinder, but rather a "cycloid" as the inventor of said patent.

The second condition is that the gas inlet and outlet in the expander cylinder are regulated by appropriately phased intake and exhaust metering valves, which results in a pressure versus volume diagram as shown in patent application No. fr 1551593.

A third condition is that the sealing means between the piston and the cylinder can operate at very high temperatures.

It should be noted that the transfer-expansion and regeneration heat engine described in patent application No. fr 1551593 meets the third condition by proposing an innovative air cushion segment formed by a continuous perforated inflatable and expandable ring, said ring being located in an annular groove designed in the expander piston. The ring and the groove together define a pressure distribution chamber connected to a source of pressurized fluid.

This new sealing arrangement without direct contact with the expander cylinder makes it possible to operate the cylinder at high temperatures, while closing the intake and exhaust metering valves in the cylinder head of said cylinder makes it possible to maximize the efficiency of the transfer-expansion and regeneration heat engine.

The innovative sealing device based on an air cushion segment is deliberately placed in patent application No. fr 1551593 in the claims depending on the independent claim. It is easily understood that by proposing his invention in this way, the inventor does not exclude other sealing solutions that can replace the segments, even if the latter are proposed in the patent application as a key element of the transmission-expansion and regenerative thermal engine.

As clearly stated in patent application FR 1551593, in order to make the efficiency of the transfer-expansion and regeneration heat engine as high as possible, the inner walls of the expander cylinders need to be raised to a high temperature so that the hot gases introduced into said cylinders do not cool when they contact these walls, or at least are cooled as little as possible by these walls. This applies at least to the inner wall of the expander cylinder, and to the inner wall of the cylinder head cooperating with said cylinder.

According to the engine thermodynamic principle proposed by Sadi Carnot, patent application FR 1551593 proposes that the efficiency of the transfer-expansion and regeneration thermodynamic engine is higher as the temperature of the gas introduced into the expander cylinder is higher.

This is why patent application FR 1551593 requires that the expander cylinder, the cylinder head of the expander cylinder and the expander piston of the transmission-expansion and regenerative thermal engine are made of a very high temperature resistant material, such as ceramics based on alumina, zircon or silicon carbide.

The hot parts and components at high temperatures of the transfer-expansion and regeneration heat engines are still the subject of the patent for the improvement of said engines. Therefore, reference may be made to patent application No. fr 1558585 on 9/14/2015, belonging to the applicant, which relates to a double-acting and self-adaptive support expander cylinder capable of operating at high temperatures and subject to thermal expansions different from those of the gearbox to which it is attached. In the same respect, it should also be noted that patent application No. fr 1558593, on 14 th of 9 th of 2015, also belonging to the applicant, relates to a double-acting piston consisting of a prestressed assembly and capable of operating at temperature.

It is noted that the patent applications No. fr 1558585 and No. fr 1558593 just cited propose very robust solutions for handling the presence of high-temperature parts and low-temperature parts in the same apparatus.

In particular, the construction proposed in said patent prevents to a large extent the migration of heat from the hot parts to the cold parts with which they cooperate. This ensures an increase in the efficiency of the transfer-expansion and regenerative thermal engine.

On the other hand, the improvements proposed in patent applications nos. fr 1558585 and fr 1558593 do not alter the fact that if the temperature of the gas introduced into the expander cylinder of the engine is, for example, 1300 degrees celsius, the temperature of the inner walls of the cylinder will locally approach 1300 degrees celsius, with the average temperature of these walls approaching, for example, 1000 degrees celsius.

The temperature of these gases therefore directly determines the temperature to which the material constituting the hot parts of the expander cylinder of the transmission-expansion and regenerative thermal engine must withstand. Indirectly, therefore, the temperature resistance of these materials determines the maximum available efficiency of the engine.

Furthermore, it should be noted that the number of materials in question capable of withstanding very high temperatures is relatively small, since they also need to provide increased mechanical strength at these same temperatures, while also having corrosion and oxidation resistance.

The material is mainly a ceramic such as alumina, zircon, silicon carbide or silicon nitride. These materials are hard and difficult to process. The sales price of the finished parts is therefore relatively high, which prevents the automotive industry from adopting the transfer-expansion and regenerative heat engine described in patent application FR 1551593. In fact, since the industry is oriented to the consumer market, it is very sensitive to the manufacturing and selling price, which needs to be as low as possible.

Therefore, it is desirable that the expander cylinder inner wall of the engine is maintained at a maximum temperature of, for example, 700 to 900 degrees celsius. Indeed, at such temperatures, more common materials, such as cast iron or stainless steel or refractory materials, which are less expensive to produce and machine than ceramics, may be used to make the expander cylinder. The same is true for the cylinder heads and their corresponding plenums and conduits that cooperate with the cylinders.

However, on the one hand the temperature of the hot gases admitted into the expander cylinders of the transfer-expansion and regenerative thermal engine must be prevented from decreasing and on the other hand the heat of these gases must be allowed to escape as pure losses through the cooler walls of the cylinders in contact with these gases. In fact, these two actions can have the detrimental consequence of significantly reducing the final efficiency of the transfer-expansion and regenerative thermal engine.

Therefore, in the prior art, there is a need to choose between very efficient but costly and difficult to produce trans-expansion and regenerative thermal engines and engines based on the same principle but employing materials that are less costly to produce but with greatly reduced efficiency. This constitutes a difficult problem.

To address this challenge, in one particular embodiment, the regenerative cooling system of the present invention allows:

significantly reducing the temperature of the internal walls of the expander cylinders and their cylinder heads of the transfer-expansion and regeneration heat engine that is the subject of patent application FR 1551593, so that said cylinders and these cylinder heads can be manufactured using materials of lower selling price, without significantly reducing the overall efficiency of said heat engine;

without the regenerative cooling system according to the invention, the higher temperature gas is allowed to enter the expander cylinder of expensive and complex material (such as ceramic);

the use of low selling price materials provides the transfer-expansion and regenerative thermal engine, which is the subject of patent application FR 1551593, with a higher final energy efficiency than would be possible with the same engine with expensive and complex materials (such as ceramics).

It should be understood that the regenerative cooling system according to the present invention is mainly directed to a transfer-expansion and regenerative thermal engine belonging to the applicant as subject of patent application FR 1551593.

However, the system may also be applied without limitation to the expander of any other engine having a brayton regeneration cycle, whether the expander is a centrifuge, a volumetric expander or any other type of expander, and provided that it cooperates with any given type of regenerator.

Further features of the invention have been described in the specification and in the dependent claims depending directly or indirectly on the independent claims.

The regenerative cooling system according to the invention is designed for a regenerative thermal engine, which comprises at least one regenerative heat exchanger, the regenerating heat exchanger has a high-pressure regenerating pipe in which a working gas is circulated to be preheated, the working gas having been previously compressed by a compressor, while at the outlet of the duct, the gas is superheated by a heat source prior to being introduced into the gas expander, said gas is expanded in said gas expander to produce work on a power take-off shaft, and then said gas is discharged at the outlet of said gas expander and introduced into a low pressure regeneration conduit of said regenerative heat exchanger, said gas releasing most of its residual heat to said working gas circulating in said high pressure regeneration conduit by circulating in said conduit, said system comprising:

at least one cooling chamber which completely or partially surrounds the gas expander and/or heat source and/or a hot gas inlet duct connecting the source to the expander, while leaving a gas circulation space between the chamber on the one hand and/or the expander and/or the source and/or the duct on the other hand;

at least one chamber inlet port directly or indirectly connected to the outlet of the gas expander and through which some or all of the working gas discharged from the expander via the outlet can enter the gas circulation space;

at least one chamber outlet port which is directly or indirectly connected to the low pressure regeneration duct and through which the working gas can exit the gas circulation space before being introduced into the low pressure duct.

The regenerative cooling system according to the invention comprises a chamber inlet port connected to the outlet of the gas expander by a chamber inlet conduit whose effective cross section is regulated by a flow control valve.

The regenerative cooling system according to the invention comprises a chamber outlet port connected to a low pressure regeneration conduit by a chamber outlet conduit, the effective cross section of which is regulated by a flow control valve.

The regenerative cooling system according to the invention comprises an outlet of the gas expander, which is connected to the low pressure regeneration conduit by a chamber bypass conduit.

The regenerative cooling system according to the invention comprises an effective cross section of the chamber bypass duct regulated by the flow control valve.

The regenerative cooling system according to the invention comprises an exterior of a cooling chamber coated with a thermally insulating layer.

The invention, its characteristics and the advantages it may provide will be better understood with respect to the following description, given as a non-limiting example and with respect to the attached drawings:

fig. 1 is a schematic side view of a regenerative cooling system according to the invention, such as may be implemented in a transfer-expansion and regenerative thermal engine belonging to the applicant as subject of patent application No. fr 1551593, and according to one variant of said system, whereby the outlet of said gas expander is connected to said low-pressure regeneration duct by a chamber bypass duct, so that the effective cross-sections of said bypass duct and chamber outlet duct are adjusted by a flow control valve.

The specific implementation mode is as follows:

various details of the regenerative cooling system 100, its components, its variations, and its accessories are shown in FIG. 1.

As shown in fig. 1, a regenerative cooling system 100 is provided for a regenerative thermal engine 1, the regenerative thermal engine 1 comprising at least one regenerative heat exchanger 5, said regenerative heat exchanger 5 having a high pressure regeneration conduit 6, in which a working gas 81 circulates, is heated in said conduit and has previously been compressed by a compressor 2.

Upon exiting the high pressure regeneration duct 6, the gas 81 is superheated by the heat source 12 before being introduced into the gas expander 78 where it expands to produce work on the power take-off shaft 17.

The working gas 81 is then discharged from the gas expander 78 and introduced into the low-pressure regeneration conduit 7 of the regenerative heat exchanger 5, said gas 81 releasing its considerable residual heat to the working gas 81 circulating in the high-pressure regeneration conduit 6 by circulating in said conduit 7.

In this context, as is clearly shown in fig. 1, the regenerative cooling system 100 according to the invention comprises at least one cooling chamber 79, said cooling chamber 79 completely or partially surrounding the gas expander 78 and/or the heat source 12 and/or the hot gas intake duct 19 connecting said source 12 to the expander 78, while a gas circulation space 80 remains between said chamber 79 on the one hand and/or said expander 78 and/or said source 12 and/or said duct 19 on the other hand, in which space 80 a working gas 81 can circulate.

It should be noted that the cooling chamber 79 may be made of drawn or hydroformed stainless steel plate and it may be realized in a plurality of parts assembled to each other by welding, screwing or riveting, after which said chamber may be attached directly or indirectly to the

part

78, 12, 19 it surrounds.

Fig. 1 shows that the regenerative cooling system 100 according to the invention further comprises at least one chamber inlet port 82, said chamber inlet port 82 being directly or indirectly connected to the gas expander outlet 78, and that some or all of the working gas 81 discharged from said expander 78 via said outlet may enter the gas circulation space 80 through said chamber inlet port 82.

Also in fig. 1, it should be noted that the regenerative cooling system 100 according to the invention further comprises at least one chamber outlet port 83, said chamber outlet port 83 being directly or indirectly connected to the low pressure regeneration duct 7, and the working gas 81 may leave the gas circulation space 80 through said chamber outlet port 83 before being introduced into said low pressure duct 7.

It should be noted that preferably the cooling chamber 79 surrounds the gas expander 78 and/or the heat source 12 and/or the hot gas inlet duct 19 in a tight manner so that the working gas 81 can enter the gas circulation space 80 only through the chamber inlet port 82, even though the gas 81 can leave said space 80 only through the chamber outlet port 83.

According to a variant embodiment of the regenerative cooling system 100 according to the invention, as shown in fig. 1, the chamber inlet port 82 can be connected to the outlet of the gas expander 78 by a chamber inlet duct 84, the effective cross section of the chamber inlet duct 84 being regulated by a flow control valve 85, said flow control valve 85 being able to prevent, allow or limit, depending on its position, the circulation of the working gas 81 in said duct 84.

As a further variant, again shown in fig. 1, the chamber outlet port 83 may be connected to the low-pressure regeneration duct 7 by a chamber outlet duct 86, the effective cross section of the chamber outlet duct 86 being regulated by a flow control valve 85, the flow control valve 85 being able to prevent, allow or limit, depending on its position, the circulation of the working gas 81 in said chamber outlet duct 86.

Fig. 1 also shows another variation of the regenerative cooling system 100 according to the present invention in that the outlet of the gas expander 78 may be connected to the low pressure regeneration duct 7 by a chamber bypass duct 87, the chamber bypass duct 87 allowing the working gas 81 discharged from the outlet of the gas expander 78 to flow directly from the outlet to the low pressure regeneration duct 7 without moving through the gas circulation space 80.

According to the latter variant, the effective cross section of the chamber bypass duct 87 can be optionally regulated by a flow control valve 85, which flow control valve 85 can prevent, allow or limit the circulation of the working gas 81 in said bypass duct 87, depending on its position.

In fig. 1, it should be noted that, advantageously, the exterior of the cooling chamber 79 may be coated with a thermally insulating layer 88, the thermally insulating layer 88 may be formed of any thermally insulating material known to those skilled in the art, and that, in addition to the cooling chamber 79, the thermally insulating layer 88 may also coat the various thermal conduits and elements constituting the regenerative thermal engine 1.

It should be noted that in this case, the insulating layer 88 is provided in order to prevent any excessive heat loss detrimental to the efficiency of the regenerative heat engine 1.

The functions of the invention are as follows:

the function of the regenerative cooling system 100 according to the invention will be readily understood by considering fig. 1.

To describe this function we will use here an exemplary embodiment of the regenerative cooling system 100 according to the invention (when the regenerative engine 1 to which it is applied consists of a transfer-expansion and regenerative thermal engine belonging to the applicant's 2015, 2-month 25-day as subject of patent application No. fr 1551593).

As can be seen from fig. 1, the regenerative engine 1 here comprises a two-stage compressor 2, which in particular consists of a low-pressure compressor 35, the low-pressure compressor 35 drawing working gas 81 from the atmosphere via a compressor inlet duct 3, the outlet of the low-pressure compressor 35 being connected to the inlet of a high-pressure compressor 36 via an intermediate compressor cooler 37.

Fig. 1 shows that at the outlet of the high-pressure compressor 36, the working gas 81 is discharged into the high-pressure regeneration duct 6 comprising a regeneration heat exchanger 5, in this case a counter-flow heat exchanger 41, known per se. It should be assumed here that the working gas 81 is discharged from the high-pressure compressor 36 at a pressure of 20 bar and a temperature of 200 degrees celsius.

By circulating in the high-pressure regeneration duct 6, the working gas 81 is preheated to a temperature of 650 degrees celsius by the hot working gas 81 circulating in the adjacent low-pressure regeneration duct 7.

For simplicity we will consider the efficiency of the recuperative heat exchanger 5 to be one hundred percent. This means that the working gas 81 circulating in the low pressure regeneration duct 7 enters the low pressure regeneration duct 7 at a temperature of 650 degrees celsius and leaves said duct 7 at a temperature of 200 degrees celsius before being discharged to the atmosphere via the engine outlet duct 33, whereas the working gas 81 circulating in the high pressure regeneration duct 6 enters the high pressure regeneration duct 6 at a temperature of 200 degrees celsius and leaves at a temperature of 650 degrees celsius.

Upon exiting the high pressure regeneration duct 6, the working gas 81 is then superheated to 1400 degrees Celsius by the heat source 12, which, according to this exemplary embodiment, the heat source 12 is comprised of a fuel-fired burner 38.

On leaving said burner 38, the working gas 81 is directed through the hot gas intake duct 19 to the gas expander 78, the gas expander 78 being in fact the expander cylinder 13 of the transmission-expansion and regeneration heat engine, said expander cylinder 13 being the subject of patent application No. fr 1551593.

It should be noted that the hot gas intake duct 19 is preferably made of ceramic having high temperature resistance until it is connected with the cover of the expander cylinder 14, thereby covering one end or the other end of the expander cylinder 13. Thus, the temperature of said duct 19 is kept approximately equal to 1400 degrees celsius, so that the working gas 81 circulating in said duct 19 maintains its temperature throughout its entire process.

Thus, as shown in fig. 1, each end of the expander cylinder 13 is capped by an expander cylinder head 14 to define two transfer-expansion chambers 16 with a double-acting expander piston 15. Note also that each cylinder head has an intake metering valve 24 and an exhaust metering valve 31.

Due to the regenerative cooling system 100 according to the present invention, the transfer-expansion and regenerative thermal engine is hot, the

expander cylinders

13 and 14 cylinder heads are maintained at a temperature close to seven hundred degrees celsius. This makes it possible to construct the cylinder 13 and the cylinder head 14 from a material that is less expensive and more common than ceramics, such as stainless steel or ferrosilicon cast iron.

For the double acting expander piston 15, and in accordance with the described non-limiting example of the regenerative cooling system 100 of the present invention, the double acting expander piston 15 is made of silicon nitride. The average operating temperature of the piston 15 is approximately 800 degrees celsius.

It should be noted in fig. 1 that said piston 15 is connected to the power take-off shaft 17 by means of a mechanical transmission 19, said means 19 being in particular constituted by a connecting rod 42 articulated to a crank 43.

Thus, the working gas 81, at a pressure of up to 20 bar and a temperature of up to 1400 degrees celsius, is introduced into one or the other of the transfer-expansion chambers 16 through the respective intake metering valve 24.

By means of the orifice held open by the inlet metering valve 24, said gas 81 starts to cool slightly, in particular upon contact with the inner wall of the cover of the expander cylinder 14 through which it passes and with the inner wall of the transfer-expansion chamber 16, in order to be expanded there by the double-acting expander piston 15, the gas 81 is introduced into the transfer-expansion chamber 16. As described above, the walls are maintained at 700 degrees celsius by the regenerative cooling system 100.

In this regard, we will assume that the working gas 81 loses on average 100 degrees celsius by flooding (wash) the inner wall of the cover of the expander cylinder 14 and the wall of the transfer-expansion chamber 16. Therefore, the temperature of the working gas 81 has dropped during its passage from the hot gas intake duct 19 to the transfer-expansion chamber 16, moving from 1400 to 1300 degrees celsius.

When the desired quantity of working gas 81 has been effectively introduced into the transfer-expansion chamber 16 by the respective intake metering valve 24, the latter is closed and the double-acting expander piston 15 expands said gas 81. In doing so, the piston 15 collects the work produced by said gas 81 and transmits it to the power take-off shaft 17, in particular via the connecting rod 42 and the crank 43.

Once the working gas 81 has been expanded by the double acting expander piston 15, the pressure of said gas 81 has dropped by about 1 bar absolute. The same is true for the temperature of this gas 81, which gas 81 has changed from 1300 to 550 degrees celsius.

The double acting expander piston 15 has reached its bottom dead center, the exhaust metering valve 31 is open, and said piston 15 exhausts said gas 81 into a chamber inlet duct 84, said chamber inlet duct 84 directing said gas 81 to the chamber inlet port 82.

The working gas 81 then enters the gas circulation space 80 and is directed via said space to the chamber outlet port 83. In doing so, the gas 81 flows over the hot outer walls of the cylinder heads of the expander cylinder 13 and the expander cylinder 14. The outer walls are designed to be completely or partially roughened and/or dispersed with a geometric pattern so as to generate forced convection when the gas 81 circulates in contact with these walls, so that the working gas 81 carries away more or less heat from the walls.

Furthermore, the internal geometry of the cooling chamber 79 and/or the external geometry of the expander cylinder 13 and/or the external geometry of the cylinder head of the expander cylinder 14 may advantageously form a channel that forces all or some of the working gas 81 to follow a path or several simultaneous paths from the chamber inlet port 82 to the chamber outlet port 83 via the gas circulation space 80.

It will be understood that the dual strategy of forced convection and forced path of the working gas 81 makes it possible to select firstly the area for outputting heat from the hot outer walls of the cylinder heads of the

expander cylinders

13 and 14 to said gas 81, secondly the temporal sequence in which said areas are swept by said gas 81, and thirdly and lastly the intensity of the forced convection along the path of said gas 81.

In any case, during the travel of the working gas 81 in the cooling chamber 79, the temperature of the working gas 81 gradually changes the temperature of the gas 81 extracted heat from the expander cylinder 13 and the hot outer wall of the cylinder head of the expander cylinder 14 from 550 degrees celsius to a point of 650 degrees celsius. In doing so and in combination with the strategy of forced convection and path selection of the working gas 81, the gas homogenizes the temperature of the expander cylinder 13 and the temperature of the cylinder head of the expander cylinder 14, said temperature being maintained around 700 degrees celsius.

The working gas 81 has reached its new temperature of 650 degrees celsius, the gas 81 reaches the chamber outlet port 83 and returns to the low pressure regeneration duct 7 via the chamber outlet duct 86.

As will be appreciated from the foregoing description, the working gas 81 discharged from the chamber outlet port 83 releases most of its heat to the working gas 81 circulating in the adjacent high pressure regeneration duct 6 by circulating in the low pressure regeneration duct 7 and before being discharged to the atmosphere via the engine outlet duct 33.

Finally, and thanks to the regenerative cooling system 100 according to the invention, the heat extracted from the cylinder heads of the

expander cylinders

13 and 14 for maintaining them at a temperature of about 700 degrees celsius is never dissipated as pure losses.

In effect, heat is reintroduced into the regenerative heat engine 1 thermodynamic cycle to replace a portion of the heat required to be provided by the fuel-fired burner 38, thereby bringing the working gas 81 to a temperature of 1400 degrees celsius before the working gas 81 is sent to the expander cylinder 13 and subsequently introduced into the transfer-expansion chamber 16.

In fig. 1 it is noted that chamber bypass conduit 87, chamber bypass conduit 87 has flow control valve 85. It should also be noted in fig. 1 that chamber outlet conduit 86 also has a flow control valve 85. These two valves 85 constitute a variant embodiment of the regenerative cooling system 100 according to the invention and are provided for regulating the temperature of the cylinder heads of the

expander cylinders

13 and 14.

In fact, if the temperature is too high, the flow control valve 85 of the chamber bypass duct 87 blocks said bypass duct 87, while the flow control valve 85 of the chamber outlet duct 86 opens said outlet duct 86. This has the effect of forcing working gas 81 discharged from the transfer-expansion chamber 16 through their respective exhaust metering valves 31 to move through the gas circulation space 80 and return to the low pressure regeneration conduit 7.

On the other hand, if the temperatures of the cylinder heads of the

expander cylinders

13 and 14 are too low, the flow control valve 85 of the chamber bypass conduit 87 opens the bypass conduit 87, while the flow control valve 85 of the chamber outlet conduit 86 closes the outlet conduit 86. This has the effect of preventing the working gas 81 discharged from the transfer-expansion chamber 16 through their respective exhaust metering valves 31 from moving through the gas circulation space 80 to return to the low-pressure regeneration pipe 7. Thus, the gas 81 is returned directly to the duct 7 via a chamber bypass duct 87.

It will be appreciated that in practice the flow control valve 85 is rarely fully open or fully closed and that said valve 85 may be kept slightly open to adjust the temperature of the

expander cylinders

13 and 14 cylinder heads without abruptly changing the flow rate of the working gas 81 circulating in the gas circulation space 80.

It will also be understood that the regulation of the temperature requires control means, consisting for example of at least one temperature sensor and one microcontroller, which are known per se, and which enable any type of servomotor to be controlled so that each motor actuates the flow control valve 85 to open or close.

According to a particular embodiment of the regenerative cooling system 100 according to the invention, the flow control valves 85 may also be connected together by a mechanical linkage to share the same servo motor. In this case, the linkage ensures that when the first valve 85 is closed, the second valve is open, and vice versa.

From the foregoing description it can be easily concluded that the regenerative cooling system 100 according to the invention brings about a number of advantages, in particular when implementing a transfer-expansion and regenerative heat engine belonging to the applicant as subject of patent application No. fr 1551593.

As a first advantage, it is no longer necessary to manufacture the cylinder heads of the

expander cylinders

13 and 14 from a ceramic material such as silicon carbide. In fact, it is well known that such materials are expensive to produce due to their high hardness and are difficult to machine with conventional cutting or grinding tools. Due to the regenerative cooling system 100 according to the invention, such ceramics may be replaced by cast iron or stainless steel. This greatly reduces the manufacturing and sales price of the transfer-expansion and regenerative thermal engine, which is decisive, in particular for such engines that can enter the automobile market.

As a second advantage, since the head of the

expander cylinders

13 and 14 are cooler, it is possible to use a material with very low thermal conductivity and great compression strength, such as quartz, to manufacture the hollow legs of the double acting expander cylinder with adaptive support, which is the subject of patent application No. fr 1558585, 2015, 9-14. In fact, while quartz is not compatible with a temperature of 1300 degrees celsius, quartz is fully compatible with a temperature of 700 degrees celsius. Bearing in mind that the dual acting expander cylinder with adaptive support in question is one of the key improvements in the transfer-expansion and regenerative thermal engine.

As a third advantage, since the cylinder heads of the expander cylinders 14 are maintained at 700 degrees celsius, they can use pre-existing silicon nitride valves compatible with these temperature levels. For example, such a valve was developed by the NGK company and has been the subject of low-cost industrial research, particularly in the context of the project number G3RD-CT-2000-00248 entitled "LIVALVES" funded within the framework of the fifth European FP5-GROWTH program.

As a fourth advantage, the air cushion section proposed in patent application No. fr 1551593, belonging to the applicant, can be made of a superalloy with permanent resistance to these temperature levels, with the temperature of the inner wall of the expander cylinder 13 maintained around 700 degrees celsius, without the risk of said section being subjected to temperatures significantly higher than 700 degrees celsius, in particular when the transfer-expansion and regenerative thermal engine is stopped and before it cools down.

As a fifth advantage, applied to the transfer-expansion and regenerative thermal engine that is the subject of patent application No. fr 1551593, the regenerative cooling system 100 according to the present invention makes it possible to limit the temperature exposure of the insulation layer 88 of the cylinder head that surrounds the

expander cylinders

13 and 14. In practice, the cooling chamber 79 is interposed between these partitions 88 on the one hand and between said cylinder 13 and said head on the other hand. Thus, the selling price and durability of the barrier 88 is greatly improved.

These advantages are obtained without compromising the final energy efficiency of the transfer-expansion and regenerative thermal engine.

In contrast, the regenerative cooling system 100 according to the invention enables the existing relationship according to patent application No. fr 1551593 to be decoupled between the temperature resistance of the materials constituting the expander cylinders 13 and the cylinder heads of the expander cylinder 14 on the one hand and the temperature of the working gas 81 leaving the fuel-fired burner 38 on the other hand.

To some extent, due to the regenerative cooling system 100 according to the invention, it is conceivable to increase the temperature of the working gas 81 exiting the fuel-fired burner 38 in order to increase the ultimate efficiency of the transfer-expansion and regenerative thermal engine, and this without compromising the temperature stability of the main elements that make up the engine.

It should be noted that the regenerative cooling system 100 according to the invention can be advantageously applied to any other regenerative heat engine 1, the configuration and temperature characteristics of which are compatible with said system 100, in addition to the transfer-expansion and regenerative heat engine which is the subject of patent application No. fr 1551593.

Thus, the possibilities of the regenerative cooling system 100 according to the invention are not limited to the application just described, and it should also be understood that the foregoing description is given by way of example only and in no way limits the scope of the invention, which will not be circumvented by substituting implementation details described by any other equivalent.

Claims

1. Regenerative cooling system (100) designed for a regenerative thermal engine (1) comprising at least one regenerative heat exchanger (5) having a high-pressure regeneration duct (6) in which a working gas (81) circulates to be preheated therein, said working gas having been previously compressed by a compressor (2), while at the outlet of said high-pressure regeneration duct (6), said working gas (81) being superheated by a heat source (12) before being introduced into a gas expander (78) in which it is expanded to produce work on a power take-off shaft (17), said working gas (81) then being discharged at the outlet of said gas expander (78) and being introduced into a low-pressure regeneration duct (7) of said regenerative heat exchanger (5), said working gas (81) leaving most of it by circulating in said low-pressure regeneration duct (7) -residual heat is released to the working gas (81) circulating in the high-pressure regeneration duct (6), the system (100) being characterized in that it comprises:

-at least one cooling chamber (79) which completely or partially surrounds the gas expander (78) and/or heat source (12) and/or a hot gas intake duct (19) connecting the heat source (12) to the expander (78), while leaving a gas circulation space (80) between the chamber (79) on the one hand and/or the expander (78) and/or the heat source (12) and/or the hot gas intake duct (19) on the other hand;

-at least one chamber inlet port (82) directly or indirectly connected to the outlet of the gas expander (78) and through which some or all of the working gas (81) discharged from the expander (78) via the outlet of the expander (78) can enter the gas circulation space (80);

-at least one chamber outlet port (83) directly or indirectly connected to the low pressure regeneration duct (7) and through which the working gas (81) can leave the gas circulation space (80) before being introduced into the low pressure regeneration duct (7).

2. A regenerative cooling system according to claim 1, characterized in that the chamber inlet port (82) is connected to the outlet of the gas expander (78) by a chamber inlet conduit (84) whose effective cross section is regulated by a flow control valve (85).

3. A regenerative cooling system according to claim 1, characterized in that the chamber outlet port (83) is connected to the low pressure regeneration duct (7) by a chamber outlet duct (86), the effective cross section of which is regulated by a flow control valve (85).

4. A regenerative cooling system according to claim 1, characterized in that the outlet of the gas expander (78) is connected to the low pressure regeneration conduit (7) by a chamber bypass conduit (87).

5. A regenerative cooling system according to claim 4, characterized in that the effective cross section of the chamber bypass duct (87) is adjusted by a flow control valve (85).

6. A regenerative cooling system according to claim 1, characterized in that the exterior of the cooling chamber (79) is coated with a heat insulating layer (88).