WO2011157662A1

WO2011157662A1 - Combustion engine with air-cooled bottom gasket

Info

Publication number: WO2011157662A1
Application number: PCT/EP2011/059733
Authority: WO
Inventors: Geert Folkers; Raymond Westers
Original assignee: Bekaert Combustion Technology B.V.
Priority date: 2010-06-14
Filing date: 2011-06-10
Publication date: 2011-12-22

Abstract

An external combustion engine comprises an engine head to be heated on its outer surface, a burner housing placed over the head and connected thereto by mounting means, a burner element provided in the housing, a fuel feed delimiting an incoming flow path for delivering a gas-air mixture to an inlet of the burner element, a combustion space present at a front side of the burner element and extending along a first part of the outer surface of the engine head, a heat exchange space in flow communication with the combustion space and extending along a second part of the outer surface of the engine head, an outlet in flow communication with the heat exchange space, a gasket provided between the mounting means of the engine head and burner housing, and a cooling chamber extending along the mounting means for cooling the gasket. The combustion space and the heat exchange space form an outgoing flow path for hot combustion gases to exchange heat towards the engine head. A starting part of the fuel feed extends through the cooling chamber for cooling the gasket with a flow of the gas-air mixture before this mixture is delivered to the inlet of the burner element.

Description

Combustion engine with air-cooled bottom gasket

Description

Technical Field

The invention relates to an external combustion engine, to a burner assembly for such an external combustion engine, as well as to a method for operating such an external combustion engine. In particular the invention relates a Stirling engine, to a burner assembly for such a Stirling engine, as well as to a method for operating such a Stirling engine. Background Art

Stirling engines are known to comprise a closed system in which a working medium is alternately heated and cooled by shifting the medium to different temperature locations within the system. For this the engine at one side comprises an engine head which needs to be heated during operation and at another side an engine head which needs to be cooled during operation.

For example WO 03/098025 shows an embodiment of a Stirling engine in which the engine head to be heated is surrounded by a burner element which is mounted inside a cap shaped burner housing fitting over the engine head. The burner element is of the gas combustion type and is designed to heat the engine head to temperatures of 500 degrees Celsius and more. In between the burner housing and the engine head a space is left open. Directly in front of the burner element, this space is referred to as the combustion space. In this combustion space the actual combustion is to take place.

During combustion, a gas-air mixture is incinerated. Because of this combustion process, heat is directly transferred to the engine head by means of convection and radiation. The combustion space merges into a so-called heat exchange space which leads the hot combustion gases coming from the combustion process towards an outlet while having the gases flow along the engine head. While flowing through the heat exchange space, the hot combustion gases not only heat up the engine head by means of convection, but also preheat an incoming flow of gas-air mixture before it is fed to the burner element. For this an incoming flow path of a fuel feed for the gas-air mixture is extending at a close distance along the heat exchange space such that a transfer of heat by means of conduction and/or convection can take place.

Between an interface of the engine head and the burner housing, a flexible seal is positioned. This seal ensures that potentially harmful combustion gases can not escape via the interface. The seal is required to operate at high temperatures, and be capable of maintaining an adequate seal under all operating conditions, including vibrations of the engine because of for example reciprocating components. In order to prevent the seal from getting overheated it needs to be cooled permanently during operation. For this WO 03/098025 discloses the use of a water coolant circuit which is positioned between the burner housing and the seal to cool of the seal and to form a protective shield for the seal in the direction of the burner element.

A disadvantage with this known construction is that the water coolant circuit makes the construction somewhat complex, expensive and vulnerable. The construction needs to be made such that the cooling water is strictly kept apart from the combustion process. Furthermore the capacity of the burner element, and therefore also of the external combustion engine it needs to heat leaves to be improved.

WO05/003542 discloses a combustor/recuperator assembly for use in an external combustion engine, such as a Stirling engine. The assembly comprises a plurality of substantially hemispherical domed members positioned in nested uniaxial spaced relation, the plurality of substantially hemispherical domed members are forming at least a first flow chamber and a second flow chamber. The first flow chamber for passing an incoming charge of air and the second flow chamber for passing an outgoing charge of combustion exhaust gases. The second chamber is positioned to be effective to heat the incoming charge of air. This disclosure is related to recovering heat. It is not related to the (temperature at the) seal (or gasket) at the interface between the engine head and the burner housing (the document is even silent whether or not a seal is used in this set-up; and where the seal would be located if it is present). The incoming air flow in the hemispherical domes is having a turning point at the base of the hemispherical dome, without there being (nor being an intention of creating) a flow radial to the axis of the domes at the turning point of the flows. The hot combustion gas flow is also having a turning point at the base of the hemispherical dome.

Disclosure of Invention

The present invention aims to at least partly overcome the abovementioned disadvantages or to provide a usable alternative. In particular the invention aims to provide a safely operating external combustion engine with a simple construction and an improved burner capacity.

This aim is achieved by an external combustion engine according to the first aspect of the invention: the engine comprises an engine head to be heated on its outer surface and a burner housing (e.g. made out of stainless steel) is placed over the head and connected thereto by mounting means. A burner element is provided in the housing. A fuel feed delimits an incoming flow path for delivering a gas-air mixture to an inlet of the burner element. Between a front side of the burner element and a first part of the outer surface of the engine head a combustion space is left open. Between the burner housing and a second part of the outer surface of the engine head a heat exchange space is left open. The combustion space and the heat exchange space form an outgoing flow path for hot combustion gases to exchange heat towards the engine head. The heat exchange space ends in an outlet via which the hot combustion gases are guided to outside the engine and for example are led towards a separate distinctive heat exchanger or are directly emitted to the environment. Between the mounting means of the engine head and the burner housing a sealing gasket is provided (e.g. the sealing gasket can be made out of silicon rubber). According to the invention the gasket is cooled via a starting part of the incoming flow path of the fuel feed. This starting part of the fuel feed is positioned such that it lies against or extends through the mounting means and thus also extends closely along the gasket. Thus the gasket can advantageously be cooled with the incoming flow of the gas-air mixture before this mixture is delivered to the actual fuel inlet at the back side of the burner element. With starting part of the fuel feed is meant that part that makes the fuel to enter the Stirling engine.

Preferably, the cooling chamber extending along the mounting means for cooling the gasket has a width in the range of 10 to 100 mm in radial direction of the external combustion engine. More preferably in the range of 30 to 70 mm, even more preferably in the range of 35 - 40 mm.

Preferably the gasket has a dimension within the range of 50 to 150 mm in radial direction of the combustion engine.

In a specific embodiment of the invention, the fuel feed is integrally formed in between wall parts of the burner housing.

Preferably, the incoming gas-air mixture is fed to the starting part of the fuel feed of the engine at a temperature which is about 50-150 degrees Celsius lower than the maximum allowable temperature that the gasket may reach. This temperature difference makes it well possible to cool the gasket sufficiently and keep the temperature thereof below said maximum allowable temperature above which the gasket would otherwise start to deteriorate. This maximum allowable temperature for the gasket is dependent on the material out of which the gasket is manufactured. If for example the gasket is made out of silicon rubber than its temperature preferably needs to remain beneath about 125 degrees Celsius. This is no problem since the gas-air mixture is well able to start flowing along the gasket at a much lower temperature. Advantageously the gas-air mixture is fed at a maximum temperature of 75 degrees Celsius, more in particular at environmental temperature (in the range of 10-35 degrees Celsius) to the starting part of the fuel feed. While cooling the gasket, the gas-air mixture at the same time is advantageously being preheated to some extent. This makes it easier for the gas-air mixture to reach a certain optimum temperature just before it is to enter the burner element. A higher preheating temperature of the gas-air mixture gives higher flame temperatures when combusted, and thus gives more heat transfer to the engine head. Therefore, the gas-air mixture preferably is preheated as much as possible as long as it stays beneath its self-ignition temperature.

The design is preferably such that no hot combustion gas flows in the

neighbourhood of the gasket in order to keep the temperature of the seal sufficiently low: preferably, the smallest distance between the gasket and the hot combustion gas flow is at least 15 mm; more preferably at least 20 mm; even more preferably at least 35 mm.

In order to further preheat the gas-air mixture after it has been able to cool the gasket, a number of measures can be taken. In an embodiment an end part of the fuel feed at least partly extends along an outer side of the heat exchange space. In addition, in a further embodiment the end part of the fuel feed extends with at least two passes in a meandering manner along the outer side of the heat exchange space. This not only further improves the preheating of the incoming gas-air mixture, but at the same time the plurality of passes help to limit any radiation loss of heat to the surrounding air. This may even make an additional outside insulation along this end part of the fuel feed redundant which would otherwise be necessary to sufficiently isolate the engine at its outer side.

The end part of the fuel feed may be guided directly alongside the heat exchange space. However, it is also possible to provide a layer of insulation material (e.g. ceramic material) between the end part of the fuel feed and the outer side of the heat exchange space. The insulation layer is able to protect the gas-air mixture from obtaining a temperature which lies above its self-incineration temperature of for example 500 degrees Celsius, and is able to protect the material of the fuel feed itself against overheating. If for example the fuel feed is made out of stainless steel, then the fuel feed walls would otherwise start to corrode. By using insulation at this position, it has appeared that an optimum amount of heat can be transferred from the heat exchange space towards the fuel feed by means of conduction. Also the provision of the insulation material has the advantage that it makes it possible to manufacture the end part of the fuel feed substantially straight without having it follow any curved shape of the engine head. This makes the construction easier and cheaper to manufacture. For example the insulation material can be a ceramic material, in particular a ceramic fibre material.

In order to further preheat the gas-air mixture after it has been able to cool the gasket, it is also possible to have an end part of the fuel feed at least partly extend along an outer side of the combustion space. In addition in a further embodiment the end part of the fuel feed may even extend with at least two passes along this outer side of the combustion space. This further improves the preheating of the incoming gas-air mixture while at the same time the plurality of passes at this location may also limit any radiation loss to the surrounding air, and may make an additional outside insulation redundant which would otherwise be necessary to isolate the burner element at its back side.

In addition or in the alternative, in an advantageous embodiment, an intermediate part of the fuel feed at least partly extends along a third part of the outer surface of the engine head at a position between the gasket/mounting means and the combustion space. Thus the incoming fuel flow is able to form a cooling shield over the entire length of the gasket even if the gasket extends up till a position close to the engine head. At the same time this flowing of the gas-air mixture at this position along the heated engine head helps to further preheat the incoming flow of the gas-air mixture immediately after it has been able to sufficiently cool of the gasket.

In a further advantageous embodiment insulation (e.g. ceramic material) may be provided which at least partly extends along a part of the outer surface of the engine head at a position between the gasket/mounting means and the combustion space. In an embodiment insulation material is present between the cooling chamber and the nearest presence of hot combustion gas. This insulation may help to shield the gasket from the combustion space. It also may help to shield the abovementioned intermediate part of the fuel feed form the combustion space. For example the insulation material can be a ceramic material, in particular a ceramic fibre material. In a further advantageous embodiment the insulation extends between the intermediate part of the fuel feed along the third part and the combustion space along the first part of the outer surface of the engine head.

A second aspect of the invention is a burner assembly of a burner housing, a burner element, and a fuel feed, to be placed over and mounted to an engine head of an external combustion engine according to anyone of the embodiments of the first aspect of the invention.

A third aspect of the invention is a method for operating an external combustion engine according to any of the embodiments of the first aspect of the invention, comprising the steps of:

- delivering a gas-air mixture to the starting part of the fuel feed at a temperature below 75 degrees Celsius; - flowing the gas-air mixture through the starting part of the fuel feed for cooling the gasket to a temperature below 150 degrees Celsius, in particular below 130 degrees Celsius; and

- delivering the gas-air mixture to the inlet of the burner element for combustion in the combustion space.

The temperature ranges in the method have been selected so as to guarantee a long lifetime of the gasket (seal).

Preferebly, the gas-air mixture, after it has flown through the starting part of the fuel feed, is flown through the end part of the fuel feed for preheating the mixture to a temperature of at least 150 degrees Celsius, in particular at least 200 degrees Celsius, before it is delivered to the inlet of the burner element.

Brief Description of Figures in the Drawings

The invention shall be explained in more detail with reference to the

accompanying drawings, in which:

Fig. 1 shows a cross section of an embodiment of a part of a Stirling engine according to the invention at the side of a heater engine head thereof;

Fig. 2 shows a view in perspective of the burner assembly of fig. 1 partially in cross section; and

Fig. 3 shows a top view of fig. 1 .

Mode(s) for Carrying Out the Invention

In fig. 1 the engine head of a Stirling engine is schematically shown and has been given the reference numeral 1 . The head 1 has the shape of a cylinder head and at its lower proximal end is provided with mounting means which are formed by an outwardly projecting flange 2. Over the engine head 1 a burner housing 3 is placed. The burner housing 3 is also cylinder shaped and is provided at its lower end with mounting means which are formed by an outwardly projecting flange 4. Between the mounting flanges 2 and 4 a silicon rubber gasket 5 is provided.

Inside the burner housing 3 a burner element 8 is mounted which is formed by a cylindrical section of a porous metal mat, for example a fibre matrix of fine metal fibres. The burner element 8 circumvents the head 1 at a radial distance. Thus between the head 1 and the element 8 a combustion space 9 is left open. The upper distal end of the head 1 is circumvented by a ceramic fibre insulation material 10. This insulation material 10 at its outer side lies against the inner side of the upper end of the burner housing 3 and at its inner side circumvents the head 1 at a radial distance. With this the insulation material 10 at its inner side follows the shape of the head 1 . Thus between the head 1 and the insulation material 10 a heat exchange space 1 1 is left open which at its lower side connects to the combustion space 9 and at its upper side merges into an outlet 12.

The walls of the burner housing 3 delimit a meandering fuel feed 15 for which the burner housing 3 is made double-walled. The fuel feed 15 begins with an inlet pipe 15a, which connects to a starting part 15b which extends all along the circumference of the double-walled flange 4 and forms a cooling chamber 16. From there it connects to an intermediate part 15c which extends with a bend along the engine head 1 . From there it connects to en end part 15d which extends with a double pass along both the back side of the burner element 8 and the outer side of the insulation material 10. Directly below the burner element 8, a cylindrical layer of ceramic fibre insulation material 18 is provided which circumvents the head 1 at that position and which extends up till against the bend of the intermediate part 15c of the fuel feed.

A smallest distance D exists between the gasket 5 and the hot combustion gas flow (or the heat exchange space 1 1 ). In the example of figure 1 , distance D is 45 mm.

As an example, during use of the engine, a gas-air mixture is fed at environmental temperature of about 20 degrees Celsius, to the inlet pipe 15a. From there the gas-air mixture flows through the flange 4 where it cools the gasket 5 via its flow through cooling chamber 16. In figure 2, dimension A is the width of the gasket in radial direction of the combustion engine. Preferably, dimension A is within the range of 50 to 150 mm; in the given example dimension A is 70 mm. The dimension B indicated in figure 2 is the width (width in radial direction of the external combustion engine) of the cooling chamber 16. In the example, width B is 38 mm.

Then the gas-air mixture is getting preheated to a temperature of about 250 degrees Celsius, at which temperature it enters the burner element 8. The preheating is obtained in the intermediate part 15c where the mixture flows directly along the lower part of the hot head 1 and the outer side of the insulation material 18, as well as in the end part 15d where the mixture flows with a double pass directly along the hot back side of the burner element 8 and the hot outer side of the insulation material 10. Then the mixture is combusted in the combustion space 9, from where the hot combustion gases flow through the heat exchange space 1 1 while heating up the engine head 1 . Finally the hot combustion gases leave the engine at a temperature of about 700 degrees Celsius.

Besides the embodiment shown, numerous variants are possible. For example the various parts may have other dimensions and shapes, and may be made from different materials. Also the fuel feed may be a separate organ instead of being integrated into the burner housing. Thus an optimized unit of a burner assembly and an engine head to be heated is achieved which combines a profitable cooling of the critical gasket with an incoming gas- air mixture while still being able to obtain a more than sufficient preheating of the incoming flow of a gas-air mixture to be combusted.

List of Reference Numbers

1 engine head of Stirling engine

2 flange of Stirling engine

3 burner housing

4 flange of housing

5 gasket

8 burner element

9 combustion space

10 insulation material

1 1 heat exchange space

12 outlet

15 fuel feed

15a inlet pipe

15b starting part

15c intermediate part

15d end part

16 cooling chamber

18 insulation material

Claims

1 . An external combustion engine, in particular a Stirling engine, comprising:

- an engine head (1 ) to be heated on its outer surface;

- a burner housing (3) placed over the head (1 ) and connected thereto by mounting means;

- a burner element (8) provided in the housing;

- a fuel feed (15) delimiting an incoming flow path for delivering a gas-air mixture to an inlet of the burner element;

- a combustion space (9) present at a front side of the burner element (8) and extending along a first part of the outer surface of the engine head;

- a heat exchange space (1 1 ) in flow communication with the combustion space (9) and extending along a second part of the outer surface of the engine head;

- an outlet (12) in flow communication with the heat exchange space (1 1 );

- a gasket (5) provided between the mounting means of the engine head and burner housing; and

- a cooling chamber (16) extending along the mounting means for cooling the gasket, in which the combustion space (9) and the heat exchange space (1 1 ) form an outgoing flow path for hot combustion gases to exchange heat towards the engine head,

wherein a starting part (15b) of the fuel feed extends through the cooling chamber (16) for cooling the gasket (5) with a flow of the gas-air mixture before this mixture is delivered to the inlet of the burner element (8).

2. An external combustion engine according to one of the preceding claims, wherein insulation material (18) is present between said cooling chamber (16) and the nearest presence of hot combustion gas.

3. An external combustion engine according to claim 1 or 2, wherein the smallest distance between said gasket (5) and the hot combustion gas flow is at least 15 mm.

4. An external combustion engine according to one of the preceding claims, wherein said cooling chamber extending along the mounting means for cooling the gasket has a width in the range of 10 to 100 mm in radial direction of the external combustion engine.

5. An external combustion engine according to one of the preceding claims, wherein an end part of the fuel feed at least partly extends along an outer side of the heat exchange space for preheating the gas-air mixture after it has cooled the gasket and before it enters the burner element via the inlet.

6. An external combustion engine according to claim 5, wherein the end part of the fuel 5 feed extends with a double pass along the outer side of the heat exchange space.

7. An external combustion engine according to claim 5 or 6, wherein insulation is provided between the end part of the fuel feed and the outer side of the heat exchange space.

10

8. An external combustion engine according to one of the preceding claims, wherein an end part of the fuel feed at least partly extends along an outer side of the combustion space for preheating the gas-air mixture after it has cooled the gasket and before it enters the burner element via the inlet.

15

9. An external combustion engine according to claim 8, wherein the end part of the fuel feed extends with a double pass along the outer side of the combustion space.

10. An external combustion engine according to one of the preceding claims, wherein an 20 intermediate part of the fuel feed at least partly extends along a third part of the outer

surface of the engine head at a position between the cooling chamber and the combustion space.

1 1 . An external combustion engine according to one of the preceding claims, wherein 25 insulation is provided which at least partly extends along a fourth part of the outer surface of the engine head at a position between the cooling chamber and the combustion space.

12. An external combustion engine according to one of the preceding claims, wherein the gasket is made out of silicon rubber.

30

13. A burner assembly of a burner housing, a burner element, and a fuel feed, to be placed over and mounted to an engine head of an external combustion engine according to one of the preceding claims.

35 14. Method for operating an external combustion engine according to one of the

preceding claims, comprising the steps: - delivering a gas-air mixture to the starting part of the fuel feed at a temperature below 75 degrees Celsius;

- flowing the gas-air mixture through the starting part of the fuel feed for cooling the gasket to a temperature below 150 degrees Celsius, in particular below 130 degrees Celsius; and - delivering the gas-air mixture to the inlet of the burner element for combustion in the combustion space.

15. Method according to claim 14, wherein, the gas-air mixture, after it has flown through the starting part of the fuel feed, is flown through the end part of the fuel feed for preheating the mixture to a temperature of at least 150 degrees Celsius, in particular at least 200 degrees Celsius, before it is delivered to the inlet of the burner element.