Air Shielded Water Cooled Exhaust Manifold With Exhaust Tube Support

Abstract

An internal combustion engine includes a cylinder block defining at least one cylinder, and a cylinder head coupled to the cylinder block. An exhaust manifold is coupled to the cylinder head and configured to receive exhaust gas from the cylinder head. The exhaust manifold includes a water jacket tube defining a plurality of liquid coolant passages and an exhaust tube received within the water jacket tube. The exhaust manifold also includes an air gap between the exhaust tube and the water jacket tube. A support mat is positioned in the air gap and compressed between an outer surface of the exhaust tube and an inner surface of the water jacket tube.

Description

TECHNICAL FIELD

The present disclosure relates generally to an air shielded water cooled exhaust manifold including an exhaust tube received within a water jacket tube, and more particularly to a support mat positioned in an air gap between the exhaust tube and the water jacket tube.

BACKGROUND

An exhaust manifold of an internal combustion engine is a collection of conduits through which exhaust gases produced during combustion are carried away from the engine. The exhaust manifold typically receives exhaust gases from each of the engine cylinders through exhaust valve ports in the cylinder head or cylinder block of the engine. The exhaust manifold then routes the exhaust gases through one or more aftertreatment components and/or one or more turbines of a turbocharger before expelling the exhaust gases into the atmosphere. During operation of the engine, the exhaust manifold becomes very hot due to the extremely high temperatures of the exhaust gases passing through the manifold. To reduce skin temperature and improve heat rejection, some exhaust manifolds include a water jacket near an exterior surface of the manifold.

An exemplary exhaust gas line for an internal combustion engine having a cooling liquid space is taught in U.S. Pat. No. 4,693,079 to Wuensche et al. (hereinafter Wuensche). In particular, the Wuensche reference teaches an exhaust gas line assembled of several housings, with each housing containing a cooling liquid space. The cooling liquid spaces of adjacent housings are connected with each other using a connecting nipple. It appears the connecting nipples, along with interconnections between exhaust tube segments, form the connections between the multiple housings. Although there exists a variety of different manifold designs in the art, it should be appreciated that there remains a continuing need for manifold designs offering improvements, including, for example, increased surface cooling, ease of manufacture or use, and improved sealing.

The present disclosure is directed to one or more of the problems or issues set forth above.

SUMMARY OF THE DISCLOSURE

In one aspect, an internal combustion engine includes a cylinder block defining at least one cylinder, and a cylinder head coupled to the cylinder block. An exhaust manifold is coupled to the cylinder head and configured to receive exhaust gas from the cylinder head. The exhaust manifold includes a water jacket tube defining a plurality of liquid coolant passages and an exhaust tube received within the water jacket tube. The exhaust manifold also includes an air gap between the exhaust tube and the water jacket tube. A support mat is positioned in the air gap and compressed between an outer surface of the exhaust tube and an inner surface of the water jacket tube.

In another aspect, a modular exhaust manifold for an internal combustion engine includes a first exhaust manifold segment including a first segment of a water jacket tube defining a first plurality of liquid coolant passages and a first segment of an exhaust tube received within the first water jacket tube segment. The first exhaust manifold segment includes a first air gap between the first exhaust tube segment and the first water jacket tube segment. A support mat is positioned in the first air gap and compressed between an outer surface of the first exhaust tube segment and an inner surface of the first water jacket tube segment.

In another aspect, a method of assembling a modular exhaust manifold for an internal combustion engine includes a step of assembling a first exhaust manifold segment by positioning a first support mat around a first segment of an exhaust tube and receiving the first exhaust tube segment within a first segment of a water jacket tube defining a first plurality of liquid coolant passages. The receiving step includes compressing the first support mat between an outer surface of the first exhaust tube segment and an inner surface of the first water jacket tube segment. The assembling step also includes maintaining an air gap between the first exhaust tube segment and the first water jacket tube segment with the first support mat.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an exemplary embodiment of an internal combustion engine including a modular exhaust manifold, according to the present disclosure;

FIG. 2 is a perspective view of a portion of an exhaust manifold segment of the exemplary modular exhaust manifold of FIG. 1;

FIG. 3 is a perspective view of an exhaust manifold segment defining an end of the modular exhaust manifold of FIG. 1;

FIG. 4 is a perspective view of an exemplary embodiment of a bypass tube of the exhaust manifold segment of FIG. 2; and

FIG. 5 is a cross-sectional view of a joint between adjacent exhaust manifold segments.

DETAILED DESCRIPTION

Referring to FIG. 1, there is shown a schematic view of an internal combustion engine 10, which, for purposes of illustration, and not limitation, may be that of a four-stroke, compression ignition engine. The engine 10 generally includes a cylinder block 12, which extends along a longitudinal axis X between opposing ends 12a and 12b and defines a plurality of combustion chambers or cylinders 14. According to the present disclosure, the engine 10 may be any type of engine (e.g., internal combustion, gas, diesel, gaseous fuel, natural gas, propane, etc.), may be of any size, with any number of cylinders, any type of combustion chamber (e.g., cylindrical, rotary spark ignition, compression ignition, 4-stroke and 2-stroke, etc.), and in any configuration (e.g., “V,” in-line, radial, etc.). According to the exemplary configuration, the cylinder block 12 defines two rows of eight longitudinally spaced cylinders 14, resulting in a V-16 configuration. However, those skilled in the art will appreciate that any configuration and number of cylinders 14 may be applicable.

The exemplary engine 10 also includes a cylinder head 16 for providing intake and exhaust flow communication with the cylinders 14 of each row. According to the exemplary embodiment, each cylinder head 16 may include a number of cylinder head modules 18 corresponding to the number of cylinders 14 defined by the cylinder block 12. However, it is contemplated that each cylinder head module 18 may serve to provide flow communication with more than one cylinder 14, such as, for example, two, three, or four cylinders 14. The cylinder head modules 18 may be configured to be decoupled individually from the cylinder block 12, thereby permitting removal of a single cylinder head module 18, without necessarily removing any other cylinder head modules 18. This exemplary configuration may serve to simplify maintenance of the engine 10, as should be appreciated by those skilled in the art.

According to the present disclosure, the exemplary engine 10 also includes an exhaust manifold or, more specifically, a modular exhaust manifold 20 coupled to each cylinder head 16 to provide flow communication between exhaust ports of the cylinder head 16 and the surroundings. The exemplary engine 10 includes four turbochargers 22 located generally at one longitudinal end of engine 10 (e.g., the opposite end 12b of the engine 10). According to the exemplary embodiment, two turbochargers 22 may be associated with each row of cylinders 14; however, other numbers of turbochargers 22 are contemplated, along with embodiments having no turbochargers. In the exemplary embodiment shown, the modular exhaust manifold 20 extends along the longitudinal axis X and provides flow communication between the cylinder heads 16 and the turbochargers 22.

As shown in FIG. 1, each exemplary modular exhaust manifold 20 includes a plurality of exhaust manifold segments 24 coupled to one another in end-to-end fashion along the common longitudinal axis X of the engine 10. Although a segmented exhaust manifold 20 is shown, it should be appreciated that a unitary, or non-segmented, manifold may alternatively be utilized. According to some embodiments, the exhaust manifold segments 24 may have a substantially circular cross-section, although other cross-sections are contemplated. According to the exemplary embodiment, the exhaust manifold segments 24 may be configured to direct exhaust gas in a first direction d₁ relative to the longitudinal axis X, while liquid coolant, such as water and/or a known coolant (e.g., a glycol-based coolant), is directed in a second direction d₂ relative to the longitudinal axis X that is opposite the first direction d₁.

In the example shown, an exhaust manifold segment 24a located at an end of the modular exhaust manifold 20 opposite turbochargers 22 (i.e., end 12a) includes an end cap 26 (e.g., a removable end cap) preventing flow communication between modular exhaust manifold 20 and the surroundings via exhaust manifold segment 24a. At an end of the modular exhaust manifold 20 opposite the exhaust manifold segment 24a (i.e., end 12b), an exhaust manifold segment 24b is coupled to a rise manifold section 28 extending between exhaust manifold segment 24b and turbochargers 22.

As shown at exhaust manifold segment 24c (shown with portions removed), each exhaust manifold segment 24 includes an exhaust tube segment 30 configured to receive exhaust gas from an exhaust port 32 of the respective cylinder head module 18. Each exhaust manifold segment 24 also includes a water jacket tube segment 34 (shown, for example, at segment 24b) configured to receive a liquid coolant. As will become more apparent below, the exhaust tube segment 30 of each exhaust manifold segment 24 is telescopically received within a respective water jacket tube segment 34. Although not discussed in detail herein, each exhaust manifold segment 24 may include an adaptor tube coupled at one end to the water jacket tube segment 24 and at an opposite end to the respective cylinder head module 18. The adaptor tubes may be configured to provide flow communication between the cylinder head 16 and the exhaust tube segment 30 of each exhaust manifold segment 24. However, alternative arrangements for fluidly connecting the exhaust tube segments 30 with the cylinder head 16 are also contemplated.

Turning now to FIG. 2, an exemplary exhaust manifold segment 24, components of which may be made from aluminum or other suitable material, will be discussed in greater detail. In particular, and according to the present disclosure, at least one end 40 of each exhaust manifold segment 24 may include a radial flange 42 defining an engagement face 44, or surface, configured for coupling adjacent exhaust manifold segments 24 together using known attachment means. For example, removable fasteners, such as bolts, may be positioned through corresponding openings, such as threaded bores, of each engagement face 44 to secure a coupled position of adjacent exhaust manifold segments 24. However, alternative coupling means are also contemplated. As shown, a first sealing member 46 may be positioned along the engagement face 44 and may include a gasket 48, such as a multiple layers steel (MLS) gasket, positioned over the engagement face 44 and around the exhaust tube segment 30.

At least one bypass opening 50 may be provided through the engagement face 44 for transferring liquid coolant from one exhaust manifold segment 24 to another. According to the exemplary embodiment, the liquid coolant passages defined by the water jacket tube segment 34 may converge toward one of exactly two bypass openings 50; however, the number of bypass openings 50 may vary. For example, as shown in FIG. 3, three bypass openings 50 may be provided. The exhaust manifold segment 24 of FIG. 3, which includes features similar to those of FIG. 2, may represent exhaust manifold segment 24a positioned at end 12a of the engine 10. The end cap 26, shown in FIG. 1, may be positioned over the engagement face 44 of the exhaust manifold segment 24 of FIG. 3. As should be appreciated, the first sealing member 46 may have differing sizes and/or shapes, depending on the particular application.

As shown in both FIG. 2 and FIG. 3, the bypass openings 50 may be radially spaced from the exhaust tube segment 30 and may be free of contact with the gasket 48. A bypass tube 52, shown also in FIG. 4, may be positioned through each bypass opening 50 of each of the adjacent exhaust manifold segments 24 to fluidly connect the liquid coolant passages of adjacent exhaust manifold segments 24. A second sealing member 54 may be positioned about the bypass tube 52 and may include a radial seal positioned within an external groove 56 within the external surface of the bypass tube 52. As shown in FIG. 4, and as will be discussed in greater detail below, each bypass tube 52 may include a first o-ring seal 58 positioned about the bypass tube 52 at a first longitudinal position and a second o-ring seal 60 positioned about the bypass tube 52 at a second longitudinal position which is spaced from the first longitudinal position.

Turning now to FIG. 5, coupled exhaust manifold segments, which are similar to exhaust manifold segments 24 described above, will be discussed. In particular, a first exhaust manifold segment 70 includes a first segment 72 of a water jacket tube 74 defining a first plurality of liquid coolant passages 76 and a first segment 78 of an exhaust tube 80 received within the first water jacket tube segment 72. Similarly, a second exhaust manifold segment 82 includes a second segment 84 of the water jacket tube 74 defining a second plurality of liquid coolant passages 86 and a second segment 88 of the exhaust tube 80 received within the second water jacket tube segment 84. The first and second exhaust tube segments 78 and 88 each receive exhaust gases from a respective cylinder head module 18 and, when coupled together to define a modular exhaust manifold such as exhaust manifold 22 of FIG. 1, define the engine exhaust tube 80. Further, each of the sets of liquid coolant passages 76 and 86 are joined together when the water jacket tube segments 72 and 84 are coupled to ultimately define the water jacket tube 74.

An air gap 91 is provided between the exhaust tube 80 and the water jacket tube 74. In particular, the first exhaust manifold segment 70 includes a first air gap 91a between the first exhaust tube segment 78 and the first water jacket tube segment 72, and the second exhaust manifold segment 82 includes a second air gap 91b between the second exhaust tube segment 88 and the second water jacket tube segment 84. The air gap 91 may provide an insulation shield between the exhaust tube 80 and the water jacket tube 74, and may contain a fluid, such as, for example, air and/or another gas. In particular, the air gap 91 may reduce the amount of energy transmitted to the liquid coolant from the exhaust tube 80.

A support mat 90 is positioned in the air gap 91 and, more particularly, is compressed between an outer surface 93 of the exhaust tube 80 and an inner surface 95 of the water jacket tube 74. The support mat 90 may assist in maintaining the air gap 91 between the exhaust tube 80 and the water jacket tube 74 and, according to some embodiments, may be made from a high temperature insulation material, such as, for example, refractory ceramic fibers, vermiculite, mullite, and/or polycrystalline. These materials may be intumescent or non-intumescent. For example, the thermal expansion of an intumescent material, such as vermiculite, may be preferred to increase the pressure acting on the support mat 90 and help secure the positioning of the support mat 90 within the air gap 91. The high temperature insulation material of the support mat 90, which may be held together using a known binder, may transfer a relatively low amount of thermal energy from the exhaust tube 80 to the water jacket tube 74, particularly when compared to support structures made from alternative materials.

According to an exemplary embodiment, the support mat 90 may define a continuous annular band 97 having a substantially uniform compressed radial thickness tx. For example, according to one particular embodiment, the compressed radial thickness tx may be between about 3 millimeters and about 20 millimeters. An axial length/of the support mat 90 may be between about 75 millimeters and about 125 millimeters. It should be appreciated that configurations of the support mat 90, including dimensions and materials, may vary depending on the particular application. Further, although a continuous structure is described, it should be appreciated that the support mat 90 may alternatively be defined by a plurality of discontinuous members.

Although any number of support mats 90 may be used, some embodiments may include a single support mat 90 positioned at a first end 92 of each of the exhaust manifold segments 70 and 82. That is, the first support mat 90a may be positioned at a first end 92a of the first exhaust manifold segment 78, and the second support mat 90b may be positioned at a first end 92b of the second exhaust manifold segment 82. At a second end 102 of each of the exhaust manifold segments 70 and 82, the exhaust tube segment 78, 88 may have a flared end 99 for receiving the exhaust tube segment 78, 88 of an adjacent exhaust manifold segment, such as exhaust manifold segments 78 and 88, when coupled. As shown, the flared end 99 of the second exhaust tube segment 88 may receive the first exhaust tube segment 78. According to some embodiments, at the second end 102 of each of the exhaust manifold segments 70 and 82, the water jacket tube segment 72, 84 may include a longitudinally extending portion 101 received within a respective one of the water jacket tube segments 72, 84. The longitudinally extending portion 101 may contact the support mat 90 and restrict axial movement of the support mat 90 beyond the longitudinally extending portion 101.

The first end 92a of the first water jacket tube segment 72 includes a first radial flange 94 defining a first engagement face 96 configured for coupling the first exhaust manifold segment 70 with the second exhaust manifold segment 82. The first water jacket tube segment 72 also defines a first radial bypass channel 98, extending radially as the channel 98 approaches the first end 92a, fluidly connecting at least one of the first plurality of liquid coolant passages 76 with a first bypass opening 100 through the first engagement face 96. Similarly, the second end 102b of the second water jacket tube segment 84 includes a second radial flange 104 defining a second engagement face 106 configured for coupling the second exhaust manifold segment 82 with the first exhaust manifold segment 70. The second water jacket tube segment 84 also defines a second radial bypass channel 108 fluidly connecting at least one of the second plurality of liquid coolant passages 86 with a second bypass opening 110 through the second engagement face 106.

A joint 112 between the first and second exhaust manifold segments 70 and 82 includes a first sealing member 114 configured to seal the exhaust tube 80 at the joint 112, and a second sealing member 116 configured to seal the liquid coolant passages 76 and 86 of the water jacket tube 74 at the joint 112. According to the present disclosure, the first and second sealing members 114 and 116 are supported on and movable with different components. For example, the first sealing member 114 may include a gasket 118 positioned between the first and second engagement faces 96 and 106 and attached in a known manner. The second sealing member 116 may include first and second o-ring seals 120 and 122 positioned about a bypass tube 124, as described above with reference to FIG. 4. The bypass tube 124 may be positioned through the first bypass opening 100 and the second bypass opening 110 to fluidly connect a portion of the first plurality of liquid coolant passages 76 and a portion of the second plurality of liquid coolant passages 86. The first o-ring seal 120 may be positioned about the bypass tube 124 and within the first radial bypass channel 98, and the second o-ring seal 122 may be positioned about the bypass tube 124 and within the second radial bypass channel 108.

Gaps 126 and 128 may be provided at either end of the bypass tube 124 between the bypass tube 124 and an end stop or shoulder within the respective radial bypass channel 98 and 108. Such gaps 126 and 128 may permit movement of the bypass tube 124 as the water jacket tube segments 72 and 84 shift or bow as a result of thermal expansion. Positioning the o-ring seals 120 and 124 within the radial bypass channels 98 and 108 allows for the sealing of the liquid coolant passages 76 and 86 of the water jacket tube 74 at the joint 112 even during any axial shifting of the bypass tube 124 that may occur. It should be appreciated that the exhaust tube segments 78 and 88 may also be joined at a slip joint to permit limited movement.

Industrial Applicability

The present disclosure may be applicable to internal combustion engines having exhaust manifolds. Further, the present disclosure may be applicable to exhaust manifolds having water jackets for reducing the skin temperature of the exhaust manifold. Further, the present disclosure may be applicable to air shielded water cooled exhaust manifolds. Yet further, the present disclosure may be applicable to modular manifold designs offering improved manufacturability and serviceability.

Referring generally to FIGS. 1-5, an exemplary internal combustion engine 10 generally includes a cylinder block 12 defining a plurality of cylinders 14. A cylinder head 16 is coupled to the cylinder block 12 and provides intake and exhaust flow communication with the cylinders 14. The exemplary engine 10 also includes a modular exhaust manifold 20, as disclosed herein, coupled to each cylinder head 16 to provide flow communication between exhaust ports of the cylinder head 16 and the surroundings. As shown in FIG. 1, each exemplary modular exhaust manifold 20 includes a plurality of exhaust manifold segments 24 coupled to one another in end-to-end fashion along a common longitudinal axis X of the engine 10.

The modularity of the exhaust manifold 20, as described herein, provides advantages at least from a manufacturability and/or serviceability standpoint. In particular, by utilizing a plurality of similar exhaust manifold segments 24, similar parts may be manufactured for engines of different sizes and/or configurations. For example, manufacturing the engine 10 shown in FIG. 1 requires the use of four exhaust manifold segments 24 for each cylinder head 16, with each exhaust manifold segment 24 corresponding to two cylinders 14. The resulting V-16 engine 10 thus requires the use of eight exhaust manifold segments 24. Manufacturing a V-12 engine, however, may only require the use of six of the exhaust manifold segments 24.

Serviceability may also be improved by the modularity of the manifold design. In particular, maintenance times and resulting costs may be reduced by minimizing the number of parts to be removed during the servicing or repair. In particular, accessing a cylinder 14 or cylinder head module 18 may require removal of only the corresponding exhaust manifold segment 24 without the need to remove the entire exhaust manifold 20. Thus, according to the modular exhaust manifold 20 disclosed herein, it may be possible to perform maintenance associated with one cylinder 14 more easily relative to an engine that includes a unitary manifold.

As described above, and with specific reference to FIG. 5, adjacent exhaust manifold segments 70 and 82 each include a water jacket tube segment 72 and 84 and an exhaust tube segment 78 and 88 received within the water jacket tube segment 72 and 84. A joint 112 between adjacent exhaust manifold segments 70 and 82 includes a first sealing member 114 configured to seal the exhaust tube 80 at the joint 112 and a second sealing member 116 configured to seal the liquid coolant passages 76 and 86 at the joint 112. For example, the first sealing member 114 may include a gasket 118 positioned bb of the adjacent exhaust manifold segments 70 and 82. In particular, adjoining ends 92a and 102b of the adjacent exhaust manifold segments 70 and 82 each include a radial flange 94 and 104 defining the engagement faces 96 and 106, which are configured for coupling the adjacent exhaust manifold segments 70 and 82 together. When the exhaust manifold segments 70 and 82 are coupled, the first sealing member 114, supported on one or both of the engagement faces 96 and 106, effectively seals the exhaust tube 80 at the joint 112.

Coupling the adjacent exhaust manifold segments 70 and 82 also secures a relative position of one or more bypass tubes 124 within radial bypass channels 98 and 108 of the respective exhaust manifold segments 70 and 82. In particular, each bypass tube 124 is positioned through bypass openings 100 and 110 through the respective engagement faces 96 and 106. A first o-ring seal 120 is positioned about the bypass tube 124 and within the radial bypass channel 98 of the first exhaust manifold segment 70, and a second o-ring seal 122 is positioned about the bypass tube 124 and within the radial bypass channel 108 of the second exhaust manifold segment 82. The second sealing member 116, which may include the first and second o-ring seals 120 and 122, is supported on the bypass tube 124 and effectively seals the liquid coolant passages 76 and 86 of the water jacket tube 74 at the joint 112.

Support mats 90a and 90b may be positioned in a respective one of air gaps 91a and 91b between the exhaust tube 80 and the water jacket tube 74. During assembly, each of the first and second exhaust manifold segments 70 and 82 may be assembled prior to coupling the first and second exhaust manifolds segments 70 and 82 as shown in FIG. 5. In particular, a first support mat 90a may be positioned around the first exhaust tube segment 78 before the first exhaust tube segment 78 is received within the first water jacket tube segment 72. During this assembly, the first support mat 90a is compressed between an outer surface 93 of the first exhaust tube segment 78 and an inner surface 95 of the first water jacket tube segment 72. After the second exhaust manifold segment 82 is similarly assembled, the first and second exhaust manifold segments 70 and 82 may be coupled together as described above. When the adjacent exhaust manifold segments 70 and 82 are coupled together, the first exhaust tube segment 78 of the first exhaust manifold segment 70 is received within a flared end 99 of the second exhaust tube segment 88. Thus, at a first end 92b of the second exhaust manifold segment 82, the second exhaust tube segment 88 is supported within the second water jacket tube segment 84 using the second support mat 90b, while, at a second end 102b of the second exhaust manifold segment 82, the flared end 99 is supported by the first exhaust tube segment 78.

The air gap 91 may provide an insulation shield between the exhaust tube 80 and the water jacket tube 74. In particular, the air gap 91 may reduce the amount of thermal energy transmitted to the liquid coolant from the exhaust tube 80. The support mats 90 may assist in supporting the exhaust tube 80 and maintaining the air gap 91. Preferably, the support mats 90 are made from a high temperature insulation material and, thus, may transfer a relatively low amount of thermal energy from the exhaust tube 80 to the water jacket tube 74, particularly when compared to support structures made from alternative materials. Further, the support mats 90 may be sized and configured to distribute forces, including vibrations, transmitted between the components over a larger area than alternative structures. Ultimately, the support mats 90 may reduce premature wear of the water jacket tube 74 that might otherwise be caused by heat and forces transferred from the exhaust tube 80.

It should be understood that the above description is intended for illustrative purposes only, and is not intended to limit the scope of the present disclosure in any way. Thus, those skilled in the art will appreciate that other aspects of the disclosure can be obtained from a study of the drawings, the disclosure and the appended claims.

Claims

1. An internal combustion engine, comprising:

a cylinder block defining at least one cylinder;

a cylinder head coupled to the cylinder block;

an exhaust manifold coupled to the cylinder head and configured to receive exhaust gas from the cylinder head, wherein the exhaust manifold includes a water jacket tube defining a plurality of liquid coolant passages and an exhaust tube received within the water jacket tube, wherein the exhaust manifold includes an air gap between the exhaust tube and the water jacket tube; and

a support mat positioned in the air gap, wherein the support mat is compressed between an outer surface of the exhaust tube and an inner surface of the water jacket tube.

2. The internal combustion engine of claim 1, wherein the support mat includes a high temperature insulation material.

3. The internal combustion engine of claim 2, wherein the support mat defines a continuous annular band.

4. The internal combustion engine of claim 2, wherein the high temperature insulation material is intumescent.

5. The internal combustion engine of claim 2, wherein the support mat has a compressed radial thickness of between about 3 millimeters and about 20 millimeters.

6. The internal combustion engine of claim 5, wherein the support mat has an axial length of between about 75 millimeters and about 125 millimeters.

7. The internal combustion engine of claim 1, wherein the exhaust manifold is a modular exhaust manifold including a plurality of exhaust manifold segments coupled together along a common axis, wherein each of the exhaust manifold segments includes a segment of the water jacket tube and a segment of the exhaust tube received within the water jacket tube segment.

8. The internal combustion engine of claim 7, wherein each exhaust manifold segment includes at least one support mat compressed between the exhaust tube segment and the water jacket tube segment.

9. The internal combustion engine of claim 8, wherein the at least one support mat is positioned at a first end of each exhaust manifold segment, and at a second end of each exhaust manifold segment the exhaust tube segment has a flared end for receiving the exhaust tube segment of an adjacent exhaust manifold segment.

10. The internal combustion engine of claim 7, wherein the exhaust tube is configured to direct exhaust gas in a first direction relative to the common axis and the liquid coolant passages are configured to direct liquid coolant in a second direction relative to the common axis that is opposite the first direction.

11. A modular exhaust manifold for an internal combustion engine, comprising:

a first exhaust manifold segment including a first segment of a water jacket tube defining a first plurality of liquid coolant passages and a first segment of an exhaust tube received within the first water jacket tube segment;

wherein the first exhaust manifold segment includes a first air gap between the first exhaust tube segment and the first water jacket tube segment; and

a first support mat positioned in the first air gap, wherein the first support mat is compressed between an outer surface of the first exhaust tube segment and an inner surface of the first water jacket tube segment.

12. The modular exhaust manifold of claim 11, wherein the first support mat includes a high temperature insulation material.

13. The modular exhaust manifold of claim 12, wherein the first support mat defines a continuous annular band.

14. The modular exhaust manifold of claim 12, wherein the high temperature insulation material is intumescent.

15. The modular exhaust manifold of claim 12, wherein the support mat has a compressed radial thickness of between about 3 millimeters and about 20 millimeters.

16. The modular exhaust manifold of claim 15, wherein the support mat has an axial length of between about 75 millimeters and about 125 millimeters.

17. The modular exhaust manifold of claim 11, further including:

a second exhaust manifold segment including a second segment of the water jacket tube defining a second plurality of liquid coolant passages and a second segment of the exhaust tube received within the second water jacket tube segment;

wherein the second exhaust manifold segment includes a second air gap between the second exhaust tube segment and the second water jacket tube segment; and

a second support mat positioned in the second air gap, wherein the second support mat is compressed between an outer surface of the second exhaust tube segment and an inner surface of the second water jacket tube segment.

18. The modular exhaust manifold of claim 17, wherein the first support mat is positioned at a first end of the first exhaust manifold segment and the second support mat is positioned at a first end of the second exhaust manifold segment, wherein at a second end of the first exhaust manifold segment the first exhaust tube segment has a flared end for receiving the second exhaust tube segment.

19. A method of assembling a modular exhaust manifold for an internal combustion engine, comprising steps of:

assembling a first exhaust manifold segment by: positioning a first support mat around a first segment of an exhaust tube; receiving the first exhaust tube segment within a first segment of a water jacket tube defining a first plurality of liquid coolant passages; wherein the receiving step includes compressing the first support mat between an outer surface of the first exhaust tube segment and an inner surface of the first water jacket tube segment; and maintaining an air gap between the first exhaust tube segment and the first water jacket tube segment with the first support mat.

20. The method of claim 19, further including:

attaching a second exhaust manifold segment to the first exhaust manifold segment;

wherein the attaching step includes receiving the first exhaust tube segment of the first exhaust manifold segment within a flared end of the second exhaust tube segment.