Patent Application
20170009708
Emission concerns associated with the operation of internal combustion engines (e.g., diesel and other types of engines) have resulted in an increased emphasis on the use of exhaust gas heat exchangers. These heat exchangers are often used as part of an exhaust gas recirculation (EGR) system, in which a portion of an engine's exhaust is returned to the combustion chambers. Such a system displaces some of the oxygen that would ordinarily be inducted into the engine as part of the fresh combustion air charge with the inert gases of the recirculated exhaust gas. The presence of the inert exhaust gas typically serves to lower the combustion temperature, thereby reducing the rate of NOx formation.
In order to achieve the foregoing, it is desirable for the temperature of the recirculated exhaust to be lowered prior to the exhaust being delivered into the intake manifold of the engine. In the usual case, engine coolant is used to cool the exhaust gas within the exhaust gas heat exchanger (typically referred to as an “EGR cooler”) in order to achieve the desired reduction in temperature. The use of engine coolant provides certain advantages in that appropriate structure for subsequently rejecting heat from the engine coolant to the ambient air is already available for use in most applications requiring an EGR system.
Due in large part to the elevated temperatures of the exhaust gas that they encounter, EGR coolers are known to be prone to thermal cycle failure. The desire for increased fuel economy continues to drive the engine operating temperatures upward, further exacerbating the problem. Above a certain temperature, the material properties of the metals used to produce the heat exchanger rapidly degrade, and the operational lifetime of the heat exchanger is substantially reduced. In order to combat this problem, it often becomes necessary either for the heat exchanger to be produced of more expensive alloys that can withstand these higher temperatures, or to increase the size and weight of the heat exchanger using the current materials, neither of which is desirable. Thus, there is still room for improvement.
According to an embodiment of the invention, a heat exchanger to transfer heat from an exhaust gas flow to a liquid coolant includes a first heat exchange section and a second heat exchange section located adjacent to the first heat exchange section. The first heat exchange section is located within a first housing that at least partially encloses a first fluid volume. The second heat exchange section is located within a second housing that at least partially encloses a second fluid volume. A first plurality of heat exchange tubes traverses the first heat exchange section, and a second plurality of heat exchange tubes traverses the second heat exchange section. An exhaust gas flow path of the heat exchanger includes the first fluid volume and the interiors of the second plurality of heat exchange tubes. A coolant flow path of the heat exchanger includes the second fluid volume and the interiors of the first plurality of heat exchange tubes.
In some embodiments, the first fluid volume is arranged upstream of the interiors of the second of the second plurality of heat exchange tubes along the exhaust gas flow path. In some embodiments the second fluid volume and the interiors of the first plurality of heat exchange tubes are arranged fluidly in parallel along the coolant flow path. In some embodiments, a header plate separates the first fluid volume from the second fluid volume.
In some embodiments the second plurality of heat exchange tubes are flattened tubes defining a tube major dimension and a tube minor dimension smaller than the tube major dimension. In some embodiments the second plurality of heat exchange tubes are spaced apart from one another in the tube minor dimension and individual ones of the first plurality of heat exchange tubes are aligned with spaces between adjacent ones of the second plurality of heat exchange tubes.
In some embodiments, the heat exchanger includes a coolant inlet manifold in fluid communication with inlet ends of at least some of the first plurality of heat exchange tubes, and a coolant outlet manifold in fluid communication with outlet ends of at least some of the first plurality of heat exchange tubes. At least one of the coolant inlet manifold and the coolant outlet manifold are located within a wall section of the first housing. In some embodiments the coolant inlet manifold, the coolant outlet manifold, and the first plurality of heat exchange tubes are part of a replaceable cartridge.
According to another embodiment of the invention, a method of recirculating a flow of exhaust gas includes receiving the flow of exhaust gas, at an exhaust gas inlet temperature above a threshold temperature, into an exhaust inlet of a heat exchanger and directing the flow of exhaust gas through an inlet diffuser of the heat exchanger from the exhaust inlet to open ends of a plurality of exhaust tubes. A liquid coolant is directed through a plurality of coolant tubes arranged within the inlet diffuser in order to maintain the tube walls of the plurality of coolant tubes at a wall temperature substantially below the threshold temperature. The temperature of the flow of exhaust gas is reduced to an intermediate exhaust temperature below the threshold temperature prior to the exhaust gas reaching the open ends of the plurality of exhaust tubes by transferring heat through the tube walls to the liquid coolant flowing through the plurality of coolant tubes. The flow of exhaust gas is directed through the plurality of exhaust tubes, and a liquid coolant is directed over outside surfaces of the plurality of exhaust tubes. The temperature of the flow of exhaust gas is reduced from the intermediate exhaust temperature to a desired exhaust gas outlet temperature by transferring heat to the liquid coolant flowing over the outside surfaces of the plurality of exhaust tubes.
In some embodiments a flow of liquid coolant is separated into a first portion and a second portion. The first portion is directed to flow through the plurality of coolant tubes, and the second portion is directed to flow over the plurality of exhaust tubes.
Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the accompanying drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless specified or limited otherwise, the terms “mounted,” “connected,” “supported,” and “coupled” and variations thereof are used broadly and encompass both direct and indirect mountings, connections, supports, and couplings. Further, “connected” and “coupled” are not restricted to physical or mechanical connections or couplings.
One exemplary embodiment of a power generation system 20 employing the present invention is illustrated in
In operation, a flow of air 30 is compressed and delivered to an intake manifold 22 of the engine 21. A supply of fuel (not shown) is delivered to the engine 21 and is combusted within the engine 21 using the air 30 to produce mechanical work. High temperature exhaust products resulting from the combustion are removed from the engine 21 by way of an exhaust manifold 23.
Otherwise wasted heat energy of the exhaust products can be recaptured and used to compress the incoming air 30 in a process commonly referred to as turbo-charging. A portion 29 of the hot exhaust products is directed through an expansion turbine 26, which is mechanically coupled to a compressor 27. Energy contained in the exhaust 29 is used to rotate the turbine 26, which in turn rotates the compressor 27. Rotation of the compressor 27 draws in and compresses the flow of air 30 that is to be directed to the engine 21. The compressed flow of air 30 can be directed through one or more heat exchangers 28 (typically referred to as a charge air cooler) in order to reduce the temperature of the air 30, thereby increasing the density of the air 30 and boosting the output of the engine 21.
A second portion 19 of the exhaust products is directed from the exhaust manifold 23 through an EGR circuit 31, and is subsequently directed back to the intake manifold 22. Located within the EGR circuit 31 is a heat exchanger 1 (the EGR cooler) wherein the temperature of the recirculated exhaust gas 19 is reduced. By supplying a flow of cooled, recirculated exhaust gas to the engine 21 along with the flow of air 30, undesirable emissions within the exhaust can be reduced to a level that complies with environmental regulations.
The recirculated exhaust gas 19 is directed through a conduit 24 from the exit manifold 23 to an exhaust inlet port 12 of the heat exchanger 1. After passing through the heat exchanger 1, the cooled recirculated exhaust gas 19 is removed from the heat exchanger 1 through an exhaust outlet 13, and is directed to the inlet manifold 22 by way of a conduit 25. Within the heat exchanger 1, heat is transferred from the recirculated exhaust gas 19 to a flow of coolant 18 directed through the heat exchanger 1.
As depicted diagrammatically in
The heat exchange section 3 is located within a housing 4, which at least partially encloses a second fluid volume 6. Tubes 8 extend through the fluid volume 6, and convey the exhaust gas 19 through the heat exchange section 3 while maintaining isolation of the exhaust gas 19 from the fluid volume 6 itself. A portion 18b of the flow of coolant 18 passes through the fluid volume 6, and flows over the outer surfaces of the tubes 8 to cool the exhaust gas 19 as it passes through the tubes 8.
The portions 18a and 18b of the coolant flow 18 can be arranged to be fluidly in parallel with one another, as indicated in
While the flow of coolant 18b in FIG.1 is arranged to flow in a co-current flow orientation to the exhaust gas 19, in some alternative embodiments it may be preferable to flow the coolant 18b in a different orientation. For example, in some embodiments it may be preferable for the coolant 18b to flow in a counter-flow or a cross-flow orientation to the exhaust gas 19.
The above described EGR circuit 31 can be especially beneficial when the exhaust gas 19 that is to be recirculated back to the engine 21 exits the exhaust manifold at an excessively high temperature. EGR coolers are known to be prone to thermal cycle failures, due to the thin walls, multiple joints, and steep thermal gradients that are inherent in such heat exchangers. Quite often an EGR cooler will be designed to operate at a maximum, or threshold, exhaust gas inlet temperature. Certain material properties (for example, yield strength, creep resistance, etc.) of the steel alloys used in fabricating the EGR cooler will degrade rapidly above that threshold temperature, leading to increases in the strain values caused by the aggressive thermal cycles of the heat exchanger. As a result, when exhaust gas temperatures entering the EGR cooler exceed that threshold temperature, the lifetime of the EGR cooler may be substantially reduced. As a non-limiting example, an EGR cooler constructed primarily of stainless steel alloys having 16-18% nickel content will typically have a threshold temperature that is less than 650° C.
The portions of the EGR cooler that are most prone to failure when exposed to exhaust gases above the threshold temperature are the thin-walled heat exchange tubes through which the exhaust gas typically flows. In order to protect those tubes 8 in the heat exchange section 3, the exhaust gas is first cooled within the heat exchange section 2 by the coolant 18a flowing through the tubes 9. Flowing the coolant 18a through the tubes 9 maintains the walls of the tubes 9 at a temperature that is substantially below the threshold temperatures, even when the temperature of the exhaust gas being received into the diffuser 5 is at an inlet temperature that is above the threshold temperature. The transfer of heat from the exhaust gas to the coolant 18a reduces the temperature of the exhaust gas to an intermediate temperature that is below the threshold temperature prior to it reaching the tubes 8, thereby extending the life of the EGR cooler.
An exemplary embodiment of the heat exchanger 1 is shown in more detail in
The housing 4 is depicted as a two-piece casing that surrounds the bundle of tubes 8 and is joined to the headers 11 and 32 by welding in order to bound the fluid volume 6. In other embodiments the housing 4 can be a single piece casing into which the bundle of tubes 8 is received. The housing 4 can be constructed of steel alloy similar to the tubes and headers. Alternatively, since the housing 4 can be maintained at a substantially lower temperature by the coolant 18b flowing therethrough, it can be constructed of other material such as, for example, aluminum alloys. An inlet 16 to receive the flow of coolant 18b into the fluid volume 6, and an outlet 17 to remove the coolant 18b from the fluid volume 6, are provided in the housing 4.
The housing 5 functions as the inlet diffuser for the exhaust flow 19 passing through the heat exchanger 1, and is provided as a cast component joined to the inlet header 11 in order to define the fluid volume 7. An exhaust gas inlet 12 is provided in the housing 5 to allow for connection of the heat exchanger 1 to the conduit 24 of the EGR circuit 31.
The tubes 9 are provided as part of a heat exchanger cartridge 10 (shown in detail in
A return manifold 18 is provided at the end of the cartridge 10 opposite the ports 14 and 15, and receives the open ends of the tubes 9 at the ends opposite of those received into the header 33. During operation of the heat exchanger 1 within an EGR circuit 31, the flow 18a of coolant is received through one of the coolant ports 14 and 15 into one of the coolant manifolds 16 and 17, flows through those ones of the tubes 9 that have an open end connected to that one of the manifolds 16 and 17, enters into the return manifold 18, flows through the remainder of the tubes 9 to the other one of the coolant manifolds 16 and 17, and is removed from the heat exchanger 1 by way of the other one of the coolant ports 14 and 15.
The cartridge 10 can be constructed as a brazed or welded subassembly that is inserted into the housing 5. As shown in
The cartridge 10 can be made to be replaceable in the event of a failure (such as for example, a coolant leak) occurring within the cartridge 10. As an example, the cartridge 10 can be readily removed and replaced by grinding away the welds that secure the cartridge 10 to the wall section 19, thereby avoiding the need to replace the entire heat exchanger 1.
By providing the ports 14 and 15 at common ends of the tubes 9, and providing a return manifold 18 at the opposing ends, the tubes 9 can be made to be thermally unconstrained within the housing 5. As a result, stresses within the tubes 9 that would otherwise result from differential thermal expansions between the housing 5 and the tubes 9 can be lessened, thereby increasing the durability of the heat exchanger 1.
The tubes 9 can advantageously be provided with twisted embossments 34 within the tube walls. These embossments 34 can provide beneficial turbulation of the coolant passing through the tubes 9, as wells as of the exhaust gas passing over the tubes 9, thereby improving the heat transfer performance within the heat exchange section 2. In addition, the embossments 34 provide the tubes 9 with structural compliance, thereby further reducing the likelihood of structural failures. In some embodiments the embossments 34 can take the form of a spiral channel formed into the wall of a tube 9 and extending along at least a portion of the length of the tube.
In some alternate embodiments of a heat exchanger 1, the structural compliance of the tubes may be sufficient to avoid the need for an unconstrained return manifold 18. In some of such alternate embodiments it may be desirable to provide the coolant manifolds 16 and 17 at opposing ends of the tubes 9, so that the flow of coolant 18a encounters only a single fluid pass through the heat exchange section 2. With such an alternative construction the manifolds 16 and 17 can be located within opposing wall sections of the housing 5, thereby further reducing the previously described structural loading of the header 11.
Heat exchange tubes 109 traverse the heat exchange section 102, and allow for the exchange of heat between the exhaust gas flowing through the fluid volume 107 and a coolant flowing through the tubes 109. The coolant can be received into the heat exchanger 101 through the coolant port 114, and can be removed through the coolant port 115, or vice-versa. The heat exchange tubes 109, ports 114 and 115, and the manifolds joining the tubes 109 to the ports 114 and 115 can be provided as a pre-assembled and brazed cartridge 110. Such a cartridge 110 can be made to be readily replaceable in case of failure by, for example, assembling the heat exchanger 101 using bolts or similar mechanical fasteners extending through the pattern of aligned holes in the housing 104, header 111, and cartridge 110.
As best seen in
In order to facilitate the flow of coolant around the heat exchange tubes 8 and 108, the tubes are preferably spaced apart from another in the tube minor dimension. As shown in
Various alternatives to the certain features and elements of the present invention are described with reference to specific embodiments of the present invention. With the exception of features, elements, and manners of operation that are mutually exclusive of or are inconsistent with each embodiment described above, it should be noted that the alternative features, elements, and manners of operation described with reference to one particular embodiment are applicable to the other embodiments.
The embodiments described above and illustrated in the figures are presented by way of example only and are not intended as a limitation upon the concepts and principles of the present invention. As such, it will be appreciated by one having ordinary skill in the art that various changes in the elements and their configuration and arrangement are possible without departing from the spirit and scope of the present invention.
This application is a Continuation of presently pending U.S. patent application Ser. No. 14/890,014 which is a National Stage Entry under 35 U.S.C. §371 of PCT Patent Application No. PCT/US2014/037446, which was filed on May 9, 2014 and which claims priority to U.S. Provisional Patent Application No. 61/822,041, filed on May 10, 2013, the entire contents of all of which are hereby incorporated by reference herein.
| Number | Date | Country | |
|---|---|---|---|
| 61822041 | May 2013 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 14890014 | Nov 2015 | US |
| Child | 15275585 | US |
