Patent Application
20190101080
The present invention relates to a heat recovery system for internal combustion engines which is arranged in an exhaust gas conduit. The system allows transferring heat from the exhaust gas conduit to a liquid coolant through a heat exchanger.
Conventional heat exchangers for exhaust gas conduits must interfere with the exhaust gas flow as little as possible since heat recovery is established in time periods that are shorter than the total time in which the exhaust gas is flowing. For this purpose, the heat exchanger intended for heat recovery is arranged adjacent to the exhaust conduit and in a bypass configuration. In this configuration, although there is a valve managing the passage of gas, regions in which heat is transferred to the heat exchanger are formed, even when this should not happen, and when there is a space between the heat exchanger and the exhaust conduit, exhaust gas recirculation regions are formed in regions which are not closed by the valve, giving rise to pressure drops. Heat transfer to the heat exchanger when the passage of the exhaust gas through the exchanger is not established leads to the liquid coolant being heated up, transferring heat to the engine cooling system when this should not happen and in an operating mode for which it is not sized. This brings about having to oversize the engine cooling system, discharging this extra heat, to prevent damage.
The present invention is characterized by a particular configuration of the exhaust gas conduit incorporating a flow guide element to prevent this undesired recirculation, allowing subsequent energetic optimization of the heat recovery device.
One of the fields of the art that has been subjected to intensive development is the field of heat recovery devices intended for recovering the heat released by an internal combustion engine through exhaust gases. If the heat is not recovered from the exhaust gases, said heat ends up in the atmosphere, giving rise to very low global engine performance with respect to the energy released by the fuel in the combustion process.
Recovering the heat from exhaust gases allows a later usage as a heat source, for example in a Rankine cycle for obtaining mechanical energy in a shaft. The mechanical energy provided by the internal combustion engine plus the energy from the Rankine cycle considerably increases global system efficiency.
There are various heat recuperators with different applications to either, as mentioned, provide a heat source for a Rankine cycle or provide heat in short time periods with uses such as reducing the oil heating time of the engine so that it operates at operating conditions as soon as possible or as heating for the passenger compartment. These are just a few of many examples.
Internal combustion engine performance depends on, among other variables, the few losses of the exhaust conduit. Throttling the exhaust conduit with the presence of elements raising the exhaust gas flow resistance involves negatively affecting performance.
When the purpose of the heat exchanger is to recover heat at given short time periods with respect to the engine operating mode, said exchanger is arranged in a bypass configuration so that the gas flow runs in a normal manner with the minimum number of elements in its path, and so that there are fewer losses in this path due to a pressure drop.
In this configuration, when the flow passes through the heat exchanger, the inlet into and outlet from the heat exchanger show a somewhat tortuous S-shaped configuration generating losses; nevertheless, this drawback is accepted in exchange for favoring a configuration with the direct passage of the exhaust gas, without transferring heat, given that the heat recovery time is much shorter than the time in which the exhaust gas passes without releasing heat, such as for example when it is released directly into the atmosphere.
The configuration of a heat exchanger for heat recovery in an exhaust conduit is known through the PCT application with number WO2014/131828, where resistance to the passage of exhaust gas has been minimized by configuring the heat exchanger like a device that can be coupled to the exhaust conduit through two windows, a first window for entry of the exhaust gas into the exchanger and a second window for the return of the cooled gas to the exhaust conduit.
This configuration is possible because the valve managing the exhaust gas bypass is configured from a flap which enters through the window, establishing support on the inner wall of the exhaust conduit, adapting a shape that adheres to said wall.
The described configuration places the bypass management valve upstream such that downstream there is located access to the outlet for the cooled gas, i.e., the gas that has already released heat to the liquid coolant through an exchange block, through which it returns to the exhaust conduit through the second window, the one arranged downstream.
Although this configuration allows the exhaust conduit to not have any inwardly-projecting element to apply resistance to the passage of the exhaust gas, the cavity formed by the space existing between the second window and the heat exchange block gives rise to a sudden expansion in the passage of the exhaust gas circulating through the exhaust gas conduit, giving rise to recirculation regions.
Throughout this description heat exchange block will refer to the segment of the heat exchanger which is formed by the heat exchange tube bundle and extends between two end baffles if it has baffles. In this particular case, according to the direction of passage of the hot gas through the tube bundle, the heat exchange block is mounted between the mentioned end baffles. It is therefore the space bound between the cooled gas outlet end baffle and the second window of the exhaust conduit which gives rise to a cavity where the exhaust gas generates a recirculation region when the heat exchanger is not used. In any other case where end baffles are not used, the heat exchange block is mounted between two sections where the heat exchange surfaces are bound between the hot gas and the liquid coolant.
The effect of this recirculation flow in the identified region causes a pressure drop due to the increased resistance and an increase in the temperature of the heat exchange block on the outlet side due to the direct impact of the hot gas. There are configurations of the exchange block, for example configured in the form of stacked flat tubes (referred to as a stacked cooler), which allow extending the exchange region to the very access window for entering the exhaust gas conduit. In this case, the recirculation region is minimized or even disappears, but the problem of the undesired heating of the liquid coolant remains due to the occurrence of exhaust gas flows the streamlines of which reach the exchange block.
This same situation occurs when the bypass valve is located downstream. The closure of the exhaust conduit by means of the bypass valve causes the flow upstream to be diverted to the heat exchanger or at least that there are streamlines reaching the exchange block. Nevertheless, in this other position of the valve, even though the valve is open for the passage of the exhaust gas without heat exchange, there is also still a region upstream for access to the exchange block, causing the subsequent heating of the coolant fluid, and in most situations a region which is defined in this case by the space between the first window and the heat exchange block, giving rise also to pressure drops.
The present invention prevents this problem by proposing a specific configuration that prevents the undesired heating of the exchange block.
The present invention relates to a heat recovery system that is suitable for being located in a conduit for the passage of exhaust gas such that during operation, the exhaust gas passes with minimal pressure drop, and in certain time periods it is diverted through a heat exchanger by means of a bypass configuration in order to transfer some of its heat to a liquid coolant. The heat transferred to the liquid coolant allows recovering part of the energy that would otherwise remain in the exhaust gas, and its final destination would be the atmosphere.
In a secondary use, the gas cooled after heat recovery can be used as EGR gas in an EGR (exhaust gas recirculation) system. In this case, a branch in the exhaust gas system, or more specifically in the outlet area of the exchanger, incorporates an EGR valve for managing the amount of cooled gas that is introduced back into the intake of the internal combustion engine.
The heat recovery system comprises:
The exhaust gas conduit can be the exhaust conduit or conduits located in an EGR system through which the exhaust gas circulates at a high temperature, hence the name “exhaust gas conduit.” In a segment of this exhaust gas conduit, the heat exchanger is arranged in a bypass configuration such that during operation, the exhaust gas circulates through the exhaust gas conduit passing through the heat exchanger when heat is being recovered and without passing through the heat exchanger when heat is not recovered, without the gas passing through a segment of the exhaust gas conduit. When the exhaust gas passes through the heat exchanger, part of the heat of the exhaust gas is transferred to the liquid coolant for subsequent use of this thermal energy.
The heat exchanger comprises a heat exchange block, wherein this heat exchange block is defined between two end baffles in most of the embodiments herein. Entry of the hot gas from the exhaust gas conduit to the heat exchanger and the exit of the cooled gas from the heat exchanger to the exhaust gas conduit are established through two openings in said exhaust gas conduit.
Between these openings in the exhaust gas conduit and the heat exchange block, in most of the embodiments, there are two spaces which communicate the exhaust gas conduit with the inlet and outlet of the heat exchanger, respectively.
By way of reference, following the longitudinal direction defined by the direction of the exhaust gas flow, each of the openings extends between two section planes, i.e., the so-called first plane and the so-called second plane, transverse to the exhaust gas conduit. The first plane is located by convention upstream and the second plane is located by convention downstream with respect to the exhaust gas flow.
In addition to these components, the system comprises:
In many of the embodiments of the two spaces identified above, between an opening and the heat exchange block, one of them is closed by the valve when it is located in the first position. Since the other opening does not have a valve, it shows the space between the exchange block and the opening as if it were a cavity of the exhaust gas conduit. Therefore, when the exhaust gas passes through the exhaust gas conduit without heat recovery, the cavity acts like a sudden expansion, giving rise to a recirculation flow. In those examples in which there is not a space between the opening and the exchange block, when the exhaust gas flow lines pass in the non-heat recovery operating mode, they also have easy access to the heat exchange block, raising the temperature of the liquid coolant without the need for a recirculation region.
The recirculation flow generates pressure drops in the exhaust gas conduit the entire time that there is no heat recovery, and this recirculation flow also generates an undesired heat transfer from the hot exhaust gas flow to the liquid coolant when the valve is in the non-heat recovery position (also referred to as direct exhaust position).
For this purpose, the system according to the invention also comprises:
When the valve is located in the first position, the flow guide prolongs the streamlines downstream without the flow impacting the heat exchange block, preventing the heating of the liquid coolant. Additionally, in those examples in which there is a cavity between the opening and the exchange block, the flow guide also prevents or minimizes the occurrence of recirculation regions, preventing the pressure drops brought about by a sudden expansion. The flow guide interferes minimally with the exhaust gas flow, slightly increasing pressure drops with respect to a conduit without openings or cavities, but nevertheless, the technical benefit obtained far overshadows the drawbacks of these minimal drops.
The flow guide does not close the opening where it is located, such that fluid communication in the form of a channel is maintained between the surface of the flow guide and the opening, such that this channel allows the passage of a considerable flow volume between the exhaust gas conduit and the heat exchange block. When the valve is located in the opening located upstream, the flow guide favors the cooled gas exiting with an outlet direction according to the direction of the exhaust gas flow. When the valve is located in the opening located downstream, the flow guide does not prevent the hot gas entering the space located between the opening and the heat exchange block of the heat exchanger, allowing heat recovery in the second position of the valve. In this second case, the flow guide preferably has a length such that it does not exceed the second reference plane.
The various configurations of the system are described in the detailed description of the invention, many of which are shown in the drawings.
The foregoing and other features and advantages of the invention will be more clearly understood based on the following detailed description of a preferred embodiment provided only by way of illustrative and non-limiting example in reference to the attached drawings.
According to the first inventive aspect, the present invention relates to a heat recovery system that can be used in an internal combustion engine which allows recovering part of the heat from the exhaust gas.
The recovered energy can be used to obtain mechanical energy, for example through a Rankine cycle, and in turn transformed into electric energy. This electric energy allows driving electric engines or can be used in auxiliary devices in the vehicle.
The recovered heat can also be used, without prior transformation, for heating either the passenger compartment of the vehicle or parts of the engine during warm-up in order for said parts to reach the operating temperature as soon as possible. These are just a few examples of the use of the recovered energy.
The most common use of this system is the recovery of heat from the exhaust gas which would otherwise end up being released into the atmosphere. Nevertheless, given that the exhaust gas has been cooled once the heat is recovered an advantage of the described system is that the cooled gas can be used as an EGR system. In other words, the cooled gas can be diverted to the intake of the internal combustion engine with the flow volume control established by means of an EGR valve.
The exhaust gas flow should not be perturbed as far as possible to reduce pressure drops given that the time during which the exhaust gas flow circulates through the conduit without requiring heat recovery is longer than the time in which it is required for there to be heat recovery.
For this purpose, the heat exchanger (1) that allows heat recovery by means of transferring thermal energy from the hot exhaust gas to a liquid coolant is arranged in a bypass configuration with respect to the exhaust gas conduit (2). The bypass configuration chosen in this embodiment places the heat exchanger (1) parallel to the exhaust gas conduit (2), where said heat exchanger (1) is fed from an exhaust gas intake opening (2.1) to an exhaust gas exhaust opening (2.2) with a space configured to cause a 90° change in the flow of the hot gas. In other words, the exhaust gas flow follows an approximately straight path when it does not pass through the heat exchanger (1) and follows a tortuous path, i.e., having an alternating turn, to enter and exit the heat exchanger (1) when the passage of the exhaust gas through the heat exchanger (1) is required, recovering part of its thermal energy.
The heat exchanger (1) according to this embodiment and all the heat exchangers shown in the embodiments discussed below are configured by means of a heat exchange tube bundle extending between two end baffles. The region bound between the end baffles is the region where the heat exchange occurs, and this heat exchange segment will be identified as exchange block (1.3) of the heat exchanger (1). According to other embodiments, the heat exchange block (1.3) is configured by a stack of flat tubes without end baffles. In this case, the exchange block is limited by the ends of the flat tubes, where the latter can fill part of the curve required for the bypass configuration, reducing or even eliminating the possible recirculation regions, but making the exchange block more accessible to the flow passing through the exhaust gas conduit in the non-heat recovery mode.
Continuing with the embodiment shown in
The exhaust gas conduit (2) comprises two openings (2.3, 2.4), a first intake opening (2.3) located upstream and a second exhaust opening (2.4) located downstream according to the direction of the exhaust gas flow.
The intake manifold (1.1) places the first intake opening (2.3) in fluid communication with the inlet of the exchange block (1.3), and the exhaust manifold (1.2) places the outlet of the exchange block (1.3) in fluid communication with the second exhaust opening (2.4).
The exchange block (1.3) of the heat exchanger (1) comprises an inlet conduit (1.3.1) and an outlet conduit (1.3.2) for the liquid coolant. The liquid coolant enters the exchange block (1.3) of the heat exchanger (1), covering the tubes of the tube bundle. The heat from the exhaust gas that passes through the exchange block (1.3) is transferred to the liquid coolant through the surface of the tubes of the tube bundle, such that the recovered heat exits the heat recovery system with the liquid coolant at a higher temperature.
As described above, the cooled exhaust gas flow exits the heat exchange block (1.3) and passes to the exhaust gas conduit (2), passing through the exhaust manifold (1.2) passing through the second exhaust opening (2.4).
According to this embodiment, the passage of the exhaust gas through either the exhaust gas conduit (2) or the heat exchanger (1) is determined by a valve (3) located on the inlet side of the heat exchanger (1). The valve (3) has a flap (3.1) that can adopt two end positions:
In the first position, i.e., the position shown in
In the first position, the exhaust gas flow goes past the position of the valve (3) and reaches, according to the longitudinal direction, the position where the second exhaust opening (2.4) communicating with the exhaust manifold (1.2) of the heat exchanger (1) is located. This exhaust manifold (1.2) defines a space that the flow would run into abruptly were it not for a flow guide (4) which prolongs the path of the streamlines of the exhaust gas flow.
According to the state of the art, the cavity forming the space defined by the exhaust manifold (1.2) gives rise to a recirculation region which introduces hot gas circulating through the exhaust gas conduit and makes it directly impact the outlet of the exchange block (1.3). This hot gas raises the temperature of the liquid coolant in an undesired manner, which may give rise to the need to oversize the engine cooling system.
According to this embodiment, the exhaust gas flow goes past the cavity following a path like the one indicated by means of the arrow F1 and continues downstream of the second exhaust opening (2.4).
Two planes transverse to the exhaust gas conduit (2), i.e., a first plane (P1) located at the point from where the second exhaust opening (2.4) starts and a second plane (P2) located at the point where the second exhaust opening (2.4) ends, considering the direction of the exhaust gas flow according to longitudinal direction X-X′, are identified in said
In this particular case, the flow guide (4) is configured by means of a sheet metal, although the use of other material is possible, and it is attached with the exhaust gas conduit (2) through a region located upstream of the first plane (P1). Once the exhaust gas flow reaches the position of the flow guide (4), its path is prolonged without entering the cavity generating the presence of the exhaust manifold (1.2). In this embodiment, the flow guide (4) is furthermore configured like a baffle since it has a curvature that leads to the exhaust gas flow moving away from the second exhaust opening (2.4).
In this embodiment, the configuration of the flow guide (4) is according to a surface which shows a first curvature, which is inwardly concave with respect to the exhaust gas conduit (2), that adapts to the shape of the inner wall of the exhaust gas conduit (2), and following the longitudinal direction downstream, the curvature of the flow guide (4) changes to be inwardly convex with respect to the exhaust gas conduit (2), i.e., inwardly concave with respect to the cavity formed by the second exhaust opening (2.4).
The technical effect of this change in curvature is the fact that it favors the flow exiting the heat exchanger when the valve is in the second position, i.e., in heat recovery mode. The arrow F2 shows how the flow guide (4) diverts the flow to the right, according to the orientation of
Other embodiments have a different change in curvature, for example from a flat configuration, for example, which is particularly suitable when the conduit has a polygonal section, to a curved configuration with a single curvature.
According to another embodiment, a flow guide (4) with a single curvature, i.e., with no change in curvature, is used.
In this embodiment, the final end of the flow guide (4) ends before reaching the second plane (P2) to leave a wide channel (C) that allows the cooled gas to exit.
In this particular case, the flow guide (4) is configured like punched and stamped sheet metal, but according to other embodiments it could be made of another material and have a cylindrical shape adhered to the inner wall of the exhaust gas conduit (2).
In a first upstream segment, the flow guide (4) is cylindrical and has a diameter (D1) coinciding with the internal diameter of the exhaust gas conduit (2), reducing the degree of interference in the exhaust gas flow (2) to a minimum when the valve is in the first position.
The flow guide has downstream a smaller diameter (D2) after an intermediate transition segment (T) between the two diameters (D1, D2). According to this embodiment, the final end is prolonged downstream past the second plane (P2) such that an annular channel (C) is formed between the cylindrical surface and the inner wall of the exhaust gas conduit.
This through channel (C) between the flow guide (4) and the exhaust gas conduit (2) allows the exit of the cooled gas with an increased section, making the exit thereof easier when the valve (3) is located in the second end position in heat recovery mode.
To increase the passage section, the flow guide (4) in this embodiment comprises a plurality of perforations (4.1) increasing the passage section offered by the channel (C) defined between the flow guide (4) and the exhaust gas conduit (2).
The flow guide (4) has a tubular configuration, with a fixation located upstream of the first plane (P1) and being prolonged downstream of the second plane (P2). According to this configuration, the exhaust gas flow (2) is led through the tubular segment of the flow guide (4) past the position of the second exhaust opening (2.4), not giving the exhaust gas flow the chance to recirculate in the space formed by the exhaust manifold (1.2).
The diameter of the flow guide (4) is smaller than the diameter of the inner wall of the exhaust conduit (2), giving rise to an annular channel (C) for the passage of the cooled gas exiting the second exhaust opening (2.4) of the heat exchanger to the exhaust gas conduit.
Even though according to one embodiment this flow guide (4) having a tubular configuration can be cantilevered; in the embodiment shown in
In this position of the flap (3.1), the intake manifold forms a cavity that is accessible through the first intake opening (2.3), which would give rise to a hot gas recirculation flow that would reach the exchange block (1.3) if the flow guide (4) located in the first intake opening (2.3) were not provided.
In this embodiment, the flow guide (4) is attached to the exhaust conduit (2) through an attachment region located upstream of the first plane (P1) and is prolonged to a position that does not reach the position of the second plane, (P2) giving rise to a through channel (C).
In this configuration where the valve (3) is located in the second exhaust opening (2.4), the preferred shape of the flow guide (4) is such that it does not reach the second plane (P2) to prevent the passage of the exhaust gas to be cooled in the second position of the valve (3) from having to turn and move forward in the opposite direction until reaching the inner space of the intake manifold (1.1).
Additionally, this schematic depiction also shows a plurality of perforations to favor the passage of the gas to be cooled when the valve (3) is located in the second position, i.e., establishing the passage of the exhaust gas through the heat exchanger (1).
According to another embodiment, the configuration of the perforations (4.1) in the flow guide (4) is embossed in the form of a grater, i.e., the surface around the edge of the perforation (4.1) projects away from the surface of the flow guide (4). When it is indicated that the relief is in the form of a grater, it refers to kitchen graters, for example for grating bread, cheese, etc.
With this configuration in the shape of a grater, in the event of a tangential flow with respect to the surface where the perforations (4.1) are located, flow from one side of the surface to the other side through the perforation is favored due to the presence of the projections. The direction of the flow that is favored depends on if it is projected to one side of the surface or the other and on if this projection is located upstream or downstream of the perforation. In the preferred configuration, the grater configuration is oriented so that the flow favors the passage of the cooled gas into the exhaust gas conduit (2); that is, the passage from the inside of the exhaust gas conduit (2) to the cavity formed by the corresponding manifold (1.1, 1.2) is hindered.
The upper part of
The lower part of each figure shows the same perforation (4.1) according to a section according to a plane perpendicular to the surface of the flow guide (4) and it passes along the length of the surface in relief in the shape of a grater. In these particular cases, the section corresponds to the midline of the perforation (4.1), shown with a horizontal orientation, as it is identified in the upper part by means of a discontinuous line.
In both figures the upper view corresponds to the surface of the flow guide seen from the exhaust gas conduit (2), and therefore the space communicating with the heat exchange block (1.3) is located behind the surface.
Following the same criterion, in both figures the lower view shows the surface of the flow guide (4) according to a horizontal line that leaves the space located inside the exhaust gas conduit (2) above said line and leaves the space communicating with the heat exchange block (1.3) below said line.
| Number | Date | Country | Kind |
|---|---|---|---|
| 17382647.0 | Sep 2017 | EP | regional |
