Patent Application
20080264081
The present disclosure is directed to an exhaust gas recirculation cooler, and more particularly, to an exhaust gas recirculation cooler having temperature control.
Internal combustion engines, including diesel engines, gasoline engines, natural gas engines, and other engines known in the art exhaust a complex mixture of air pollutants. The air pollutants are composed of solid particulate matter and gaseous compounds including nitrous oxides (NOx). In addition, some types of fuels such as, for example, diesel fuels often contain sulfur that, at times, convert to potentially corrosive and environmentally unfriendly byproducts. Due to increased attention on the environment, exhaust emission standards have become more stringent, and the amount of solid particulate matter and gaseous compounds emitted to the atmosphere from an engine is regulated depending on the type of engine, size of engine, and/or class of engine.
Several methods have been implemented by engine manufacturers to comply with the regulation of these engine emissions. Some methods include using an exhaust gas recirculation (EGR) system. EGR systems operate by recirculating cooled exhaust gas back to the intake of the engine. There, the exhaust gas mixes with fresh air. The resulting mixture contains less oxygen than pure air, thereby lowering the combustion temperature in the combustion chambers, which results in less NOx production. Simultaneously, some of the particulate matter contained within the exhaust is burned upon re-introduction to the combustion chamber.
The cooling of the recirculated exhaust gas is often performed by directing exhaust gas through an air-to-gas or a water-to-gas heat exchanger using engine coolant as the cooling medium. Such a cooling system is inexact and functions merely to reduce the overall temperature of the exhaust gas rather than cool the exhaust gas to a specified temperature. Because there is little control over the temperature of the exhaust gas exiting the cooler, sulfur and water in the exhaust gas can combine and condense on the interior of the EGR equipment as sulfuric acid. Sulfuric acid can corrode the surface of the equipment and can lead to maintenance issues.
One attempt to address corrosion due to sulfuric acid condensation can be found in U.S. Pat. No. 5,732,688 (the '688 patent) issued to Charlton et al. on Mar. 31, 1998. The '688 patent discloses a system for controlling the temperature of recirculated exhaust. The system includes an EGR cooler having multiple conduits for conveying exhaust gas through the cooler. The conduits are surrounded by a liquid coolant supplied from an engine coolant source such as a radiator. A controller regulates the flow of exhaust gas and coolant in response to inlet and outlet exhaust gas temperatures. The flow of exhaust gas is regulated by actuating valves located at an exhaust gas inlet to selectively open and close groups of conduits. In addition, the coolant flow is regulated by modulating a valve located at a coolant inlet. When the exhaust temperature at the EGR cooler exhaust gas outlet is too low, the flow of coolant is restricted and/or a group of exhaust gas conduits are isolated from the exhaust gas. Furthermore, when the exhaust temperature at the EGR cooler exhaust gas outlet is too high, the controller increases the coolant and/or the number of conduits through which exhaust gas is allowed to flow.
Although the system in the '688 patent may reduce sulfuric acid condensation by controlling the temperature of exhaust gas exiting the EGR cooler, intermittently isolating a subset of conduits from the exhaust gas may adversely affect engine performance and the NOx reducing ability of the EGR system. In particular, closing off some of the conduits reduces the area through which the exhaust gas flows leading to a change in exhaust backpressure. If the backpressure increases, engine performance may be negatively affected. Furthermore, because of the change in backpressure, an EGR valve set to a particular flow setting may recirculate a certain amount of the exhaust gas when all the conduits are open and a different amount of exhaust gas when only a fraction of conduits are open. Such a temperature control strategy can increase the complexity of the system because the controller must compensate for the discrepancy between the two circumstances. An increased complexity is more likely to lead to errors concerning the composition of the air intake mixture and ultimately the amount of NOx produced by the engine.
In addition, particulate matter contained within the exhaust gas can settle on an interior surface of a conduit wall during operation, thereby fouling the surface and reducing the heat transfer properties of the conduit. Conduits that only sometimes receive exhaust gas endure less fouling than conduits that always receive exhaust gas. This discrepancy of fouling can adversely affect the cooling properties of the EGR cooler, which can further increase control complexity. In addition, the discrepancy may produce two or more streams of exhaust gas at varying temperatures causing the temperature sensor located at the EGR cooler exhaust gas outlet to make an inaccurate temperature reading. Such an inaccurate temperature reading may cause the controller to allow the temperature of the exhaust gas to fall below a level conducive to producing sulfuric acid condensation.
Furthermore, the system in the '688 patent does not efficiently utilize the coolant when only a fraction of the conduits are open to the flow of exhaust gas. When the exhaust gas is directed through all of the conduits, the coolant is fully utilized because the entire volume of coolant is able to absorb heat from the exhaust gas. However, when the exhaust gas is directed through only some of the conduits, a significant portion of the coolant does not flow close enough to the conduits in use to absorb heat from the exhaust gas, thereby not fully utilizing the coolant. Such inefficient use of the coolant may consume energy that may otherwise be saved or utilized by other systems.
The disclosed system is directed to overcoming one or more of the problems set forth above.
In one aspect, the present disclosure is directed toward a cooling system for cooling a gas flow that includes a heat exchanger having a plurality of chambers through which a coolant may flow. The system also includes a plurality of chamber valves, each of the plurality of chamber valves being configured to selectively control coolant flowing through an associated one of the plurality of chambers. In addition, the system includes at least one gas sensor situated to sense a parameter indicative of a temperature of a gas flowing through the heat exchanger. The system further includes a controller configured to actuate at least one of the plurality of chamber valves to prevent the flow of coolant through at least one of the plurality of chambers when the gas temperature is below a threshold temperature.
Consistent with another aspect of the disclosure, a method is provided for regulating a temperature of a gas. The method includes directing a coolant fluid and a gas through a plurality of coolant chambers. The method also includes sensing at least one parameter indicative of a temperature of the gas. The method further includes discontinuing the flow of coolant fluid through at least one of the plurality of coolant chambers when the gas temperature is below a threshold temperature.
Cylinder 16, the piston, and the cylinder head may form a combustion chamber 26 fluidly connected to air intake manifold 18 and exhaust manifold 22 via fluid passageways 28 and 30, respectively. In the illustrated embodiment, engine 12 includes six such combustion chambers 26. However, it is contemplated that engine 12 may include a greater or lesser number of combustion chambers 26 and that combustion chambers 26 may be disposed in an “in-line” configuration, a “V” configuration, or in any other suitable configuration.
Power system 10 may also include an exhaust recirculation (EGR) system 32 for directing a predetermined portion of exhaust back to an intake of engine 12. EGR system 32 may include components that cooperate to redirect a portion of the exhaust provided by engine 12 from exhaust passageway 24 into air intake passageway 20. Specifically, EGR system 32 may include an inlet port 34, a recirculation valve 36, an EGR cooling system 38, and a discharge port 40. Inlet port 34 may be fluidly connected to EGR cooling system 38 via a fluid passageway 42, while discharge port 40 may be fluidly connected to EGR cooling system 38 via fluid passageway 44. Recirculation valve 36 may be disposed within fluid passageway 42, between inlet port 34 and EGR cooling system 38. It is contemplated that inlet port 34 may be located upstream or downstream of any turbochargers present (if any) and/or additional emission control devices disposed within exhaust passageway 24 (not shown) such as, for example, particulate filters and catalytic devices.
Recirculation valve 36 may be located to regulate the flow of exhaust through EGR system 32. Recirculation valve 36 may be any type of valve such as, for example, a butterfly valve, a diaphragm valve, a gate valve, a ball valve, a globe valve, or any other valve known in the art. Recirculation valve 36 may be solenoid-actuated, hydraulically-actuated, pneumatically-actuated or actuated in any other manner to selectively restrict the flow of exhaust through fluid passageway 42.
As illustrated in
Heat exchanger 46 may include multiple chambers 52 separated by dividing walls 54 and configured to receive coolant fluid from coolant source 48. It should be understood that although heat exchanger 46 is disclosed as having two chambers 52, heat exchanger 46 may include any number of chambers 52. Heat exchanger 46 may also include multiple conduits 56 for directing exhaust gas through heat exchanger 46. Conduits 56 may pass through dividing walls 54 so that exhaust gas may have an unobstructed path through heat exchanger 46. Furthermore, heat exchanger 46, dividing walls 54, and conduits 56 may be constructed from corrosion resistant materials such as, for example, stainless steel, carbon steel, brass, copper, aluminum, nickel, or alloys thereof. It is contemplated that the interior surface of heat exchanger 46 may also be coated with corrosion resistant materials, wear resistant materials, heat resistant materials, and the like, if desired.
Exhaust gas may enter heat exchanger 46 through an inlet 58 and exit heat exchanger 46 through an outlet 60. A sensor 62 may be located anywhere within inlet 58 and outlet 60 and may include one or more temperature and/or pressure sensing devices for sensing a temperature and a pressure of the exhaust gas entering and exiting heat exchanger 46. It is contemplated that sensor 62 at inlet 58 may be omitted, if desired. It is further contemplated that inlet 58 and outlet 60 may contain a plurality of independent sensors, wherein each sensor is configured to only sense temperature or only sense pressure.
Sensor 62 may include any type of temperature sensing device known in the art. For example, sensor 62 may include a surface-type temperature sensing device that measures a wall temperature at inlet 58 and/or 60. Alternately, sensor 62 may include a gas-type temperature sensing device that directly measures the temperature of the exhaust gas within inlet 58 and/or 60. Upon measuring the temperature of the exhaust gas, sensor 62 may generate an exhaust gas temperature signal and send this signal to controller 50 via a communication line 64, as is known in the art. This temperature signal may be sent continuously, on a periodic basis, or only when prompted to do so by controller 50, if desired.
Sensor 62 may also include any type of pressure sensing device known in the art. Upon measuring the pressure of the exhaust gas, sensor 62 may generate an exhaust gas pressure signal and send this signal to controller 50 via communication line 64, as is known in the art. This pressure signal may be sent with or independent of the above-mentioned temperature signal. Furthermore, the pressure signal may be sent continuously, on a periodic basis, or only when prompted to do so by controller 50.
Coolant fluid may enter each chamber 52 of heat exchanger 46 through an associated inlet passageway 66 and exit each chamber 52 through an associated outlet passageway 68. Each inlet passageway 66 may include a shut-off valve 70 positioned to at least partially isolate the associated inlet passageway 66 and chamber 52 from coolant source 48 when it is desired to restrict the flow of coolant to the associated chamber 52. In addition, each outlet passageway 68 may include a shut-off valve 72 positioned to at least partially isolate the associated outlet passageway 68 and chamber 52 from coolant source 48 when it is desired to restrict the flow of coolant from the associated chamber 52. Shut-off valves 70 and 72 associated with a particular chamber 52 may be operationally connected so that they are both either set to be open or closed at the same time. It is contemplated that cooling system 38 may alternately include only shut-off valve 70 or only shut-off valve 72, if desired.
Inlet passageways 66 and outlet passageways 68 may receive and direct coolant fluid to and from coolant source 48 via a supply passageway 74 and a return passageway 76, respectively. A sensor 78 may be associated with return passageway 76 and configured to sense a temperature and a flow rate of the fluid exiting heat exchanger 46. In addition, a valve 80 may be positioned within supply passageway 74 to modulate the flow of coolant through inlet passageways 66. Valve 80 may be any type of proportional valve such as, for example, a shutter valve, a butterfly valve, a diaphragm valve, a gate valve, a ball valve, a globe valve, or any other valve known in the art.
Similar to sensor 62, sensor 78 may include any type of temperature sensing device mounted within return passageway 76. For example, temperature sensor 78 may include a surface-type temperature sensing device known in the art. Alternately, sensor 78 may include a liquid-type temperature sensing device that directly measures the temperature of the coolant within return passageway 76. Sensor 78 may generate a coolant temperature signal and send this signal to controller 50 via a communication line 82, as is known in the art. This temperature signal may be sent continuously, on a periodic basis, or only when prompted to do so by controller 50.
Sensor 78 may also include a flow sensing device, such as, for example, a hot wire anemometer or a venturi-type sensor. Upon measuring the flow of the coolant fluid, sensor 78 may generate a coolant fluid flow signal and send this signal to controller 50 via a communication line 82, as is known in the art. This flow signal may be sent with or independent of the above-mentioned temperature signal transmitted by sensor 78. Furthermore, the flow signal may be sent continuously, on a periodic basis, or only when prompted to do so by controller 50.
Coolant source 48 may include a radiator 84 for releasing heat absorbed by the coolant from the exhaust gas. Radiator 84 may receive coolant fluid via return passageway 76. It is contemplated that radiator 84 may be an air cooled radiator for an automobile integrated cooling system, wherein high temperature coolant is passed through a variety of coils cooled by the circulation of air flowing between and around the coils. It is also contemplated that radiator 84 may be a dedicated heat exchanger used only to remove heat from the coolant flowing through EGR cooling system 38, if desired. Alternatively, the coolant may be directed to an engine block (not shown) of engine 12 instead of radiator 84.
Coolant source 48 may also include a pump 86. Pump 86 may receive coolant from radiator 84 via a fluid passageway 88 and discharge pressurized fluid to supply passageway 74. Pump 86 may be a variable displacement pump, a fixed displacement pump, or any other source of pressurized fluid known in the art. It is contemplated that pump 86 may be associated with an air cooled radiator for an automobile integrated cooling system, if desired. It is also contemplated that pump 86 may be dedicated for pumping coolant only into and out of EGR cooling system 38, if desired.
Controller 50 may include one or more microprocessors, a memory, a data storage device, a communication hub, and/or other components known in the art and may be associated only with EGR cooling system 38. However, it is contemplated that controller 50 may be integrated within a general control system capable of controlling additional functions of power system 10, e.g., selective control of engine 12, and/or additional systems operatively associated with power system 10, e.g., selective control of a transmission system (not shown).
Controller 50 may receive signals from sensors 62 and 78 and analyze the data to determine whether the temperature of the exhaust gas and/or coolant is within a desired temperature range by comparing the data to threshold temperatures stored in or accessible by controller 50. Upon receiving input signals from sensors 62 and 78, controller 50 may perform a plurality of operations, e.g., algorithms, equations, subroutines, reference look-up maps or tables to determine a heat transfer rate between the exhaust gas and coolant and establish an output to influence the operation of shut-off valves 70 and 72, valve 80, and/or pump 86. Alternatively, it is contemplated that controller 50 may receive signals from various sensors (not shown) located throughout EGR system 32 and/or power system 10 instead of sensors 62 and 78. Such sensors may sense parameters that may be used to calculate the temperature and pressure of exhaust gas flowing through conduits 56. The signals from the various sensors may also be used to calculate the temperature and flow coolant flowing through heat exchanger 46.
The disclosed cooling system may ensure that an exhaust gas temperature does not fall below a critical temperature, at which sulfuric acid and/or other corrosive elements can condense on the surface of the cooling system. The flow of coolant fluid through the cooling system can be manipulated in response to sensed exhaust gas temperatures and pressures, and a sensed fluid temperature. In particular, the surface area through which thermal energy is transferred can be reduced or increased when the exhaust gas temperature falls below or rises above a desired temperature at a particular exhaust gas pressure. Furthermore, the flow rate of coolant can be reduced or increased when the exhaust gas temperature and/or coolant temperature falls below or rises above a desired temperature. The operation of EGR cooling system 38 will now be explained.
In addition, controller 50 may determine which of chambers 52 are open to the flow of coolant fluid from coolant source 48 (step 208). Such a determination may be made by determining the positions of shut-off valves 70 and 72 for each chamber 52. If a particular set of shut-off valves 70 and 72 regulating coolant flow into a particular chamber 52 are in a “closed” position, then the associated chamber 52 is considered to be closed off from the flow of coolant fluid from coolant source 48. However, if the particular set of shut-off valves 70 and 72 regulating coolant flow to a particular chamber 52 are in an “open” position, then the associated chamber 52 is considered to be open to the flow of coolant fluid from coolant source 48.
Upon receiving data indicative of the coolant temperature and coolant flow within cooling system 38, along with data indicating which of chambers 52 are open to the flow of coolant fluid, controller 50 may compare the data to tables, graphs, and/or equations stored in its memory to determine a heat transfer rate between the exhaust gas and the coolant fluid (step 210). Controller 50 may then incrementally reduce the heat transfer rate between the exhaust gas and coolant fluid by adjusting the flow of coolant fluid (step 212). Such a reduction may be made by reducing or increasing the overall flow rate of coolant and/or isolating (i.e. completely blocking) a particular chamber 52 from coolant flow. By performing various combinations of the above-mentioned adjustments, the heat transfer rate may be decreased as quickly or slowly as desired. Such adjustments made by controller 50 may be based on tables, graphs, maps, and/or equations stored in the memory of controller 50. It should be understood that the maps, graphs, tables, and/or equations may be designed to prevent the temperature of the coolant fluid from reaching a boiling point. Upon adjusting the flow of coolant, step 200 may be repeated, wherein controller 50 may receive new temperature and pressure signals from sensor 62 indicative of a new pressure and temperature of the exhaust gas flowing through heat exchanger 46.
As disclosed above, when controller 50 determines that the sensed temperature and pressure combination is unlikely to produce sulfuric acid condensation (step 202: No), controller 50 may determine whether the exhaust gas temperature is above a threshold temperature (step 204). Because the temperature of exhaust gas mixing with ambient air may affect the combustion temperature in combustion chambers 26, and consequently the level of NOx produced by the combustion process, the threshold temperature may be the maximum exhaust gas temperature capable of producing a desired level of NOx. If controller 50 determines that the exhaust gas temperature is below the threshold temperature (step 204: No), step 200 may be repeated (i.e. controller 50 may receive new temperature and pressure signals from sensor 62 indicative of a new pressure and temperature of the exhaust gas flowing through heat exchanger 46). However, when controller 50 determines that the exhaust gas temperature is above the threshold temperature (step 204: Yes), controller 50 may receive a signal indicative of a temperature and flow of the coolant fluid exiting heat exchanger 46 from sensor 78 (step 214). In addition, controller 50 may determine which chambers 52, if any, are closed-off from the flow of coolant fluid from coolant source 48 (step 216). Such a determination may be made in a similar manner to the determination made in step 208 disclosed above.
Similar to the method disclosed in step 210 above, controller 50 may determine a heat transfer rate between the exhaust gas and the coolant fluid by comparing the data indicative of the coolant temperature and coolant flow along with data indicating which chambers 52, if any, are open to the flow of coolant fluid to tables, graphs, and/or equations stored in its memory (step 218).
Controller 50 may then incrementally increase the heat transfer rate between the exhaust gas and coolant fluid by adjusting the flow of coolant fluid and opening particular chambers 52 to the flow of coolant fluid (step 220). Such an increase of heat transfer rate may be made by increasing the flow of coolant. Also, allowing coolant fluid to flow through a particular chamber 52, which was previously closed may increase the heat transfer rate between the exhaust gas and coolant fluid. By performing various combinations of the above-mentioned adjustments, the heat transfer rate may be increased as quickly or slowly as desired. Such adjustments made by controller 50 may be based on tables, graphs, maps, and/or equations stored in the memory of controller 50.
Because the flow rate and volume of the coolant may be manipulated rather than the flow rate of the exhaust gas, the backpressure affecting the flow of recirculated exhaust gas may be more consistent. Such consistency may simplify the process of recirculating exhaust gas back to the air intake manifold. In particular, the controller may not need to compensate for varying backpressures when setting the recirculation valve to allow a desired amount of exhaust gas to flow back to the power source. Simplifying the system may also reduce the likelihood of errors concerning the composition of the air intake mixture and ultimately the amount of NOx produced by the engine.
In addition, because all conduits of cooling system 38 may be exposed to about the same amount of exhaust gas for about the same amount of time, fouling of the conduits may be more evenly distributed. The even distribution of fouling may lead to a consistent heat transfer from the conduits over the life of the cooler. With a consistent heat transfer over the conduits, the temperature of the exhaust gas may be more consistent leading to more accurate temperature readings from temperature sensors located within the cooler. More accurate temperature readings reduce the likelihood of sulfuric acid being allowed to condense on the surface of the cooler.
Furthermore, by adjusting the volume and flow rate of coolant flowing through the EGR cooler, the EGR system may efficiently utilize the coolant. In particular, the full capacity of coolant being used may be utilized independent of the volume or flow rate of exhaust gas flowing through the EGR cooler. By adjusting the flow, volume, and mass of coolant being utilized, energy that would otherwise be used to direct unused coolant may be redirected to other systems. Such efficiency may reduce the amount of fuel required to power the power system reducing overall operational costs.
It will be apparent to those skilled in the art that various modifications and variations can be made in the disclosed system without departing from the scope of the disclosure. Other embodiments will be apparent to those skilled in the art from consideration of the specification disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope being indicated by the following claims and their equivalents.
