Exhaust gas recirculation and selective catalytic reduction system

A power source is provided for use with an exhaust gas recirculation and selective catalytic reduction system. The power source has a main air-intake passage fluidly connected to a first air-intake passage and a second air-intake passage. A first cylinder group may be fluidly connected to the first air-intake passage and a first exhaust passage, wherein the first exhaust passage may include an ammonia-producing catalyst configured to convert at least a portion of a fluid in the first exhaust passage into ammonia. Further, a second cylinder group may be fluidly connected to the second air-intake passage and a second exhaust passage. A third cylinder group may be fluidly connected to the second air-intake passage. The power source may have a recirculation loop that includes the second air-intake passage and the third cylinder group. The power source may also have a merged exhaust passage configured to connect the first exhaust passage and the second exhaust passage to facilitate a reaction between ammonia and NOx to at least partially remove NOx from the merged exhaust passage.

TECHNICAL FIELD

This disclosure relates generally to an exhaust gas recirculation and selective catalytic reduction system, and more particularly, to a high pressure exhaust gas recirculation system with on-board ammonia production.

BACKGROUND

Engines, including diesel engines, gasoline engines, gaseous fuel-driven engines, and other engines known in the art, traditionally exhaust a complex mixture of pollutants. These emissions may include gaseous and solid material, such as, particulate matter, nitrogen oxides (NOx), and sulfur compounds. Heightened environmental concerns have led regulatory agencies to increase the stringency of emission standards for such engines, forcing engine manufactures to develop systems to further reduce levels of engine emissions.

One method used by engine manufacturers to reduce engine emissions includes exhaust gas recirculation (EGR). EGR systems recirculate a portion of the engine exhaust stream into the air-intake supply of the engine to reduce oxygen concentration within a combustion chamber. Recirculated exhaust gas may further act to lower combustion temperatures, and in combination with reduced oxygen concentration, may lead to reduced emission levels.

Selective catalytic reduction (SCR) provides another method for reducing engine emission levels. During SCR, a catalyst facilitates a reaction whereby ammonia and NOx react in an exhaust stream to produce water and nitrogen gas, thereby reducing NOx levels in the exhaust gas. Generally, the ammonia used for the SCR system may be either produced during engine operation or stored for injection as required. However, because of the high reactivity of ammonia, storage of ammonia can be hazardous. Further, on-board production of ammonia can be costly and may require specialized equipment.

One system configured to reduce emission levels with an EGR system is described in U.S. Pat. No. 6,286,489 (“the '489 patent”) issued on Sep. 11, 2001 to Bailey. The '489 patent describes an EGR system in which a portion of the exhaust gas from a first cylinder group is cooled by an exhaust gas cooler before being directed to an intake manifold of an engine. The system further includes a valve configured to adjust a flow rate of exhaust gas from the first cylinder group to the air intake manifold.

While the system of the '489 patent may reduce NOx from an exhaust stream through use of EGR, the system can be further improved. In particular, some engines may operate under conditions whereby an EGR system may not provide sufficient emission reduction. Such engines may benefit by having an additional system configured to further reduce emission levels, such as an SCR system. However, the engine of the '489 patent includes only an EGR system and is not configured to operate with an SCR system that may further reduce emissions.

The present disclosure is directed at overcoming one or more of the limitations in the prior art.

SUMMARY OF THE INVENTION

One aspect of the present disclosure includes a power source for use with an exhaust gas recirculation and selective catalytic reduction system. The power source includes a main air-intake passage fluidly connected to a first air-intake passage and a second air-intake passage. A first cylinder group may be fluidly connected to the first air-intake passage and a first exhaust passage, wherein the first exhaust passage may include an ammonia-producing catalyst configured to convert at least a portion of a fluid in the first exhaust passage into ammonia. Further, a second cylinder group may be fluidly connected to the second air-intake passage and a second exhaust passage. A third cylinder group may be fluidly connected to the second air-intake passage. The power source may include a recirculation loop that includes the second air-intake passage and the third cylinder group. The power source may also include a merged exhaust passage configured to connect the first exhaust passage and the second exhaust passage to facilitate a reaction between ammonia and NOx to at least partially remove NOx from the merged exhaust passage.

A second aspect of the present disclosure includes a method of operating a power source for use with an exhaust gas recirculation and selective catalytic reduction system. The method includes supplying air to a first cylinder group via a first air-intake passage that may be fluidly connected to a main air-intake passage, supplying air to a second cylinder group via a second air-intake passage that may be fluidly connected to the main air-intake passage, and supplying air to a third cylinder group via the second air-intake passage. A first exhaust stream from the first cylinder group may be supplied to a first exhaust passage fluidly connected to the first cylinder group and at least a portion of the first exhaust stream may be converted to ammonia. The method may also include supplying a second exhaust stream from the second cylinder group to a second exhaust passage fluidly connected to the second cylinder group. A third exhaust stream from the third cylinder group may be supplied to a recirculation loop such that at least a portion of the third exhaust stream may be supplied to the second cylinder group and the third cylinder group. Further, the method may include merging the exhaust stream of the first exhaust passage with the exhaust stream of the second exhaust passage to form a merged exhaust stream in a merged exhaust passage fluidly connected to the first exhaust passage and the second exhaust passage.

A third aspect of the present disclosure includes a machine having a power source. The power source may include a main air-intake passage fluidly connected to a first air-intake passage and a second air-intake passage. A first cylinder group of the power source may be fluidly connected to the first air-intake passage, and a second cylinder group and a third cylinder group may be fluidly connected to the second air-intake passage. The machine may also include an exhaust system further including a first exhaust passage fluidly connected to the first cylinder group. A second exhaust passage of the exhaust system may be fluidly connected to the second cylinder group and a recirculation loop may include the third cylinder group and the second air-intake passage. The exhaust system may also include an ammonia-producing catalyst disposed within the first exhaust passage and configured to convert at least a portion of a fluid in the first exhaust passage into ammonia. -Further, the exhaust system may include a merged exhaust passage configured to connect the first exhaust passage and the second exhaust passage to facilitate a reaction between ammonia and NOx to at least partially remove NOx from the merged exhaust passage. Also, the recirculation loop may be configured to supply at least a portion of exhaust gas from the third cylinder group to the second cylinder group and the third cylinder group.

DETAILED DESCRIPTION

FIG. 1provides a schematic representation of a machine10of the present disclosure including a power source12. In some embodiments, power source12may include any type of internal combustion engine. For example, power source12may include a diesel engine, a gasoline engine, a gaseous fuel-powered engine, or any other engine known in the art. Further, power source12may be configured to provide power to an on-highway vehicle, construction or mining equipment, or a factory or power plant.

Power source12may include a plurality of cylinders, including a first cylinder group14, a second cylinder group16, and a third cylinder group18. Each of cylinder groups14,16,18may include one or more cylinders configured to permit fuel combustion in addition, each cylinder group may be configured to operate at different-operating conditions. For example, one cylinder group may be operated to provide power, another cylinder group may be operated to recirculate at least a portion of exhaust gas, and another cylinder group may be operated to produce ammonia for use with an SCR system. In some embodiments, the operational conditions of each cylinder of cylinder groups14,16,18may be varied by controlling the ratios of air to fuel-vapor injected into each cylinder.

Power source12may also include one or more air-intake passages configured to supply one or more cylinders with air and/or fuel. In some embodiments, first cylinder group14may be fluidly connected to a first air-intake passage20, and second cylinder group16and third cylinder group18may be fluidly connected to a second air-intake passage22. Further, a main air-intake passage24may be fluidly connected to first air-intake passage20and second air-intake passage22, whereby main air-intake passage24may provide a single air intake for power source12. In other embodiments, first air-intake passage20may be fluidly isolated from second air-intake passage22such that power source12may have two separate air intakes.

Main air-intake passage24may be configured to receive atmospheric air and supply air to one or more cylinders of power source12. In some embodiments, main air-intake passage24may be operably associated with a forced-induction system32. Power source12may include forced-induction systems to increase power output and/or control the air to fuel-vapor ratios within the cylinders of first cylinder group14or second cylinder group16.

Forced-induction systems may include, for example, turbochargers and/or superchargers. In one embodiment, forced-induction system32may include a turbocharger. The turbocharger may utilize the exhaust gas from one or more cylinders of power source12to generate power for a compressor (not shown). The compressor may include a fixed geometry type compressor, a variable geometry type compressor, or any other type of compressor known in the art. The compressor may operate to provide additional air to main-air-intake passage24, first air-intake passage20, and/or second air-intake passage22.

In another embodiment, forced-induction system32may include a supercharger. A supercharger may include a compressor (not shown) configured to compress air. Power to operate the compressor may be derived from a crank-shaft and transferred to the compressor via a belt connected directly to an engine. As such, superchargers do not need to be operably associated with an exhaust stream from one or more cylinders of power source12. Further, power source12may include one or more turbochargers and/or superchargers, and combinations thereof.

Main air-intake passage24may include one or more coolers34configured to lower a temperature of a fluid. For example, cooler34may include one or more air coolers, such as, a pre-cooler, an inter-cooler, or an after-cooler. Cooler34may include any type of cooler, such as, for example, an air-to-air cooler, a water cooler, or suitable heat exchanging device. In some embodiments, cooler34may include an air-to-air after-cooler (“ATAAC”), and/or any cooler configured to cool compressed air. It is also contemplated that first air-intake passage20and/or second air-intake passage22may include one or more coolers34.

Main air-intake passage24may be configured to supply air to first air-intake passage20and second air-intake passage22. In some embodiments, first air-intake passage20may include a valve36. Valve36may include any device configured to modify one or more air properties, such as, for example, air pressure, flow rate and/or temperature. Valve36may include a throttle, an inductive venturi aperture, or other similar device configured to modify an air property. For example, valve36may be configured to reduce air pressure or flow rate downstream of valve36. Valve36may be configured to reduce air pressure within first air-intake passage20relative to second air-intake passage22such that first cylinder group14may be supplied with air at a lower pressure than air supplied to-second and third cylinder groups16,18. Supplying first cylinder group14and second and third cylinder groups16,18with air at different properties may permit first cylinder group14and second and third cylinder groups16,18to operate at different combustion efficiencies and produce different emission levels from each cylinder.

In some embodiments, valve36may be configured to selectively modify an air property within first air-intake passage20during variable load operation of power source12. For example, valve36may modify an air property based on an operational condition of power source12, such as, engine speed or engine load. As engine speed increases, valve36may be configured to increase the pressure difference between air in first air-intake passage20and second-air intake passage22by decreasing air flow rate through valve36.

Second air-intake passage22may be configured to supply air and/or fuel to second cylinder group16and third cylinder group18. In some embodiments, second cylinder group16may be configured to supply an exhaust stream to provide power to forced-induction system32, as described above. Second cylinder group16may be operated to produce power.

In some embodiments, third cylinder group18may be configured to recirculate an exhaust stream to one or more cylinders of power source12. For example, third cylinder group18may be configured to supply an exhaust stream to second air-intake passage22. In addition, second air-intake passage22may be configured to mix a fluid stream from main air-intake passage24and the recirculated exhaust stream from third cylinder group18to permit one or more cylinders of second cylinder group16and third cylinder group18to operate with at least a portion of recirculated exhaust gas.

Power source12may also include one or more exhaust passages configured to permit exhaust to exit one or more cylinders. In some embodiments, first cylinder group14may be fluidly connected to a first exhaust passage26, and second cylinder group16may be fluidly connected to a second exhaust passage28. In addition; third cylinder group18may form part of a recirculation loop30.

Recirculation loop30may include one or more devices and/or systems configured to permit recirculation of at least a portion of an exhaust stream into one or more cylinders of power source12. In some embodiments, recirculation loop30may include third cylinder group18and second air-intake passage22such that an exhaust stream from third cylinder group18may be directed into second air-intake passage22. In other embodiments, recirculation loop30may be fluidly connected to one or more air-intake and/or exhaust passages of power source12.

Recirculation loop30may also include one or more filters38, such as, for example, a diesel particulate filter38. Filter38may be configured to collect particulate matter, and may be disposed in recirculation loop30at any suitable location. Recirculation loop30may also include one or more coolers34, as described above. In addition, one or more valves (not shown) may be provided in recirculation loop30, wherein the valves may be configured to regulate exhaust flow into second air-intake passage22. Recirculation loop30may also include one or more pumps, compressors or other systems configured to recirculate exhaust gas from third cylinder group18into second air-intake passage22.

In some embodiments, recirculation loop30may be fluidly connected to an exhaust shunt40. In particular, exhaust shunt40may be configured to permit exhaust to flow out of recirculation loop30. For example, exhaust shunt40may be fluidly connected to second exhaust passage28such that exhaust shunt40may permit exhaust from third cylinder group18to flow into second exhaust passage28.

Exhaust shunt40may include a valve42configured to regulate a flow of exhaust from third cylinder group18into second exhaust passage28. Valve42may include any suitable valve type as previously described. In some embodiments, exhaust shunt40and valve42may be configured to permit variable EGR, wherein a variable portion of exhaust gas may be supplied to one or more cylinders. Further, providing recirculated exhaust gas to second cylinder group16and third cylinder group18may permit first cylinder group14to operate combustion reactions at different efficiencies.

In some embodiments, first cylinder group14and second and third cylinder groups16,18may operate with combustion reactions at different efficiencies. Supplying different cylinder groups with air at different properties may permit combustion reactions at different efficiencies within the different cylinder groups. In particular, combustion reactions at different efficiencies may produce different combustion products and different levels of emissions from first cylinder group14and second and third cylinder groups16,18. For example, supplying first cylinder group14with air at a lower pressure than air supplied to second and third cylinder groups16,18may permit first cylinder group14to produce an exhaust stream more suitable for ammonia production than second and third cylinder groups16,18. Emission levels may also be affected by other operational parameters of power source12, such as, for example, air to fuel-vapor ratio, valve timing, and/or fuel injection timing.

During operation of power source12, first cylinder group14may operate at or near a stoichiometric air to fuel-vapor ratio. Further, second and third cylinder groups16,18may operate under leaner conditions, wherein lambda is greater than one. Air pressure and/or flow rate may be reduced in first air-intake passage20such that first cylinder group14may operate at lambda approximately equal to one. Operation of first cylinder group14at lambda approximately equal to one may cause increased NOx production by first cylinder group14relative to NOx emissions from a leaner combustion reaction within second and third cylinder groups16,18. In some embodiments, NOx generated by combustion in first cylinder group14may be converted into ammonia, whereby this ammonia may be used to remove NOx produced by second and third cylinder groups16,18.

In some embodiments, first exhaust passage26may include an ammonia-producing catalyst43configured to convert at least a portion of the exhaust stream from first cylinder group14into ammonia. In particular, ammonia may be produced by a reaction between NOx and other substances in an exhaust stream from first cylinder group14. For example, ammonia may be produced by NOx reacting with a variety of other combustion byproducts, such as, H2(hydrogen gas), C3H6(propene), or CO (carbon monoxide).

Ammonia-producing catalyst43may be made from a variety of materials. In one embodiment, ammonia-producing catalyst43may include at least one of platinum, palladium, rhodium, iridium, copper, chrome, vanadium, titanium, iron, or cesium. Combinations of these materials may be used, and the catalyst material may be chosen based on the type of fuel used, the air to fuel-vapor ratio desired, or for conformity with environmental standards.

The efficiency of conversion of NOx to ammonia by ammonia-producing catalyst43may be improved under rich conditions. Therefore, to increase ammonia production, fuel may be supplied to NOx-containing exhaust to produce a rich, NOx-containing exhaust gas that can be used to produce ammonia by ammonia-producing catalyst43. For example, one or more cylinders of first cylinder group14may operate to produce an exhaust-gas stream that contains NOx. The NOx-containing exhaust stream may flow into first exhaust passage26where the exhaust stream may be mixed with fuel to create an environment suitable for ammonia production.

To create the rich conditions favorable for ammonia production, a fuel-supply device44may be configured to supply fuel into first exhaust passage26upstream of ammonia-producing catalyst43. For example, a NOx-containing exhaust may be supplied to first exhaust passage26, and fuel-supply device44may be configured to supply fuel into first exhaust passage26, thereby making the exhaust stream rich. Thus, the exhaust stream in first exhaust passage26may be rich downstream of fuel-supply device44, thereby providing an environment suitable for ammonia production.

In some embodiments, first exhaust passage26and second exhaust passage28may be fluidly connected at a point downstream of ammonia-producing catalyst43to form a merged exhaust passage46. Merged exhaust passage46may contain a mixture of an exhaust stream produced by second cylinder group16and an ammonia-containing, exhaust stream produced by ammonia-producing catalyst43in first exhaust passage26.

A NOx-reducing catalyst48may be disposed in merged exhaust passage46. NOx-reducing catalyst48may facilitate a reaction between ammonia and NOx to at least partially remove NOx from the exhaust stream in merged exhaust passage46. For example, NOx-reducing catalyst48may facilitate a reaction between ammonia and NOx to produce nitrogen gas and water, among other reaction products.

In some embodiments, merged exhaust passage46may include one or more filters38as previously described. It is also contemplated that first exhaust passage26and/or second exhaust passage28may include one or more filters (not shown). In addition, any number and type of catalysts may be included in first-exhaust passage26, second exhaust passage28and/or merged exhaust passage46. These catalysts may include any suitable catalytic device and/or system configured to enhance a chemical reaction. For example, in some embodiments second exhaust passage28may include an oxidation catalyst50. NOx may include several oxides of nitrogen including nitric oxide (NO) and nitrogen dioxide (NO2), and NOx-reducing catalyst48may function most effectively with a ratio of NO:NO2of about 1:1. Oxidation catalyst50may be configured to control a ratio of NO:NO2in second exhaust passage28and/or merged exhaust passage46.

As shown inFIG. 1, power source12includes forced-induction system32operably associated with main air-intake passage24and second exhaust passage28. It is also contemplated that forced-induction system32may be operably associated with any suitable passage, such as, for example, first air-intake passage20, second air-intake passage22, first exhaust passage26, recirculation loop30, and/or merged exhaust passage46. Further, power source12may include one or more forced-induction systems32operably associated with any suitable passage.

In some embodiments, passages20,22,24,26,28,46may include additional and/or fewer components. For example, first exhaust passage26may include a filter (not shown) and/or be operably associated with forced-induction system (not shown). Further, second air-intake passage22may include one or more valves (not shown), filters (not shown), and/or coolers (not shown). For example, second air-intake passage22may include one or more valves configured to control a flow of gas from recirculation loop30into second cylinder group16and/or third cylinder group18.

In some embodiments, main air-intake passage24may include one or more filters (not shown) and/or valves (not shown). Alternatively, in the exemplary embodiment shown inFIG. 2, power source12may include an air-cooling passage52fluidly connected to main air-intake24. Air-cooling passage52may be configured to provide cooling air for cooler34configured to at least partially cool a fluid within recirculation loop30. Specifically, cooler34may be a cross flow cooler whereby heat within exhaust gas from third cylinder group18may be transferred to air supplied by main air-intake passage24. Such heat exchange may function to cool exhaust within recirculation loop30before directing the exhaust into second air-intake passage22.

In some embodiments, air-cooling passage52may also be fluidly connected to an exhaust passage. For example, air-cooling passage52may be fluidly connected to main air-intake24and second exhaust passage28such that air within main air-intake24may be supplied to second exhaust passage28. Such additional gas flow into second exhaust passage28may increase a pressure within second exhaust passage28and may improve the performance of power source12. It is also contemplated that air-cooling passage52may further include one or more devices and/or systems as described above, such as, for example, a filter, and a valve.

INDUSTRIAL APPLICABILITY

The present disclosure provides a power source for use with an exhaust gas recirculation and selective catalytic reduction system. The system may be useful in a variety of engine types to reduce emission levels.

The power source of the present disclosure provides a method that may offer improved control of emission levels. In particular, power source.12includes recirculation loop30configured to recirculate at least a portion of exhaust gas into one or more cylinders to reduce oxygen concentration within the one or more cylinders and reduce NOx production. Recirculation loop30may be further configured to clean and/or cool exhaust gas recirculated into power source12. As a result, levels of particulate matter, and/or other pollutants contained in the exhaust gas may be reduced when the exhaust is recirculated into power source12. Therefore, recirculation loop30may protect power source12against problems caused by intake of particles, and/or other pollutants.

In addition, the present disclosure provides a method for permitting variable EGR. Specifically, exhaust shunt40and valve42may permit variable EGR wherein the portion exhaust gas recirculated into power source12may be varied. For example, exhaust shunt40and valve42may be configured to permit EGR into second air-intake22wherein approximately 20% of the fluid within each cylinder of second and third cylinder groups16,18may be exhaust gas. Such variable EGR may permit an engine to produce reduced emission levels over a range of engine operating conditions.

The power source of the present disclosure may provide improved control of ammonia production and NOx emissions. To increase ammonia production, one cylinder group may operate under lean conditions, while another cylinder group may operate under approximately stoichiometric conditions to facilitate ammonia production. Fuel may also be injected into the high NOx-containing exhaust stream to produce a rich, NOx-containing exhaust that may be converted to ammonia for use with an SCR system. The combined EGR and SCR system may permit greater reduction of emissions than use of an EGR system or SCR system alone.