US20070227143A1

US20070227143A1 - Exhaust purification with on-board ammonia production

Info

Publication number: US20070227143A1
Application number: US11/496,376
Authority: US
Inventors: Wade Robel; James Driscoll; William Easley; Stephan Roozenboom
Original assignee: Individual
Current assignee: Caterpillar Inc
Priority date: 2004-11-08
Filing date: 2006-07-31
Publication date: 2007-10-04

Abstract

A first aspect of the present disclosure includes a power source for use with selective catalytic reduction systems for exhaust-gas purification. The power source may comprise a first cylinder group with a first air-intake passage and a first exhaust passage, and a second cylinder group with a second air-intake passage and a second exhaust passage. The power source may further include a first forced-induction system in fluid communication with the first air-intake passage, and a second forced-induction system in fluid communication with the second air-intake passage. A catalyst may be disposed downstream of the fuel-supply device to convert at least a portion of the exhaust stream in the first exhaust passage into ammonia.

Description

This application is a continuation-in-part of U.S. patent application Ser. No. 11/412,834, filed Apr. 28, 2006, which is a continuation-in-part of U.S. patent application Ser. No. 10/982,921, filed Nov. 8, 2004, both of which are hereby incorporated by reference.

U.S. GOVERNMENT RIGHTS

This invention was made with government support under the terms of Contract No. DE-FC05-00OR22806 awarded by the Department of Energy. The government may have certain rights in this invention.

TECHNICAL FIELD

This disclosure pertains generally to exhaust-gas purification systems for engines, and more particularly, to selective catalytic reduction systems with on-board ammonia production.

BACKGROUND

Selective catalytic reduction (SCR) provides a method for removing nitrogen oxides (NOx) emissions from fossil fuel powered systems for engines, factories, and power plants. During SCR, a catalyst facilitates a reaction between exhaust-gas ammonia and NOx to produce water and nitrogen gas, thereby removing NOx from the exhaust gas.
The ammonia that is used for the SCR system may be produced during the operation of the NOx-producing system or may be stored for injection when needed. 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 method of on-board ammonia production for an engine is disclosed in U.S. Pat. No. 6,047,542, issued to Kinugasa on Apr. 11, 2000 (hereinafter the '542 patent). The method includes the use of multiple cylinder groups for purifying exhaust gas. In the method of the '542 patent, the exhaust gas of one cylinder group may be made rich by controlling the amount of fuel injected into the cylinder group. The rich exhaust gas of this cylinder group may then be passed over an ammonia-synthesizing catalyst to convert a portion of the NOx in the exhaust gas into ammonia. The exhaust gas and ammonia of the first cylinder group are then combined with the exhaust gas of a second cylinder group and passed through an SCR catalyst where the ammonia reacts with NOx to produce nitrogen gas and water.
While the method of the '542 patent may reduce NOx from an exhaust stream through use of on-board ammonia production, the method of the '542 patent has several drawbacks. For example, an engine may function less efficiently and with lower power output when rich combustion occurs in one cylinder group. Furthermore, using the method of the '542 patent, it may be more difficult to provide adequate and controlled air intake to both cylinder groups, and the two cylinder groups, operating as described in the '542 patent, may cause significant engine vibration.
The present disclosure is directed at overcoming one or more of the problems or disadvantages in the prior art.

SUMMARY OF THE INVENTION

A first aspect of the present disclosure includes a power source for use with selective catalytic reduction systems for exhaust-gas purification. The power source may comprise a first cylinder group with a first air-intake passage and a first exhaust passage, and a second cylinder group with a second air-intake passage and a second exhaust passage. The power source may further include a first forced-induction system in fluid communication with the first air-intake passage, and a second forced-induction system in fluid communication with the second air-intake passage. A catalyst may be disposed downstream of the first cylinder group to convert at least a portion of the exhaust stream in the first exhaust passage into ammonia.
A second aspect of the present disclosure includes a method of operating a power source for use with selective catalytic reduction systems for exhaust-gas purification. The method may include supplying air through a first air-intake passage to a first cylinder group including one or more cylinders using a first turbocharger and supplying fuel to the one or more cylinders of the first cylinder group. The method may further include supplying air through a second air-intake passage to a second cylinder group including at least two cylinders using a second turbocharger and supplying fuel to the cylinders of the second cylinder group. The flow of air and fuel to the cylinders of the first and second cylinder group may be controlled to produce a substantially equal power output in each of the cylinders of both the first and second cylinder group.
A third aspect of the present disclosure includes a power source for use with selective catalytic reduction systems for exhaust-gas purification. The power source may comprise a first cylinder group with a first air-intake passage and a first exhaust passage, and a second cylinder group with a second air-intake passage and a second exhaust passage. The power source may further include a first forced-induction system in fluid communication with the first air-intake passage, and a second forced-induction system in fluid communication with the second air-intake passage. An engine control unit may be configured to control the flow of air and fuel into each of the cylinders of the first and second cylinder groups to produce substantially equal power output from each of the cylinders of the first and second cylinder groups, and a catalyst may be disposed downstream of the first cylinder group to convert at least a portion of the exhaust stream in the first exhaust passage into ammonia. A merged exhaust passage may be formed downstream of the catalyst and may be in fluid communication with the first exhaust passage and second exhaust passage. A NOx-reducing catalyst may be placed in fluid communication with the merged exhaust passage.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate exemplary embodiments of the disclosure and, together with the written description, serve to explain the principles of the disclosed system. In the drawings:
FIG. 1 provides a schematic diagram of a power source according to an exemplary disclosed embodiment.
FIG. 2 provides a diagrammatic representation of first and second cylinder groups according to an exemplary disclosed embodiment.
FIG. 3 provides a schematic diagram of first and second cylinder groups according to an exemplary disclosed embodiment.
FIG. 4 provides a chart of relative power outputs of multiple cylinders, as shown in FIG. 2, at three distinct times according to an exemplary embodiment.
FIG. 5 provides a schematic representation of a power source according to another exemplary disclosed embodiment.
FIG. 6A provides a schematic representation of an exhaust passage according to an exemplary disclosed embodiment.
FIG. 6B provides a schematic representation of an exhaust passage according to another exemplary disclosed embodiment.
FIG. 6C provides a schematic representation of an exhaust passage according to another exemplary disclosed embodiment.
FIG. 7A provides a schematic representation of an exhaust system configuration according to an exemplary disclosed embodiment.
FIG. 7B provides a schematic representation of an exhaust system configuration according to another exemplary disclosed embodiment.
FIG. 8 provides a schematic representation of a power source according to another exemplary disclosed embodiment.

DETAILED DESCRIPTION

FIG. 1 provides a schematic representation of a machine 10 of the present disclosure including a power source 12. Power source 12 may include a first cylinder group 14 and a second cylinder group 16. First cylinder group 14 may be fluidly connected to a first air-intake passage 18 and a first exhaust passage 20. Second cylinder group 16 may be fluidly connected to a second air-intake passage 22 and a second exhaust passage 24. In one embodiment, first air-intake passage 18 is fluidly isolated from second air-intake passage 22.
The operation of engine cylinders may be dependant on the ratio of air to fuel-vapor that is injected into the cylinders during operation. The air to fuel-vapor ratio is often expressed as a lambda value, which is derived from the stoichiometric air to fuel-vapor ratio. The stoichiometric air to fuel-vapor ratio is the chemically correct ratio for combustion to take place. A stoichiometric air to fuel-vapor ratio may be considered to be equivalent to a lambda value of 1.0.
Engine cylinders may operate at non-stoichiometric air to fuel-vapor ratios. An engine cylinder with a lower air to fuel-vapor ratio has a lambda less than 1.0 and is said to be rich. An engine cylinder with a higher air to fuel-vapor ratio has a lambda greater than 1.0 and is said to be lean.
Lambda may affect cylinder NOx emissions and fuel efficiency. A lean-operating cylinder may have improved fuel efficiency compared to a cylinder operating under stoichiometric or rich conditions. However, lean operation may increase NOx production or may make elimination of NOx in the exhaust gas difficult.
The cylinders of first cylinder group 14 and/or second cylinder group 16 may include a variety of suitable engine cylinder types. For example, suitable engine types may include diesel engine cylinders, natural gas cylinders, or gasoline cylinders. The specific cylinder type may be selected based on the specific application, desired power output, available fuel infrastructure, and/or any other suitable factor. For example, natural gas engines may be selected for some engine types, such as generator sets. Diesel engines may be selected for on-highway trucks. However, as the available fuel infrastructure, fuel costs, and emission standards change, different engine types may be selected for any application.
SCR systems provide a method for decreasing exhaust-gas NOx emissions through the use of ammonia. In an exemplary embodiment of the present disclosure, engine NOx generated by lean combustion in first cylinder group 14 may be converted into ammonia. This ammonia may be used with an SCR system to remove NOx produced as a byproduct of fuel combustion in power source 12.
In one embodiment, power source 12 of the present disclosure may include an ammonia-producing catalyst 26 that may be configured to convert at least a portion of the exhaust-gas stream from first cylinder group 14 into ammonia. This ammonia may be produced by a reaction between NOx and other substances in the exhaust-gas stream from first cylinder group 14. For example, NOx may react with a variety of other combustion byproducts to produce ammonia. These other combustion byproducts may include, for example, H₂(hydrogen gas), C₃H₆(propene), or CO (carbon monoxide).
Ammonia-producing catalyst 26 may be made from a variety of materials. In one embodiment, ammonia-producing catalyst 26 may 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.
Lean operation of first cylinder group 14 may allow increased NOx production as compared to stoichiometric or rich operation of first cylinder group 14. Further, the efficiency of conversion of NOx to ammonia by ammonia-producing catalyst 26 may be improved under rich conditions. Therefore, to increase ammonia production, engine cylinders may be operated under lean conditions in order to produce a NOx-containing exhaust gas, and fuel may be supplied to this NOx-containing exhaust gas to produce a rich, NOx-containing exhaust gas that can be used to produce ammonia by ammonia-producing catalyst 26.
First cylinder group 14 may include one or more cylinders, and second cylinder group 16 may include at least two cylinders. For example, first cylinder group 14 may include between one and ten cylinders, and second cylinder group 16 may include between two and twelve cylinders. In one embodiment, first cylinder group 14 may include only one cylinder, and second cylinder group 16 may include five cylinders. In another embodiment, first cylinder group 14 may include one cylinder, and second cylinder group 16 may include seven cylinders. In another embodiment, first cylinder group 14 may include one cylinder, and second cylinder group 16 may include eleven cylinders. The number of cylinders in first cylinder group 14 and the number of cylinders in second cylinder group 16 may be selected based on a desired power output to be produced by power source 12.
In one embodiment, first cylinder group 14 may operate with a lean air-to-fuel ratio within the one or more cylinders of first cylinder group 14. The one or more cylinders of first cylinder group 14, operating with a lean air to fuel-vapor ratio, may produce a lean exhaust-gas stream that contains NOx. The lean, NOx-containing exhaust-gas stream may flow into first exhaust passage 20, which may be fluidly connected with the one or more cylinders of first cylinder group 14.
In order to produce the rich conditions that favor conversion of NOx to ammonia, a fuel-supply device 28 may be configured to supply fuel into first exhaust passage 20. In one embodiment, a lean, NOx-containing exhaust-gas stream may be delivered to first exhaust passage 20, and fuel-supply device 28 may be configured to supply fuel into first exhaust passage 20, thereby making the exhaust-gas stream rich. In one embodiment, the exhaust-gas stream in first exhaust passage 20 may be lean upstream of fuel-supply device 28 and rich downstream of fuel-supply device 28.
First exhaust passage 20 may fluidly communicate with second exhaust passage 24 at a point downstream of fuel-supply device 28 to form a merged exhaust passage 30. Merged exhaust passage 30 may contain a mixture of an exhaust-gas stream produced by second cylinder group 16 and an ammonia-containing, exhaust-gas stream produced by ammonia-producing catalyst 26 in first exhaust passage 20.
A NOx-reducing catalyst 32 may be disposed in merged exhaust passage 30. In one embodiment, NOx-reducing catalyst 32 may facilitate a reaction between ammonia and NOx to at least partially remove NOx from the exhaust-gas stream in merged exhaust passage 30. For example, NOx-reducing catalyst 32 may facilitate a reaction between ammonia and NOx to produce nitrogen gas and water, among other reaction products.
Power source 12 may include forced-induction systems to increase power output and/or control the air to fuel-vapor ratios within the cylinders of first cylinder group 14 or second cylinder group 16. Forced-induction systems may include, for example, turbochargers and/or superchargers. In one embodiment, a first forced-induction system 34 may be operably connected with first air-intake passage 18, and a second forced-induction system 36 may be operably connected with second air-intake passage 22.
In one embodiment, first forced-induction system 34 or second forced-induction system 36 may include a turbocharger. The turbocharger may utilize the exhaust gas in first exhaust passage 20 or second exhaust passage 24 to generate power for a compressor, and this compressor may provide additional air to first air-intake passage 18 or second air-intake passage 22. Therefore, if first forced-induction system 34 or second forced-induction system 36 includes a turbocharger, the turbocharger may be operably connected with both an exhaust passage 20, 24 and an air- intake passage 18, 22, as shown in FIG. 1.
In one embodiment, ammonia-producing catalyst 26 may be positioned downstream of first forced induction system 34. The exhaust stream in first exhaust passage 20 may be cooler downstream of first forced-induction system 34 than upstream of first forced-induction system 34. Ammonia-producing catalyst 26 may function more efficiently when exposed to a cooler exhaust-gas downstream of first forced-induction system 34.
In one embodiment, first forced-induction system 34 or second forced-induction system 36 may include a supercharger. A supercharger may derive its power from a belt that connects directly to an engine. Further, superchargers do not need to be connected with an exhaust stream. Therefore, if first forced-induction system 34 or second forced-induction system 36 includes a supercharger, the supercharger may be operably connected with first air-intake passage 18 or second air-intake passage 22, but the supercharger need not be operably connected with first exhaust passage 20 or second exhaust passage 24.
In an alternative embodiment, first air-intake passage 18 or second air-intake passage 22 may be naturally aspirated. A naturally aspirated air-intake passage may include no forced-induction system. Alternatively, an air-intake passage may include a forced-induction system, but the forced-induction system may be turned on and off based on demand. For example, when increased airflow is needed, first forced-induction system 34 or second forced-induction system 36 may be turned on to supply additional air to first air-intake passage 18 and/or second air-intake passage 22. When lower air-intake is needed, such as when little power is needed from power source 12, first air-intake passage 18 and/or second air intake passage 22 may be naturally aspirated. In one embodiment, second air-intake passage 22 may be operably connected with second forced-induction system 36, and first air-intake passage 18 may be naturally aspirated.
In one embodiment, second exhaust passage 24 may include an oxidation catalyst 37. NOx may include several oxides of nitrogen including nitric oxide (NO) and nitrogen dioxide (NO₂), and NOx-reducing catalyst 32 may function most effectively with a ratio of NO:NO₂of about 1:1. Oxidation catalyst 37 may be configured to control a ratio of NO:NO₂in second exhaust passage 24. Further, by controlling a ratio of NO:NO₂in second exhaust passage 24, oxidation catalyst 37 may also control a ratio of NO:NO₂in merged exhaust passage 30.
A variety of additional catalysts and/or filters may be included in first-exhaust passage 20 and/or second exhaust passage 24. These catalysts and filters may include particulate filters, NOx traps, and/or three-way catalysts. In one embodiment, first-exhaust passage 20 and/or second exhaust passage 24 may include, for example, one or more diesel particulate filters.
In one embodiment of the present disclosure, the power outputs of the one or more cylinders of first cylinder group 14 may be different than the power outputs of the cylinders of second cylinder group 16. To avoid potential vibration that may result from unbalanced cylinder operation, the stroke cycles of one or more cylinders of first cylinder group 14 may be matched with the stoke cycles of one or more cylinders of second cylinder group 16.
In one embodiment shown in FIG. 2, the stroke cycle of one or more cylinders of first cylinder group 14 may be matched with the stroke cycle of one or more cylinders of second cylinder group 16. In this embodiment, first cylinder group 14 includes only a single cylinder 38, and second cylinder group 16 includes five cylinders, including a cylinder 40 and all other cylinders 42, 44, 46, 48 of second cylinder group 16. Further, single cylinder 38 of first cylinder group 14 has a stroke cycle that is matched with the stroke cycle of cylinder 40 of second cylinder group 16. All the other cylinders 42, 44, 46, 48 of the second cylinder group 16 may have unique stroke cycles.
FIG. 3 illustrates the fluid communications of air-intake passages and exhaust passages with the cylinders of FIG. 2. In this embodiment, first air-intake passage 18 and first exhaust passage 20 may fluidly communicate with single cylinder 38 of first cylinder group 14. Further, second air-intake passage 22 may fluidly communicate with cylinder 40 of second cylinder group 16, as well as all the other cylinders 42, 44, 46, 48 of second cylinder group 16, and second air-intake passage 22 may be fluidly isolated from first air-intake passage 18. In addition, second exhaust passage 24 may fluidly communicate with cylinder 40 of second cylinder group 16, as well as all the other cylinders 42, 44, 46, 48 of second cylinder group 16.
In one embodiment, the power outputs of each cylinder of power source 12 may be controlled during operation of power source 12. FIG. 4 illustrates exemplary power outputs of each of the cylinders of power source 12. In this embodiment, the power output of each of the cylinders of power source 12 may be expressed as a relative power output. The relative power output is a numeric value multiplied by a variable, in this case (x), wherein the total power output of power source 12 equals the number of cylinders multiplied by the variable, x. Therefore, in the embodiment of FIG. 4, where power source 12 includes six cylinders, the total power output of power source 12 may be expressed as 6x.
The variable, x, may be any power value. For example, x may be a number of horsepower (hp), watts, or foot-pounds per unit time. If, for example, the total power output of all the cylinders 38, 40, 42, 44, 46, 48 of power source 12 equals 30 hp, then x will equal 5 hp.
In one embodiment, illustrated at Time 1 in FIG. 4, the relative power output of each of the cylinders of power source 12, including single cylinder 38, cylinder 40, and all the other cylinders 42, 44, 46, 48 of second cylinder group 16, is approximately 1.0x. The total power output of all the cylinders 38, 40, 42, 44, 46, 48 of power source 12, therefore, equals 6x. In this embodiment, the power output of power source 12 is distributed equally between each of the cylinders of power source 12.
In one embodiment, illustrated at Time 2 in FIG. 4, the relative power output of single cylinder 38 of first cylinder group 14 equals 0.25x, and the relative power output of cylinder 40 of second cylinder group 16 equals 0.75x. Further, the relative power output of all of the other cylinders 42, 44, 46, 48 is approximately 1.25x, and the total power output of all the cylinders 38, 40, 42, 44, 46, 48 of power source 12 equals 6x.
In another embodiment, illustrated at Time 3 in FIG. 4, the relative power output of single cylinder 38 of first cylinder group 14 equals 0.25x, and the relative power output of cylinder 40 of second cylinder group 16 equals 0.95x. Further, the relative power output of all of the other cylinders 42, 44, 46, 48 is approximately 1.2x, and the total power output of all the cylinders 38, 40, 42, 44, 46, 48 of power source 12 equals 6x.
The embodiments at Time 2 and Time 3 of FIG. 4 may allow power source 12 to operate with the minimum possible vibration, while also allowing the relative power outputs of the cylinders of power source 12 to be changed during operation. In these embodiments, matching of the stroke cycles of single cylinder 38 and cylinder 40 may allow these two cylinders to produce combined power and force similar to any one of the other cylinders 42, 44, 46, 48 of second cylinder group 16. Further, the force produced by single cylinder 38 and cylinder 40 may be balanced by the power and force of all the other cylinders 42, 44, 46, 48 of second cylinder group 16.
Controlling the power outputs of each of the cylinders of power source 12 may affect ammonia production, NOx emissions, maximum power output, and/or fuel efficiency. For example, when increased power output is needed, all cylinders of power source 12 may operate at maximum power. In another embodiment, the power output of any one of the one or more cylinders of first cylinder group 14 may be less than the power output of each of the cylinders of second cylinder group 16, as shown at Time 2 and Time 3 of FIG. 4. In this embodiment, first cylinder group 14 may produce less power, but the operation of first cylinder group 14 may be controlled to match ammonia production with NOx production from second cylinder group 16.
FIG. 5 provides a schematic diagram of power source 12 according to another exemplary disclosed embodiment. As described above, power source 12 may include first cylinder group 14 and second cylinder group 16, wherein first cylinder group 14 may be fluidly connected to first air-intake passage 18 and first exhaust passage 20, and second cylinder group 16 may be fluidly connected to second air-intake passage 22 and second exhaust passage 24.
In some embodiments, first air-intake passage 18 may be configured to provide air having a first set of characteristics to first cylinder group 14, and second-air intake passage 22 may be configured to provide air having a second set of characteristics to second cylinder group 16. Air-intake passages may be configured to modify one or more air properties, such as, for example, air pressure, flow rate or temperature. In particular, first air-intake passage 18 and second air-intake passage 22 may be configured such that air at the first set of characteristics may be different from air at the second set of characteristics, wherein the first and second set of characteristics may include one or more air properties. For example, first air-intake passage 18 may include a smaller cross-sectional area than second air-intake passage 22 to reduce the pressure of air supplied to first cylinder group 14. Supplying first cylinder group 14 and second cylinder group 16 with air at different properties may permit first cylinder group 14 and second cylinder group 16 to produce different emission levels while producing substantially similar power outputs from each cylinder.
In some embodiments, first air-intake passage 18 may be fluidly connected to second air-intake passage 22, wherein first air-intake passage 18 may include a valve 50. Valve 50 may include any device configured to modify one or more air properties. In particular, valve 50 may be configured to modify one or more air properties such that air downstream of valve 50 may have a first set of characteristics and air upstream of valve 50 may have a second set of characteristics. For example, valve 50 may be configured to reduce air pressure and/or flow rate downstream of valve 50. Valve 50 may be configured to reduce air pressure within first air-intake passage 18 relative to second air-intake passage 22 such that first cylinder group 14 may be supplied with air at a lower pressure than air supplied to second cylinder group 16.
Valve 50 may include a throttle, an inductive venturi aperture, or other similar device configured to modify an air property. In some embodiments, valve 50 may be configured to selectively modify an air property within first air-intake passage 18 during variable load operation of power source 12. For example, valve 50 may modify an air property based on an operational condition of power source 12, such as, engine speed or engine load. As engine speed increases valve 50 may increase the pressure difference between air in first air-intake passage 18 and second-air intake passage 22 by decreasing air flow rate through valve 50.
In some embodiments, first cylinder group 14 and second cylinder group 16 may operate with combustion reactions at different efficiencies. Supplying first cylinder group 14 and second cylinder group 16 with air at different properties may permit combustion reactions at different efficiencies within first cylinder group 14 and second cylinder group 16. Combustion reactions at different efficiencies may produce different combustion products and different levels of emissions from first cylinder group 14 and second cylinder group 16. For example, supplying first cylinder group 14 with air at a lower pressure than air supplied to second cylinder group 16 may permit first cylinder group 14 to produce increased levels of NOx relative to second cylinder group 16. Emission levels may also be affected by other operational parameters of power source 12, such as, for example, air to fuel-vapor ratio, valve timing, or fuel injection timing.
During operation of power source 12, first cylinder group 14 may operate at or near stoichiometric air to fuel-vapor ratios, wherein the lambda value is approximately 1.0, while second cylinder group 16 may operate under leaner conditions, wherein lambda is greater than 1.0. According to an exemplary embodiment, valve 50 may be configured to reduce the air pressure and/or flow rate in first air-intake passage 18 such that first cylinder group 14 may operate at lambda approximately equal to one. Operation of first cylinder group 14 at lambda approximately equal to 1.0, or slightly richer, may facilitate ammonia production at catalyst 26.
As discussed above, a power output of each cylinder of first cylinder group 14 may be different than a power output of each cylinder of second cylinder group 16. It is also contemplated that the power outputs of the one or more cylinders of first cylinder group 14 may be similar to the power outputs of the cylinders of second cylinder group 16. Specifically, each cylinder of first cylinder group 14 may operate to produce a power output similar to each cylinder of second cylinder group 16. For example, a quantity of fuel supplied to each cylinder of first cylinder group 14 may be approximately equal to a quantity of fuel supplied to each cylinder of second cylinder group 16. Also, fuel injection timing and/or valve timing for each cylinder of first cylinder group 14 may be varied such that the power output of each cylinder of first cylinder group 14 may be similar to the power output of each cylinder of second cylinder group 16. Such operating conditions may permit power source 12 to produce substantially similar power output from a cylinder of first cylinder group 14 and a cylinder of second cylinder group 16 while first cylinder group 14 may operate at approximately stoichiometric air to fuel-vapor ratio and second cylinder group 16 may operate at leaner combustion conditions.
Power source 12 may include one or more forced-induction systems to increase power output, as previously described. As shown in FIG. 5, a forced-induction system 54 may be operably connected to second air intake passage 22 and first air-intake passage 18, wherein first air-intake passage 18 may include valve 50. Forced-induction system 54 may include a supercharger, operably connected to power source 12 via a belt and/or gear assembly. The supercharger may utilize a portion of the energy produced by power source 12 to compress air in first air-intake passage 18 and second air-intake passage 22, thereby increasing the power output of power source 12.
In some embodiments, forced-induction system 54 may include a turbocharger. As described above, the turbocharger may utilize the exhaust gas in second exhaust passage 24 and/or first exhaust passage 20 to generate power for a compressor. The compressor may further be configured to compress the air in first air-intake passage 18 and second air-intake passage 22.
Various catalysts and/or filters may be included in first-exhaust passage 20 and/or merged passage 30. Exemplary catalysts and filters may include particulate filters, NOx traps, and/or three-way catalysts. As described previously, first exhaust passage 20 may include fuel-supply device 28 and/or ammonia-producing catalyst 26 configured to facilitate ammonia production in first exhaust passage 20. First exhaust passage 20 may also include a diesel particulate filter 27, configured to collect solid and liquid particulate matter emissions. Diesel particulate filter 27 may also be disposed in merged exhaust passage 30. In addition, first exhaust passage 20 may also include a partial oxidation catalyst 29, configured to reduce emissions of gaseous hydrocarbons and liquid hydrocarbon particles.
FIGS. 6A-6C provide schematic diagrams of first exhaust passage 20 according to several exemplary disclosed embodiments. As well as various catalysts and/or filters, first exhaust passage 20 may include a turbo-compound 52 configured to provide additional energy to machine 10. Turbo-compound 52 may be configured to convert energy in exhaust gases of power source 12 into rotational energy that may be added to power source 12.
As described above, exhaust gases in first exhaust passage 20 and/or second exhaust passage 24 may be used to drive a conventional turbocharger. Following passage through the conventional turbocharger, exhaust gases may then be directed into turbo-compound 52 to spin a turbine. The turbine may be configured to provide additional power to power source 12. For example, the revolutions of the turbine may be stepped down by mechanical gears and/or a hydraulic coupling to drive a shaft mechanically connected to power source 12.
As shown in FIG. 6A, turbo-compound 52 may be placed at any position within first exhaust passage 20. Specifically, turbo-compound 52 may be located upstream or downstream of diesel particulate filter 27, partial oxidation catalyst 29 and/or ammonia-producing catalyst 26. Further, first exhaust passage 20 may or may not include fuel-supply device 28 upstream or downstream of diesel particulate filter 27.
In some embodiments, first exhaust passage 20 may include additional and/or fewer components. For example as shown in FIG. 6B, first exhaust passage 20 may include fuel-supply device 28 and ammonia-producing catalyst 26. First exhaust passage 20 may also include turbo-compound 52 located upstream or downstream of fuel-supply device 28 and ammonia-producing catalyst 26.
First exhaust passage 20 may include one or more branched configurations. As shown in FIG. 6C, first exhaust passage 20 may split into two sub-passages, a first exhaust sub-passage 20′ and a second exhaust sub-passage 20″. Each sub-passage may include at least one of the various catalysts, filters and/or turbo-compound 52. Specifically, first exhaust sub-passage 20′ may include fuel-supply device 28 and/or partial oxidation catalyst 29. First exhaust passage 20 may include diesel particulate filter 27 upstream or downstream of each sub-passage. It is also contemplated that turbo-compound 52 may be positioned anywhere within first exhaust passage 20, first exhaust sub-passage 20′, or second exhaust sub-passage 20″.
FIGS. 7A-7B provide schematic diagrams of one or more exhaust passages according to several exemplary disclosed embodiments. As discussed above, first-exhaust passage 20, second exhaust passage 24 and/or merged passage 30 may include various catalysts and/or filters. For example, merged passage 30 may include an ammonia-reducing catalyst 31 configured to remove ammonia from the exhaust gas to substantially prevent ammonia release to the atmosphere.
As shown in FIG. 7A, turbo-compound 52 may be placed at any suitable position within first exhaust passage 20 and/or merged passage 30. Specifically, turbo-compound 52 may be located upstream or downstream of ammonia-producing catalyst 26 in first exhaust passage 20. Turbo-compound 52 may also be located upstream of diesel particulate filter 27 in merged passage 30.
In some embodiments, first exhaust passage 20, second exhaust passage 24 and/or merged passage 30 may include additional and/or fewer components. For example as shown in FIG. 7B, first exhaust passage 20 may include diesel particulate filter 27 and ammonia-producing catalyst 26 and second exhaust passage 24 may include diesel particulate filter 27. Further, merged passage 30 may include NOx-reducing catalyst 32 and ammonia-reducing catalyst 31. Turbo-compound 52 may also be located upstream or downstream of diesel particulate filter 27 in first exhaust passage 20, upstream of NOx-reducing catalyst 32 in merged passage 30, or downstream of diesel particulate filter 27 in second exhaust passage 24.
FIG. 8 provides a schematic representation of a machine 10′, including a power source 12 according to another exemplary disclosed embodiment. This embodiment is similar to the embodiment of FIG. 1, wherein power source 12 may include a first cylinder group 14 and a second cylinder group 16. First cylinder group 14 may be fluidly connected to a first air-intake passage 18 and a first exhaust passage 20. Second cylinder group 16 may be fluidly connected to a second air-intake passage 22 and a second exhaust passage 24.
Machine 10′ further includes first and second forced-induction systems 34, 36 (e.g. turbochargers). First and second forced- induction systems 34, 36 may be configured to separately supply air to first air-intake passage 18 and second air-intake passage 22. In some embodiments, the separate forced- induction systems 34, 36 may allow rapid and accurate control of the power output within each of the cylinders of first cylinder group 14 and second cylinder group 16.
The power output of each of the cylinders of first cylinder group 14 and second cylinder group 16 may be controlled by a number of different factors, including, for example, air-to-fuel ratio, absolute amounts of air and fuel in the cylinders, and/or injection timing. In some embodiments, power source 12 may include an engine control unit 33, configured to control the power output of each of the cylinders of first cylinder group 14 and second cylinder group 16.
Control unit 33 may include a variety of suitable machine electronic control units. For example, control unit 33 may include one or more microprocessors, a memory unit, a data storage device, a communications hub, and/or other components known in the art. It is contemplated that control unit 33 may be integrated within a general control system capable of controlling various functions of power source 12 and/or other components of machine 10. Further, control unit may determine various machine operational parameters and deliver output signals to effect desired operation by power source 12 or any other exhaust system or machine components.
In some embodiments, control unit 33 may control the amount and timing of air and/or fuel supplied to the cylinders of power source 12. For example, control unit 33 may control the operation of turbochargers 34, 36 to control cylinder air-fuel ratios. In addition, first and or second intake passage 18, 22 may further include suitable valves 35 or other systems for controlling the supply of air through from turbochargers 34, 36 or an intake manifold.
In addition, control unit 33 may control the amount and timing of fuel supplied to cylinders of power source 12. For example, first and second cylinder groups 14, 16 may include fuel supply systems, such as fuel injectors 15, 17. Control unit 33 may be configured to control fuel injection to control the power output and emissions from each cylinder of first and second cylinder groups 14, 16.
In some embodiments, control unit 33 may be configured to produce a substantially equal power output from each of the cylinders of first and second cylinder groups 14, 16 to control power source vibration. Further, while producing substantially equal power outputs from each cylinder, control unit may effect production of different exhaust gas compositions. For example, as noted previously, it may be desirable to produce a higher amount of NOx in first cylinder group 14, thereby allowing NOx to be converted to ammonia at a downstream ammonia-producing catalyst 26.
As noted previously, the amount of NOx produced by first cylinder group 14 may be affected by a number of factors. For example, in some embodiments, first cylinder group 14 may be run lean, and a fuel supply device 28 may be positioned downstream of first cylinder group 14 to enrich the exhaust gas, thereby facilitating ammonia production at ammonia-producing catalyst 26. In other embodiments, first cylinder group 14 may be run at stoichiometric or slightly rich air-to-fuel ratios to increase power output and/or match the power output of the cylinders of second cylinder group. Further, in some embodiments, a premixed engine type, such as a natural gas engine, may be selected. Under some conditions, premixed fuels will allow a higher level of NOx production without excess soot formation. Any suitable operating condition or engine type may be selected as long as the power output from each cylinder in first cylinder group 14 and second cylinder group 16 is approximately equal.

INDUSTRIAL APPLICABLITY

The present disclosure provides an exhaust-gas purification system including a power source with on-board ammonia production. This purification system may be useful in all engine types that produce NOx emissions.
The power source of the present disclosure provides a method for improved control of ammonia production, power output, and NOx emissions. The power source includes first and second cylinder groups with fluidly isolated air-intake passages. The fluidly isolated air-intake passages may be connected to separate forced-induction systems to rapidly change air-intake in either one or both of the cylinder groups. Further, in order to increase ammonia production, one cylinder group may operate under lean conditions, and fuel may be injected into the NOx-containing exhaust gas to produce a rich, NOx-containing exhaust that may be converted to ammonia for use with SCR systems.
In addition, the present disclosure provides a method for reducing engine vibrations due to differences in power output of individual engine cylinders. The method includes matching the cylinder stroke cycles of two or more cylinders so that these cylinders may function as a single cylinder. Matching of stroke cycles in this way may reduce engine vibrations by balancing power output and vibrations of each engine cylinder. This method may also allow low engine vibration, while operating the engine at different load levels.
The present disclosure also provides a method to produce similar power output by each cylinder of first cylinder group 14 and second cylinder group 16. For example, air flow to first air-intake passage 18 may be reduced relative to air flow to second air-intake passage 22 using valve 50 and/or first forced-induction system 34 and second forced-induction system 36. Reduced air flow and injection of similar fuel quantities to each cylinder of power source 12 may permit first cylinder group 14 to operate at lambda approximately equal to one and second cylinder group 16 to operate at leaner combustion conditions where lambda is greater than one. Such operating conditions may result in similar power output from each cylinder of power source 12 while maintaining higher NOx emissions from first cylinder group 14. Variation of injection timing and/or cam timing may also permit each cylinder of power source 12 to produce similar power output while maintaining appropriate emission levels. In addition, the present disclosure provides systems and methods for rapidly and accurately controlling the flow of air an fuel into separate cylinder groups. Theses methods may include the use of separate turbochargers for each cylinder group, or providing a separate valve system for controlling the flow of turbocharged air to each cylinder group. The separate forced-induction systems and/or turbocharger flow control systems may allow rapid and accurate control of the power output from each of the cylinder, even when using conventional drive shaft designs. The rapid control of the power output from the cylinders of the first and second cylinder group will minimize engine vibrations, while allowing different emissions from the separate cylinder groups.
Another advantage of the present disclosure may be the enhanced fuel efficiency of power source 12. Specifically, additional energy may be extracted from the fuel by power source 12 through the use of turbo-compound 52. Turbo-compound 52 may permit additional energy contained within exhaust gases to be converted into additional mechanical energy provided by power source 12.
It will be apparent to those skilled in the art that various modifications and variations can be made in the disclosed systems and methods without departing from the scope of the disclosure. Other embodiments of the disclosed systems and methods will be apparent to those skilled in the art from consideration of the specification and practice of the embodiments disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope of the disclosure being indicated by the following claims and their equivalents.

Claims

1. A power source for use with selective catalytic reduction systems for exhaust-gas purification, comprising:

a first cylinder group with a first air-intake passage and a first exhaust passage;

a second cylinder group with a second air-intake passage and a second exhaust passage;

a first forced-induction system in fluid communication with the first air-intake passage;

a second forced-induction system in fluid communication with the second air-intake passage; and

a catalyst disposed downstream of the first cylinder group to convert at least a portion of the exhaust stream in the first exhaust passage into ammonia.

2. The power source of claim 1, further including a valve for controlling the flow of air into the first air-intake passage.

3. The power source of claim 1, further including a fuel-supply device configured to supply fuel into the first exhaust passage.

4. The power source of claim 3, wherein an exhaust stream in the first exhaust passage is lean upstream from the fuel-supply device.

5. The power source of claim 4, wherein the exhaust stream in the first exhaust passage is rich downstream from the fuel-supply device.

6. The power source of claim 1, wherein the first forced-induction system and second forced-induction system include turbochargers.

7. The power source of claim 1, wherein the second exhaust passage includes an oxidation catalyst.

8. The power source of claim 1, wherein the first exhaust passage and the second exhaust passage are fluidly connected downstream from the fuel-supply device to form a merged exhaust passage.

9. The power source of claim 8, further including a catalyst disposed in the merged exhaust passage and configured to facilitate a reaction between ammonia and NOx to at least partially remove NOx from the merged exhaust passage.

10. A method of operating a power source for use with selective catalytic reduction systems for exhaust-gas purification, comprising:

supplying air through a first air-intake passage to a first cylinder group including one or more cylinders using a first turbocharger;

supplying fuel to the one or more cylinders of the first cylinder group;

supplying air through a second air-intake passage to a second cylinder group including at least two cylinders using a second turbocharger;

supplying fuel to the cylinders of the second cylinder group; and

controlling the flow of air and fuel to the cylinders of the first and second cylinder group to produce a substantially equal power output in each of the cylinders of both the first and second cylinder group.

11. The method of claim 10, further including supplying a first exhaust stream from the first cylinder group to a first exhaust passage in fluid communication with the one or more cylinders of the first cylinder group, wherein the at least a portion of the first exhaust stream includes NOx.

12. The method of claim 11, further including converting at least a portion of the first exhaust stream into ammonia.

13. The method of claim 12, further including using the fuel-supply device to make the first exhaust stream rich downstream of the fuel-supply device.

14. The method of claim 12, further including merging the exhaust stream of the first exhaust passage with the exhaust stream of the second exhaust passage to form a merged exhaust stream.

15. The method of claim 14, further including exposing the merged exhaust stream to a catalyst configured to facilitate a reaction between ammonia and NOx;

and at least partially removing NOx from the merged exhaust stream.

16. A machine for use with selective catalytic reduction systems for exhaust-gas purification, comprising:

a second forced-induction system in fluid communication with the second air-intake passage;

an engine control unit configured to control the flow of air and fuel into each of the cylinders of the first and second cylinder groups to produce substantially equal power output from each of the cylinders of the first and second cylinder groups;

a catalyst disposed downstream of the first cylinder group to convert at least a portion of the exhaust stream in the first exhaust passage into ammonia;

a merged exhaust passage downstream of the catalyst and in fluid communication with the first exhaust passage and second exhaust passage; and

a NOx-reducing catalyst in fluid communication with the merged exhaust passage.

17. The power source of claim 16, wherein the first and second cylinders are diesel cylinders.

18. The power source of claim 16, wherein the first and second cylinders are natural gas cylinders.

19. The power source of claim 16 wherein the first and second cylinders are gasoline cylinders.

20. The power source of claim 16, wherein the first forced-induction system and second forced-induction system include turbochargers.