US20070068142A1

US20070068142A1 - Engine system with low and high NOx generation algorithms and method of operating same

Info

Publication number: US20070068142A1
Application number: US11/236,076
Authority: US
Inventors: Wade Robel; Josh Driscoll
Original assignee: Caterpillar Inc
Current assignee: Caterpillar Inc
Priority date: 2005-09-27
Filing date: 2005-09-27
Publication date: 2007-03-29

Abstract

In certain engine systems, there may be a need, such as exhaust purification, to operate two power-producing portions of the engine system in different manners. The engine system of the present disclosure includes at least one engine that includes a first power-producing portion and a second power-producing portion. At least one electronic control module includes a high NOx generation algorithm in communication with the first power-producing portion and a low NOx generation algorithm in communication with the second power-producing portion. The high NOx generation algorithm is operable to signal at least one fuel injector within the first power-producing portion to inject fuel into at least one combustion chamber in a predetermined high NOx generation sequence that includes an injection during non-auto ignition conditions.

Description

TECHNICAL FIELD

The present disclosure relates generally to engine systems, and more specifically to operating an engine system including a low NOx generation algorithm and a high NOx generation algorithm.

BACKGROUND

In order to meet increasingly stringent federal regulations of NOx and other undesirable emissions, engineers are constantly seeking new strategies of reducing the production of undesirable emissions. One method of reducing NOx emissions is NOx selective catalytic reduction (SCR) systems. These systems use ammonia (NH₃) to reduce NOx to nitrogen (N₂) and water. Although these systems can reduce NOx emissions, NOx selective catalytic reduction systems often require ammonia storage on the vehicle. Ammonia tanks can consume valuable space within an engine system and must be replenished periodically. Further, because of the high reactivity of ammonia, on-board storage of the ammonia can be hazardous.
Some of the drawbacks associated with the use of NOx selective catalysts can be eliminated by the use of on-board ammonia generation systems. For instance, the on-board ammonia production system set forth in U.S. Pat. No. 6,047,542, issued to Kinugasa on Apr. 11, 2000, injects an increased amount of fuel into one cylinder group within a plurality of cylinders in order to create a rich exhaust from the one cylinder group. The rich exhaust is then passed over an ammonia-producing catalyst that converts a portion of the NOx in the rich exhaust into ammonia. It has been found that the efficiency of conversion of NOx to ammonia by the ammonia-producing catalyst may be improved under rich conditions. The exhaust and the ammonia is then combined with the exhaust from a second cylinder group and passed through a NOx selective catalyst where the ammonia reacts with NOx to produce nitrogen gas and water.
Although the Kinugasa method allows for on-board generation of ammonia, operating one cylinder group of an engine in a manner to create a rich exhaust can create drawbacks. For instance, the amount of ammonia that can be created by the cylinder group is limited. It has been found that amount of ammonia produced is dependent on the amount of NOx in the exhaust being passed over the ammonia-producing catalyst. Because current combustion strategies can only produce a limited amount of NOx, the amount of ammonia created is also limited. Thus, in order to produce a sufficient amount of ammonia, a relatively significant percentage of the exhaust must be made rich and passed over the ammonia-producing catalyst, thereby resulting in a significant fuel penalty.
Moreover, the Kinugasa engine may function less efficiently and with lower power output when rich combustion occurs in a portion of the cylinders. Operating the two cylinder groups, as done in the Kinugasa method, may also cause significant power imbalance within the engine, resulting in engine vibrations.
The present disclosure is directed at overcoming one or more of the problems set forth above.

SUMMARY OF THE INVENTION

In one aspect of the present disclosure, an engine system includes at least one engine that includes a first power-producing portion and a second power-producing portion. At least the first power-producing portion includes at least one fuel injector that is operable to inject fuel into at least one combustion chamber. An electronic control module includes a high NOx generation algorithm that is in communication with the first power-producing portion and a low NOx generation algorithm that is in communication with the second power-producing portion. The high NOx generation algorithm is operable to signal the at least one fuel injector of the first power-producing portion to inject fuel into the at least one combustion chamber in a predetermined high NOx generation sequence that includes an injection during non-auto ignition conditions.
In another aspect of the present disclosure, an engine system is operated by controlling a first power-producing portion of at least one engine to produce exhaust with a high NOx concentration, at least in part, by signaling at least one fuel injector to inject fuel in a predetermined high NOx generation sequence that includes an injection during non-auto ignition conditions. A second power-producing portion of the at least one engine is controlled to produce exhaust with a low NOx concentration.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of an engine system, according to a first embodiment of the present disclosure;
FIG. 2 is a schematic representation of the engine system, according to a second embodiment of the present disclosure;
FIG. 3 is an enlarged sectioned side diagrammatic view of a tip portion of a mixed-mode fuel injector within the engine systems of FIGS. 1 and 2;
FIG. 4 is a sectioned side diagrammatic view of an upper portion of the mixed-mode fuel injector of FIG. 3;
FIG. 5 is a bottom view of a first spray pattern from the mixed-mode fuel injector of FIG. 3; and
FIG. 6 is a flow chart of a high NOx generation algorithm and a low NOx generation algorithm, according to the first and second embodiments of the present disclosure.

DETAILED DESCRIPTION

Referring to FIG. 1, there is shown a schematic representation of an engine system 10, according to a first embodiment of the present disclosure. The engine system 10 includes a single engine 16. Although the present disclosure illustrates a six-cylinder internal combustion engine 16, it should be appreciated that the present disclosure contemplates an engine including various numbers of cylinders. The engine 16 includes a first power-producing portion 11 and a second power producing portion 12. The first power-portion 11 and the second power-portion 12 are operable to run simultaneously. The disclosure also contemplates first and second portions of equal displacements. But the disclosure also contemplates, the first power-producing portion 11 as a low-displacement portion with a first power output 61 (illustrated in FIG. 6), and the second power-producing portion 12 as a high-displacement portion with a second power output 62 (illustrated in FIG. 6). Thus, the second power-producing portion 12 will provide the majority of a common power output 63 (illustrated in FIG. 6) of the engine system 10. The first power-producing portion 11 includes a first portion 20 a of a plurality of fuel injectors 20. Although the first portion 20 a is illustrated as including only one fuel injector 20 a, it should be appreciated that the first portion 20 a could include any number of cylinders and fuel injectors. The fuel injector 20 a is operable to inject fuel into a combustion chamber 17 a defined by a cylinder 15 a. A piston 13 a is positioned within the combustion chamber 17 a and reciprocates between top dead center and bottom dead center. Although the present disclosure is illustrated for a four-stroke engine, the present disclosure contemplates use with a two-stroke engine, or even an engine with a mix of two and four stroke cylinders. The second power-producing portion 12 of the engine 16 includes a second portion 20 b of the fuel injectors 20. The second portion 20 b is illustrated as including five cylinders and fuel injectors 20 b, each operable to inject fuel into a combustion chamber 17 b in which a piston 13 b reciprocates. The number of cylinders 15 b, and thus fuel injectors 20 b, within the second portion 12 can also vary.
Fuel is supplied to the fuel injectors 20 a and 20 b from a fuel tank 21 via at least one conventional fuel pump 24. The fuel pump 24 is fluidly connected to a common rail 22 that is fluidly connected to each fuel injector 20 a and 20 b via individual branch passages 23. This disclosure also contemplates other fuel injection systems, including but not limited to cam actuated and hydraulically actuated, etc. The fuel pump 24 is preferably in communication with an electronic control module 30 such that the pressure of the fuel being supplied to the fuel injectors 20 a and 20 b can be controlled. The fuel injectors 20 a and 20 b are fluidly connected to the fuel tank 21 via a return line 25. The fuel not injected into the combustion chambers 17 a and 17 b can be returned to the fuel tank 21 for re-circulation through the system 10. In the illustrated embodiment, an additional fuel injector 20 c is positioned within a first or high NOx, section 18 a of an exhaust passage 18. Because each fuel injector 20 a, 20 b and 20 c is in communication with the electronic control module 30 via respective injector communication lines 26, each fuel injector 20 a, 20 b and 20 c can be separately controlled by the electronic control module 30.
The combustion chamber 17 a of the first power-producing portion 11 is in fluid communication with a first air-intake manifold 34, and the combustion chambers 17 b of the second power-producing portion 12 are in fluid communication with a second air-intake manifold 35. Although the present disclosure contemplates only one air-intake manifold shared by both power-producing portions 11 and 12, by separating the air-intake manifold into two air- intake manifolds 34 and 35, the air intake for each power-producing portion 11 and 12 can be controlled separately. The combustion chamber 17 a of the first power-producing portion 11 is also in fluid communication with the first exhaust passage 18 a via a first exhaust manifold 27, and the combustion chambers 17 b of the second power-producing portion 12 are also in fluid communication with a second exhaust passage 18 b via a second exhaust manifold 28.
Preferably, the second power-producing portion 12 includes a forced-induction system 37 to increase power output and/or control the air to fuel-vapor ratios within the combustion chambers 17 b of the second power-producing portion 12. In the illustrated embodiment, the forced induction system 37 includes a turbocharger 38 operably connected with the second air-intake manifold 35. The turbocharger 38 utilizes the exhaust in the second exhaust passage 18 b to generate power for a compressor, and this compressor may provide additional air to the second air intake manifold 35. Although not shown, those skilled in the art should appreciate that the compressor could also provide air to the first air-intake manifold 34 of the first power-producing portion 11. It should also be appreciated that the forced induction system 37 may include superchargers and/or be turned on and off based on demand. For instance, when lower air-intake is needed, such as when little power is needed from the second power-producing portion 12, the combustion chambers 17 b can be naturally aspirated. It should be appreciated that the power output and/or air to fuel-vapor ratio of each combustion chamber could be controlled by other means, including but not limited to, an air-intake throttle valve(s).
A reductant-producing catalyst 29, herein referred to as the ammonia-producing catalyst, is positioned within the first exhaust passage 18 a. The ammonia-producing catalyst 29 is operable to convert at least a portion of the exhaust-gas stream from the combustion chamber 17 a of the first power-producing portion 11 into ammonia, or possibly some other higher order reductant. The ammonia may be produced by a reaction between NOx and other substances in the exhaust-gas stream from the combustion chamber 17 a. For example, NOx may react with a variety of other combustion byproducts to produce ammonia and other related reductants. These other combustion byproducts may include, for example, H₂(hydrogen gas), C₃H₆(propene), or CO (carbon monoxide). This disclosure also contemplates reductant (ammonia) production by serially passing the NOx over several different catalysts, with the end result being ammonia and/or another suitable reductant.
The ammonia-producing catalyst 29 may be made from a variety of materials. In one embodiment, the ammonia-producing catalyst 29 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 and other known considerations.
The first and second exhaust passages 18 a (high NOx) and 18 b (low NOx) fluidly connect the first power-producing portion 11 and the second power-producing portion 12 to a merged exhaust passage 18 c, respectively. A NOx selective catalyst 19 is positioned in the merged exhaust passage 18 c such that combined exhaust from the combustion chambers 17 a and 17 b of the first and second power-producing portions 11 and 12 pass over the NOx selective catalyst 19. In one embodiment, the NOx selective catalyst 19 may facilitate a reaction between ammonia and NOx to at least partially remove NOx from the exhaust-gas stream in the merged exhaust passage 18 c. For example, the NOx selective catalyst 19 may facilitate a reaction between ammonia and NOx to produce nitrogen gas and water, among other reaction products. NOx sensor 31 a 31 b and 31 c are preferably positioned within the respective exhaust passages 18 a, 18 b, and 18 c in communication with the electronic control module 30 via a sensor communication line 32 a, 32 b and 32 c, respectively. The illustrated NOx sensors 31 a, 31 b and 31 c may be conventional sensors that are readily commercially available and operable to sense both a NOx concentration and maybe other gases, such as an ammonia, within the exhaust passages. Other strategies for sensing and predicting NOx concentrations are contemplated. Three NOx sensors as shown would allow the ECM 30 to monitor the state of NOx production and cancellation throughout the system. This information could be exploited to allow for fine adjustments in first and second power producing portions to further reduce NOx levels seen by sensor 31 c. Those skilled in the art will appreciate that information provided to ECM 30 form even one NOx sensor at an appropriate location, such as in high NOx exhaust passage 18 a, could allow for a substantial improvement over no NOx sensors in an open loop control strategy.
It should be appreciated that a variety of additional catalysts and/or filters may be included in the exhaust passages 18 a, 18 b and 18 c, including, but not limited to, particulate filters, NOx traps, and/or three-way catalysts. For instance, in the illustrated embodiment, an oxidation catalyst can be positioned within the low NOx exhaust passage 18 b downstream from turbocharger 38. Because the NOx selective catalyst 19 functions most effectively with a ratio of NO:NO₂of about 1:1, the oxidation catalyst is operable to control a ratio of NO:NO₂in the merged exhaust passage 18 c.
Referring to FIG. 2, there is shown a schematic representation of an engine system 110, according to a second embodiment of the present disclosure. The engine system 110 is similar to the engine system 10 except that a first power-producing portion 111 is a low-displacement portion and the second power-producing portion 112 is a high-displacement portion. However, the first and second power producing portions 111 and 112 of the second embodiment include a first engine 116 a and a second engine 116 b, respectively. It should be appreciated that the first engine 111, being the low-displacement engine, may include various types of engines, including, but not limited to, a free-piston engine and a conventional two-stroke or four-stroke internal combustion engine. The disclosure also contemplates two engines of equal displacements. Preferably, the first engine 111 is a conventional four-stroke internal combustion engine as shown. Although the first engine 111 can include any number of cylinders, the present disclosure illustrates the first engine 111 including two cylinders 15 a. Although the second engine 112, being the high displacement engine, may include various types of engines, the second engine 112 is preferably also a conventional internal combustion engine. Although the second engine 112 can include any number of cylinders, the present disclosure illustrates the second engine 112 including six cylinders 15 b. Although the present disclosure contemplates fuel being delivered to one common rail from the fuel tank 21 via one fuel pump, each engine 111 and 112 in the illustrated embodiment includes a fuel pump 124 a and 124 b delivering fuel to separate common rails 122 a and 122 b, respectively. Thus, each fuel pump 124 a and 124 b can separately control the fuel pressure being delivered to the fuel injectors 20 a and 20 b of each engine 116 a and 116 b, respectively.
In the illustrated embodiment, a power output 161 (illustrated in FIG. 6) of the first engine 111 and a power output 162 (illustrated in FIG. 6) of the second engine 112 are coupled into a common power output 163 (illustrated in FIG. 6) by coupling a first output shaft 170 of the first engine 111 and a second output shaft 171 of the second engine 112 to one another. The output shafts 171 and 172 can be coupled together by any conventional means known in the art, including a coupling gear train. It should be appreciated that the first engine 111 and the second engine 112 can be coupled to one another by any other conventional means, including, but not limited to, hydraulic couplings and electric couplings. Although not shown, the present disclosure contemplates the rotation of the second outputs shaft 171 powering a primary apparatus, such as a drive shaft and/or hydraulic implement of a work machine or a generator, and the first output shaft 170 powering an auxiliary apparatus, such as a pump. Thus, the present disclosure contemplates the first power output 161 and the second power output 162 not being coupled to one another.
Referring to FIG. 3, there is shown an enlarged sectioned side diagrammatic view of a tip portion of the fuel injectors 20 a, 20 b within the engine systems 10, 110 of FIGS. 1 and 2. Although any type of conventional fuel injector with only one set of nozzle outlets can be used, the fuel injector 20 a may be a mixed-mode fuel injector that is operable to inject fuel in at least a first spray pattern (shown in FIG. 5) through a first nozzle outlet set 42 and a second spray pattern, which may be a conventional well known pattern, through a second nozzle outlet set 43. Although not necessary, fuel injectors 20 b may also be, and are illustrated as, mixed-mode fuel injectors. The first nozzle outlet set 42 is referred to as semi-homogenous or homogenous charge nozzle outlet set and has a relatively small average angle theta with respect to a centerline 40 of the combustion chambers 17 a and 17 b. These outlets may be relatively small and arranged in a showerhead pattern as shown in FIG. 5. Thus, the first spray pattern, referred to as a homogeneous charge spray pattern, includes a relatively small average angle theta with respect to the centerline 40 of the combustion chamber 17 a, 17 b. The second nozzle outlet set 43 is referred to as conventional nozzle outlet set typical of those in the art and has a relatively large average angle alpha with respect to the centerline 40. These outlets are typically associated with fuel injections in the vicinity of piston top dead center as is known in the art. The second spray pattern, referred to as a conventional spray pattern, includes a relatively large average angle alpha with respect to the centerline 40 of the combustion chamber 17 a, 17 b. The opening and closing of the second nozzle outlet set 43 and the first nozzle outlet set 42 may be controlled by an inner needle valve member 44 of a second direct control needle valve 47 and an outer needle valve member 46 of a first direct control needle valve 45, respectively. The fuel injectors 20 a, 20 b have the ability to controllably inject fuel through the first nozzle outlet set 42, the second nozzle outlet set 43, or both.
Referring to FIG. 4, there is shown a sectioned side diagrammatic view of an upper portion of the fuel injectors 20 a, 20 b of FIG. 3. A first and second needle control valves 48 and 49 control the positioning of the first and second direct control needle valves 45 and 47, respectively. Both needle control valves 48 and 49 operate in a similar manner and are preferably three-way valves that are substantially identical in structure. The first and second needle control valves 48 and 49 are operably coupled to a first and second electrical actuators 50 and 51, respectively. In order to open the first nozzle outlet set 42, the first electrical actuator 50 is energized, and the first needle control valve 48 moves to a position that relieves pressure acting on a closing hydraulic surface of the outer needle valve member 46. The outer needle valve member 46 can be lifted off its seat by high pressure fuel within the injector 20 a, 20 b, and the fuel can be injected through the first nozzle outlet set 42. Similarly, in order to open the second nozzle outlet set 43, the second electrical actuator 51 is energized, moving the second needle control valve 49 to a position that relieves pressure acting on a closing hydraulic surface of the inner needle valve member 44. The inner needle valve member 44 can be lifted off its seat by high pressure fuel within the fuel injector 20 a, 20 b and inject the fuel through the second nozzle outlet set 43. Both the first and second electrical actuators 50 and 51 can be activated in various timings, including simultaneously, to inject fuel in different sequences and spray patterns. It should be appreciated that any fuel injector with the ability to inject fuel in more than one spray pattern may be considered a mixed-mode injector for use within the present disclosure regardless of the means for controlling the opening and closing of the different nozzle outlet sets.
Referring to FIG. 5, there is shown an example first spray pattern 52. The first spray pattern 52 is illustrated to include 18 nonintersecting plumes 53 that are directed downward with an average angle theta, as shown in FIG. 3. Average angle theta is preferably substantially small compared to the average angle alpha of the second spray pattern injected through the conventional nozzle outlet set 43. Generally, the engine piston 13 a, 13 b is farther away from top dead center during non-auto ignition conditions than during auto-ignition conditions. Thus, in order to avoid spraying the walls of the cylinder 15 a, 15 b and the piston 13 a, 13 b during non-auto ignition conditions, fuel can be injected in the first spray pattern 52 with the relatively small average angle with respect to the centerline 40 of the combustion chamber 17 a, 17 b. If fuel is being injected in a conventional manner in auto-ignition conditions when the piston 13 a, 13 b is nearer to top dead center, fuel can be injected in the conventional second spray pattern with the relatively large average angle with respect to the centerline 40.
Referring to FIG. 6, there is shown a flow chart of a high NOx generation algorithm 55 and a low NOx generation algorithm 56 of the engine systems 10, 110, according to the first and second embodiments of the present disclosure. The electronic control module 30 includes the high NOx generation algorithm 55 that is in communication with the first power-producing portion 11, 111 and the low NOx generation algorithm 56 that is in communication with the second power-producing portion 12, 112. Although the high NOx generation algorithm 55 preferably runs while the low NOx generation algorithm 56 is running, the present disclosure contemplates the high NOx algorithm 55 running when the second power-producing portion 12, 112 is not operating. The extra NOx produced could be stored for further exhaust after treatment of the low NOx concentration created during normal operation when the second power-producing portion 12, 112 is operating. The present disclosure also contemplates the high NOx generation algorithm 55 being included on a separate electronic control module than the low NOx generation algorithm 56. The high NOx generation algorithm 55 is operable to produce a high NOx concentration 66 within the exhaust from the combustion chamber(s) 17 a when an expected NOx concentration 54 the exhaust from the second power-producing portion 12, 112 is greater than a predetermined threshold NOx concentration 39. The predetermined threshold NOx concentration 39 is a NOx concentration within the exhaust from the second power-producing portion 12, 112 that is sufficiently low that the NOx need not be further reduced over the NOx selective catalyst 19 before being released into the atmosphere from the engine system 10, 110.
In order to produce the high NOx concentration 66, the high NOx generation algorithm 55 is operable to signal the fuel injector(s) 20 a of the first power-producing portion 11, 111 to inject fuel into the combustion chamber(s) 17 a in a predetermined high NOx generation sequence 57 that includes at least an injection during non-ignition conditions within the combustion chamber(s) 17 a. Preferably, the predetermined high NOx generation sequence 57 includes a first fuel injection during non-auto ignition conditions followed by a second fuel injection during auto-ignition conditions within the combustion chamber(s) 17 a. It should be appreciated that the predetermined high NOx generation sequence 57 could include additional early or late injections. Those skilled in the art will also appreciate that auto-ignition conditions within each combustion chamber 17 a generally occurs when the engine piston 13 a is relatively close to top dead center of a compression or expansion stroke, and non-auto ignition conditions generally occur when the piston 13 a is relatively far from top dead center of the compression or expansion stroke. Thus, the first fuel injection will mix with air within each combustion chamber 17 a as each engine piston 13 a advances before igniting. The second injection will ignite upon injection shortly after or during combustion of the first injection. The first injection preferably is injected in the first spray pattern 52 illustrated in FIG. 5. Because the first injection occurs during non-auto ignition conditions within the combustion chamber(s) 17 a, the relatively small angle of the injection will allow the fuel to be injected within the open space of the combustion chamber(s) 17 a rather than on the walls of the cylinder(s) 15 a. The second injection preferably is injected in the second spray pattern, being the conventional spray pattern. Because the second injection occurs during auto ignition conditions near top dead center, the second injection will ignite upon injection. Thus, the second injection can be injected at a relatively large angle with respect to the centerline 40 as compared with the first injection.
The high NOx generation algorithm 55 preferably includes a setting algorithm 59 that is operable to set a high NOx production amount 65 from the first power-producing portion 11, 111 to correspond to an ammonia production amount. The high NOx production amount 65 is the amount of NOx produced from the combustion chamber(s) 17 a. The ammonia production amount is the amount of ammonia needed to convert the expected NOx concentration 54 from the second power-producing portion 12, 112 to harmless gases. The setting algorithm 59 will set the timing and the amounts of the first and second injections to generate the high NOx production amount 65. Those skilled in the art will appreciate that the NOx production amount 65 can be adjusted by adjusting at least one of the timing of the first injection, the amount of the first injection, the timing of the second injection and the amount of the second injection. Those skilled in the art will appreciate that the NOx production amount 65 to the ammonia production amount within the first exhaust passage 18 a is about 1:1.
Generally, in the case of engine system 10, the apportioning of the injected fuel between the first and second injections will vary for different engine speeds and loads. Around mid-range engine speed and 50-75% loads, the first and second injections will each include about 50% of the amount of fuel being injected into the combustion chamber 17 a each engine cycle. As the engine load and speed decreases below the mid-speed and load range, more fuel will be apportioned from the second injection to the first injection. At the lowest speeds and loads, the first injection could include 80% or more of the fuel being injected. As the engine load and speed increases above the mid-speed and load range, more fuel will be apportioned from the first injection to the second injection. At the highest speeds and loads, the second injection could include about 80% or more of the fuel being injected. Although the amount of fuel injected can vary, preferably the setting algorithm 59 adjusts the amounts of the fuel injection such that the algorithm 59 creates slightly lean combustion conditions. Those skilled in the art will appreciate that lean combustion conditions exist when lambda is less than one. Lambda is the air-to fuel ratio divided by stoichiometric air-to-fuel ratio.
The expected NOx concentration 54 from the combustion chambers 17 b may or may not change based on engine operating conditions. The present disclosure contemplates the determination of the expected NOx concentration 54 by various conventional open or closed loop means. In the illustrated embodiment, the electronic control module 20 includes a map with predetermined expected NOx concentrations based on engine operating conditions, such as engine speed and load. For each predetermined expected NOx concentration 54, there is a corresponding NOx production amount 65 and predetermined timing and amounts of the first and second injections into the combustion chamber(s) 17 a. In addition, the NOx sensors 31 a, 31 b and 31 c is positioned within the exhaust passages 18 a, 18 b and 18 c to communicate a sensed NOx concentration 70 and other gases, including a sensed ammonia concentration 71 to the electronic control module 30. The setting algorithm 59 may adjust the high NOx production amount 65 such that the NOx and/or ammonia concentrations 70 and/or 71 downstream from the NOx selective catalyst 19 are at or below a predetermined NOx and ammonia concentration amounts. It should also be appreciated that the NOx being produced within the combustion chambers 17 b of the second power-producing portions 12, 112 could be increased in order to match the ammonia production rather than the ammonia production being reduced. Those skilled in the art will appreciate that even a single NOx sensor in either the high or low NOx exhaust passages 18 a or 18 b could be useful for the setting algorithm in a closed loop control configuration.
The high NOx generation algorithm 55 also preferably includes an alternative operation algorithm 36 that is operable to produce a low NOx production amount 64 from the first power-producing portion 11, 111 when the expected NOx concentration 54 is less than the predetermined threshold NOx concentration 39. For purposes of the instant discussion, the low NOx production amount 64 is a NOx amount less than the high NOx production amount 65 created by the normal operation of the high NOx algorithm 55. Those skilled in the art will appreciate that the expected NOx concentration 54 may fall below the predetermined threshold NOx concentration 39 in low power situations, such as operation of the second power-producing portion 12, 112 at idle. When the expected NOx concentration 54 falls below the predetermined threshold NOx concentration 39, the fuel injector(s) 20 a can inject fuel in a low NOx generation sequence that may or may not be the same injection strategy discussed below used by the fuel injectors 20 b of the second power-producing portion 12, 112. For instance, any fuel injected in this mode could be during non-autoignition conditions, with a corresponding low NOx producing combustion event. Alternatively, in the second embodiment, the fuel injectors 20 a of the first engine 111 may not be operated at all, and the desired power output of the engine system 110 could be derived solely from the second engine 112 when the expected NOx concentration 54 falls below the predetermined threshold concentration 39.
The injection strategy of the alternative operation algorithm 36 is, in part, based in a conventional manner, on the desired power output 61, 161 of the first engine power-producing portion 11, 111. The present disclosure contemplates the electronic control module 30 including a map with the desired power outputs 61, 161, and known injection strategies to achieve the desired power output 61, 161. Those skilled in the art will appreciate that conventional injection strategies generally create the low NOx production amount 64. For instance, it is known that a single injection after top dead center may create the low NOx production amount 64 at certain known engine speeds and loads. Those skilled in the art will appreciate that the mixed mode fuel injector 20 a will provide more variability in and control over the injection strategies used to create the low NOx production amount 64 at various engine speeds and loads. The use of mixed-mode fuel injectors 20 a will provide the ability to inject more fuel in the first injection and to inject earlier in the engine cycle.
The low NOx generation algorithm 56 is operable to signal the fuel injectors 20 b of the second power-producing portion 12, 112 to inject fuel in a predetermined low NOx generation sequence 58. The low NOx generation algorithm 56 may be based, at least in part, on the desired power output 63, 163 of the engine system 10, 110. In both embodiments, the desired power output 63, 163 of the engine system 10, 110 is a combination of the first power output 61, 161 of the first power-producing portion 11, 111 and the second power output 62, 162 of the second power-producing portion 12, 112. However, the second power-producing portion 12, 112 provides the majority of the desired power output 63, 163. The low NOx generation algorithm 56 will determine the second power output 62 needed to achieved the desired power output 63, 163 and set the timing(s) and amount(s) of the fuel injections within the predetermined low NOx generation sequence 58 in order to achieve the second power output 63, 163. The electronic control module 30 may include a map with predetermined low NOx generation sequences including injection(s) timing and amount(s) that are known to produce relatively low NOx generation amounts at known engine speeds and loads. This same map, or a similar map, may be used to determine the injection sequence to produce the low NOx production amount 64 created by the alternative operation algorithm 36 of the high NOx generation algorithm 55. Preferably, the predetermined low NOx generation sequence 58 creates lean combustion conditions. In the illustrated example, the combustion conditions created by the predetermined low NOx generation sequence 58 are leaner than the combustion conditions created by the predetermined high NOx generation sequence 57. Although lambda of the exhaust from the second engine 12, 112 can vary, generally the exhaust will have a lambda of about three.
Although the predetermined low NOx generation sequence 58 can vary, the low NOx generation sequence 58 is illustrated as including a first injection during non-auto ignition conditions and a second injection during auto ignition conditions. Similar to the predetermined high NOx generation sequence 57, the first injection may be in the first spray pattern 52 and the second injection may be in the second spray pattern. However, the second injection of the low NOx generation sequence 58 may be injected later in the engine cycle than the second injection of the high NOx generation sequence 57. Generally, the second injection of the low NOx generation sequence 57 will be injected after top dead center in the expansion stroke. By retarding the second injection, the combustion chambers 17 b have time to cool after the combustion of the first injection. It has been found that injecting a second amount of fuel into a cooler combustion chamber 17 b creates less NOx than injecting into a hot combustion chamber 17 a. Further, the apportioning of the fuel between the first and second injections in the predetermined low NOx generation sequence 58 is different than in the predetermined high NOx generation sequence 57. More of the fuel injected in each engine cycle will be injected in the first injection of the high NOx generation sequence 57 than will be injected in the first injection of the low NOx generation sequence 58. The timing and apportioned amounts of the first and second injections may vary based on the desired second power output 62, 162 in a similar manner as the injections of the high NOx generations sequence 57. Although a predetermined low NOx generation sequence 58 has been described with a first and second injection, it should be appreciated that the low NOx generation sequence 58 can include any number of injections, including a single injection in the vicinity of top dead center of the compression stroke.
Those skilled in the art will appreciate that, in the first embodiment, the different injection strategies between the fuel injector 20 a injecting fuel into the combustion chamber 17 a and the second fuel injectors 20 b injecting fuel into the combustion chambers 17 b may create different power outputs for the combustion chambers 17 a and 17 b in the first power-producing portion 11 and the second power producing portion 12. Engine vibrations caused by the possible varying power outputs can be reduced by matching stroke cycles of one or more cylinders in order to cause the cylinders to function as one cylinder, or other strategies known in the art. Moreover, in the second embodiment, the utilization of two engines, the first engine 111 primarily for increasing NOx and the second engine 112 primarily for providing power, also eliminates engine vibrations caused by the power imbalance
Industrial Applicability
Referring to FIGS. 1-6, a method of operating the engine system 10, 110 will be discussed. The first power-producing portion 11, 111 and the second power-producing portions 12, 112 are preferably running simultaneously. In order to provide power to the engine system 10, 110, the low NOx generating algorithm 56 will preferably signal the fuel injectors 20 b of the second power-producing portion 12, 112 to inject fuel in the predetermined low NOx generation sequence 58 that is based on the desired power output 63, 163 of the engine system 10, 110. The second power-producing portion 12, 112 will generate exhaust with the low NOx concentration, which is illustrated as the expected NOx concentration 54. In the illustrated embodiment, the power output from each cylinder 15 b in the second power-producing portion 12, 112 will be more than the power output from each cylinder 15 a in the first power-producing portion 11, 111 because the second power-producing portion 12, 112 is turbocharged. In both illustrated embodiments, the desired power output 63, 163 of the engine system 10, 110 is a common power output resulting from the second power output 62, 162 of the second power-producing portion 12, 112 and the first power output 61, 161 of the first power-producing portion 11, 111. The low NOx generation algorithm 56 will sense and determine the desired power output 63, 163 of the engine system 10, 110 in any conventional manner known in the art. The low NOx generation algorithm 56 may then determine the portion of the desired power output 63, 163 that is generated by the second power output 62, 162 of the second power-producing portion 12, 112. Although the second embodiment is illustrated in FIG. 2 with the power outputs 161 and 162 of the first and second engines 116 a and 116 b being coupled to one another, the present disclosure contemplates the output shaft of the first engine being uncoupled from the second engine, and instead coupled to an auxiliary apparatus, such as a pump, which may support the first engine, or not. The low NOx generation algorithm 56 may set the predetermined NOx generation injection sequence 58 including injection timings and amounts needed to generate the second power output 62, 162 to produce the desired power output 63, 163. Those skilled in the art will appreciate that various conventional injection strategies, including a single fuel injection after top dead center of the compression stroke, will produce the expected NOx concentration 54.
In the illustrated embodiment, the predetermined low NOx generation sequence 58 includes the first injection during non-auto ignition conditions and the second injection during auto-ignition conditions. The low NOx generation algorithm 56 will signal the fuel injections 20 b of the second power-producing portion 12, 112 to inject the first injection approximately between 80°-40° before top dead center of the compression stroke. The higher the desired second power output 62, 162, the less fuel injected during each engine cycle apportioned to the first injection. However, the proportion of fuel being injected through the first injection is generally less in the low NOx generation sequence 58 than in the high NOx generation sequence 57. As the engine pistons 13 b advance during the compression or expansion stroke, the first injection will mix with the air and eventually combust. The relatively homogenous combustion of the first injection will create very low NOx concentrations. The low NOx generation algorithm 58 will signal the fuel injectors 20 b to inject the second injection after top dead center in the expansion stroke. Thus, the combustion chambers 17 b will have cooled before the second injection, thereby limiting the NOx produced by the second injection. At high engine speeds and loads, the majority of the fuel may be injected through the second injection.
If the high NOx generation algorithm 55 determines that the expected NOx concentration 54, based on the sensed NOx concentration 70, ammonia concentration 71 and/or predetermined map, being produced from the second power-producing portion 12, 112 is greater than the predetermined threshold NOx concentration 39, the high NOx generation algorithm 55 will signal the first power-producing portion 11, 111 to produce exhaust with the high NOx concentration 66. Although there may be different injection strategies used to produce the high NOx concentration 66, preferably the high NOx generation algorithm 55 will signal the fuel injector(s) 20 a to inject fuel in the predetermined high NOx generation sequence 57. The fuel injector(s) 20 a are signaled to inject the first injection during non-auto ignition conditions of the combustion chamber(s) 17 a and the second injection during auto-ignition conditions of the combustion chamber(s) 17 a when the cylinder is hot in the vicinity of top dead center.
The setting algorithm 59 of the high NOx generation algorithm 55 determines the amount, and injection timing, of the first and second injections necessary to create the high NOx production amount 65. The setting algorithm 59 is operable to set the high NOx production amount 65 from the combustion chamber(s) 17 a of the first power-producing portion 11, 111 to correspond to the ammonia production amount necessary to reduce the expected NOx concentration 54 created by the second power-producing portion 12, 112. Those skilled in the art will appreciate that the expected NOx concentration 54 is determined by either a closed or open loop system. In the illustrated embodiment, the expected NOx concentrations at various engine operating conditions may be predetermined and included within a map in the electronic control module 30. Each predetermined expected NOx concentration 54 will have a corresponding high NOx production amount 65 from the first power-producing portion 11, 111. The map can include the predetermined amount and timing of each injection to achieve the high NOx production amount 65 needed to reduce the expected NOx concentration 54 at the sensed engine operating conditions. For instance, the map could include the high NOx generation sequence 57 with the first injection occurring about 60° before top dead center of the compression stroke and the second injection occurring about 20° before top dead center.
The expected NOx concentration 54, and thus, the high NOx production amount 65, can be adjusted based on the sensed NOx concentration 70 and/or the sensed ammonia concentration 71. If the sensed NOx concentration 70 exceeds a predetermined NOx concentration, the setting algorithm 59 will determine that there is insufficient ammonia to reduce the NOx within the merged exhaust passage 18 c, and will adjust the NOx production amount 65 to correspond to an increased ammonia production amount necessary to reduce the expected NOx concentration 54. In order to increase the NOx production amount 65, those skilled in the art will appreciate that the timing and the amounts of the first and second injections within the predetermined high NOx generation sequence 57, including the first injection about 60° before top dead center and the second injection about 20° before top dead center of the compression or expansion stroke, can be adjusted. For instance, to increase the high NOx production amount 65 while maintaining the slightly lean environment, the timing and the first injection can be advanced and/or some of the fuel in the second injection can be reapportioned to the first injection.
If the NOx sensor 31 a senses an ammonia concentration 70 in the exhaust that exceeds a predetermined ammonia concentration, the setting algorithm 59 will determine that there is more ammonia being produced than necessary to reduce the expected NOx concentration 54. The setting algorithm 59 can reduce the high NOx production amount 65 to correspond to a decreased ammonia production amount needed to reduce the expected NOx concentration 54. The high NOx production amount 65 can be reduced by adjusting the timing and/or amounts of the first and second injection of the predetermined high NOx generation sequence 57, including the first injection about 60° before top dead center and the second injection at about 20° before top dead center. For instance, while maintaining the slightly lean environment, the timing of the second injection can be retarded and /or some of the fuel in the first injection can be reapportioned to the second injection. Although the present disclosure illustrates the expected NOx concentration 54, and thus, the high NOx production amount 65, being based on the map and the sensed NOx and ammonia concentrations 70 and 71, it should be appreciated that the expected NOx concentration could be determined solely on the map or the sensed concentrations. Regardless of the procedure for setting the NOx production amount 65, the present disclosure can assure that the ammonia produced within the first exhaust passage 18 a will reduce the NOx concentration 54 within the merged exhaust passage 18 c such that very little, if any, NOx and ammonia are present in the exhaust downstream from the NOx selective catalyst 19.
During each engine cycle, the first fuel injection of the predetermined high NOx generation strategy 57 occurs during non-auto ignition conditions within the combustion chamber(s) 17 a. Preferably, the timing of the first injection will be sufficiently early within the engine cycle to allow some mixing of the fuel within the air before ignition. Thus, the first injection is referred to as a semi-homogeneous injection that creates a high NOx generating environment within the combustion chamber(s) 17 a. Although the timing of the injection can vary, the first injection may occur generally at 40-80° before top dead center of the compression stroke in the preferred embodiment with the mixed-mode fuel injector(s) 20 a. Because the first injection is preferably injected in the second spray pattern 52 as shown in FIG. 5, the fuel will spray at a relatively small average angle with respect to the centerline 40 of the combustion chamber(s) 17 a, thereby reducing the risk of spraying the walls of the cylinder(s) 15 a and piston(s) 13 a. However, with the conventional fuel injector, the fuel will be injected in the conventional spray pattern with the relatively large angle with respect to the centerline 40. In order to avoid spraying the walls of the cylinder(s) 15 a and the piston(s) 13 a, the first injection from the conventional fuel injector will occur generally between 40-60° before top dead center of the compression stroke. Thus, with the mixed-mode injector, the first injection can occur earlier than with a conventional injector without diluting engine lubricating oil due to wall wetting and allowing more time for the fuel within the first injection to mix with the air in the cylinder. Generally, the first injection will include 20-80% of the total amount of fuel injected in each engine cycle, with 20% being at the high engine speeds and loads and 80% being at the low engine speeds and loads. Regardless of whether a conventional or the preferred mixed-mode fuel injection is used, because the first injection occurs during non-auto ignition conditions, the fuel within the combustion chamber(s) 17 a will have time to partially mix with the air prior to ignition.
As the engine piston(s) 13 a advance during the compression stroke, the fuel from the first fuel injection will combust. Generally, the first fuel injection will combust around 20-25° before top dead center of the compression stroke. Preferably, during or soon after combustion of the first fuel injection while the combustion chamber 17 a is relatively hot, the high NOx generation algorithm 55 will signal the fuel injector(s) 20 a to inject in the second spray pattern, being the conventional spray pattern. The second electrical actuator 51 will be activated, thereby lifting the inner direct needle valve member 44 off its seat and opening the conventional nozzle outlet set 43. Regardless of whether the fuel injector is the preferred mixed-mode fuel injector 20 a or a conventional injector, the fuel will be injected at a relatively small angle with respect to the centerline 40 of the combustion chamber(s) 17 a. It has been found that the combination of the semi-homogeneous first injection followed by the conventional second injection during or shortly after the first combustion creates a greater NOx concentration within the exhaust than either of the first or second injection alone.
As the engine piston(s) 13 a retract during an expansion stroke and/or advance during an exhaust stroke, the combustion chamber(s) 17 a will return to a non-combustible environment. It should be appreciated that the electronic control module 30 may signal the fuel injector(s) 20 a to inject an additional amount of fuel in the non-combustible environment during at least one of the expansion stroke and an exhaust stroke. Since the engine piston(s) 13 a will be at a relatively substantial distance from top dead center of the compression stroke when the combustion chamber(s) 17 a are in the non-combustible environment, the fuel injectors will preferably inject the fuel in the first spray pattern, avoiding spraying the piston(s) 13 a and cylinder walls. The advancing piston(s) 13 a during the exhaust stroke can push the exhaust with the high NOx concentration 66 and the amount of unbumt fuel out of the combustion chamber(s) 17 a and into the first exhaust manifold 27 via an open exhaust valve. This unbumt fuel can create the rich exhaust conditions desirable for NOx to ammonia conversion without the need for the additional fuel injector 20 c within the exhaust passage 18 a. However, in the illustrated embodiment of FIGS. 1 and 2, unburnt fuel is added to the exhaust by injecting the fuel into the first exhaust passage 18 a downstream from the combustion chamber(s) 17 a. The electronic control module 30 can signal the additional fuel injector 20 c to inject the additional amount of fuel in order to create the rich conditions desirable for NOx to ammonia conversion over the ammonia-producing catalyst 29. It should be appreciated that the rich exhaust conditions can be created by other methods, such as injecting more fuel within the predetermined high NOx generation sequence. Although the predetermined high NOx generation sequence 57 can create rich conditions within the exhaust from the combustion chamber(s) 17 a, preferably the predetermined high NOx generation sequence 57 creates a slightly lean exhaust, and unburnt fuel is added thereafter.
The high NOx within the exhaust from the combustion chamber(s) 17 a of the first power-producing portion 11, 111 is converted to ammonia by passing the exhaust over the ammonia-producing catalyst 29 within the first exhaust passage 18 a. In the rich conditions created by the addition of the unburnt fuel, the NOx to ammonia conversion within the first exhaust passage 18 c is approximately 1:1. The exhaust from the first power-producing portion 11, 111 will be combined with the exhaust from the second power-producing portion 12, 112 and passed over the NOx selective catalyst 19 within the merged exhaust passage 18 c. Those skilled in the art will appreciate that the NOx selective catalyst 19 uses the ammonia, and any other related reductants within the merged exhaust, to reduce the NOx to harmless gases, such as nitrogen and water, that are emitted from the exhaust tail pipe.
If the high NOx generation algorithm 55 determines that the expected NOx concentration 54 is less than the predetermined threshold NOx concentration 39, the alternative operation algorithm 36 will produce the low NOx production amount 64. If the expected NOx concentration 54 is less than the predetermined threshold NOx concentration 39, the ammonia needed to reduce the NOx within the second power-producing portion exhaust is minimal. Those skilled in the art will appreciate that there are certain low-power situations, such as idle, in which the NOx concentration 54 in the exhaust from the second engine 12, 112 is so low that it need not be further reduced by the NOx selective catalyst 19. Thus, the alternative operation algorithm 36 of the high NOx generation algorithm 55 will signal the first power-producing portion 11, 111 to provide the first power output 16, 161 while producing exhaust with the low NOx production amount 64, or the first power producing portion is temporarily turned off all together, or vice versa.
Although the present disclosure contemplates various methods of decreasing the NOx concentration within the exhaust from the first power-producing portions 11, 111, such as ceasing operation of the first engine 111, the fuel injectors 20 a could inject fuel in predetermined NOx injection strategies to create various first power outputs 61, 161. Those skilled in the art will appreciate that conventional injection strategies produce less NOx than the known high NOx generation sequence 57. For instance, injecting once or more in the vicinity of top dead center of the compression stroke can create the low NOx production amount 64 while also creating the first power output 61, 161. Moreover, the alternative operation algorithm 36 could inject fuel in the illustrated predetermined low NOx generation sequence 58 including the first injection during non-auto ignition conditions and the second injection during auto-ignition conditions and after the combustion chambers 17 a have cooled. Using a conventional fuel injector, the first injection can be injected around 40° before top dead center of the compression stroke. Using the mixed-mode fuel injectors 20 a, the first injection can occur earlier, such as 80° or 60° before top dead center. At lower desired first power output 61, 161, more fuel can be apportioned to the first injection and the first injection can occur earlier in the engine cycle. Regardless of whether a conventional or mixed-mode fuel injector 20 a is used, the second injection generally occurs after top dead center. Because the NOx concentration 54 is less than the predetermined NOx concentration 39, there is no need to further reduce the NOx concentration 54 with ammonia, and thus, no need to operate the first power-producing portion 111, 11 in a manner to create the high NOx concentration 66.
The present disclosure is advantageous because it provides on-board generation of ammonia for reduction of NOx without compromising the power output or performance of the engine system 10, 110. The present disclosure provides an engine system 10, 110 with an electronic control module 30 that can control one portion 11, 111 of the engine system 10, 110 to produce NOx for exhaust purification while controlling another portion 12, 112 of the engine system 10, 110 to produce the power output of the engine system 10, 110. Because a significant amount of NOx can be produced from the predetermined high NOx generation sequence 55, the first power-producing portion 11, 111 used to create the NOx can be relatively small and produce less exhaust. Because only a small percentage of the exhaust stream is needed to create the desired NOx concentration, less fuel is need to create the rich conditions required for ammonia production over the ammonia-producing catalyst 29. The reduced fuel penalty conserves fuel and reduces the cost of the exhaust after-treatment system. Moreover, the power output. 61 of the first power-producing portion 11, 111 is not wasted, but rather coupled to the power output 62 of the second power-producing portion 12, 112 or used to power an auxiliary apparatus, such as a pump.
It should be understood that the above description is intended for illustrative purposes only, and is not intended to limit the scope of the present invention in any way. Thus, those skilled in the art will appreciate that other aspects, objects, and advantages of the invention can be obtained from a study of the drawings, the disclosure and the appended claims

Claims

1. An engine system comprising:

at least one engine including a first power-producing portion and a second power-producing portion, and at least the first power-producing portion including at least one fuel injector operable to inject fuel into at least one combustion chamber;

at least one electronic control module including a high NOx generation algorithm in communication with the first power-producing portion and a low NOx generation algorithm in communication with the second power-producing portion; and

the high NOx generation algorithm being operable to signal the at least one fuel injector within the first power-producing portion to inject fuel into the at least one combustion chamber in a predetermined high NOx generation sequence including an injection during non-auto ignition conditions.

2. The engine system of claim 1 wherein the first power-producing portion and the second power-producing portion being operable to run simultaneously.

3. The engine system of claim 1 wherein the predetermined high NOx generation sequence includes a first injection being the injection during non-auto ignition conditions and a second injection during auto ignition conditions.

4. The engine system of claim 3 wherein the high NOx generation algorithm being operable to create relatively lean combustion conditions.

5. The engine system of claim 3 wherein the at least one fuel injector includes a mixed-mode fuel injector being operable to inject fuel in a first spray pattern with a relative small average angle relative to a centerline of the combustion chamber, and a second spray pattern with a relative large average angle relative to the centerline of the combustion chamber; and

the predetermined high NOx generation sequence includes the first injection in the first spray pattern and the second injection in the second spray pattern.

6. The engine system of claim 1 wherein the first power-portion includes a low-displacement portion, and the second power-producing portion includes a high-displacement portion.

7. The engine system of claim 6 wherein the low NOx generation algorithm being based, at least in part, on a desired power output of the engine system.

8. The engine system of claim 1 wherein the first power-producing portion of the at least one engine includes a first engine, and the second power-producing portion of the at least one engine includes a second engine.

9. The engine system of claim 1 wherein the at least one engine includes a single engine with a plurality of fuel injectors associated with a plurality of combustion chambers, the first power-producing portion includes a first portion of the plurality of fuel injectors including the at least one fuel injector, and the second power-producing portion includes a second portion of the plurality of fuel injectors; and

the low NOx generation algorithm being operable to signal the second portion of fuel injectors to inject in a predetermined low NOx generation sequence.

10. The engine system of claim 1 including a first exhaust passage and a second exhaust passage fluidly connecting the first power-producing portion and the second power-producing portion of the at least one engine to a merged exhaust passage, respectively; and

a reductant-producing catalyst being positioned within the first exhaust passage, and a NOx selective catalyst being positioned within the merged exhaust passage.

11. The engine system of claim 10 wherein the high NOx generation algorithm includes a setting algorithm operable to set a high NOx production amount from the first power-producing portion to correspond to an ammonia production amount operable to reduce an expected NOx concentration from the second power-producing portion.

12. The engine system of claim 11 wherein the high NOx generation algorithm includes an alternative operation algorithm being operable to produce a low NOx production amount from the first power-producing portion when the expected NOx concentration is less than a predetermined threshold NOx concentration.

13. The engine system of claim 11 including a NOx sensor positioned within the low NOx section of the exhaust passage and being in communication with the electronic control module.

14. The engine system of claim 13 wherein the first power-producing portion and the second power-producing portion being operable to run simultaneously;

the at least one fuel injector of the first power-producing portion includes a mixed-mode fuel injector being operable to inject fuel in a first spray pattern with a relative small average angle relative to a centerline of the combustion chamber, and a second spray pattern with a relative large average angle relative to the centerline of the combustion chamber; and

the predetermined high NOx generation sequence includes the first injection being the injection during non-auto ignition conditions in the first spray pattern and a second injection in the second spray pattern during auto-ignition conditions.

15. A method of operating an engine system:

controlling a first power-producing portion of at least one engine to produce exhaust with a high NOx concentration, at least in part, by signaling at least one fuel injector to inject fuel in a predetermined high NOx generation sequence including an injection during non-auto ignition conditions; and

controlling a second power-producing portion of the at least one engine to produce exhaust with a low NOx concentration.

16. The method of claim 15 including a step of operating the first power-producing portion and the second power-producing portion simultaneously.

17. The method of claim 15 wherein the step of controlling the first power-producing portion includes a step of signaling at least one fuel injector to inject a first injection being the injection during non-auto ignition conditions within at least one combustion chamber and a second injection during auto-ignition conditions within the at least one combustion chamber.

18. The method of claim 15 wherein the step of controlling the second power-producing portion includes a step of signaling at least one fuel injector to inject fuel in a predetermined low NOx generation sequence based, at least in part, on a desired power output of the engine system.

19. The method of claim 15 includes the steps of:

passing the exhaust from the first power-producing portion over a reductant-producing catalyst;

combining the exhaust from the first power-producing portion with the exhaust from the second power-producing portion; and

passing the combined exhaust over a NOx selective catalyst.

20. The method of claim 15 includes a step of controlling the first power-producing portion to produce a low NOx production amount when an expected concentration of NOx from the second power-producing portion is less than a predetermined threshold NOx concentration.