Engine cold start system and method

Abstract

The present disclosure provides an "Engine Cold Start System and Method". A method and system for reducing emissions from an internal combustion engine is described. In one example, a burner is applied after shutdown to extract stored NOx from a passive NOx adsorber in preparation for a subsequent engine start. The trapped NOx is then reduced via a selective catalytic reduction catalyst.

Description

Technical Field

[0001] The present description generally relates to methods and systems for cold starting an internal combustion engine. Background Art

[0002] Cold start emissions from an internal combustion engine may account for a significant portion of the emissions exiting the tailpipe of a vehicle. The engine may be operated in a manner that increases the engine heat output so that the engine aftertreatment device may start more quickly after a cold start of the engine, but even with the engine operation adjustments, the tailpipe emissions may be higher than desired. One way to more quickly increase the operating temperature of the engine aftertreatment device may be to use a burner in parallel with the engine. However, the burner may generate its own emissions, which may contribute to the vehicle tailpipe emissions. Therefore, it may be desirable to provide an emissions control system that can warm the engine aftertreatment system at the speed of a system including the burner, but generate lower tailpipe emissions. Summary of the invention

[0003] The inventors of this document have recognized the above-mentioned shortcomings and have developed an exhaust system for an internal combustion engine, the exhaust system comprising: a burner air pump, which selectively supplies air to a burner positioned along a first channel; a second channel, which is arranged in parallel with the first channel; a three-way valve, which is connected to the first channel and the second channel downstream of the burner; a third channel, which is positioned downstream of the three-way valve; a fourth channel, which is positioned in parallel with the third channel, and the third channel and the fourth channel are fluidly connected to a fifth channel, and the fifth channel is fluidly connected to the engine exhaust channel; a passive NOx adsorber (PNA), which is positioned along the engine exhaust channel; a selective catalytic reduction (SCR) catalyst, which is positioned downstream of the PNA along the engine exhaust channel; and a NOx sensor, which is positioned downstream of the SCR along the engine exhaust channel.

[0004] By equipping a vehicle with a burner, an electric heater, an oxidation catalyst, and a passive NOx adsorber (PNA), a technical result of rapidly heating an aftertreatment device in an engine exhaust passage and NOx generated by the burner in the PNA can be provided, so that NOx can be reduced at a later time when a downstream SCR is activated. Thus, the burner can heat the engine aftertreatment device more quickly, so that engine starting can occur more quickly, and so that less NOx generated by the burner can leave the vehicle exhaust tailpipe.

[0005] The present description may provide several advantages. Specifically, the method may reduce tailpipe emissions by treating burner emissions. Additionally, the method may enable a lower engine emission start more quickly after requesting engine aftertreatment device warm-up. Furthermore, the method provides a way to extract PNA after an engine shutdown request so that PNA can be ready to store NOx during a subsequent engine restart.

[0006] The above advantages and other advantages and features of the present specification will be readily apparent from the following detailed description when read alone or in conjunction with the accompanying drawings.

[0007] It should be understood that the above summary is provided to introduce a series of concepts further described in the detailed description in a simplified form. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is uniquely defined by the claims following the detailed description. Furthermore, the claimed subject matter is not limited to embodiments that address any disadvantages described above or in any part of this disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 A detailed schematic diagram of an example engine is shown;

[0009] Figure 2 Shows Figure 1 a schematic diagram of an example exhaust system configuration for an example engine;

[0010] Figure 3 Shown according to Figure 4 An example sequence of operations for the method;

[0011] Figure 4 A flow chart showing a method for preparing an engine exhaust system for an engine restart is shown; and

[0012] Figure 5 A flow chart of a method for starting an engine is shown. DETAILED DESCRIPTION

[0013] This instruction manual relates to operating the engine and exhaust system aftertreatment devices during engine shutdown and in preparation for a cold engine start. Figure 1 An example engine is shown in FIG. Figure 2 The Figure 1 An example exhaust system for an engine. Figure 3 It is shown in Figure 4 An example sequence of operations for the method and Figure 1 and Figure 2 system. Figure 4 and Figure 5A method for operating an engine and aftertreatment system including a PNA is shown.

[0014] refer to Figure 1 , an internal combustion engine 10 (which includes a plurality of cylinders, Figure 1 The electronic engine controller 12 controls the cylinders of the engine. Figure 1 and Figure 2 The controller 12 also uses various sensors to receive signals. Figure 1 and Figure 2 Various actuators are used to adjust engine and vehicle operation based on received signals and instructions stored in the controller's memory.

[0015] Engine 10 includes combustion chamber 30 and cylinder walls 32, with piston 36 positioned in the cylinder walls and connected to crankshaft 40. Cylinder head 13 is fastened to engine block 14. Combustion chamber 30 is shown as being in communication with intake manifold 44 and exhaust manifold 48 via respective intake valve 52 and exhaust valve 54. Each intake valve and exhaust valve may be operated by an intake cam 51 and an exhaust cam 53. However, in other examples, the engine may operate the valves via a single camshaft or pushrod. The position of intake cam 51 may be determined by intake cam sensor 55. The position of exhaust cam 53 may be determined by exhaust cam sensor 57. Intake poppet valve 52 may be operated by variable valve activation / deactivation actuator 59. Similarly, exhaust poppet valve 54 may be operated by variable valve activation / deactivation actuator 58. For one or more complete engine cycles (e.g., two engine revolutions), intake poppet valve 52 and exhaust poppet valve 54 may be deactivated and maintained in a closed position, thereby preventing flow into and out of cylinder 30, thereby deactivating cylinder 30. When cylinder 30 is deactivated, fuel flow to cylinder 30 may also be stopped.

[0016] Fuel injector 68 is shown positioned in cylinder head 13 to inject fuel directly into combustion chamber 30, which is known to those skilled in the art as direct injection. Fuel is delivered to fuel injector 68 by a fuel system including fuel tank 26, a low pressure fuel pump (not shown), a high pressure fuel pump 21, a fuel pump flow control valve 25, and a fuel rail (not shown).

[0017] The engine intake system 9 includes an intake manifold 44, a throttle 62, a grid heater 16, a charge air cooler 163, a turbocharger compressor 162, and an intake plenum 42. The intake manifold 44 is shown in communication with an optional electronic throttle 62, which adjusts the position of the throttle plate 64 to control the air flow from the intake plenum 46. The compressor 162 draws air from the intake plenum 42 to supply the plenum 46. The compressor vane actuator 84 adjusts the position of the compressor vanes 19. The exhaust rotates the turbine 164, which is coupled to the turbocharger compressor 162 via a shaft 161. In some examples, a charge air cooler 163 may be provided. In addition, an optional grid heater 16 may be provided to warm the air entering the cylinder 30 when the engine 10 is cold started. The compressor speed may be adjusted by adjusting the position of the turbine variable vane control actuator 78 or the compressor recirculation valve 158. In an alternative example, the wastegate 79 may replace the turbine variable vane control actuator 78 or be used in addition thereto. The turbine variable vane control actuator 78 adjusts the position of the variable geometry turbine vane 166. When the vane is in the open position, the exhaust gas can pass through the turbine 164, supplying little energy to rotate the turbine 164. When the vane 166 is in the closed position, the exhaust gas can pass through the turbine 164 and exert an increased force on the turbine 164. Alternatively, the wastegate 79 or bypass valve may allow the exhaust gas to flow around the turbine 164 so as to reduce the amount of energy supplied to the turbine. The compressor recirculation valve 158 allows the compressed air at the outlet 15 of the compressor 162 to return to the inlet 17 of the compressor 162. Alternatively, the position of the turbine variable vane actuator 78 may be adjusted to change the efficiency of the compressor 162. In this way, the efficiency of the compressor 162 may be reduced so as to affect the flow of the compressor 162 and reduce the possibility of compressor surge. In addition, by returning the air to the inlet 17 of the compressor 162, the work performed on the air can be increased, thereby raising the temperature of the air. An optional motor 165 is also shown coupled to the shaft 161. When the engine 10 is not rotating, when the engine 10 is rotating at a low speed (e.g., a cranking speed such as 250 RPM), or when the exhaust energy is low, the optional motor 165 can rotate the compressor 162 to provide additional boost. Air flows into the engine 10 in the direction of arrow 5.

[0018] Flywheel 97 and ring gear 99 are coupled to crankshaft 40. Starter 96 (e.g., a low voltage (operating at less than 30 volts) motor) includes pinion shaft 98 and pinion 95. Pinion shaft 98 can selectively advance pinion 95 to engage ring gear 99 so that starter 96 can rotate crankshaft 40 during engine cranking. Starter 96 can be mounted directly to the front of the engine or the rear of the engine. In some examples, starter 96 can selectively supply torque to crankshaft 40 via a belt or chain. In one example, when not engaged to the engine crankshaft, starter 96 is in a basic state. Engine start / stop can be requested via a human-machine interface (e.g., a key switch, a button, a remote radio frequency transmission device, etc.) 69 or in response to vehicle operating conditions (e.g., a foot lever position, a driver demand pedal position, a battery SOC, etc.). Battery 8 can supply power to starter 96 and motor 165. Controller 12 can monitor the battery state of charge.

[0019] Combustion is initiated in combustion chamber 30 when the fuel auto-ignites via the combustion chamber temperature reaching the auto-ignition temperature of the fuel injected into cylinder 30. The temperature in the cylinder increases as piston 36 approaches top dead center compression stroke. In some examples, universal exhaust gas oxygen (UEGO) sensor 126 may be coupled to exhaust manifold 48 upstream of engine aftertreatment device 71. In other examples, the UEGO sensor may be located downstream of one or more exhaust aftertreatment devices. Further, in some examples, the UEGO sensor may be replaced by a NOx sensor having both a NOx sensing element and an oxygen sensing element.

[0020] At lower engine temperatures, optional glow plug 66 can convert electrical energy into thermal energy to create a hot spot next to one of the fuel spray cones of the injector in the combustion chamber 30. By creating a hot spot next to the injected fuel in the combustion chamber 30, the fuel spray plume in the cylinder can be more easily ignited, thereby releasing heat that propagates throughout the cylinder, raising the temperature in the combustion chamber, and improving combustion. Cylinder pressure can be measured via optional pressure sensor 67, which can alternatively or additionally sense cylinder temperature.

[0021] In one example, the engine aftertreatment device 71 can be a selective catalytic reduction catalyst (SCR), which can be referred to as an upstream SCR. The engine aftertreatment device 72 can be an oxidation catalyst or a three-way catalyst, which can be referred to as a diesel exhaust catalyst. The engine aftertreatment device 73 can be a passive NOx adsorber (PNA), which can be composed of a palladium-exchanged zeolite. The engine aftertreatment device 74 can be an SCR, which can be referred to as a downstream SCR. The exhaust flows in the direction of arrow 7. The burner system 199 can supply heated air to the aftertreatment device via a channel or conduit 198 upstream of the engine aftertreatment devices 71 to 74 and downstream of the turbine 164. The channel or conduit 198 can merge into the exhaust channel or conduit 185.

[0022] Exhaust gas recirculation (EGR) may be provided to the engine via a high pressure EGR system 83. The high pressure EGR system 83 includes an EGR valve 80, an EGR passage 81, and an EGR cooler 85. The EGR valve 80 is a valve that blocks or allows exhaust gas to flow from upstream of the engine aftertreatment device 71 to a location in the engine intake system downstream of the compressor 162. The EGR may be cooled by passing through the EGR cooler 85. EGR may also be provided via a low pressure EGR system 75. The low pressure EGR system 75 includes an EGR passage 77 and an EGR valve 76. The low pressure EGR may flow from downstream of the engine aftertreatment device 71 to a location upstream of the compressor 162. The low pressure EGR system 75 may include an EGR cooler 89.

[0023] The controller 12 Figure 11 is shown as a conventional microcomputer, including: a microprocessor unit 102, input / output ports 104, read-only memory (eg, non-transitory memory) 106, random access memory 108, keep alive memory 110, and a conventional data bus. Controller 12 is shown receiving various signals from sensors coupled to engine 10 in addition to those signals previously discussed, including: engine coolant temperature (ECT) from temperature sensor 112 coupled to cooling sleeve 114; position sensor 134 coupled to driver demand pedal 130 for sensing driver demand pedal position adjusted by a person's foot 132; a measurement of engine manifold pressure (MAP) from pressure sensor 121 coupled to intake manifold 44 (alternatively or additionally, pressure sensor 121 may sense intake manifold temperature); boost pressure from pressure sensor 122; exhaust oxygen content from oxygen sensor 126; engine position sensor from engine position sensor 118 sensing position of crankshaft 40; a measurement of air mass entering the engine from sensor 120 (e.g., a hot wire air flow meter); and a measurement of throttle position from sensor 60. Barometric pressure may also be sensed (sensor not shown) for processing by controller 12. In a preferred aspect of the present description, engine position sensor 118 produces a predetermined number of equally spaced pulses every revolution of the crankshaft from which engine speed (RPM) can be determined.

[0024] The controller 12 may receive data and requests from a remote device 86 external to the vehicle to which the controller and engine belong. The remote device 86 may be a key fob, a cloud server, a phone, or other device. The request may include an engine cold start preparation request, an engine start request, etc.

[0025] During operation, each cylinder within engine 10 typically undergoes a four-stroke cycle: the cycle includes an intake stroke, a compression stroke, an expansion stroke, and an exhaust stroke. During the intake stroke, generally, exhaust valve 54 is closed and intake valve 52 is opened. Air is introduced into combustion chamber 30 via intake manifold 44, and piston 36 moves to the bottom of the cylinder to increase the volume within combustion chamber 30. The position of piston 36 near the bottom of the cylinder and at the end of its stroke (e.g., when combustion chamber 30 is at its largest volume) is typically referred to by those of skill in the art as bottom dead center (BDC). During the compression stroke, intake valve 52 and exhaust valve 54 are closed. Piston 36 moves toward the cylinder head to compress the air within combustion chamber 30. The point at which piston 36 is at the end of its stroke and closest to the cylinder head (e.g., when combustion chamber 30 is at its smallest volume) is typically referred to by those of skill in the art as top dead center (TDC). In a process hereinafter referred to as injection, fuel is introduced into the combustion chamber. In some examples, fuel may be injected into a cylinder multiple times during a single cylinder cycle.

[0026] In a process hereinafter referred to as ignition, the injected fuel is ignited by compression ignition, resulting in combustion. During the expansion stroke, the expanding gases push piston 36 back to BDC. Crankshaft 40 converts piston movement into rotational torque of the rotating shaft. Finally, during the exhaust stroke, exhaust valve 54 opens to release the combusted air-fuel mixture to exhaust manifold 48, and the piston returns to TDC. It should be noted that the above is described only as an example, and the intake and exhaust valve opening and / or closing timings may vary, such as to provide positive or negative valve overlap, late intake valve closing, or various other examples. Further, in some examples, a two-stroke cycle may be used instead of a four-stroke cycle.

[0027] Reference now Figure 2 , a detailed schematic diagram of the burner system 199 is shown. Electrical connections are shown via dashed lines. Components including conduits or channels are shown via solid lines. Fluid communication can occur between connected conduits or channels. The burner system 199 can supply heated air and / or combustion gases to heat the engine aftertreatment devices 71 to 74. The controller 12 can adjust the operating states of the valves, injectors, pumps, igniters, and burners to operate the burner system 199.

[0028] The burner system includes a burner air pump 202 that supplies fresh air to the burner 208 via a first passage 250 and a burner flow control valve 204. A bypass passage or conduit 252 is arranged in parallel with the passage or conduit 250. The passage or conduit 252 allows fresh air to mix with the output gas of the burner 208, thereby controlling the temperature of the gas flowing to the three-way valve 210. In this way, the passage or conduit 252 allows dilution and cooling of the gas leaving the burner 208. The bypass flow control valve 203 controls the air flow through the bypass passage 252. The burner flow control valve 204 and the bypass flow control valve 203 can be cycled open and closed (e.g., modulated) to control the air flow into the burner 208 and the dilution / cooling of the gas leaving the burner 208 before the gas flows through the three-way valve 210.

[0029] Figure 2 The burner system of the invention provides the advantage of adjusting the temperature of the gas entering the three-way valve 210 by controlling the mixing of the fresh air flow from the burner air pump 202 with the combustion gases exiting the burner 208. When the burner 208 is started (e.g., burning fuel to generate heat), this may be beneficial in controlling the temperature of the burner aftertreatment device 214 (e.g., a burner oxidation catalyst).

[0030] Fuel injector 206 may provide fuel to combustor 208 to mix with air, which may be supplied via combustor air pump 202. Igniter 207 may initiate combustion within combustor 208.

[0031] Air or a combination of air and combustion gases may be delivered to three-way valve 210. Three-way valve 210 may be closed in a first position, preventing flow through aftertreatment bypass passage or conduit 254 and through burner aftertreatment passage or conduit 252. When three-way valve 210 is in a second position, three-way valve 210 may deliver air and / or combustion gases to passage or conduit 252 instead of passage or conduit 254. When three-way valve 210 is in a third position, three-way valve 210 may deliver air and / or combustion gases to passage or conduit 254 instead of passage or conduit 252.

[0032] The passage or conduit 253 may be referred to as a burner aftertreatment bypass passage or conduit. During conditions where the temperature of the engine aftertreatment devices 71 to 74 exceeds their light-off temperature, but the heat output of the engine is low and the temperature of the engine aftertreatment devices 71 to 74 cannot be maintained, air or burner byproducts may be directed through the bypass passage or conduit 253 instead of through the burner aftertreatment passage or conduit 254. The electric heater 212 and the burner aftertreatment device 214 (e.g., a diesel oxidation catalyst or a three-way catalyst) are positioned along the passage or conduit 252. The burner aftertreatment device 214 may be referred to as a burner aftertreatment device (e.g., a burner oxidation catalyst) because they are configured to treat burner gases, while the engine aftertreatment devices 71 to 74 may be referred to as an engine aftertreatment device because they are configured to treat engine exhaust. The passage or conduit 252 and the passage or conduit 253 are combined or merged into the passage or conduit 198 before entering the exhaust passage or conduit 185. Passage 252 may be provided to reduce the likelihood of catalyst degradation when burner 208 is operated under high power / warm exhaust conditions.

[0033] The exhaust passage or conduit 185 includes an upstream urea injector 236, an upstream NOx sensor 237, a downstream urea injector 238, and a downstream NOx sensor 239. The urea injector 236 can supply urea 240 to the engine aftertreatment device 71 (e.g., an upstream SCR catalyst), which can be referred to as an engine selective catalytic reduction catalyst because it is configured to reduce NOx from the engine 10. The urea injector 238 can supply urea 240 to the engine aftertreatment device 74 (e.g., a downstream SCR catalyst), which can also be referred to as an engine selective catalytic reduction catalyst. The passage or conduit is arranged to place the burner system 199 in parallel with the engine 10. The exhaust and burner gases flow in the direction indicated by the arrows placed along the passage or conduit.

[0034] Temperature sensors 280-284 indicate the temperature of burner aftertreatment device 214, engine aftertreatment device 73 (eg, PNA), and engine aftertreatment device 74 (eg, downstream SCR). Alternatively or additionally, the temperature of devices within engine exhaust passage 185 and burner system 199 may be inferred.

[0035] Figure 1 and Figure 2The system provides an exhaust system for an internal combustion engine, the exhaust system comprising: a burner air pump, the burner air pump selectively supplies air to a burner positioned along a first passage; a burner, the burner positioned along the first passage downstream of the burner air pump; a second passage, the second passage arranged in parallel with the first passage; a three-way valve, the three-way valve coupled to the first passage and the second passage downstream of the burner; a third passage, the third passage positioned downstream of the three-way valve; a fourth passage, the fourth passage positioned in parallel with the third passage, the third passage and the fourth passage fluidly coupled to a fifth passage, the fifth passage fluidly coupled to an engine exhaust passage; a passive NOx adsorber (PNA), the adsorber positioned along the engine exhaust passage; a selective catalytic reduction (SCR) catalyst, the catalyst positioned downstream of the PNA along the engine exhaust passage; and a NOx sensor, the NOx sensor positioned downstream of the SCR along the engine exhaust passage. In a first example, the exhaust system comprises: wherein the PNA is composed of a palladium-exchanged zeolite. In a second example, which may include the first example, the exhaust system further includes: an electric heater, the electric heater is positioned along the fourth passage; and an oxidation catalyst, the oxidation catalyst is positioned downstream of the electric heater along the fourth passage. In a third example, which may include one or both of the first and second examples, the exhaust system further includes a urea injector, the urea injector is positioned downstream of the PNA and upstream of the SCR along the engine exhaust system. In a fourth example, which may include one or more of the first to third examples, the exhaust system further includes: a first flow control valve, the first flow control valve is positioned upstream of the burner along the first passage; and a second flow control valve, the second flow control valve is positioned along the second passage. In a fifth example, which may include one or both of the first to fourth examples, the exhaust system further includes: a diesel exhaust catalyst, the diesel exhaust catalyst is positioned upstream of the PNA along the engine exhaust passage. In a sixth example, which may include one or more of the first to fifth examples, the exhaust system further includes: a second SCR, the second SCR is positioned upstream of the PNA along the engine exhaust passage. In a seventh example, which may include one or more of the first to sixth examples, the exhaust system further includes a urea injector positioned along the engine exhaust passage upstream of the second SCR.

[0036] Reference now Figure 3 , showing that according to Figure 4 The method operates Figure 1 and Figure 2An example of a system that predicts vehicle operation sequences. Figure 3 The sequence of operations can be Figure 1 and Figure 2 One of the systems and execute Figure 4 The instructions of the method described are used to generate. Figure 3 The graphs of are aligned in time and occur simultaneously. The vertical marks at t0 to t5 indicate times of particular interest during the sequence.

[0037] from Figure 3 The first graph from the top of is a graph of engine operating state versus time. The vertical axis represents the engine operating state, and when the trace 302 is at a higher level near the vertical axis arrow, the engine is started (e.g., burning fuel and spinning). When the trace 302 is at a lower level near the horizontal axis, the engine is not started. The horizontal axis represents time, and time increases from the left side of the graph to the right side of the graph. The trace 302 represents the engine operating state.

[0038] from Figure 3 The second graph from the top of FIG. 3 is a graph of downstream SCR temperature versus time. The vertical axis represents downstream SCR temperature, and downstream SCR temperature increases in the direction of the vertical axis arrow. The horizontal axis represents time, and time increases from the left side of the graph to the right side of the graph. Trace 304 represents downstream SCR temperature. Dashed line 350 represents a threshold downstream SCR temperature, such as a downstream SCR light-off temperature, where the light-off temperature is a temperature at which the aftertreatment device exhibits a threshold efficiency (e.g., a conversion efficiency of 50 mol % for a particular gas species).

[0039] from Figure 3 The third graph from the top of is a graph of burner diesel oxidation catalyst (DOC) temperature versus time. The vertical axis represents burner DOC temperature, and the burner DOC temperature increases in the direction of the vertical axis arrow. The horizontal axis represents time, and time increases from the left side of the graph to the right side of the graph. Trace 306 represents the burner DOC temperature. Dashed line 352 represents a threshold burner DOC temperature, where the light-off temperature is the temperature at which the burner DOC exhibits a threshold efficiency (e.g., a conversion efficiency of 50 mole % for NOx).

[0040] from Figure 3 The fourth graph from the top of FIG. 3 is a graph of passive NOx adsorber (PNA) temperature versus time. The vertical axis represents PNA temperature, and PNA temperature increases in the direction of the vertical axis arrow. The horizontal axis represents time, and time increases from the left side of the graph to the right side of the graph. The horizontal dashed line 354 represents the PNA extraction temperature (e.g., the temperature at which the PNA releases stored NOx).

[0041] from Figure 3 The fifth graph from the top of is a graph of the electric heater operating state versus time. The vertical axis represents the electric heater operating state, and when the trace 312 is at a higher level near the vertical axis arrow, the electric heater is activated. When the trace 312 is at a lower level near the horizontal axis, the electric heater is not activated. The horizontal axis represents time, and time increases from the left side of the graph to the right side of the graph. The trace 312 represents the electric heater operating state.

[0042] from Figure 3 The sixth graph from the top of FIG. 3 is a graph of burner operating state versus time. The vertical axis represents the burner operating state, and when the trace 314 is at a higher level near the vertical axis arrow, the burner is activated (e.g., burning fuel and generating heat). When the trace 314 is at a lower level near the horizontal axis, the burner is not activated. The horizontal axis represents time, and time increases from the left side of the graph to the right side of the graph. The trace 314 represents the burner operating state.

[0043] from Figure 3 The seventh graph from the top of FIG. 3 is a graph of urea injector operating state versus time. The vertical axis represents the urea injector operating state, and when the trace 316 is at a higher level near the vertical axis arrow, the urea injector is activated (e.g., urea is injected). When the trace 316 is at a lower level near the horizontal axis, the urea injector is not activated. The horizontal axis represents time, and time increases from the left side of the graph to the right side of the graph. The trace 316 represents the urea injector operating state.

[0044] from Figure 3 The eighth graph from the top of is a graph of burner air pump operating status versus time. The vertical axis represents the burner air pump status, and when the trace 318 is at a higher level near the vertical axis arrow, the burner air pump is activated. When the trace 318 is at a lower level near the horizontal axis, the burner air pump is not activated. The horizontal axis represents time, and time increases from the left side of the graph to the right side of the graph. Trace 318 represents the burner air pump operating status.

[0045] from Figure 3 The ninth graph from the top of FIG. 3 is a graph of downstream NOx content in the exhaust gas versus time. The vertical axis represents downstream NOx content, and downstream NOx content increases in the direction of the vertical axis arrow. The horizontal axis represents time, and time increases from the left side of the graph to the right side of the graph. The horizontal dashed line 356 represents a threshold NOx content level in the exhaust gas.

[0046] At time t0, the engine is running (e.g., spinning and burning fuel), and the downstream SCR temperature is low. The burner DOC temperature is also low, and the PNA temperature is low. The electric heater is not activated, and the burner is not activated. In addition, the urea injector is not activated, and the burner air pump is not activated. The downstream NOx level is low. Such operating conditions may indicate operating the engine at low load and low speed for a period of time.

[0047] At time t1, the engine is deactivated and the remaining operating conditions are unchanged. However, shortly after time t1, at time t2, the electric heater and the burner air pump are activated to begin extracting NOx from the PNA. In response to the downstream SCR temperature being below threshold 350 and the burner DOC temperature being below temperature threshold 352, the electric heater is activated. The burner remains deactivated, and the urea injector remains deactivated. Because the engine is deactivated, the downstream NOx level is at a lower level.

[0048] At time t3, the engine remains off and the burner DOC temperature reaches its threshold temperature. Therefore, the electric heater is deactivated and the burner is activated to increase the rate at which the engine PNA heats up, thereby facilitating extraction of NOx from the PNA. The burner air pump remains on, and the downstream SCR and burner DOC temperatures continue to increase. The urea injector remains off, and the PNA temperature remains below threshold 354. Downstream NOx levels remain low.

[0049] At time t4, the engine remains off and the PNA temperature exceeds its threshold temperature 356. Therefore, the burner is deactivated, but the burner air pump remains active to continue moving heat toward the PNA and downstream SCR. The urea injector is activated to support NOx reduction by the downstream SCR. The PNA begins to release NOx. The burner DOC temperature and downstream SCR temperature remain above their respective thresholds. The downstream NOx content increases above its threshold 358.

[0050] At time t5, the downstream NOx content upstream of the downstream SCR drops below threshold 356. Therefore, the PNANOx purging cycle begins to end. Specifically, the urea injector is deactivated, and the burner air pump is deactivated. The engine remains off and the burner DOC temperature continues to drop.

[0051] Thus, NOx may be purged from the PNA in response to an engine shutdown request so that the PNA may be ready to absorb or store NOx during a subsequent engine restart. PNA NOx purging may be performed after the engine is stopped (e.g., not spinning and not burning fuel) by heating the PNA via an electric heater and / or a burner.

[0052] Reference now Figure 4, a method for operating an engine and extracting a PNA is shown. Figure 4 The method may be implemented at least in part by storing Figure 1 and Figure 2 In addition, Figure 4 The method may include actions taken by the controller in the physical world to transform Figure 1 and Figure 2 The operating status of the system. Figure 4 The method can provide Figure 3 Method 400 may begin while the vehicle's engine is running (eg, burning fuel and spinning).

[0053] At 402, method 400 determines whether there has been a request to shut down the engine (e.g., a request to stop engine operation). If so, the answer is yes, and method 400 proceeds to 404. Otherwise, the answer is no, and method 400 proceeds to exit. In one example, the request to shut down the engine can be generated via an application button, leaving the vicinity of the vehicle, or via a key or other device.

[0054] At 404 , method 400 judges whether the temperature of the downstream SCR (eg, downstream SCR temperature) is greater than a threshold temperature. If so, the answer is yes and method 400 proceeds to 406 . Otherwise, the answer is no and method 400 proceeds to 420 .

[0055] At 406 , method 400 judges whether a diesel exhaust catalyst (eg, Figure 2 Is the aftertreatment device 72 (eg, oxidation catalyst) above a threshold temperature? If so, the answer is yes and method 400 proceeds to 408. Otherwise, the answer is no and method 400 proceeds to 420.

[0056] At 408 , method 400 proceeds via a diesel exhaust catalyst (eg, Figure 2 72) to extract NOx from the PNA. Specifically, if the air pump is inactive, method 400 starts the burner air pump. The burner is deactivated (e.g., not burning fuel and fuel injection to the burner is deactivated). Method 400 may also adjust valves 204, 203, and 210 so that air flows from the burner air pump 202 to the exhaust passage 185. The air may flow through passage 252 and passage 253. Alternatively, the air may flow through passage 250 and passage 254 on its way to the exhaust passage 185. Because the engine was recently running, the exhaust gas from the diesel exhaust catalyst (e.g., Figure 2 72) and directs it to the PNA (e.g., Figure 273). Downstream urea injector 238 may also be activated so that NOx can be reduced to N2 and H2O via engine aftertreatment device 74 (e.g., downstream SCR). Heat from the diesel exhaust catalyst may cause NOx to be released from the PNA and converted via the downstream SCR. Method 400 proceeds to 410.

[0057] At 410 , method 400 judges whether or not the NOx sensed via the downstream NOx sensor (eg, 239 ) is less than a threshold NOx level. If so, the answer is yes and method 400 proceeds to 412 . Otherwise, the answer is no and method 400 returns to 404 .

[0058] At 412, method 400 deactivates the burner (e.g., stops injecting fuel to the burner), deactivates the burner air pump, and deactivates the downstream urea injector to stop urea injection. NOx is extracted from the PNA, so the burner can be deactivated to save fuel, and the burner air pump and urea injector can be deactivated to save power and urea. Valves 203, 204, and 210 can also be adjusted to prevent flow through Figure 2 of channel 198. Method 400 proceeds to exit.

[0059] At 420 , method 400 judges whether the temperature of the burner DOC (eg, burner DOC temperature) is greater than a threshold DOC temperature (eg, DOC light-off temperature). If so, the answer is yes and method 400 proceeds to 430 . Otherwise, the answer is no and method 400 proceeds to 422 .

[0060] At 422 , method 400 activates a heater (eg, Figure 2 212) and burner air pump (e.g. Figure 2 The burner is deactivated. The diesel oxidation catalyst can be heated by activating the heater and starting the burner air pump (e.g. Figure 2 214), downstream SCR and PNA. In addition, upstream SCR, diesel exhaust catalyst (e.g., Figure 2 72) and PNA (e.g., Figure 2 73) can be ready to process emissions from the burner. In addition, valves 204 and 210 can be positioned to allow airflow through passage 254 without passing through passage 253 so that the oxidation catalyst can reach its threshold temperature (e.g., light-off temperature) more quickly. Method 400 returns to 420.

[0061] At 430, method 400 activates the burner air pump, deactivates the heater, and activates the burner. The burner may be activated by supplying fuel to the burner and igniting the air-fuel mixture in the burner via an igniter. Valves 204, 203, and 210 may be adjusted to allow air to flow from the burner air pump 202 to the burner 208 and to the burner aftertreatment device 214 without allowing air to flow through passage 253 and passage 252. The downstream urea injector and the upstream urea injector are also deactivated. Method 400 proceeds to 432.

[0062] At 432, method 400 determines the PNA (eg, Figure 2 The method 400 determines whether the temperature of the PNA (e.g., 73) is greater than a threshold PNA NOx storage temperature (e.g., a maximum desired NOx storage temperature). If so, the answer is yes, and the method 400 proceeds to 434. Otherwise, the answer is no, and the method 400 returns to 430. This decision allows the PNA to reach the maximum desired NOx storage temperature and maintain the PNA at the maximum desired NOx storage temperature so that the downstream SCR can reach operating temperature without extracting NOx from the PNA.

[0063] At 434 , method 400 judges whether the temperature of the downstream SCR (eg, downstream SCR temperature) is greater than a threshold temperature. If so, the answer is yes and method 400 proceeds to 436 . Otherwise, the answer is no and method 400 proceeds to 438 .

[0064] At 438 , method 400 turns the air pump on and turns off the burner and heater so that heat from the upstream device can be transferred to the downstream SCR. Method 400 returns to 432 .

[0065] At 436 , method 400 extracts NOx from the PNA. Method 400 may activate the downstream urea injector and supply urea to the downstream SCR before and while releasing NOx from the PNA. The burner remains activated and method 400 proceeds to 410 .

[0066] In this way, method 400 can extract NOx from the PNA in response to an engine stop so that the PNA can be ready to absorb NOx during a subsequent engine restart. The PNA can be first warmed by the electric heater and then warmed by the burner after the diesel oxidation catalyst reaches its light-off temperature so that the burner emissions can be treated. Therefore, the electric heater can make the treatment of the burner emissions more likely, thereby reducing tailpipe emissions during PNA purging.

[0067] Reference now Figure 5 , a method for preheating an engine aftertreatment system is shown. Figure 5 The method may be implemented at least in part by storing Figure 1 and Figure 2 In addition, Figure 5 The method may include taking a transformation in the physical world by the controller Figure 1 and Figure 2 Method 500 may begin when the vehicle's engine is stopped and not rotating.

[0068] At 502 , method 500 judges whether or not there has been a need to warm up the engine aftertreatment device (eg, Figure 1 71 to 74). If so, the answer is yes and method 500 proceeds to 504. Otherwise, the answer is no and method 500 proceeds to exit. In one example, a request to preheat the engine aftertreatment system may be generated in preparation for vehicle startup. The request to preheat the engine aftertreatment device may be generated by a vehicle operator, a cloud server, or other device. For example, a request to preheat the engine aftertreatment device may be generated in response to a person or device entering the vicinity of the device or based on a planned vehicle departure time.

[0069] At 504 , method 500 judges whether the downstream SCR temperature (eg, temperature of the downstream SCR) is greater than a threshold temperature (eg, catalyst light-off temperature or SCR light-off temperature). If so, the answer is yes and method 500 proceeds to 520 . Otherwise, the answer is no and method 500 proceeds to 506 .

[0070] At 520, method 500 determines whether the PNA NOx storage efficiency is greater than a threshold efficiency. If method 500 determines that the PNA NOx storage efficiency is greater than a threshold efficiency, the answer is yes and method 500 proceeds to 530. Otherwise, the answer is no and method 500 proceeds to 522. In one example, method 500 may estimate the PNA NOx storage efficiency by subtracting the amount of NOx flowing out of the PNA from the amount of NOx flowing into the PNA over a time interval and dividing the result by the total amount of NOx flowing into the PNA over the time interval. The amount of NOx flowing into and out of the PNA may be determined via the output of an upstream NOx sensor and a downstream NOx sensor.

[0071] At 522, method 500 extracts NOx from the PNA and injects urea via a downstream urea injector. During these conditions, the PNA may be filled with NOx, and NOx may leak through the PNA and reach the downstream SCR. The burner may have raised the temperature of the burner oxidation catalyst to above its light-off temperature and raised the temperature of the downstream SCR to above its light-off temperature. The NOx extracted by the PNA may be processed into N2 and H2O by the downstream SCR. To achieve NOx extraction of the PNA, method 500 adjusts the flow control valve 203 to reduce dilution air (e.g., enriching the burner air-fuel mixture) and increase the temperature of the gas leaving the burner. These actions may increase the PNA temperature to above the PNA light-off temperature. The downstream urea injector injects urea upstream of the downstream SCR. When the downstream NOx sensor output is less than the threshold NOx value, the PNA NOx extraction stops. Once the PNA NOx extraction stops, the burner is deactivated by stopping the fuel flow to the burner. The downstream urea injector is also deactivated. This allows the PNA temperature to drop so that the PNA can once again store NOx. Method 500 proceeds to 510 .

[0072] At 530, method 500 judges whether there is an engine start request. If so, the answer is yes and method 500 proceeds to 532. If not, the answer is no and method 500 returns to 502. The engine start request may be received from a remote device, a button, or a remote server.

[0073] At 532 , method 500 starts the engine via spinning the engine and supplying fuel to the engine. Method 500 deactivates the burner air pump, deactivates the electric heater, and deactivates the burner. Method 500 proceeds to exit.

[0074] At 506 , method 500 judges whether the burner oxidation catalyst has reached or exceeded its light-off temperature. If so, the answer is yes and method 500 proceeds to 508 . Otherwise, the answer is no and method 500 proceeds to 540 .

[0075] At 540, method 500 starts the burner air pump and electric heater. Method 500 may also adjust the positions of valves 203, 204, and 210 to allow flow through burner 208 and burner aftertreatment device 214. Passage 252 and passage 253 are blocked. If burner 208 is warm, these actions allow heat to be removed and burner aftertreatment device 214 to be ignited. Method 500 returns to 502.

[0076] At 508, method 500 starts the burner air pump, starts the burner (e.g., supplies fuel to the burner and operates the igniter), and deactivates the electric heater. Method 500 may also adjust the positions of valves 203, 204, and 210 to allow flow through burner 208, prevent flow through passage 254, and adjust flow through passage 251 so that the temperature of burner aftertreatment device 214 is within a specified temperature range. Method 500 proceeds to 510.

[0077] At 510, method 500 determines a PNA (eg, Figure 2 The method 500 determines whether the temperature of the PNA (e.g., 73) is greater than a threshold PNA NOx storage temperature (e.g., a maximum desired NOx storage temperature). If so, the answer is yes, and the method 500 proceeds to 550. Otherwise, the answer is no, and the method 500 returns to 508. This decision allows the PNA to reach the maximum desired NOx storage temperature and maintain the PNA at the maximum desired NOx storage temperature so that the downstream SCR can reach operating temperature without extracting NOx from the PNA.

[0078] At 550, the burner air pump is started, the burner is deactivated (e.g., fuel and igniter are not supplied to the burner), and the electric heater is deactivated. Method 500 may also adjust the positions of valves 203, 204, and 210 by opening valve 204 to allow flow through burner 208, preventing flow through passage 253, closing valve 203 to prevent flow through passage 252, and adjusting valve 210 to allow flow through passage 254. The PNA temperature is sufficient to extract NOx from the PNA and convert the NOx via the downstream SCR. Method 500 returns to 502.

[0079] In this way, method 500 can activate an emission device of an engine aftertreatment system so that tailpipe emissions can be reduced. Method 500 can begin by activating an electric heater to bring an oxidation catalyst to operating temperature. The oxidation catalyst can treat emissions from the burner, and the burner can heat the engine aftertreatment device to reduce tailpipe emissions.

[0080] therefore, Figure 4 and Figure 5A method for operating an engine is provided, the method comprising: via a controller, when a downstream selective catalytic reduction (SCR) catalyst temperature is below a threshold and a burner catalyst temperature is below a second threshold, activating a burner air pump and an electric heater in response to a request to preheat an exhaust aftertreatment system of an engine; and via the controller, deactivating the electric heater and activating a burner in response to the combustion catalyst temperature exceeding the second threshold. In a first example, the method includes wherein activating the burner includes supplying fuel to the burner. In a second example that may include the first example, the method further includes: deactivating the burner in response to a temperature of a passive NOx adsorber (PNA) exceeding a third threshold. In a third method that may include one or both of the first method and the second method, the method further includes starting the engine in response to a NOx storage efficiency of the PNA exceeding a fourth threshold. In a fourth method that may include one or more of the first method to the third method, the method further includes extracting NOx from the PNA in response to the NOx storage efficiency of the PNA being less than the fourth threshold. In a fifth method that may include one or more of the first to fourth methods, the method includes wherein the electric heater is in a passage downstream of the burner air pump. In a sixth method that may include one or more of the first to fifth methods, the method also includes treating combustion products output from the burner via an oxidation catalyst, and delivering the treated combustion products output from the oxidation catalyst to an exhaust system.

[0081] Figure 4 and Figure 5The method also provides a method for operating an engine, the method comprising: via a controller, when a downstream selective catalytic reduction (SCR) catalyst temperature is below a threshold and a burner catalyst temperature is below a second threshold, activating a burner air pump and an electric heater in response to a request to afterheat an exhaust aftertreatment system of the engine (e.g., heating the aftertreatment system after engine stop and before an indication of engine start); via the controller, deactivating the electric heater and activating the burner in response to the burner catalyst temperature exceeding the second threshold; and purging a passive NOx adsorber (PNA) via activating the combustion air pump in response to an engine shutoff request. In a first example, the method further comprises: activating the electric heater and the burner air pump in response to the SCR catalyst temperature being below a third threshold to purge the PNA. In a second example that may include the first example, the method further comprises: activating the electric heater and activating the burner to purge the PNA in response to an oxidation catalyst temperature being above a fourth threshold. In a third example that may include one or both of the first and second examples, the method further comprises deactivating the burner and the burner air pump in response to an output of a NOx sensor. In a fourth example, which may include one or more of the first to third examples, the method includes: wherein the NOx sensor is positioned downstream of the PNA.

[0082] It should be noted that the example control and estimation routines included herein can be used with various engine and / or vehicle system configurations. The control methods and programs disclosed herein can be stored as executable instructions in a non-transitory memory and can be executed by a control system including a controller in combination with various sensors, actuators and other engine hardware. In addition, parts of the method can be physical actions taken in the real world to change the state of the device. The specific routines described herein may represent one or more of any number of processing strategies (such as event-driven, interrupt-driven, multi-tasking, multi-threading, etc.). To this end, the various actions, operations and / or functions shown may be performed in the order described, performed in parallel, or omitted in some cases. Similarly, the processing order is not necessarily required to achieve the features and advantages of the exemplary examples described herein, but is provided for ease of illustration and description. One or more of the actions, operations and / or functions shown may be repeatedly performed according to the specific strategy used. In addition, the described actions, operations and / or functions may graphically represent code to be programmed into a non-transitory memory of a computer-readable storage medium in an engine control system, wherein the described actions are implemented by executing the instructions in conjunction with an electronic controller in a system including various engine hardware components. If desired, one or more of the method steps described herein may be omitted.

[0083] It should be understood that the configurations and procedures disclosed herein are exemplary in nature, and these specific examples should not be construed as limiting, as numerous variations are possible. For example, the above techniques may be applied to V-6, I-4, I-6, V-12, opposed 4, and other engine types. The subject matter of the present disclosure includes all novel and non-obvious combinations and sub-combinations of the various systems and configurations and other features, functions, and / or properties disclosed herein.

[0084] The appended claims particularly point out certain combinations and subcombinations regarded as novel and non-obvious. These claims may refer to "an" element or "a first" element or the equivalent thereof. Such claims may be understood to include incorporation of one or more such elements, neither requiring nor excluding two or more such elements. Other combinations and subcombinations of the disclosed features, functions, elements, and / or properties may be claimed by amendment of the present claims or by presentation of new claims in this or a related application. Such claims, whether broader, narrower, equal, or different in scope to the original claims, are also deemed to be included in the subject matter of the present disclosure.

[0085] According to the present invention, an exhaust system for an internal combustion engine is provided, the exhaust system comprising: a burner air pump, the burner air pump selectively supplies air to a burner positioned along a first channel; a second channel, the second channel being arranged in parallel with the first channel; a three-way valve, the three-way valve being connected to the first channel and the second channel downstream of the burner; a third channel, the third channel being positioned downstream of the three-way valve; a fourth channel, the fourth channel being positioned in parallel with the third channel, the third channel and the fourth channel being fluidly connected to a fifth channel, the fifth channel being fluidly connected to an engine exhaust channel; a passive NOx adsorber (PNA), the adsorber being positioned along the engine exhaust channel; a selective catalytic reduction (SCR) catalyst, the catalyst being positioned downstream of the PNA along the engine exhaust channel; and a NOx sensor, the NOx sensor being positioned downstream of the SCR along the engine exhaust channel.

[0086] According to an embodiment, the PNA consists of a palladium-exchanged zeolite.

[0087] According to an embodiment, the present invention is also characterized by: an electric heater positioned along the fourth passage; and an oxidation catalyst positioned downstream of the electric heater along the fourth passage.

[0088] According to an embodiment, the present invention is also characterized by a urea injector positioned along the engine exhaust passage downstream of the PNA and upstream of the SCR.

[0089] According to an embodiment, the present invention is also characterized by: a first flow control valve, the first flow control valve is positioned upstream of the burner along the first passage; and a second flow control valve, the second flow control valve is positioned along the second passage.

[0090] According to an embodiment, the invention is also characterized by a diesel exhaust catalyst positioned upstream of the PNA along the engine exhaust passage.

[0091] According to an embodiment, the invention is further characterized by a second SCR positioned upstream of the PNA along the engine exhaust passage.

[0092] According to an embodiment, the present invention is further characterized by a urea injector positioned upstream of the second SCR along the engine exhaust passage.

[0093] According to the present invention, a method for operating an engine includes: via a controller, when a downstream selective catalytic reduction (SCR) catalyst temperature is lower than a threshold value and a burner catalyst temperature is lower than a second threshold value, starting a burner air pump and an electric heater in response to a request for afterheating an exhaust aftertreatment system of the engine; and via the controller, deactivating the electric heater and starting the burner in response to the burner catalyst temperature exceeding the second threshold value.

[0094] In one aspect of the invention, starting the burner includes supplying fuel to the burner.

[0095] In one aspect of the invention, the method includes deactivating the burner in response to a passive NOx adsorber (PNA) temperature exceeding a third threshold.

[0096] In one aspect of the invention, the method includes starting the engine in response to the NOx storage efficiency of the PNA exceeding a fourth threshold.

[0097] In one aspect of the invention, the method includes purging NOx from the PNA in response to the NOx storage efficiency of the PNA being less than the fourth threshold.

[0098] In one aspect of the invention, the electric heater is in the passage downstream of the burner air pump.

[0099] In one aspect of the invention, the method includes treating combustion products output from the burner via an oxidation catalyst, and delivering the treated combustion products output from the oxidation catalyst to an exhaust system.

[0100] According to the present invention, a method for operating an engine includes: starting a burner air pump and an electric heater via a controller in response to a request to preheat an exhaust aftertreatment system of the engine when a downstream selective catalytic reduction (SCR) catalyst temperature is lower than a threshold and a burner catalyst temperature is lower than a second threshold; deactivating the electric heater and starting the burner via the controller in response to the burner catalyst temperature exceeding the second threshold; and purging a passive NOx adsorber (PNA) via starting the burner air pump in response to an engine shutdown request.

[0101] In one aspect of the present invention, the method includes activating the electric heater and the burner air pump to purge the PNA in response to the SCR catalyst temperature being lower than a third threshold.

[0102] In one aspect of the present invention, the method includes: in response to the oxidation catalyst temperature being above a fourth threshold, deactivating the electric heater and activating the burner to purge the PNA.

[0103] In one aspect of the invention, the method includes deactivating the burner and the burner air pump in response to an output of a NOx sensor.

[0104] In one aspect of the invention, the NOx sensor is positioned downstream of the PNA.

Claims

1. An exhaust system for an internal combustion engine, comprising: a burner air pump that selectively supplies air to a burner positioned along the first passage; a second channel, the second channel being arranged in parallel with the first channel; a three-way valve coupled to the first passage and the second passage downstream of the burner; a third passage, the third passage being positioned downstream of the three-way valve; a fourth passage positioned in parallel with the third passage, the third passage and the fourth passage fluidly coupled to a fifth passage fluidly coupled to an engine exhaust passage; a passive NOx adsorber (PNA) positioned along the engine exhaust passage; a selective catalytic reduction (SCR) catalyst positioned downstream of the PNA along the engine exhaust passage; as well as A NOx sensor is positioned along the engine exhaust passage downstream of the SCR.

2. The exhaust system of claim 1, wherein the PNA is comprised of a palladium-exchanged zeolite.

3. The exhaust system of claim 1, further comprising: an electric heater positioned along the fourth passage; as well as An oxidation catalyst is positioned along the fourth passage downstream of the electric heater.

4. The exhaust system of claim 1 further comprising a urea injector positioned along the engine exhaust passage downstream of the PNA and upstream of the SCR.

5. The exhaust system of claim 1, further comprising: a first flow control valve positioned upstream of the burner along the first passage; as well as A second flow control valve is positioned along the second passage.

6. The exhaust system of claim 1 further comprising a diesel exhaust catalyst positioned upstream of the PNA along the engine exhaust passage.

7. The exhaust system of claim 6 further comprising a second SCR positioned upstream of the PNA along the engine exhaust passage.

8. The exhaust system of claim 7 further comprising a urea injector positioned along the engine exhaust passage upstream of the second SCR.

9. A method for operating an engine, comprising: activating, via a controller, a burner air pump and an electric heater in response to a request to afterheat an exhaust aftertreatment system of the engine when a downstream selective catalytic reduction (SCR) catalyst temperature is below a threshold and a burner catalyst temperature is below a second threshold; and The electric heater is deactivated and a burner is activated, via the controller, in response to the burner catalyst temperature exceeding the second threshold.

10. The method of claim 9, wherein starting the burner includes supplying fuel to the burner.

11. The method of claim 9, further comprising: The burner is deactivated in response to a passive NOx adsorber (PNA) temperature exceeding a third threshold.

12. The method of claim 11, further comprising: The engine is started in response to the NOx storage efficiency of the PNA exceeding a fourth threshold.

13. The method of claim 12, further comprising: NOx is purged from the PNA in response to the NOx storage efficiency of the PNA being less than the fourth threshold.

14. The method of claim 9 wherein the electric heater is in a passage downstream of the burner air pump.

15. The method of claim 9, further comprising: Combustion products output from the burner are treated via an oxidation catalyst, and the treated combustion products output from the oxidation catalyst are delivered to an exhaust system.

Images