Method for operating an engine

Abstract

Methods and systems for operating an engine during and after particulate filter regeneration are described. In one example, in response to stopping regeneration of a particulate filter, exhaust flow increases and exhaust temperature decreases, thereby improving SCR efficiency for a short period of time.

Description

Technical Field

[0001] The present invention relates to vehicle engines and, more particularly, to methods for operating vehicle engines.

[0002] Background Art / Summary of the Invention

[0003] A diesel engine may include a selective catalytic reduction (SCR) catalyst to convert NOx into N2, H2O, and CO2. A diesel engine may also include a particulate filter to capture soot. The soot may be stored until the particulate filter is full, and then the soot may be burned to regenerate the particulate filter. The particulate filter may be regenerated by heating the exhaust gas in an oxidation catalyst and supplying the heated exhaust gas to the particulate filter, where the heated exhaust gas may heat the soot until it begins to burn in an oxygen-rich environment. However, the SCR is heated when the particulate filter is heated, and heating the SCR reduces the efficiency of the SCR. Even after the particulate filter is regenerated, the SCR may still be above the desired temperature for a period of time. Therefore, it may be desirable to provide a method for reducing the length of time that the SCR is at a temperature above a threshold temperature at which the SCR efficiency may be below a threshold.

[0004] The present inventors have recognized the above-mentioned shortcomings and have developed a method of engine operation that includes increasing turbocharger boost pressure via a controller while driver demand torque is substantially constant in response to ceasing regeneration of a particulate filter.

[0005] By increasing boost pressure in response to stopping particulate filter regeneration when the driver demand torque is substantially constant, the SCR can be cooled after particulate filter regeneration, thereby improving SCR efficiency in a short period of time. Boost pressure can be increased and the charge air cooler bypass valve can be closed to increase exhaust flow and reduce exhaust temperature, thereby cooling the SCR. When the SCR temperature is below a first threshold, the exhaust flow rate can be reduced to a first flow rate, and when the SCR temperature is below a second threshold, the exhaust flow rate can be reduced to a second flow rate. This reduction in exhaust flow allows for SCR cooling while improving engine efficiency.

[0006] The present disclosure can provide several advantages. Specifically, the method can reduce engine emissions by increasing SCR efficiency over a reduced time period. Furthermore, the method can improve engine efficiency while still reducing SCR temperature. Furthermore, the method can be applied to both four-stroke and two-stroke diesel engines.

[0007] The above advantages and other advantages and features of the present specification will become apparent from the following "Detailed Description" when read alone or in conjunction with the accompanying drawings.

[0008] It should be understood that the foregoing summary is provided to introduce, in simplified form, a range of concepts further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is solely defined by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that address any disadvantages noted above or in any part of this disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 A schematic diagram of a first example engine is shown;

[0010] Figure 2 shows a schematic diagram of a second example engine;

[0011] Figures 3A to 3B An example engine operating sequence is shown;

[0012] Figure 4 A method for operating an engine is shown. DETAILED DESCRIPTION

[0013] This description relates to operating a diesel engine including a particulate filter and an SCR. Figure 1 An example of a supercharged diesel engine is shown. Figure 2 A second example of a supercharged diesel engine is shown. Figure 3A and Figure 3B An example engine operating sequence for improving SCR efficiency after regenerating a particulate filter is shown. Figure 4 An example method for operating an engine to increase SCR efficiency is shown.

[0014] Reference Figure 1 Internal combustion engine 10, comprising a plurality of cylinders, is controlled by electronic engine controller 12, wherein one cylinder is Figure 1 As shown in FIG. 1 . The controller 12 Figure 1 The various sensors receive signals and based on the received signals and the instructions stored in the memory of the controller, use Figure 1 Various actuators are used to regulate engine operation.

[0015] Engine 10 includes combustion chamber 30 and cylinder walls 32, with piston 36 positioned therein and connected to crankshaft 40. Cylinder head 13 is fixed to engine block 14. Combustion chamber 30 is shown communicating with intake manifold 44 and exhaust manifold 48 via intake valve 52 and exhaust valve 54, respectively. Each intake and exhaust valve may be operated by an intake cam 51 and an exhaust cam 53. Although in other examples, the engine may operate the valves via a single camshaft or pushrods. 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.

[0016] Fuel injector 68 is shown positioned in cylinder head 13 for injecting fuel directly into combustion chamber 30, a process known to those skilled in the art as direct injection. Fuel is delivered to fuel injector 68 by a fuel system comprising fuel tank 95, fuel pump 91, fuel pump control valve 93, and a fuel rail (not shown). The pressure of the fuel delivered by the fuel system can be adjusted by varying a position valve that adjusts flow to the fuel pump (not shown). Additionally, a metering valve may be positioned in or near the fuel rail for closed-loop fuel control. The pump metering valve can also adjust the fuel flow to the fuel pump, thereby reducing the amount of fuel pumped to the higher-pressure fuel pump.

[0017] Intake manifold 44 is shown communicating with optional electronic throttle valve 62, which adjusts the position of throttle plate 64 to control air flow from intake boost chamber 46. Compressor 162 draws air from intake port 42 to supply boost chamber 46. Exhaust gas spins turbine 164, which is coupled to compressor 162 via shaft 161. In some examples, a charge air cooler may be provided. Compressor speed can be adjusted by adjusting the position of variable vane control 78 or compressor bypass valve 158. In alternative examples, wastegate 79 may be used in place of or in addition to variable vane control 78. Variable vane control 78 adjusts the position of variable geometry turbine vanes 77. When the vanes are in the open position, exhaust gas can pass through turbine 164, providing less energy to rotate turbine 164. When the vanes are in the closed position, exhaust gas can pass through turbine 164, exerting increased force on turbine 164. Alternatively, wastegate 79 or a bypass valve allows exhaust gas to flow around turbine 164, reducing the energy supplied to the turbine. Compressor bypass valve 158 allows compressed air at the outlet of compressor 162 to return to the input of compressor 162. In this way, the efficiency of compressor 162 can be reduced, thereby affecting the flow rate of compressor 162 and reducing the possibility of compressor surge.

[0018] Combustion begins in combustion chamber 30 when fuel auto-ignites as piston 36 approaches top dead center during the compression stroke. In some examples, universal exhaust gas oxygen (UEGO) sensor 126 may be coupled to exhaust manifold 48 upstream of emissions 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 with a NOx sensor having both NOx and oxygen sensing elements.

[0019] At lower engine temperatures, glow plug 66 can convert electrical energy into heat, thereby raising the temperature in combustion chamber 30. By raising the temperature of combustion chamber 30, the cylinder air-fuel mixture can be more easily ignited via compression.

[0020] In one example, emissions device 71 may include an oxidation catalyst and may be followed by SCR 72 and diesel particulate filter (DPF) 73. In another example, DPF 73 may be located upstream of SCR 72. Temperature sensor 75 provides an indication of SCR temperature.

[0021] High-pressure exhaust gas recirculation (EGR) can be provided to the engine via high-pressure EGR valve 80 and high-pressure EGR passage 81. High-pressure EGR valve 80 is a valve that blocks or allows exhaust gas to flow from upstream of exhaust device 71 to a location in the engine intake system upstream of compressor 162. High-pressure EGR can bypass EGR cooler 85, or alternatively, high-pressure EGR can be cooled by passing through EGR cooler 85. Low-pressure EGR can be provided to the engine via low-pressure EGR valve 84 and low-pressure EGR passage 83.

[0022] The controller 12 Figure 1 1 , a conventional microcomputer is shown including: a microprocessor unit 102, input / output ports 104, read-only memory (e.g., non-volatile 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, including, in addition to those previously discussed, engine coolant temperature (ECT) from temperature sensor 112 coupled to cooling sleeve 114; position sensor 134 coupled to accelerator pedal 130 for sensing accelerator position as regulated by a person's foot 132; a measurement of engine manifold pressure (MAP) from pressure sensor 121 coupled to intake manifold 44; boost pressure from pressure sensor 122; exhaust gas oxygen concentration from oxygen sensor 126; an engine position sensor sensing crankshaft 40 position from Hall effect sensor 118; 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 58. 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.

[0023] 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. Typically, during the intake stroke, exhaust valve 54 closes and intake valve 52 opens. Air is introduced into combustion chamber 30 via intake manifold 44, and piston 36 moves to the bottom of the cylinder, increasing the volume within combustion chamber 30. Those skilled in the art typically refer to 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) 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, compressing the air within combustion chamber 30. Those skilled in the art typically refer to the point where 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) as top dead center (TDC). Fuel is introduced into the combustion chamber in a process herein referred to as injection. In some examples, fuel may be injected into a cylinder multiple times during a single cylinder cycle.

[0024] 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 the piston's motion 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. Note that the above is described only as an example, and the intake and exhaust valve opening and / or closing timing can be varied, for example to provide positive or negative valve overlap, delayed intake valve closing, or various other examples. Furthermore, in some examples, a two-stroke cycle may be used instead of a four-stroke cycle.

[0025] Now refer to Figure 2 , an alternative engine is shown. The engine 20 is an opposed piston internal combustion engine comprising a plurality of cylinders, controlled by an electronic engine controller 212, wherein one cylinder is Figure 2 As shown in FIG. Controller 212 Figure 2 The various sensors receive signals and based on the received signals and the instructions stored in the memory of the controller, use Figure 2 Various actuators are used to regulate engine operation.

[0026] Engine 20 includes a cylinder 230 and cylinder walls 232, with an intake piston 236a and an exhaust piston 236b positioned therein and connected to crankshafts 240a and 240b, respectively. Crankshafts 240a and 240b may be coupled together by a belt, chain, or gears. Crankshafts 240a and 240b may be rotated by a motor 27 (e.g., a starter motor) to start engine 20. Cylinder 230 is shown communicating with intake manifold 244 and exhaust manifold 248 via intake passages 244a and 244b and exhaust passages 248a and 248b.

[0027] First and second fuel injectors 269 and 268 are shown located in cylinder wall 232 and can inject fuel directly into cylinder 230, a process known to those skilled in the art as direct injection. Fuel is delivered to first and second fuel injectors 269 and 268 via a fuel system comprising fuel tank 295, fuel pump 291, fuel pump control valve 293, and a fuel rail (not shown). The fuel pressure delivered by the fuel system can be adjusted by varying a position valve that regulates flow to the fuel pump (not shown). Additionally, a metering valve can be located in or near the fuel rail for closed-loop fuel control. The pump metering valve can also adjust the fuel flow to the fuel pump, thereby reducing the amount of fuel pumped to the higher-pressure fuel pump.

[0028] Intake manifold 244 is shown communicating with an optional electronic throttle valve 262, which adjusts the position of throttle plate 264 to control the flow of air from intake boost chamber 246. Supercharger compressor 262 is mechanically driven and draws air from downstream of turbocharger compressor 235. Turbocharger compressor 235 draws air from intake port 242. Supercharger compressor 262 supplies air to boost chamber 246. Exhaust gas rotates turbocharger variable geometry turbine 237, which is connected to turbocharger compressor 235 via shaft 236. Supercharger compressor 262 is mechanically driven by crankshaft 240b via shaft 261 and gearbox 263, which may be connected to crankshaft 240b via mechanism 264 (e.g., gears, chain, or belt). Supercharger gearbox 263 includes multiple gear ratios for varying the speed of supercharger compressor 262 relative to the speed of crankshaft 240b. Supercharger compressor speed can be adjusted by selecting and engaging gear 263a of gearbox 263. In one example, at a given engine crankshaft speed, supercharger compressor 262 can be rotated at a first speed and a second speed by switching between a first gear ratio and a second gear ratio in gearbox 263.

[0029] Supercharger compressor bypass valve 258 can be selectively opened to reduce the air pressure in boost chamber 246 and return air and exhaust gas recirculation (EGR) upstream of supercharger compressor 262. In some examples, charge air cooler 256 can be positioned downstream of supercharger compressor 262 to cool the charge air entering cylinder 230. Charge air cooler bypass valve 257 can be selectively opened to bypass charge air cooler 256. The position of vane actuator 237a can be adjusted by controller 212 to increase or decrease the speed of turbine 237. In alternative examples, wastegate 237b can be used instead of, or in addition to, vane actuator 237a. Vane actuator 237a adjusts the position of the variable geometry turbine vanes. When the vanes are in the open position, exhaust gas can pass through turbine 237, providing minimal energy to rotate turbine 237. When the vanes are in the closed position, exhaust gas can pass through turbine 237, exerting increased force on turbine 237. Alternatively, a wastegate 237b or bypass valve allows exhaust gas to flow around the turbine 237, thereby reducing the energy supplied to the turbine.

[0030] In an alternative example, supercharger compressor 262 may be located upstream of turbocharger compressor 235. Additionally, a charge air cooler (not shown) may be positioned downstream of where EGR passage 282 meets inlet 243 between supercharger compressor 262 and turbocharger compressor 235. The charge air cooler would eliminate the need for an EGR cooler.

[0031] Exhaust gas may be recirculated to cylinders 230 via EGR system 281. The EGR system includes an optional EGR cooler 285, an EGR valve 280, an EGR passage 282, an EGR cooler bypass 284, and a cooled EGR passage 283. Exhaust gas may flow from exhaust manifold 248 to engine intake 243 between supercharger compressor 262 and turbocharger compressor 235. When the pressure in exhaust manifold 248 is greater than the pressure between turbocharger compressor 235 and supercharger compressor 262, EGR may flow to the engine intake. EGR may flow through EGR cooler 285 to reduce engine exhaust temperature. When engine exhaust temperature is low, EGR may bypass EGR cooler 285.

[0032] After intake piston 236a covers intake passages 244a and 244b and exhaust piston 236b covers exhaust passages 248a and 248b, fuel can be injected into cylinder 230 as pistons 236a and 236b approach each other. Then, as piston 236 approaches top dead center in a compression stroke, the fuel can combust with the air in cylinder 230. The fuel and air ignite via compression ignition. In some examples, a universal exhaust gas oxygen (UEGO) sensor 226 can be coupled to exhaust manifold 248 upstream of emissions device 271. In other examples, the UEGO sensor can be located downstream of one or more exhaust aftertreatment devices. Furthermore, in some examples, the UEGO sensor can be replaced by a NOx sensor having both NOx and oxygen sensing elements.

[0033] The engine 20 does not include glow plugs or spark plugs because the engine is a compression ignition engine and does not include a cylinder head. In addition, the engine 20 does not include a poppet valve to adjust the air and exhaust flow into and out of the cylinder 230.

[0034] Exhaust system 231 carries exhaust gas away from engine 20 and processes the exhaust gas. Exhaust valve 240 is shown located in exhaust passage 249 downstream of turbine 237a and upstream of exhaust device 271. Alternatively, exhaust valve 240 may be located downstream of exhaust device 271. Exhaust valve 240 can be opened and closed to control pressure in exhaust manifold 48. Closing exhaust valve 240 restricts flow through exhaust valve 240 and may increase pressure in exhaust manifold 248. Opening exhaust valve 240 may increase flow through exhaust valve 240 and reduce pressure in exhaust manifold 248.

[0035] In one example, emissions device 271 may be an oxidation catalyst and may be located upstream of SCR 272 and particulate filter 273. Temperature sensor 275 provides the temperature of the SCR.

[0036] The controller 212 Figure 21 is a conventional microcomputer including a microprocessor unit 202, input / output ports 204, read-only memory (eg, non-volatile memory) 206, random access memory 208, keep alive memory 210, and a conventional data bus. Controller 212 is shown receiving various signals from sensors coupled to engine 20. In addition to those previously discussed, these signals include: engine coolant temperature (ECT) from temperature sensor 212 coupled to cooling sleeve 214; position sensor 234 coupled to accelerator pedal 230 for sensing accelerator position as adjusted by a person's foot 232; a measurement of engine manifold pressure (MAP) from pressure sensor 221 coupled to intake manifold 244; boost pressure from pressure sensor 222; exhaust oxygen concentration from oxygen sensor 226; an engine position sensor sensing the position of crankshaft 240b from Hall effect sensor 218; a measurement of the mass of air entering the engine from sensor 220 (e.g., a hot wire air flow meter); and a measurement of throttle position from sensor 258. Barometric pressure may also be sensed (sensor not shown) for processing by controller 212. In a preferred aspect of the present disclosure, engine position sensor 218 generates a predetermined number of equally spaced pulses per revolution of the crankshaft, from which engine speed (RPM) can be determined.

[0037] During operation, each cylinder within engine 20 typically undergoes a two-stroke cycle: the cycle includes a first stroke, during which intake piston 236a moves toward exhaust piston 236b and exhaust piston 236b moves toward intake piston 236a. During a second stroke, intake piston 236a moves away from exhaust piston 236b and exhaust piston 236b moves away from intake piston 236a. Intake piston 236a controls flow through intake passages 244a and 244b. Exhaust piston 236b controls flow through exhaust passages 248a and 248b. In this example, exhaust piston 236b leads intake piston 236a by reaching its top dead center position (e.g., its maximum distance from crankshaft 240b) a number of crankshaft degrees (e.g., depending on the configuration, this difference may range between 0 and 20 crankshaft degrees). Thus, exhaust piston motion is offset from intake piston motion by a number of crankshaft degrees.

[0038] Typically, during the first stroke, intake piston 236a and exhaust piston 236b move toward each other to compress the air that has entered cylinder 230. This stroke begins at bottom dead center (BDC) of intake piston 236a (intake piston 236a is closest to crankshaft 240a) and ends at top dead center (intake piston 236a is farthest from crankshaft 240a). As previously mentioned, exhaust piston 236b leads intake piston 236a by several degrees, so that when the intake piston is at BDC, exhaust piston 236b has already moved toward its TDC position. Furthermore, exhaust piston 236b reaches its TDC position just before intake piston 236a reaches its TDC position. When intake piston 236a reaches its TDC position, exhaust piston 236b is just behind its TDC position. When intake piston 236a and exhaust piston 236b are near their respective TDC positions, the cylinder volume is minimized. As intake piston 236a and exhaust piston 236b advance toward their respective TDC positions, air and fuel are compressed in cylinder 230. When intake piston 236a and exhaust piston 236b approach their respective BDC positions, intake ports 244a and 244b open, allowing compressed air to flow into cylinder 230. As intake piston 236a and exhaust piston 236b approach BDC, exhaust ports 248a and 248b also open. Supercharger compressor 262 and turbocharger compressor 235 provide compressed air to intake manifold 244, allowing compressed air to flow into cylinder 230 when intake ports 244a and 244b open. As intake piston 236a and exhaust piston 236b advance toward their respective TDC positions, exhaust ports 248a and 248b close, and then, after several crankshaft degrees, intake ports 244a and 244b close to prevent additional air from entering cylinder 236. After exhaust ports 244a and 244b are closed, fuel is injected into cylinder 230, and the fuel-air mixture is ignited as intake piston 236a and exhaust piston 236b approach their respective TDC positions. The fuel-air mixture is ignited by compression ignition rather than by a spark plug or energy from the spark plug. Fuel may be injected into cylinder 230 via multiple injections, including a pilot injection, a main injection, and a post injection.

[0039] During the second stroke, typically after combustion occurs in cylinder 230, intake piston 236a and exhaust piston 236b move apart. The second stroke begins at intake piston 236a's TDC and ends at intake piston 236a's BDC. Intake piston 236a and exhaust piston 236b approach their respective BDC positions, near the point where cylinder 230's volume is maximum. The expanding gases in cylinder 230 push intake piston 236a and exhaust piston 236b toward their respective BDC positions. Exhaust piston 236b passes exhaust passages 248a and 248b as it moves toward its BDC. As exhaust piston 236b moves toward crankshaft 240b, exhaust passages 248a and 248b are opened when the top of exhaust piston 236d passes exhaust passages 248a and 248b. As exhaust piston 236b travels toward bottom dead center (BDC), exhaust gas exits cylinder 230 after passing through exhaust passages 248a and 248b. Intake piston 236a and exhaust piston 236b continue to travel toward their respective bottom dead center positions, and after a predetermined number of actual total crankshaft rotations, intake piston 236a exposes intake passages 244a and 244b. As intake piston 236a travels toward crankshaft 240a, the top of intake piston 236c passes over intake passages 244a and 244b, opening intake passages 244a and 244b. When intake passages 244a and 244b are opened, fresh air enters cylinder 230 via intake passages 244a and 244b. Intake piston 236a and exhaust piston 236b continue to travel toward their respective bottom dead center (BDC) positions. After the intake pistons reach BDC, the cylinder cycle repeats.

[0040] Thus, the engine cycle includes two strokes and is one engine revolution. Other engine cylinders operate in a similar manner, but these other cylinders may combust air and fuel out of phase with the cylinder shown. For example, the top dead center compression stroke of one engine cylinder may be at zero crankshaft degrees, while the top dead center of another cylinder may be at one hundred and eighty crankshaft degrees.

[0041] Figure 1 and Figure 2An engine system is provided, comprising: a two-stroke opposed-piston diesel engine including at least one cylinder; an exhaust system coupled to the two-stroke engine, comprising an oxidation catalyst, an SCR, and a particulate filter; and a controller comprising executable instructions stored in non-volatile memory for increasing exhaust gas flow to the SCR in response to cessation of regeneration of the particulate filter and an SCR temperature exceeding a first threshold temperature. The engine system includes instructions for increasing exhaust gas flow to the SCR by increasing boost pressure in response to cessation of regeneration of the particulate filter. The engine system also includes instructions for closing a charge air cooler bypass valve and a supercharger bypass valve in response to cessation of regeneration of the particulate filter. The engine system also includes instructions for closing an EGR cooler bypass valve in response to cessation of regeneration of the particulate filter. The engine system also includes instructions for decreasing exhaust gas flow to the SCR in response to the SCR temperature being below the first threshold temperature. The engine system further includes additional instructions for reducing exhaust flow to the SCR in response to the SCR temperature being below a second threshold temperature. The engine system further includes injecting urea into the SCR in response to stopping regeneration of the particulate filter and the SCR temperature being below the first threshold.

[0042] Now refer to Figure 3A and Figure 3B , showing that according to Figure 4 Example engine operating sequence of the method. This sequence can be Figure 1 and Figure 2 systems are provided, and their respective controllers may include Figure 4 The vertical lines represent the times of interest in each sequence plot (e.g., t1-t3). The sequences in the plots appear simultaneously, and the plots are aligned in time.

[0043] from Figure 3A The first graph from the top shows a particulate filter (PF) regeneration request versus time. Trace 302 represents the PF regeneration request status. The vertical axis represents the PF regeneration status, and when trace 302 is at a higher level near the vertical axis arrow, PF regeneration is being requested. When trace 302 is near the horizontal axis, PF regeneration is not being requested. The horizontal axis represents time, and time increases from the left side of the graph to the right side.

[0044] from Figure 3AThe second graph from the top shows variable geometry turbocharger (VGT) vane position versus time. Trace 304 represents vane position. The vertical axis represents vane position, with the vanes opening in the direction of the vertical axis arrow. The horizontal axis represents time, with time increasing from the left side of the graph to the right side.

[0045] from Figure 3A The third graph from the top shows engine intake throttle valve position versus time. Trace 306 represents throttle valve position. The vertical axis represents throttle valve position, with the throttle valve opening in the direction of the vertical axis arrow. The horizontal axis represents time, with time increasing from the left side of the graph to the right side.

[0046] from Figure 3A The fourth graph from the top shows exhaust throttle valve position versus time. Trace 308 represents throttle valve position. The vertical axis represents exhaust throttle valve position, with the exhaust throttle valve opening in the direction of the vertical axis arrow. The horizontal axis represents time, with time increasing from the left side of the graph to the right side.

[0047] from Figure 3A The fifth graph from the top shows the relationship between the EGR cooler bypass valve state and time. Trace 310 represents the EGR cooler bypass valve state. The vertical axis represents the EGR cooler bypass valve state, and when trace 310 is at a higher level near the vertical axis arrow, the EGR bypass valve is open to bypass the EGR cooler. When trace 310 is at a lower level near the horizontal axis, the EGR cooler bypass valve is closed, so that the EGR cooler is not bypassed. The horizontal axis represents time, and time increases from the left side of the graph to the right side.

[0048] from Figure 3A The sixth graph from the top shows charge air cooler (CAC) bypass valve state versus time. Trace 312 represents CAC bypass valve position. The vertical axis represents CAC bypass valve state, and when trace 312 is at a higher level near the vertical axis arrow, the CAC bypass valve is open to bypass the CAC. When trace 312 is at a lower level near the horizontal axis, the CAC bypass valve is closed, so that the CAC is not bypassed. The horizontal axis represents time, with time increasing from the left side of the graph to the right side.

[0049] from Figure 3A The seventh graph from the top shows the state of the compressor bypass valve versus time. Trace 314 represents the position of the compressor bypass valve. The vertical axis represents the compressor bypass valve state, and when trace 314 is at a higher level near the vertical axis arrow, the compressor bypass valve is open to bypass the compressor. When trace 314 is at a lower level near the horizontal axis, the compressor bypass valve is closed, so that the compressor cooler is not bypassed. The horizontal axis represents time, with time increasing from the left side of the graph to the right side.

[0050] from Figure 3B The first graph from the top shows the relationship between urea injection amount and time. Trace 318 shows the urea injection amount. The vertical axis shows the urea injection amount, and the urea injection amount increases in the direction of the vertical axis arrow. The horizontal axis shows time, and time increases from the left side of the graph to the right side.

[0051] from Figure 3B The second graph from the top shows SCR temperature versus time. Trace 320 represents SCR temperature. The vertical axis represents SCR temperature, with SCR temperature increasing in the direction of the vertical axis arrow. The horizontal axis represents time, with time increasing from the left side of the graph to the right side. Horizontal line 350 represents a first threshold, above which SCR efficiency is less than a threshold value (e.g., 30%). Horizontal lines 352 and 354 represent the upper and lower limits of a desired SCR temperature range, within which SCR efficiency can be greater than a threshold value (e.g., 90%).

[0052] from Figure 3B The third graph from the top shows engine boost pressure (e.g., pressure in boost chamber 46 or 246) versus time. Trace 322 represents boost pressure. The vertical axis represents boost pressure, and boost pressure 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.

[0053] from Figure 3B The fourth graph from the top shows low-pressure EGR flow versus time. Trace 324 represents low-pressure EGR flow. The vertical axis represents low-pressure EGR flow, with low-pressure EGR flow increasing in the direction of the vertical arrow. The horizontal axis represents time, with time increasing from the left side of the graph to the right side.

[0054] from Figure 3B The fifth graph from the top shows the relationship between supercharger compressor gear ratio and time. Trace 326 represents the supercharger compressor gear ratio. The vertical axis represents the supercharger compressor gear ratio, and the supercharger compressor gear ratio 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.

[0055] from Figure 3B The sixth graph from the top shows high-pressure EGR flow versus time. Trace 328 represents high-pressure EGR flow. The vertical axis represents high-pressure EGR flow, with the high-pressure EGR flow increasing in the direction of the vertical arrow. The horizontal axis represents time, with time increasing from the left side of the graph to the right side.

[0056] Although not shown, Figure 3A and Figure 3B Throughout the sequence, the driver demand torque is substantially constant (eg, varies by less than ±5% of the desired value) and the engine speed is substantially constant.

[0057] At time t0, the engine is running and burning air and fuel (not shown). The particulate filter is regenerating, as indicated by the PF state trace at a higher level. The VGT vane is partially closed and the intake throttle valve is in a neutral position. The exhaust throttle valve is partially open and the EGR cooler bypass valve is fully open to bypass the EGR cooler. The CAC valve is fully open and the compressor bypass valve is partially open. The EGR valve is partially open and no urea is being injected. The SCR temperature is above threshold 350, so its efficiency is low. The boost pressure is at an upper-middle level. The low-pressure EGR flow is at a middle level, and the high-pressure EGR flow is at a higher-middle level. The gear ratio of the supercharger compressor is a lower gear ratio.

[0058] At time t1, particulate filter regeneration is complete, as indicated by a transition from a higher level to a lower level of particulate filter regeneration request. In response to particulate filter regeneration being complete, the VGT vane is fully closed and the intake throttle valve is fully opened. In response to particulate filter regeneration being complete, the exhaust throttle valve is also fully opened and the EGR cooler bypass valve is closed. In response to particulate filter regeneration being complete, the CAC valve is also fully closed, and the compressor bypass valve is also fully closed. When SCR conversion efficiency is low, the EGR valve is opened in response to engine speed and driver demand torque to control engine NOx output. Urea is not injected when SCR temperature is high, so that urea can be stored until SCR efficiency can be higher. The SCR temperature remains above threshold 350. In response to ceasing particulate filter regeneration, boost pressure is increased. Low-pressure EGR flow is increased, and high-pressure EGR flow is decreased. Additionally, the supercharger compressor gear ratio is increased.

[0059] By increasing boost pressure and closing the CAC, exhaust gas flow to the SCR can be increased. Furthermore, closing the CAC can help reduce exhaust gas temperatures, allowing cooler exhaust gas to flow to the SCR, thereby cooling the SCR. Closing the compressor bypass improves compressor efficiency, increasing exhaust gas flow, and closing the EGR cooler bypass cools the EGR, thereby cooling the engine exhaust gas directed to the SCR. Opening the engine throttle and / or exhaust throttle can increase engine air flow, allowing the SCR to cool more quickly. Increasing the gear ratio of the supercharger compressor increases air flow through the engine. Increasing low-pressure EGR also increases flow through the engine, which can be particularly useful at engine idle, where engine boost can be limited by low engine speeds. Reducing the amount of high-pressure EGR prevents EGR flow from being excessive.

[0060] Between t1 and t2, the SCR temperature decreases, and exhaust gas continues to flow to the SCR at a higher rate than if boost pressure and exhaust flow were adjusted solely in response to driver demand torque and engine speed. Particulate filter regeneration is not required, and the VGT vane is fully closed. The intake and exhaust throttle valves are fully open, and the EGR cooler bypass valve is fully closed. The CAC bypass valve is fully closed, and the compressor bypass valve is fully closed. No urea is injected, and boost pressure increases and then stabilizes at a higher level. Low-pressure EGR flow increases and then levels off. High-pressure EGR decreases and then stabilizes at a constant value. The supercharger compressor gear ratio remains elevated.

[0061] At time t2, the SCR temperature is below threshold 350, causing the boost pressure to decrease to reduce exhaust flow and improve engine efficiency. Urea injection is also initiated in response to the SCR temperature being below threshold 350. A small amount of urea is injected to improve SCR efficiency. The VGT vane position is opened to reduce boost pressure, and the engine intake throttle and exhaust throttle valves remain fully open. The EGR cooler bypass valve remains closed, and the CAC cooler bypass valve is also fully closed. The compressor bypass valve remains closed, and the SCR temperature continues to decrease after time t2, and SCR efficiency continues to increase (not shown). The supercharger compressor gear ratio remains unchanged, and the low-pressure and high-pressure EGR flows remain at their previous values.

[0062] At time t3, the SCR temperature drops below threshold 352. When the SCR temperature drops to a temperature below threshold 352, the NOx conversion efficiency of the SCR increases (not shown). The boost pressure is further reduced to a level corresponding to the current engine speed and driver demand torque. The amount of urea injected is also increased to further increase the SCR efficiency. Particulate filter regeneration is not required, and the VGT vane is opened in response to the SCR temperature to reduce the boost pressure. In response to the SCR temperature being below threshold 350, the exhaust throttle valve and the intake throttle valve are partially closed, and the EGR cooler bypass valve is opened. In response to the SCR temperature being below threshold 350, the CAC and compressor bypass valve are also closed. The EGR valve position remains stable. The supercharger compressor gear ratio is reduced, and the high-pressure EGR flow rate is increased. The low-pressure EGR flow rate is reduced.

[0063] In this way, after particulate filter regeneration, SCR efficiency can be increased to reduce engine emissions. Exhaust gas flow to the SCR can be increased, and exhaust gas temperature can be reduced to lower SCR temperature. Furthermore, when the SCR temperature drops below a first threshold temperature, the rate of SCR cooling can be reduced, thereby increasing engine efficiency even as SCR cooling continues.

[0064] Now refer to Figure 4, a method for operating an engine is shown. Specifically, a flow chart of a method for operating an internal combustion engine is shown. Figure 4 Methods can be stored as executable instructions in a program such as Figure 1 and Figure 2 In non-transitory memory in the system shown. Figure 4 The method can be combined with Figure 1 and Figure 2 In addition, Figure 4 At least a portion of the method may be incorporated as executable instructions stored in a non-volatile memory, while other portions of the method may be performed by a controller that converts the operating states of devices and actuators in the physical world. The controller may use engine actuators of an engine system to adjust engine operation according to the method described below.

[0065] At 402, method 400 determines engine operating conditions. Engine operating conditions may include, but are not limited to, engine temperature, accelerator pedal position, particulate filter soot loading, ambient temperature, ambient pressure, driver demand torque, and engine speed. Engine operating conditions may be determined by engine sensors and an engine controller. Method 400 proceeds to 404.

[0066] At 404, method 400 determines whether diesel particulate filter (DPF) regeneration is required. In one example, method 400 determines whether diesel particulate filter regeneration is required responsive to a pressure drop across the particulate filter. In other examples, method 400 may determine that particulate filter regeneration is required after the vehicle has traveled more than a threshold distance. If method 400 determines that diesel particulate filter regeneration is required, the answer is "yes" and method 400 proceeds to 406. Otherwise, the answer is "no" and method 400 proceeds to 424.

[0067] At 406 , method 400 increases boost pressure (e.g., pressure in the engine intake) compared to boost pressure at the same engine speed and driver demand torque without diesel particulate filter regeneration. Additionally, the engine intake throttle valve is partially closed to increase exhaust gas temperature. Method 400 proceeds to 408 .

[0068] At 408, method 400 begins post-injection of fuel into the engine cylinders. The post-injection fuel is injected after the main fuel injection, and at least a portion of the post-injection fuel is exhausted from the engine cylinders to be oxidized in the oxidation catalyst, where it can increase exhaust temperature, thereby promoting particulate filter regeneration. Method 400 proceeds to 410 after initiating post-injection of fuel.

[0069] At 410, method 400 judges whether diesel particulate filter regeneration is complete. In one example, if the pressure drop across the diesel particulate filter is less than a threshold, method 400 judges particulate filter regeneration is complete. If method 400 judges particulate filter regeneration is complete, the answer is yes and method 400 proceeds to 412. Otherwise, method 400 returns to 408.

[0070] At 412, method 400 stops post-injection fuel and stops particulate filter regeneration. In addition, method 400 increases boost pressure, or alternatively, maintains boost pressure after particulate filter regeneration stops. Boost pressure can be increased while the driver demand torque remains substantially constant (e.g., varies less than ±5% of the desired value). In addition, boost pressure can be increased even if driver demand is decreasing or increasing. Boost pressure can be increased by a turbocharger compressor or a supercharger compressor. Method 400 also opens the engine intake throttle valve and / or exhaust throttle valve. By increasing boost and opening the intake throttle valve and / or exhaust throttle valve, exhaust flow to the SCR can be increased to cool the SCR. Method 400 proceeds to 414.

[0071] At 414, method 400 closes the CAC bypass valve, closes the EGR cooler bypass valve, and closes the supercharger bypass valve. The CAC bypass, EGR bypass, and supercharger bypass are closed to cool the exhaust gas. In addition, method 400 may increase the supercharger compressor gear ratio to increase flow through the engine and SCR. Increasing the supercharger gear ratio increases the compressor speed relative to the crankshaft speed. The variable geometry turbocharger (VGT) vanes and the supercharger (SC) bypass valve may also be closed to increase engine air flow. In some cases, in response to stopping particulate filter regeneration and other engine operating conditions, the VGT vanes may be partially closed to a position that provides an upper threshold boost pressure (e.g., maximum boost pressure). Method 400 proceeds to 416.

[0072] At 416, method 400 adjusts the EGR valve in response to engine speed and driver demand torque. Thus, if engine speed and load are constant, the EGR valve position remains constant. However, if the engine includes a high-pressure EGR passage and a low-pressure EGR passage, the low-pressure EGR flow rate may be increased, and the high-pressure EGR flow rate may be decreased, to further increase engine air flow while reducing engine NOx. After increasing the ratio of low-pressure EGR to high-pressure EGR (e.g., low-pressure EGR amount or flow rate / high-pressure EGR amount or flow rate), the low-pressure and high-pressure EGR valve positions may be adjusted in response to engine speed and load. Increasing the low-pressure EGR flow rate and decreasing the high-pressure EGR flow rate may increase engine efficiency while maintaining engine NOx emissions.

[0073] At 418, method 400 judges whether the SCR temperature is less than a first threshold temperature. The first threshold temperature may be a temperature above which the SCR NOx conversion efficiency is less than a threshold value (e.g., less than 30%) (e.g., 380° C.). If method 400 judges that the SCR temperature is less than the first threshold temperature, the answer is yes and method 400 proceeds to 420. Otherwise, method 400 returns to 418 to continue SCR cooling.

[0074] At 420, method 400 reduces boost pressure. Boost pressure can be reduced based on driver demand torque and SCR temperature. In one example, a desired boost pressure is empirically determined and stored in a table or function that is referenced or indexed by SCR temperature and driver demand torque. In one example, boost pressure is reduced to provide a desired level of engine efficiency improvement for the desired reduction in SCR cooling. Method 400 reduces boost pressure by opening a wastegate or opening variable position turbocharger vanes and proceeds to 422.

[0075] At 422, method 400 judges whether the SCR temperature is less than a second threshold temperature. In one example, the second threshold temperature is a temperature above which the SCR NOx conversion efficiency is less than a threshold efficiency (e.g., 90%). If method 400 judges that the SCR temperature is less than the second threshold temperature, the answer is yes and method 400 proceeds to 424. Otherwise, the answer is no and method 400 returns to 422.

[0076] At 424, method 400 adjusts the CAC bypass valve, EGR valve, EGR cooler bypass valve, boost, low-pressure EGR, high-pressure EGR, and supercharger gear ratio, as well as the supercharger bypass valve, in response to driver demand torque and engine speed. In other words, the SCR is operating within a desired temperature range, and therefore, the aforementioned actuators are not adjusted to cool the SCR, but rather to provide the desired demand torque while operating the engine efficiently. Method 400 continues to exit.

[0077] Thus, method 400 provides an engine operating method, comprising: in response to stopping regeneration of a particulate filter, increasing boost pressure in an engine intake via a controller while maintaining a substantially constant driver demand torque. The engine method includes increasing boost pressure by at least partially closing turbocharger vanes, and the engine method further includes increasing low-pressure exhaust gas recirculation flow and decreasing high-pressure exhaust gas recirculation flow in response to stopping regeneration of the particulate filter. The engine method further includes opening an intake throttle valve and increasing a gear ratio of a supercharger compressor to increase boost pressure in response to stopping regeneration of the particulate filter. The engine method further includes closing an EGR cooler bypass valve in response to stopping regeneration of the particulate filter. The engine method further includes closing a charge air cooler bypass valve in response to stopping regeneration of the particulate filter. The engine method further includes closing a compressor bypass valve in response to stopping regeneration of the particulate filter. The engine method further includes opening an exhaust throttle valve in response to stopping regeneration of the particulate filter.

[0078] Figure 4 The method also provides an engine operating method, comprising: in response to stopping regeneration of a particulate filter, increasing boost pressure in an engine intake via a controller while a driver demand torque is substantially constant; and in response to stopping regeneration of the particulate filter and before an SCR temperature falls below a first threshold temperature, adjusting an EGR valve position based on the driver demand torque and engine speed. The engine method includes wherein the EGR valve is a low-pressure EGR valve, and further includes further adjusting the low-pressure EGR valve to increase low-pressure EGR flow; and in response to stopping regeneration of the particulate filter and before an SCR temperature falls below the first threshold temperature, increasing exhaust flow to the SCR. The engine method further includes decreasing exhaust flow to the SCR in response to the SCR temperature falling below the first threshold temperature. The engine method further includes injecting urea into the SCR in response to the SCR temperature falling below the first threshold temperature. The engine method further includes decreasing exhaust flow to the SCR in response to the SCR temperature falling below a second threshold temperature.

[0079] Note that the example control and estimation routines included herein can be used with various engine and / or vehicle system configurations. The control methods and routines disclosed herein can be stored as executable instructions in non-volatile memory and executed by a control system including a controller in conjunction with various sensors, actuators, and other engine hardware. Furthermore, portions of the methods may be physical actions taken in the real world to change device states. 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, and the like. Thus, the various actions, operations, and / or functions shown may be performed in parallel in the order shown, or in some cases omitted. Similarly, the order of processing is not necessarily required to achieve the features and advantages of the illustrative examples described herein but is provided for ease of illustration and description. Depending on the specific strategy used, one or more of the actions, operations, and / or functions shown may be performed repeatedly. Furthermore, the described actions, operations, and / or functions may graphically represent code to be programmed into the non-volatile memory of a computer-readable storage medium in an engine control system, where 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.

[0080] It should be understood that the configurations and procedures disclosed herein are exemplary in nature, and that these specific examples should not be considered limiting, as many variations are possible. For example, the above technology can be applied to V-6, I-4, I-6, V-12, opposed 4-cylinder, 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.

[0081] The following claims specifically point out certain combinations and subcombinations believed to be novel and non-obvious. These claims may refer to "an" element or "a first" element or the equivalent thereof. Such claims should 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 within the subject matter of the present disclosure.

[0082] According to the present invention, a method of operating an engine includes increasing boost pressure in an engine intake via a controller while a driver demand torque is substantially constant in response to discontinuing regeneration of a particulate filter.

[0083] According to one embodiment, boost pressure is increased by at least partially closing vanes of a turbocharger, and the engine method further comprises increasing a low pressure exhaust gas recirculation flow and decreasing a high pressure exhaust gas recirculation flow in response to stopping regeneration of the particulate filter.

[0084] According to one embodiment, the invention is further characterized by opening an intake throttle valve and increasing a gear ratio of a supercharger compressor to increase the boost pressure in response to stopping regeneration of the particulate filter.

[0085] According to one embodiment, the invention is further characterized by closing an EGR cooler bypass valve in response to stopping regeneration of the particulate filter.

[0086] According to one embodiment, the invention is further characterized by closing a charge air cooler bypass valve in response to stopping regeneration of the particulate filter.

[0087] According to one embodiment, the invention is further characterized by closing a compressor bypass valve in response to stopping regeneration of the particulate filter.

[0088] According to one embodiment, the invention is further characterized in that in response to stopping regeneration of the particulate filter, an exhaust throttle valve is opened.

[0089] According to the present invention, an engine operating method includes: in response to stopping regeneration of a particulate filter, increasing, via a controller, boost pressure in an engine intake while a driver demand torque is substantially constant; and in response to stopping regeneration of the particulate filter and before an SCR temperature falls below a first threshold temperature, adjusting an EGR valve position based on the driver demand torque and engine speed.

[0090] According to the present invention, the EGR valve is a low-pressure EGR valve, and the engine method further includes: further adjusting the low-pressure EGR valve to increase low-pressure EGR flow; and increasing exhaust gas flow to the SCR in response to stopping regeneration of the particulate filter, the exhaust gas flow increasing before the SCR temperature falls below the first threshold temperature.

[0091] According to one embodiment, the above invention is further characterized by reducing the exhaust gas flow to the SCR in response to the SCR temperature being below the first threshold temperature.

[0092] According to one embodiment, the above invention is further characterized by injecting urea into the SCR in response to the SCR temperature being lower than the first threshold temperature.

[0093] According to one embodiment, the above invention is further characterized by reducing the exhaust gas flow to the SCR in response to the SCR temperature being below a second threshold temperature.

[0094] According to the present invention, an engine system is provided having: a two-stroke opposed-piston diesel engine including at least one cylinder; an exhaust system coupled to the two-stroke engine, the exhaust system including an oxidation catalyst, an SCR, and a particulate filter; and a controller including executable instructions stored in a non-volatile memory to increase exhaust gas flow to the SCR in response to cessation of regeneration of the particulate filter and a temperature of the SCR being above a first threshold temperature.

[0095] According to one embodiment, the first threshold temperature is a temperature above which the SCR efficiency falls below a threshold.

[0096] According to one embodiment, the invention is further characterized by an additional instruction to increase exhaust gas flow to the SCR by increasing boost pressure in response to ceasing regeneration of the particulate filter.

[0097] According to one embodiment, the invention also features additional instructions for closing a charge air cooler bypass valve and a supercharger bypass valve in response to ceasing regeneration of the particulate filter.

[0098] According to one embodiment, the invention also features an additional instruction to close the EGR cooler bypass valve in response to ceasing regeneration of the particulate filter.

[0099] According to one embodiment, the invention also features an additional instruction to reduce exhaust gas flow to the SCR in response to the SCR temperature being below the first threshold temperature.

[0100] According to one embodiment, the invention also features an additional instruction to reduce exhaust gas flow to the SCR in response to the SCR temperature being below a second threshold temperature.

[0101] According to one embodiment, the invention is further characterized by injecting urea into the SCR in response to stopping regeneration of the particulate filter and the SCR temperature being below the first threshold.

Claims

1. A method for operating an engine, comprising: In response to ceasing regeneration of the particulate filter, boost pressure in the engine intake is increased by a controller while driver demand torque is substantially constant.

2. The engine operating method of claim 1 , wherein boost pressure is increased by at least partially closing vanes of a turbocharger, and the engine operating method further comprises: In response to stopping regeneration of the particulate filter, a low pressure exhaust gas recirculation flow rate is increased and a high pressure exhaust gas recirculation flow rate is decreased. 3 . The engine operating method of claim 1 , further comprising opening an intake throttle valve and increasing a gear ratio of a supercharger compressor to increase the boost pressure in response to stopping regeneration of the particulate filter. 4 . The engine operating method of claim 3 , further comprising closing an EGR cooler bypass valve in response to stopping regeneration of the particulate filter. 5 . The engine operating method of claim 4 , further comprising closing a charge air cooler bypass valve in response to stopping regeneration of the particulate filter. 6 . The engine operating method of claim 5 , further comprising closing a compressor bypass valve in response to stopping regeneration of the particulate filter. 7 . The engine operating method of claim 1 , further comprising opening an exhaust throttle valve in response to stopping regeneration of the particulate filter.

8. The engine operating method of claim 1 , further comprising: In response to discontinuing regeneration of the particulate filter and before SCR temperature falls below a first threshold temperature, adjusting EGR valve position based on driver demand torque and engine speed, wherein the first threshold temperature is a temperature above which SCR efficiency falls below a threshold.

9. The engine operating method of claim 8, wherein the EGR valve is a low-pressure EGR valve, and the engine operating method further comprises: further adjusting the low-pressure EGR valve to increase the low-pressure EGR flow; as well as Exhaust flow to the SCR is increased in response to stopping regeneration of the particulate filter, the exhaust flow increasing before the SCR temperature falls below the first threshold temperature. 10 . The engine operating method of claim 9 , further comprising reducing exhaust flow to the SCR in response to an SCR temperature being below the first threshold temperature.

11. An engine system comprising: A two-stroke opposed-piston diesel engine comprising at least one cylinder; an exhaust system coupled to the two-stroke engine, comprising an oxidation catalyst, an SCR, and a particulate filter; and A controller including executable instructions stored in non-volatile memory is configured to increase exhaust gas flow to the SCR by increasing boost pressure while maintaining a substantially constant driver demand torque in response to discontinuing regeneration of the particulate filter and an SCR temperature exceeding a first threshold temperature, wherein the first threshold temperature is a temperature above which SCR efficiency falls below a threshold.

12. The engine system of claim 11 further comprising additional instructions for increasing exhaust flow to the SCR by increasing boost pressure in response to ceasing regeneration of the particulate filter.

13. The engine system of claim 12 further comprising additional instructions to close a charge air cooler bypass valve and a supercharger bypass valve in response to ceasing regeneration of the particulate filter.

14. The engine system of claim 13 further comprising additional instructions to close an EGR cooler bypass valve in response to ceasing regeneration of the particulate filter.

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