EGR system and method for opposed-piston engine

Abstract

The present disclosure provides an "EGR system and method for an opposed piston engine". A method and system for providing exhaust gas recirculation to a two-stroke opposed piston diesel engine is described. In one example, a high pressure exhaust gas recirculation system and a low pressure exhaust gas recirculation system can be activated or deactivated in response to exhaust gas hydrocarbon concentration and particulate matter flow rate from the engine. In addition, the operation of the low pressure exhaust gas recirculation system and the high pressure exhaust gas recirculation system can be responsive to the operating state of a supercharger compressor.

Description

Technical Field

[0001] The present disclosure relates to an exhaust gas recirculation system for an opposed-piston engine. Background Art

[0002] An opposed piston two-stroke diesel engine may have a high pressure (HP) exhaust gas recirculation (EGR) system and a low pressure (LP) EGR system. The HP EGR system may pass exhaust gas from the upstream of the turbocharger turbine to a position downstream of the turbocharger compressor. The exhaust gas from the HP EGR system may also be directed to the supercharger compressor before it enters the engine cylinder. The LP EGR system may pass exhaust gas from the downstream of the aftertreatment device and the downstream of the turbocharger turbine to a position upstream of the turbocharger compressor. The exhaust gas from the LP EGR system may flow through the turbocharger compressor and the supercharger compressor. The LP EGR system may be activated when the HP EGR system is deactivated. In addition, the HP EGR system may be activated when the LP EGR system is deactivated. However, there may be vehicle operating conditions in which operating the HP EGR system or the LP EGR system may reduce engine performance over time. Summary of the invention

[0003] The inventors herein have recognized that an LP EGR system may have advantages over an HP EGR system during some vehicle operating conditions, and an HP EGR system may have advantages over an LP EGR system during some vehicle operating conditions. Therefore, the inventors have developed a two-stroke diesel engine operating method comprising: receiving data indicative of a concentration of hydrocarbon (HC) and / or particulate matter (PM) emissions flowing out of the engine to a controller; and deactivating a high pressure exhaust gas recirculation (EGR) system and activating a low pressure EGR system in response to the concentration of HC emissions and / or particulate matter (PM) flowing out of the engine.

[0004] By activating and deactivating the high-pressure and low-pressure EGR systems in response to the concentration of hydrocarbon emissions flowing out of the engine, the following technical effects can be provided: EGR is provided to the engine while reducing hydrocarbons and / or particulate matter that may form deposits on the compressor or foul the charge air cooler. Specifically, the LP EGR system can be activated and the HP EGR system can be deactivated to reduce the possibility of hydrocarbon / particulate matter deposited on the compressor blades, so that compressor balance and efficiency can be maintained and charge air cooler fouling / clogging can be avoided. Hydrocarbons leaving the engine can be oxidized in the aftertreatment system, so that EGR with a low concentration of hydrocarbons can be provided upstream of the supercharger compressor. Similarly, a diesel particulate filter (DPF) can remove PM leaving the engine to avoid compressor and / or charge air cooler fouling. In this way, the exhaust gas can be purified before the exhaust gas enters the supercharger compressor during conditions where high concentrations of HC and / or PM may exist in the engine exhaust.

[0005] The present description may provide several advantages. Specifically, the method may allow a two-stroke diesel engine to operate with EGR even when engine emissions containing HC or particulate matter are higher than desired. Furthermore, the method may reduce degradation of a supercharger compressor and / or charge air cooler. Furthermore, the method may adjust EGR system operation in response to whether a supercharger compressor is operating such that an activated EGR system is consistent with other engine operating conditions.

[0006] The above advantages and other advantages and features of the present specification will be easily understood through the following detailed description alone or in combination with the accompanying drawings.

[0007] It should be understood that the above summary of the invention is provided to introduce some concepts that will be further described in the detailed description in a simplified form. This is not meant to identify key or essential features of the claimed subject matter, the scope of which is uniquely defined by the appended claims. In addition, 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

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

[0009] Figure 2 and Figure 3 Shown for Figure 1 An example predicted engine operating sequence for the illustrated engine; and

[0010] Figure 4 An example method for operating an engine having an LP EGR system and an HP EGR system is shown. DETAILED DESCRIPTION

[0011] The present description relates to providing EGR to a two-stroke diesel engine. Figure 1 An example of a supercharged two-stroke diesel engine including a mechanically driven supercharger and a turbocharger is shown. Figure 2 and Figure 3 An example engine operating sequence for supplying EGR to a two-stroke diesel engine via an HP EGR system and an LP EGR system is shown. Figure 4 An example method for operating a two-stroke diesel engine and providing EGR to the engine is shown. The LP EGR system may be activated to reduce the likelihood of supercharger compressor degradation, and the HP EGR system may be activated during engine operating conditions where the turbocharger compressor lacks the ability to provide the desired pressure in the engine's intake system.

[0012] refer to Figure 1 , an opposed-piston two-stroke internal combustion engine 10 (which includes a plurality of cylinders, Figure 1 The electronic engine controller 12 receives the information from the Figure 1 The signals of various sensors are used Figure 1 Various actuators are used to adjust engine operation based on received signals and instructions stored in the memory of the controller.

[0013] Engine 10 includes cylinder 30 and cylinder wall 32, wherein pistons 36a and 36b are positioned therein and connected to crankshafts 40a and 40b, respectively. Crankshafts 40a and 40b may be coupled together via a chain or gears. Crankshafts 40a and 40b may be rotated by motor 77 (e.g., a starter motor) to turn and start engine 10. Cylinder 30 is shown to be in communication with intake manifold 44 and exhaust manifold 48 via intake passages 44a and 44b and exhaust passages 48a and 48b.

[0014] Fuel injectors 68 and 69 are shown positioned in cylinder wall 32, and they can inject fuel directly into cylinder 30, which is referred to as direct injection by those skilled in the art. Fuel is delivered to fuel injectors 68 and 69 by a fuel system including fuel tank 95, fuel pump 91, fuel pump control valve 93, and a fuel rail (not shown). The pressure of fuel delivered by the fuel system can be adjusted by changing a position valve that regulates flow to the fuel pump (not shown). In addition, a metering valve can be positioned in or near the fuel rail for closed-loop fuel control. The pump metering valve can also regulate the fuel flow to the fuel pump, thereby reducing the fuel pumped to the high-pressure fuel pump.

[0015] The engine intake system 115 includes an intake manifold 44, which is shown as being in communication with a mechanically driven supercharger compressor 162, which draws air from the downstream of the turbocharger compressor 135. The supercharger compressor 162 is driven via the crankshaft 40b, the shaft 161, and the supercharger ratio changing device 163, which can be coupled to the crankshaft 40b via a mechanism 164 (e.g., a gear, chain, or belt). The supercharger ratio changing device 163 changes the speed of the supercharger compressor 162 relative to the speed of the crankshaft 40b. The gears within the device 163 may be disengaged, or the clutch may be opened to deactivate the supercharger compressor 162. The supercharger compressor may be activated by closing the clutch or engaging the gears within the device 163.

[0016] Supercharger compressor bypass valve 158 may be selectively opened to reduce air pressure in intake manifold 44 and return air and / or exhaust gas upstream of supercharger compressor 162 in the direction of airflow into the engine (e.g., from air intake 14 to cylinder intake passages 44a and 44b). Supercharger bypass valve 158 may also be opened to allow pressurized air to bypass supercharger compressor 162 when supercharger compressor 162 is deactivated. In some examples, charge air cooler 156 may be positioned downstream of supercharger compressor 162 to cool the air charge entering cylinder 30.

[0017] The turbocharger compressor 135 draws air from the air intake 42 and supplies the air to the mechanically driven supercharger compressor 156. The exhaust gas causes the turbocharger variable geometry turbine 137 coupled to the turbocharger compressor 135 to rotate via the shaft 136. The position of the vane actuator 137a can be adjusted via the controller 12 to increase or decrease the rotation speed of the turbine 137. In an alternative example, the wastegate 137b can replace the vane actuator 137a, or can be used in addition to the vane actuator. The vane actuator 137a adjusts the position of the variable geometry turbine vane 137c. When the vane 137c is in the open position, the exhaust gas can pass through the turbine 137, providing little energy to rotate the turbine 137. When the vane 137c is in the closed position, the exhaust gas can pass through the turbine 137 and exert an increased force on the turbine 137. Alternatively, the wastegate 137b or bypass valve allows the exhaust gas to flow around the turbine 137 to reduce the energy supplied to the turbine.

[0018] Exhaust gas may be recirculated to cylinder 30 via low pressure (LP) exhaust gas recirculation (EGR) system 81. The LP EGR system may include an EGR cooler 85, an LP EGR valve 80, and an LP EGR passage 84. LP exhaust gas may flow from exhaust aftertreatment device 70 and downstream of turbocharger turbine 137. When the pressure in exhaust system 129 downstream of turbocharger compressor 135 and upstream of exhaust pressure control valve 140 is greater than the pressure upstream of turbocharger compressor 135, LP EGR may flow to engine intake system 115. LP EGR may flow through LP EGR cooler 85 to reduce engine exhaust temperature.

[0019] Exhaust gas may also be recirculated to cylinder 30 via high pressure (HP) exhaust gas recirculation (EGR) system 53. The HP EGR system may include an EGR cooler 51, an HP EGR valve 50, and an HP EGR passage 54. HP exhaust gas may flow from exhaust manifold 48 and upstream of exhaust aftertreatment device 70. When the pressure in exhaust system 129 upstream of exhaust aftertreatment device 70 is greater than the pressure downstream of turbocharger compressor 135, HP EGR may flow to engine intake system 115. HP EGR may flow through HP EGR cooler 50 to reduce engine exhaust temperature.

[0020] After piston 36a covers intake passages 44a and 44b, fuel may be injected into cylinder 30 as pistons 36a and 36b approach each other. When piston 36 approaches top dead center compression stroke, fuel may then be combusted with air in cylinder 30. The fuel and air may be ignited via compression ignition. In some examples, universal exhaust gas oxygen (UEGO) sensor 126 may be coupled to exhaust manifold 48 upstream of emission device 70. In other examples, the UEGO sensor may be positioned 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. A hydrocarbon sensor 127 may sense the concentration of hydrocarbons exhausted from engine 10. A particle sensor 128 may sense particles (e.g., carbonaceous soot) exhausted from engine 10.

[0021] The engine 10 does not include glow plugs or spark plugs because it is a compression ignition engine and because it does not include a cylinder head. In addition, the engine 10 does not include a poppet valve for regulating air flow and exhaust flow into and out of the cylinder 30.

[0022] An exhaust valve 140 (e.g., a butterfly valve) is shown positioned in exhaust passage 49 downstream of turbine 137a and downstream of exhaust device 70. Exhaust valve 140 may be opened and closed to control pressure in exhaust manifold 48 and flow through exhaust manifold 48. Closing exhaust valve 140 restricts flow through exhaust valve 140 and may increase pressure in exhaust manifold 48 and decrease flow through exhaust manifold 48. Opening exhaust valve 140 may improve flow through exhaust valve 140 and decrease pressure in exhaust manifold 48 and increase flow through exhaust manifold 48. Exhaust valve 140 may be adjusted to increase or decrease exhaust flow through LP EGR system 81 and HP EGR system 53.

[0023] In one example, the emission device 70 may include an oxidation catalyst and a particulate filter. In another example, multiple emission control devices may be used, each having multiple bricks. In one example, the emission device 70 may include an oxidation catalyst. In other examples, the emission device may include a lean NOx trap or a selective catalytic reduction (SCR), and / or a diesel particulate filter (DPF).

[0024] The controller 12 Figure 1 10 is shown as a conventional microcomputer, which includes: a microprocessor unit (CPU) 102; input / output ports 104; read-only memory (ROM) (e.g., non-volatile memory) 106; random access memory (RAM) 108; keep alive memory (KAM) 110; and a conventional data bus. Controller 12 is shown as receiving various signals from sensors coupled to engine 10 in addition to those previously discussed, including: 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 adjusted by a person's foot 132; measurement of engine manifold pressure (MAP) from pressure sensor 121 coupled to intake manifold 44; exhaust oxygen concentration from oxygen sensor 126; engine position sensor from Hall effect sensor 118, sensing the position of crankshaft 40b; and measurement of air mass entering the engine from sensor 120 (e.g., a hot wire air flow meter). 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.

[0025] During operation, each cylinder within the engine 10 typically undergoes a two-stroke cycle: the cycle includes a first stroke, in which the intake piston 36a moves toward the exhaust piston 36b and the exhaust piston 36b moves toward the intake piston 36a. In the second stroke, the intake piston 36a moves away from the exhaust piston 36b, and the exhaust piston 36b moves away from the intake piston 36a. The intake piston 36a controls the flow through the intake passages 44a and 44b. The exhaust piston 36b controls the flow through the exhaust passages 48a and 48b. In this example, the exhaust piston 36b leads the intake piston 36a by reaching the top dead center position (e.g., the maximum distance of the exhaust piston 36b from the crankshaft 40b) by several crankshaft degrees (e.g., depending on the configuration, the difference can range between 0 and 20 crankshaft degrees). Therefore, the exhaust piston motion is offset by several crankshaft degrees relative to the intake piston motion.

[0026] Typically, during the first stroke, the intake piston 36a and the exhaust piston 36b move toward each other to compress the air that has entered the cylinder 30. For the intake piston 36a, the stroke starts at the bottom dead center (BDC) (the intake piston 36a is closest to the crankshaft 40a), and for the intake piston 36a, the stroke ends at the top dead center (the intake piston 36a is at the farthest distance from the crankshaft 40a). As previously described, the exhaust piston 36b leads the intake piston 36a by several degrees, so that when the intake piston is at BDC, it has already traveled toward its TDC position. In addition, the exhaust piston 36b reaches its TDC position just before the intake piston 36a reaches its TDC position. When the intake piston 36a reaches its TDC position, the exhaust piston 36b is just behind its TDC position. When the intake piston 36a and the exhaust piston 36b are close to their respective TDC positions, the cylinder volume is minimum. As the intake piston 36a and the exhaust piston 36b advance toward their respective TDC positions, air and fuel are compressed in the cylinder 30. When the intake piston 36a and the exhaust piston 36b approach their respective BDC positions, the intake passages 44a and 44b open and pressurized air flows into the cylinder 30. When the intake piston 36a and the exhaust piston 36b approach BDC, the exhaust passages 48a and 48b also open. The supercharger compressor 162 and the turbocharger compressor 135 provide pressurized air to the intake manifold 44, which can flow into the cylinder 30 when the intake passages 44a and 44b are open. When the intake piston 36a and the exhaust piston 36b move toward their respective TDC positions, the exhaust passages 48a and 48b are closed. The crankshaft continues to rotate and after a predetermined actual total crankshaft degree, the intake passages 44a and 44b are closed to prevent additional air from entering the cylinder 36. Thus, the exhaust port opens before the intake port, and the exhaust port remains open for substantially the entire duration that the intake port is open. Fuel is injected into cylinder 30 after exhaust ports 44a and 44b are closed, and then the fuel and air mixture is ignited when intake piston 36a and exhaust piston 36b are near their respective TDC positions. The fuel and air mixture is ignited by compression ignition rather than via a spark plug or energy from a glow plug. Fuel may be injected into cylinder 30 via multiple injections, including a pilot injection, a main injection, and a post injection.

[0027] Typically, during the second stroke, after combustion occurs in the cylinder 30, the intake piston 36a and the exhaust piston 36b move apart from each other. The second stroke starts at the TDC of the intake piston 36a and ends at the BDC of the intake piston 36a. The intake piston 36a and the exhaust piston 36b approach their respective BDC positions near the position where the volume of the cylinder 30 is the largest. The expansion of the gas in the cylinder 30 pushes the intake piston 36a and the exhaust piston 36b apart toward their respective BDC positions. The exhaust piston 36b passes through the exhaust passages 48a and 48b as it travels toward its BDC. When the top of the exhaust piston 36d passes through the exhaust passages 48a and 48b while the exhaust piston 36b travels toward the crankshaft 40b, the exhaust passages 48a and 48b are uncovered. After the exhaust piston 36b travels toward the bottom dead center through the exhaust passages 48a and 48b at the same time, the exhaust gas leaves the cylinder 30. The intake piston 36a and the exhaust piston 36b travel further toward their respective bottom dead center positions, and after a predetermined actual total crankshaft degree, the intake piston 36a exposes the intake passages 44a and 44b. The intake passages 44a and 44b are exposed when the top of the intake piston 36c passes through the intake passages 44a and 44b while the intake piston 36a travels toward the crankshaft 40a. When the intake passages 44a and 44b are exposed, fresh air enters the cylinder 30 via the intake passages 44a and 44b. The intake piston 36a and the exhaust piston 36b continue to travel toward their respective BDC positions. After the intake piston reaches BDC, the cylinder cycle repeats.

[0028] Thus, an engine cycle includes two strokes, and an engine cycle is one engine rotation. The other engine cylinders operate in a similar manner, but these other cylinders may combust air and fuel out of phase with the cylinders 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.

[0029] Figure 1 The system provides an engine system including: an opposed-piston two-stroke diesel engine; a supercharger coupled to the opposed-piston two-stroke diesel engine, the supercharger including a supercharger compressor bypass valve; a turbocharger coupled to the opposed-piston two-stroke diesel engine, the turbocharger including a turbocharger compressor bypass valve; and a controller including executable instructions stored in a non-transitory memory for causing the controller to operate the opposed-piston two-stroke engine at less than a threshold particulate matter mass flow rate output and less than a threshold hydrocarbon concentration output, and additional instructions for deactivating a low-pressure EGR system and activating a high-pressure EGR system in response to the opposed-piston two-stroke engine operating at less than a threshold particulate matter mass flow rate output and less than a threshold hydrocarbon concentration output.

[0030] In some examples, the engine system also includes additional instructions for causing the controller to operate the opposed piston two-stroke engine at a particulate matter mass flow rate output greater than a threshold, and additional instructions for activating the low-pressure EGR system and deactivating the high-pressure EGR system in response to the opposed piston two-stroke engine operating at a particulate matter mass flow rate output greater than a threshold. The engine system also includes additional instructions for causing the controller to operate the opposed piston two-stroke engine at a particulate matter mass flow rate output greater than a threshold, and additional instructions for activating the low-pressure EGR system and deactivating the high-pressure EGR system in response to the opposed piston two-stroke engine operating at a hydrocarbon concentration output greater than a threshold. The engine system also includes additional instructions for causing the controller to deactivate the high-pressure EGR system and activate the low-pressure EGR system in response to activating a supercharger. The engine system also includes additional instructions for causing the controller to open a supercharger compressor bypass valve in response to deactivating the supercharger. The engine system also includes an exhaust backpressure control valve positioned in an exhaust system of the opposed piston two-stroke diesel engine.

[0031] Reference now Figure 2 , showing a first predicted engine operating sequence. The engine 10 may be operated as shown in FIG. Figure 1 The system shown (including Figure 4 In this example engine operating sequence, when the turbocharger is capable of providing the desired air flow to the engine, the supercharger compressor is deactivated to reduce system parasitic losses. Figure 2 It includes nine curves, which are arranged in time and represent the control variables of the series time.

[0032] Figure 2 The first curve from top to bottom is a curve of engine exhaust flow rate (e.g., the flow rate of exhaust gas leaving the engine) versus time. The vertical axis represents the engine exhaust flow rate, and the exhaust flow rate increases in the direction of the vertical axis arrow. The horizontal axis represents time, and time increases from the left side of the curve to the right side of the curve. Horizontal line 250 represents a threshold engine exhaust flow rate. When the engine exhaust flow rate is below threshold 250, the energy provided to the turbocharger may be low. Therefore, if the engine exhaust flow rate is less than threshold 250, the turbocharger may not provide the desired amount of airflow to the engine. Trace 202 represents the engine exhaust flow rate.

[0033] Figure 2 The second curve from top to bottom is a curve of vehicle speed and time. The vertical axis represents vehicle speed and the vehicle speed increases in the direction of the vertical axis arrow. The horizontal axis represents time and time increases from the left side of the curve to the right side of the curve. Trace 204 represents vehicle speed.

[0034] Figure 2The third curve from top to bottom is a curve of engine speed and time. The vertical axis represents engine speed and the engine speed increases in the direction of the vertical axis arrow. The horizontal axis represents time and time increases from the left side of the curve to the right side of the curve. Trace 206 represents engine speed.

[0035] Figure 2 The fourth curve from top to bottom is a curve of engine load and time. The vertical axis represents engine load and the engine load increases in the direction of the vertical axis arrow. The horizontal axis represents time and time increases from the left side of the curve to the right side of the curve. Trace 208 represents engine load.

[0036] Figure 2 The fifth curve from top to bottom is a curve of engine hydrocarbon concentration in engine exhaust emissions versus time. The vertical axis represents engine hydrocarbon concentration in engine exhaust emissions, and the engine hydrocarbon concentration in engine exhaust emissions increases in the direction of the vertical axis arrow. The horizontal axis represents time and time increases from the left side of the curve to the right side of the curve. Trace 210 represents the engine hydrocarbon concentration in engine exhaust emissions.

[0037] Figure 2 The sixth curve from top to bottom is a curve of engine particulate matter (e.g., carbonaceous soot) mass in engine exhaust emissions versus time. The vertical axis represents engine particulate matter (PM) mass in engine exhaust emissions, and the engine particulate matter mass in engine exhaust emissions increases in the direction of the vertical axis arrow. The horizontal axis represents time and time increases from the left side of the curve to the right side of the curve. Trace 212 represents the engine particulate matter mass in engine exhaust emissions.

[0038] Figure 2 The seventh curve from top to bottom is a curve of engine HP EGR state versus time. The vertical axis represents the engine HP EGR state, and when trace 214 is at a higher level near the vertical axis arrow, the HP EGR system is activated (e.g., exhaust flows through the HP EGR system). When trace 214 is at a lower level near the horizontal axis, the HP EGR system is not activated. The horizontal axis represents time and time increases from the left side of the curve to the right side of the curve. Trace 214 represents the engine HP EGR state.

[0039] Figure 2The eighth curve from top to bottom is a curve of engine LP EGR state versus time. The vertical axis represents the engine LP EGR state, and when trace 216 is at a higher level near the vertical axis arrow, the LP EGR system is activated (e.g., exhaust flows through the LP EGR system). When trace 216 is at a lower level near the horizontal axis, the LP EGR system is not activated. The horizontal axis represents time and time increases from the left side of the curve to the right side of the curve. Trace 216 represents the engine LP EGR state.

[0040] Figure 2 The ninth curve from top to bottom is a curve of supercharger compressor state versus time. The vertical axis represents the supercharger compressor operating state, and when trace 218 is close to the vertical axis arrow, the supercharger compressor is activated. When trace 218 is close to the horizontal axis, the supercharger compressor is deactivated. The supercharger compressor can be deactivated by opening the clutch or disengaging the gear in the supercharger ratio changing device 163 so that the supercharger compressor does not rotate via the engine crankshaft. Trace 218 represents the supercharger compressor state.

[0041] At time t0, the engine is running, burning air and fuel, and the engine exhaust flow is greater than a threshold value 250. Since the mechanical turbocharger compressor has the ability to provide a larger amount of air to the engine when the engine exhaust flow is greater than the threshold value 250, the mechanical supercharger compressor is deactivated. The vehicle speed is at an intermediate level, and the engine speed is also at an intermediate level. The engine load is at a higher intermediate level, and the engine HC concentration emissions are low. The engine particulate matter emissions are also low and the HP EGR system is deactivated. The LP EGR system is activated so that EGR flows into the turbocharger compressor instead of upstream of the turbocharger compressor, where the exhaust pressure must exceed the pressure downstream of the turbocharger compressor to direct the EGR flow to the engine. Therefore, by providing LP EGR upstream of the turbocharger compressor, the exhaust pressure can be reduced to improve engine efficiency while providing EGR to the engine.

[0042] At time t1, the engine load decreases in response to a decrease in accelerator pedal position (not shown). As the torque produced by the engine decreases, the vehicle speed and engine speed also begin to decrease. The engine exhaust flow decreases, but it remains greater than a threshold of 250, so the supercharger compressor remains deactivated. The engine HC concentration and particulate matter (PM) levels remain low. The LP EGR system remains activated, and the HP EGR system remains deactivated.

[0043] At time t2, the engine load begins to increase in response to the accelerator pedal being depressed (not shown). The engine speed, exhaust flow, and vehicle speed also begin to increase in response to the increase in engine load. The engine HC and PM emissions remain at their previous levels. The HP EGR system remains deactivated, and the LP EGR system remains activated. The supercharger compressor also remains deactivated.

[0044] Between time t2 and time t3, vehicle speed, engine load, engine speed, and exhaust flow continue to increase. PM also increases, but HC concentration in the engine exhaust is lower. The HP EGR system remains deactivated, and the LP EGR system remains activated. The supercharger compressor remains deactivated.

[0045] At time t3, the engine load stabilizes to a higher constant value. The engine speed and vehicle speed also stabilize to higher constant values. Exhaust flow is at a higher level and HC emissions are lower. PM emissions have increased to a higher level, but PM may be trapped in the aftertreatment system so that a small amount of PM can flow into the turbocharger compressor, thereby reducing soot accumulation within the turbocharger compressor and air charge cooler. The HP EGR system remains deactivated and the LP EGR system remains activated. The supercharger compressor remains deactivated.

[0046] At time t4, the engine load begins to decrease in response to the accelerator pedal being partially released (not shown). The engine speed, exhaust flow, and vehicle speed also begin to decrease in response to the decrease in engine load. Engine HC emissions remain low, and PM emissions begin to drop. The HP EGR system remains deactivated, and the LP EGR system remains activated. The supercharger compressor also remains deactivated.

[0047] Between time t4 and time t5, vehicle speed, engine load, engine speed, and exhaust flow continue to decrease. PM also decreases, but HC concentration in the engine exhaust remains low. The HP EGR system remains deactivated, and the LP EGR system remains activated. The supercharger compressor remains deactivated.

[0048] At time t5, the engine load stabilizes to a lower constant value, and the engine speed and vehicle speed also stabilize to lower constant values. Exhaust flow is at a lower level, but remains greater than the threshold 250. PM emissions have been reduced to a lower level, but EGR continues to flow because LP EGR is supplied to the inlet of the turbocharger compressor. The HP EGR system remains deactivated, and the LP EGR system remains activated. The supercharger compressor remains deactivated.

[0049] In this way, LP EGR can be supplied to the engine and PM (which can flow to the turbocharger compressor) can be reduced when exhaust flow is greater than a threshold so that the supercharger compressor can be deactivated to reduce parasitic losses. Thus, when the supercharger compressor is deactivated, the HP EGR system can be deactivated and the LP EGR system can be activated to control NOx generation within the engine.

[0050] Reference now Figure 3 , showing a second predicted engine operation sequence. The engine 10 may be operated as shown in FIG. Figure 1 The system shown (including Figure 4 In this example engine operating sequence, the supercharger compressor is activated to increase airflow to the engine 10 when the turbocharger may not be able to provide the desired airflow to the engine. Figure 3 include Figure 2 The same nine curves shown in FIG. 1 are arranged in time and represent the control variables of the time series. For the sake of brevity, the above are not described to avoid redundancy. Figure 3 curve, but the curve follows the Figure 2 Descriptions of curves are provided unless otherwise specified below.

[0051] At time t10, the engine is running, burning air and fuel, and the engine exhaust flow is less than threshold 350. Since the turbocharger compressor does not have the ability to provide a larger amount of air to the engine when the engine exhaust flow is less than threshold 350, the supercharger compressor is activated. The vehicle speed is at a lower intermediate level, and the engine speed is also at a lower intermediate level. The engine load is at a lower intermediate level, and the engine HC concentration emissions are low. The engine particulate matter (PM) emissions are also low, and the HP EGR system is activated. The HP EGR system is activated so that EGR flows into the supercharger compressor, which may have a lower pressure, especially because the turbocharger compressor may not have enough ability to provide a higher air flow rate to the engine. Therefore, by providing HP EGR downstream of the turbocharger compressor, EGR can be provided to the engine when the turbocharger compressor may not have a high flow and when the engine HC and PM emissions may be low. The supercharger compressor remains activated, as shown by the supercharger compressor state being at a higher level.

[0052] At time t11, the engine load decreases in response to a decrease in the accelerator pedal position (not shown). As the torque produced by the engine decreases, the vehicle speed and engine speed also begin to decrease. The engine exhaust flow decreases and remains less than the threshold 350, so that the supercharger compressor remains activated. The engine HC concentration begins to increase shortly after time t11, and the LP EGR system is activated shortly after time t11 in response to the increased HC concentration. The HP EGR system is deactivated in response to the increased HC level. By activating the LP EGR system, hydrocarbons entering the engine intake system 115 can be reduced to reduce the possibility of hydrocarbons depositing on the compressor blades and fouling the air charge cooler in the engine intake system. Hydrocarbons leaving the engine can be reduced by passing through an aftertreatment system in the engine exhaust system 129.

[0053] At time t12, the engine load begins to increase in response to the accelerator pedal being depressed (not shown). The engine speed, exhaust flow, and vehicle speed also begin to increase in response to the increase in engine load. The engine HC emissions remain low and PM emissions from the engine begin to decrease a short time after time t12. The HP EGR system is activated a short time after time t12 in response to the reduction in engine HC emissions. The LP EGR system is deactivated in response to the reduction in engine HC emissions shortly after time t12. The supercharger compressor also remains activated.

[0054] Between time t12 and time t13, vehicle speed, engine load, engine speed, and exhaust flow continue to increase. PM increases in response to the increased engine load, and the LP EGR system is activated in response to the increased PM emissions. The HP EGR system is deactivated in response to the increased PM emissions and the supercharger compressor remains activated.

[0055] At time t13, the engine load stabilizes to a higher constant value. The engine speed and vehicle speed also stabilize to higher constant values. Exhaust flow remains below threshold 350 and PM emissions are at a higher level. HC emissions remain at a lower level. The HP EGR system remains deactivated and the LP EGR system remains activated. The supercharger compressor remains activated.

[0056] At time t14, the engine load begins to decrease in response to the accelerator pedal being partially released (not shown). The engine speed, exhaust flow, and vehicle speed also begin to decrease in response to the decrease in engine load. Engine HC emissions remain low, and PM emissions begin to drop. The LP EGR system is deactivated shortly after time t14 in response to reduced PM emissions. The HP EGR system is activated shortly after time t14 in response to lower PM emissions. The HP EGR system can be reactivated because there is a lower chance of degradation of the compressor and charge air cooler in the engine intake system 115 when there is less PM in the exhaust. The supercharger compressor also remains deactivated.

[0057] At time t15, the engine load stabilizes to a lower constant value, and the engine speed and vehicle speed also stabilize to lower constant values. Exhaust flow is at a lower level and it remains less than threshold 350. Since HP EGR is supplied to the inlet of the supercharger compressor, PM emissions have been reduced to a lower level and EGR continues to flow. The LP EGR system remains deactivated. The supercharger compressor remains deactivated.

[0058] In this way, HP EGR can be supplied to the engine when the exhaust gas flow is less than a threshold value so that the supercharger compressor can be deactivated to reduce parasitic losses. HP EGR can be activated when the HC concentration in the engine exhaust is less than a threshold value and the PM in the engine exhaust is less than a threshold value. Therefore, the HP EGR system and the LP EGR system can be selectively activated and deactivated to control NOx generation in the engine and reduce degradation of the compressor and air charge cooler when the supercharger compressor is activated.

[0059] Reference now Figure 4 , a method for operating a two-stroke diesel engine is shown. Figure 4 Methods can be stored as executable instructions in a program such as Figure 1 In the non-transitory memory in the system shown. Figure 4 The method can be combined with Figure 1 In addition, Figure 4 At least a portion of the method may be incorporated as executable instructions stored in a non-transitory memory, and other portions of the method may be executed via a controller that converts operating states of devices and actuators in the physical world. The controller may employ engine actuators of the engine system to adjust engine operation and operate the engine according to the method described below. Figure 1 Executable instructions for operating the engine under the conditions described herein may also be included.

[0060] At 402, method 400 determines vehicle operating conditions. Vehicle operating conditions (eg, data) may include, but are not limited to, vehicle speed, engine speed, engine load, concentration of engine HC emissions, mass flow rate of engine PM emissions, supercharger operating state, and exhaust flow rate. Figure 1 The operating conditions are determined based on the outputs of the sensors and actuators shown in the system. Method 400 proceeds to 404.

[0061] At 404, method 400 determines whether supercharger 162 is disabled. Method 400 may determine that supercharger 162 is disabled based on the value of a variable stored in controller memory. The value of the variable may change if the supercharger is commanded off or on. In other examples, the speed of the supercharger may be the basis for determining whether the supercharger is activated or disabled. If method 400 determines that the supercharger is activated, method 400 proceeds to 406. If method 400 determines that the supercharger is not activated, the answer is no, and method 400 proceeds to 430.

[0062] The supercharger may be activated and deactivated in response to the engine exhaust flow rate or other conditions such as engine speed and engine load. For example, the supercharger may be deactivated in response to the engine exhaust flow being greater than a threshold value, so that the turbocharger compressor has the ability to provide an airflow greater than a threshold air flow rate to the engine. The supercharger may be activated in response to the engine exhaust flow being less than a threshold value, so that the turbocharger compressor has no ability to provide an airflow greater than a threshold air flow rate to the engine. The supercharger compressor bypass valve may be opened when the supercharger is deactivated, so that less air and EGR may flow through the supercharger compressor, thereby further reducing the possibility of supercharger compressor degradation when EGR flows into the engine air intake 115.

[0063] At 430, method 400 deactivates the HP EGR system. The HP EGR system may be deactivated by closing the HP EGR valve. By deactivating the HP EGR system when the supercharger is deactivated, pressurized air may not flow from the turbocharger compressor to the exhaust system via the HP EGR passage. Additionally, improved exhaust pressure control may be provided via the exhaust back pressure valve 140 when the HP EGR system is deactivated and the LP EGR system is activated. Method 400 proceeds to 432.

[0064] At 432, method 400 activates the LP EGR system. The LP EGR system may be activated by at least partially opening the LP EGR valve. By activating the LP EGR system when the supercharger is deactivated, hydrocarbons and particulate matter in the exhaust gas may be oxidized or captured before the exhaust gas is introduced into the engine intake system 115. By reducing the particulate matter and hydrocarbons in the exhaust gas, degradation of the turbocharger compressor, the supercharger compressor, and the air charge cooler in the engine intake system 115 may be reduced. After activating the LP EGR system, method 400 proceeds to exit.

[0065] The engine controller may include instructions for operating at higher levels of engine speed and engine load in response to engine speed and driver demand torque or engine load where the concentration of HC emissions may be less than a threshold level and the mass flow rate of PM from the engine may be greater than a threshold level. Such conditions may exist when the answer at 408 is yes. The driver demand torque may be input via an accelerator pedal, and the accelerator pedal position may be converted to the driver demand torque.

[0066] EGR can be provided via the LP EGR system within a certain engine speed and load range after the LP EGR system is activated. In addition, after the LP EGR system is activated, the amount of EGR mass can vary in response to vehicle operating conditions. Specifically, the EGR amount can be adjusted by adjusting the position of the exhaust backpressure control valve 140. In addition, the exhaust backpressure valve can be at least partially closed in response to the HP EGR system being deactivated and the LP EGR system being activated. The exhaust backpressure control valve can be further closed when the HP EGR system is deactivated and the LP EGR system is activated to increase the pressure difference on the LP EGR system, so that the EGR flow rate can be maintained during the switch from HP EGR to LP EGR.

[0067] At 406, method 400 judges whether the concentration of HC emissions in the exhaust gas exiting the engine is greater than a threshold. Method 400 may judge that the concentration of HC emissions in the exhaust gas exiting the engine is greater than a threshold by comparing the output of the HC sensor to a threshold. If method 400 judges that the concentration of HC emissions in the exhaust gas exiting the engine is greater than the threshold, the answer is yes and method 400 proceeds to 420. Otherwise, the answer is no and method 400 proceeds to 408.

[0068] At 420 , method 400 deactivates the HP EGR system. The HP EGR system may be deactivated by closing the HP EGR valve. By deactivating the HP EGR system, HC in the exhaust may not be deposited on the supercharger compressor or the charge air cooler positioned downstream of the supercharger compressor. Method 400 proceeds to 422 .

[0069] At 422, method 400 activates the LP EGR system. The LP EGR system can be activated by at least partially opening the LP EGR valve. By activating the LP EGR system when the concentration of HC emissions in the engine exhaust exceeds a threshold, degradation of the supercharger compressor and the air charge cooler can be prevented while EGR still flows to the engine. Specifically, hydrocarbons can be oxidized within an oxidation catalyst located upstream of the LP EGR system in the engine exhaust system 129, so that degradation of the supercharger compressor and the turbocharger compressor can be reduced. In addition, degradation of the air charge cooler in the engine intake system 115 can be reduced by reducing hydrocarbons entering the engine intake system 115. Method 400 proceeds to exit.

[0070] The engine controller may include instructions for operating at lower levels of engine speed and engine load in response to engine speed and driver demand torque or engine load where the concentration of HC emissions may be greater than a threshold level and the mass flow rate of PM from the engine may be less than a threshold level. Such conditions may exist when the answer at 406 is yes. The driver demand torque may be input via an accelerator pedal, and the accelerator pedal position may be converted to the driver demand torque.

[0071] At 408, method 400 determines whether the PM mass flow rate in the exhaust gas leaving the engine is greater than a threshold. Method 400 can determine that the PM mass flow rate in the exhaust gas leaving the engine is greater than a threshold by comparing the output of the PM sensor to a threshold. If method 400 determines that the PM mass flow rate in the exhaust gas leaving the engine is greater than a threshold, the answer is yes and method 400 proceeds to 430. Otherwise, the answer is no and method 400 proceeds to 410.

[0072] At 410, method 400 activates the HP EGR system. The HP EGR system may be activated by at least partially opening the HP EGR valve. By activating the HP EGR system, EGR may be provided to the engine at lower engine loads when the turbocharger compressor lacks the ability to provide a desired amount of airflow to the engine. Additionally, the engine may be operated with less exhaust throttling via the exhaust pressure control valve, thereby improving engine efficiency because the pressure of the HP EGR entering the engine intake system 115 may be lower when the compressor is operating. Method 400 proceeds to 412.

[0073] At 412, method 400 deactivates the LP EGR system. The LP EGR system may be deactivated by closing the LP EGR valve. By deactivating the LP EGR system when HC and PM mass flow rates in the engine exhaust are low, exhaust throttling via the exhaust valve may be reduced to improve engine efficiency. Additionally, since HC and PM are low, the likelihood of supercharger compressor degradation may be lower. Method 400 proceeds to exit.

[0074] The engine controller may include instructions for operating at lower intermediate levels of engine speed and engine load in response to engine speed and driver demand torque or engine load where the concentration of HC emissions may be less than a threshold level and the mass flow rate of PM from the engine may be less than a threshold level. Such conditions may exist when the answer at 408 is no. The driver demand torque may be input via an accelerator pedal, and the accelerator pedal position may be converted to the driver demand torque.

[0075] The LP EGR system and the HP EGR system may be activated and deactivated in this manner to improve engine efficiency and reduce engine component degradation. Additionally, the supercharger bypass valve may be opened when the supercharger compressor is deactivated so that all air and exhaust gas in the engine's intake system does not have to pass through the supercharger compressor. This may further reduce the potential for engine component degradation.

[0076] Thus, method 400 may provide a two-stroke diesel engine operating method, the two-stroke diesel engine operating method comprising: receiving data indicating HC emissions flowing from the engine to a controller; and deactivating a high pressure exhaust gas recirculation (EGR) system and activating a low pressure EGR system in response to HC emissions flowing from the engine. The two-stroke diesel engine operating method comprises a case where deactivating the high pressure EGR system and activating the low pressure EGR system is performed in response to data indicating that engine HC emissions are greater than a threshold concentration. The two-stroke diesel engine operation comprises a case where deactivating the high pressure EGR comprises closing a high pressure EGR valve. The two-stroke diesel engine operating method also comprises adjusting a position of an exhaust back pressure valve in response to deactivating the high pressure EGR system and activating the low pressure EGR system. The two-stroke diesel engine operating method comprises a case where the high pressure EGR system provides exhaust gas to the engine into an engine intake system at a position upstream of a supercharger compressor and downstream of a turbocharger compressor. The two-stroke diesel engine operating method comprises a case where the low pressure EGR system provides exhaust gas to the engine into an engine intake system from a position in the exhaust system downstream of an aftertreatment device and a turbocharger turbine at a position upstream of a turbocharger compressor. The two-stroke diesel engine operating method also includes flowing exhaust gas from the low-pressure EGR system through three coolers before returning the exhaust gas to the engine cylinders.

[0077] Method 400 also provides a two-stroke diesel engine operating method, the two-stroke diesel engine operating method including: receiving data indicating a mass flow rate of particulate matter emissions flowing from the engine to a controller; and deactivating a high pressure exhaust gas recirculation (EGR) system and activating a low pressure EGR system in response to the engine particulate emission mass flow rate exceeding a threshold flow rate. The two-stroke diesel engine operating method also includes: receiving data indicating HC emissions flowing from the engine; and deactivating the high pressure EGR system and activating the low pressure EGR system in response to the HC emissions flowing from the engine. The two-stroke diesel engine operating method also includes: operating the engine when the HC emissions flowing from the engine are less than a first threshold and the mass flow rate of particulate matter from the engine is less than a second threshold; and deactivating the low pressure EGR system and activating the high pressure EGR system in response to the HC emissions flowing from the engine being less than the first threshold and the mass flow rate of particulate matter from the engine being less than the second threshold. The two-stroke diesel engine operating method includes a case where deactivating the low pressure EGR system includes closing a low pressure EGR valve. The two-stroke diesel engine operating method includes a case where activating the high pressure EGR system includes opening a high pressure EGR valve. The two-stroke diesel engine operating method further includes: operating the engine with the supercharger compressor disabled; and activating the low-pressure EGR system and deactivating the high-pressure EGR system in response to the supercharger compressor being disabled. The two-stroke diesel engine operating method further includes opening a supercharger bypass valve in response to the supercharger compressor being disabled.

[0078] 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 routines 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, part of the method can be a physical action taken in the real world to change the state of the device. The specific routines described herein can represent one or more of any number of processing strategies, such as event-driven, interrupt-driven, multi-tasking, multi-threading, etc. In this way, the various actions, operations and / or functions shown can be performed in the order shown, in parallel, or omitted in some cases. Similarly, the processing order is not necessarily required to achieve the features and advantages of the example embodiments described herein, but is provided for ease of illustration and description. One or more of the actions, operations and / or functions shown can be repeatedly performed according to the specific strategy used. In addition, at least a portion of the described actions, operations and / or functions can graphically represent the code in the non-transitory memory of the computer-readable storage medium to be programmed into the control system. If necessary, one or more of the method steps described herein can be omitted.

[0079] It should be understood that the configurations and routines disclosed herein are exemplary in nature, and these specific examples should not be viewed in a limiting sense, as many variations are possible. For example, the above techniques can 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.

[0080] The following claims particularly point out certain combinations and subcombinations regarded as novel and non-obvious. The 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.

[0081] According to the present invention, a two-stroke diesel engine operating method includes: receiving data indicative of HC emissions flowing from the engine to a controller; and deactivating a high pressure exhaust gas recirculation (EGR) system and activating a low pressure EGR system in response to HC emissions flowing from the engine.

[0082] According to one embodiment, the above invention is further characterized in that deactivating the high pressure EGR system and activating the low pressure EGR system is performed in response to data indicative of engine HC emissions indicating that engine HC emissions are greater than a threshold concentration.

[0083] According to one embodiment, deactivating high pressure EGR includes closing a high pressure EGR valve.

[0084] According to one embodiment, the invention is further characterized by adjusting a position of the exhaust back-pressure valve in response to deactivating the high pressure EGR system and activating the low pressure EGR system.

[0085] According to one embodiment, a high pressure EGR system provides exhaust gas to the engine into an engine intake system at a location upstream of a supercharger compressor and downstream of a turbocharger compressor.

[0086] According to one embodiment, a low pressure EGR system provides exhaust gas to the engine from an aftertreatment device and a location in the exhaust system downstream of a turbocharger turbine into an engine intake system at a location upstream of a turbocharger compressor.

[0087] According to one embodiment, the invention is further characterized by flowing exhaust gas from the low pressure EGR system through three coolers before returning the exhaust gas to the engine cylinders.

[0088] According to the present invention, a two-stroke diesel engine operating method includes: receiving data indicative of a particulate matter emission mass flow rate out of the engine to a controller; and deactivating a high pressure exhaust gas recirculation (EGR) system and activating a low pressure EGR system in response to the engine particulate emission mass flow rate exceeding a threshold flow rate.

[0089] According to one embodiment, the invention is further characterized by: receiving data indicative of HC emissions flowing from the engine; and deactivating the high pressure EGR system and activating the low pressure EGR system in response to the HC emissions flowing from the engine.

[0090] According to one embodiment, the invention is further characterized by: operating the engine when HC emissions flowing from the engine are less than a first threshold and a particulate matter mass flow rate from the engine is less than a second threshold; and deactivating the low-pressure EGR system and activating the high-pressure EGR system in response to HC emissions flowing from the engine being less than the first threshold and the particulate matter mass flow rate from the engine being less than the second threshold.

[0091] According to one embodiment, deactivating the low-pressure EGR system includes closing a low-pressure EGR valve.

[0092] According to one embodiment, activating the high pressure EGR system comprises opening a high pressure EGR valve.

[0093] According to one embodiment, the invention is further characterized by operating the engine with the supercharger compressor deactivated; and activating the low-pressure EGR system and deactivating the high-pressure EGR system in response to the supercharger compressor being deactivated.

[0094] According to one embodiment, the invention is further characterized by opening a supercharger bypass valve in response to the supercharger compressor being deactivated.

[0095] According to the present invention, an engine system is provided, the engine system having: an opposed-piston two-stroke diesel engine; a supercharger coupled to the opposed-piston two-stroke diesel engine, the supercharger including a supercharger compressor bypass valve; a turbocharger coupled to the opposed-piston two-stroke diesel engine, the turbocharger including a turbocharger compressor bypass valve; and a controller including executable instructions stored in a non-transitory memory for causing the controller to operate the opposed-piston two-stroke engine at less than a threshold particulate matter mass flow rate output and less than a threshold hydrocarbon concentration output, and additional instructions for deactivating a low-pressure EGR system and activating a high-pressure EGR system in response to the opposed-piston two-stroke engine operating at less than a threshold particulate matter mass flow rate output and less than a threshold hydrocarbon concentration output.

[0096] According to one embodiment, the invention further features additional instructions for causing the controller to operate the opposed-piston two-stroke engine at greater than a threshold particulate matter mass flow rate output, and additional instructions for activating the low-pressure EGR system and deactivating the high-pressure EGR system in response to the opposed-piston two-stroke engine operating at greater than a threshold particulate matter mass flow rate output.

[0097] According to one embodiment, the invention further features additional instructions for causing the controller to operate the opposed-piston two-stroke engine at greater than a threshold particulate matter mass flow rate output, and additional instructions for activating the low-pressure EGR system and deactivating the high-pressure EGR system in response to the opposed-piston two-stroke engine operating at greater than a threshold hydrocarbon concentration output.

[0098] According to one embodiment, the invention also features additional instructions for the controller to activate the high pressure EGR system and deactivate the low pressure EGR system in response to activating the supercharger.

[0099] According to one embodiment, the invention also features additional instructions for the controller to open a supercharger compressor bypass valve in response to deactivating the supercharger.

[0100] According to one embodiment, the invention also features an exhaust backpressure control valve positioned in the exhaust system of an opposed-piston two-stroke diesel engine.

Claims

1. A two-stroke diesel engine operating method, wherein include: receiving data indicative of HC emissions flowing from the engine to a controller; deactivating a high pressure EGR system and activating a low pressure EGR system in response to the HC emissions flowing from the engine; and A position of an exhaust back-pressure valve is adjusted in response to deactivating the high pressure EGR system and activating the low pressure EGR system.

2. The two-stroke diesel engine operating method of claim 1, wherein deactivating the high pressure EGR system and activating the low pressure EGR system is performed in response to the data indicative of HC emissions flowing out of the engine indicating that engine HC emissions are greater than a threshold concentration. 3 . The two-stroke diesel engine operating method of claim 2 , wherein deactivating the high pressure EGR system comprises closing a high pressure EGR valve.

4. The two-stroke diesel engine operating method of claim 1, wherein the high pressure EGR system provides exhaust gas to the engine into an engine intake system at a location upstream of a supercharger compressor and downstream of a turbocharger compressor.

5. The two-stroke diesel engine operating method of claim 4, wherein the low pressure EGR system provides exhaust gas to the engine from a location in the exhaust system downstream of an aftertreatment device and a turbocharger turbine into the engine intake system at a location upstream of the turbocharger compressor.

6. The two-stroke diesel engine operating method of claim 1 further comprising flowing the exhaust gas from the low pressure EGR system through three coolers before returning the exhaust gas to the engine cylinders.

7. The two-stroke diesel engine operating method according to claim 1, further comprising: include: receiving data indicative of a mass flow rate of particulate matter emissions out of the engine to a controller; as well as A high pressure EGR system is deactivated and a low pressure EGR system is activated in response to the engine particulate emission mass flow rate exceeding a threshold flow rate.

8. The two-stroke diesel engine operating method according to claim 7, further comprising: include: receiving data indicative of HC emissions flowing from the engine; and deactivating the high pressure EGR system and activating a low pressure EGR system in response to the HC emissions flowing from the engine.

9. The two-stroke diesel engine operating method according to claim 7, further comprising: include: operating an engine with HC emissions outflowing from the engine less than a first threshold and the particulate matter mass flow rate from the engine less than a second threshold; and deactivating the low-pressure EGR system and activating the high-pressure EGR system in response to the HC emissions flowing from the engine being less than the first threshold and the particulate matter mass flow rate from the engine being less than the second threshold.

10. An engine system, wherein include: Opposed piston two-stroke diesel engine; a supercharger coupled to the opposed-piston two-stroke diesel engine, the supercharger including a supercharger compressor bypass valve; a turbocharger coupled to the opposed-piston two-stroke diesel engine, the turbocharger including a turbocharger compressor bypass valve; as well as a controller including executable instructions stored in non-transitory memory that cause the controller to operate the opposed-piston two-stroke diesel engine at less than a threshold particulate matter mass flow rate output and less than a threshold hydrocarbon concentration output, additional instructions to deactivate a low pressure EGR system and activate a high pressure EGR system in response to the opposed-piston two-stroke diesel engine operating at less than the threshold particulate matter mass flow rate output and less than the threshold hydrocarbon concentration output, and additional instructions to cause the controller to activate the high pressure EGR system and deactivate the low pressure EGR system in response to activating the supercharger.

11. The engine system of claim 10 further comprising additional instructions for causing the controller to operate the opposed-piston two-stroke diesel engine at greater than the threshold particulate matter mass flow rate output, and additional instructions for activating the low pressure EGR system and deactivating the high pressure EGR system in response to the opposed-piston two-stroke diesel engine operating at greater than the threshold particulate matter mass flow rate output.

12. The engine system of claim 10 further comprising additional instructions for causing the controller to operate the opposed-piston two-stroke diesel engine at greater than the threshold particulate matter mass flow rate output, and additional instructions for activating the low pressure EGR system and deactivating the high pressure EGR system in response to the opposed-piston two-stroke diesel engine operating at greater than the threshold hydrocarbon concentration output.

13. The engine system of claim 10 further comprising additional instructions causing said controller to open said supercharger compressor bypass valve in response to deactivating said supercharger.

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