System and method for controlling engine operating parameters during engine warm-up to reduce emissions

A system includes a temperature sensor configured to measure a temperature of exhaust gas produced by an engine, and a boost error module configured to determine a boost error of the engine. The system further includes a combustion control module configured to select at least one of a target boost pressure of the engine, a target EGR flow rate of the engine, and a target fuel injection parameter of the engine from a first set of target values when the exhaust gas temperature is less than a predetermined temperature and the boost error is less than a predetermined value, and to select the at least one of the target boost pressure, the target EGR flow rate, and the target fuel injection parameter from a second set of target values when the exhaust gas temperature is less than the predetermined temperature and the boost error is greater than the predetermined value.

FIELD

The present disclosure relates to systems and methods for controlling engine operating parameters during engine warm-up to reduce emissions.

BACKGROUND

Aftertreatment systems include components that reduce emissions in exhaust produced by a diesel engine. Some aftertreatment systems include a diesel oxidation catalyst, a selective catalytic reduction filter (SCRF) catalyst, and a selective catalytic reduction (SCR) catalyst. The diesel oxidation catalyst reduces carbon monoxide, hydrocarbons, and particulate matter emissions. The SCRF catalyst reduces nitrogen oxide emissions and traps soot (PM emissions). The SCR catalyst simply reduces nitrogen oxide emissions.

When an engine is started after the engine is shutdown for a while, components of an aftertreatment system do not operate efficiently (i.e., reduce emissions effectively) until the components are heated to their respective normal operating temperatures. In addition, an engine may produce more emissions when the engine completes a dynamic maneuver, such a rapid acceleration, relative to the amount of emissions produced by the engine during steady-state conditions, such as an unchanging engine speed. Thus, reducing emissions to acceptable levels during engine warmup and/or during a dynamic maneuver presents unique challenges.

SUMMARY

A first system according to the present disclosure includes a first exhaust gas temperature sensor, a boost error module, and a combustion control module. The first exhaust gas temperature sensor is configured to measure a first temperature of exhaust gas produced by an engine at a first location in an exhaust system of the engine. The boost error module is configured to determine a boost error of the engine. The boost error is a difference between a target boost pressure of the engine and a current boost pressure of the engine. The combustion control module is configured to take the following actions when the first exhaust gas temperature is less than a first predetermined temperature: select at least one of the target boost pressure, a target exhaust gas recirculated (EGR) flow rate of the engine, and a target fuel injection parameter of the engine from a first set of target values when the boost error is less than or equal to a predetermined value; and select the at least one of the target boost pressure, the target EGR flow rate, and the target fuel injection parameter from a second set of target values when the boost error is greater than the predetermined value, where the second set of target values is different than the first set of target values.

In one example, the combustion control module is configured to select the at least one of the target boost pressure, the target EGR flow rate, and the target fuel injection parameter from the first and second sets of target values based on at least one of a speed of the engine and a load on the engine.

In one example, when the first exhaust gas temperature is less than the first predetermined temperature, the combustion control module is configured to: select the target fuel injection parameter from the first set of target values when the boost error is less than or equal to the predetermined value; and select the target fuel injection parameter from the second set of target values when the boost error is greater than the predetermined value.

In one example, the target fuel injection parameter includes at least one of a target fuel injection timing and a target number of fuel injections for a cylinder of the engine during each combustion cycle of the engine.

In one example, when the first exhaust gas temperature is less than the first predetermined temperature, the combustion control module is configured to: adjust the target fuel injection timing to a first fuel injection timing when the boost error is less than or equal to the predetermined value; and adjust the target fuel injection timing to a second fuel injection timing when the boost error is greater than the predetermined value, where the second fuel injection timing is advanced relative to the first fuel injection timing.

In one example, when the first exhaust gas temperature is less than the first predetermined temperature, the combustion control module is configured to: adjust the target number of fuel injections to a first number when the boost error is less than or equal to the predetermined value; and adjust the target number of fuel injections to a second number when the boost error is greater than the predetermined value, where the second number is less than the first number.

In one example, when the first exhaust gas temperature is less than the first predetermined temperature, the combustion control module is configured to: select the target boost pressure, the target EGR flow rate, and the target fuel injection parameter from the first set of target values when the boost error is less than or equal to the predetermined value; and select the target boost pressure, the target EGR flow rate, and the target fuel injection parameter from the second set of target values when the boost error is greater than the predetermined value.

In one example, the first system further includes a second exhaust gas temperature sensor configured to measure a second temperature of exhaust gas produced by the engine at a second location in the exhaust system, where the combustion control module is configured to: select the target boost pressure, the target EGR flow rate, and the target fuel injection parameter from the first set of target values when the boost error is less than or equal to the predetermined value and the second exhaust gas temperature is less than or equal to a second predetermined temperature; select the target boost pressure, the target EGR flow rate, and the target fuel injection parameter from the second set of target values when the boost error is greater than the predetermined value and the second exhaust gas temperature is less than or equal to the second predetermined temperature; select the target boost pressure, the target EGR flow rate, and the target fuel injection parameter from a third set of target values when the boost error is less than or equal to the predetermined value and the second exhaust gas temperature is greater than the second predetermined temperature; and select the target boost pressure, the target EGR flow rate, and the target fuel injection parameter from a fourth set of target values when the boost error is greater than the predetermined value and the second exhaust gas temperature is greater than the second predetermined temperature.

In one example, for the same engine speed and the same engine load, the target boost pressure in the first set of target values is greater than the target boost pressure in the third set of target values, and the target boost pressure in the second set of target values is greater than the target boost pressure in the fourth set of target values.

In one example, for the same engine speed and the same engine load, the target EGR flow rate in the first set of target values is less than the target EGR flow rate in the third set of target values, and the target EGR flow rate in the second set of target values is less than the target EGR flow rate in the fourth set of target values.

In one example, the target fuel injection parameter includes a target injection quantity, the target injection quantity in the first and second sets of target values has a first variability, and the target injection quantity in the third and fourth sets of target values has a second variability that is greater than the first variability.

In one example, the first exhaust gas temperature sensor is located at an inlet of a selective catalytic reduction (SCR) catalyst in the exhaust system, the second exhaust gas temperature sensor is located at an inlet of a diesel oxidation catalyst in the exhaust system, and the second predetermined temperature is greater than the first predetermined temperature.

A second system according to the present disclosure includes a first exhaust gas temperature sensor configured to measure a first temperature of exhaust gas produced by an engine at a first location in an exhaust system of the engine, a second exhaust gas temperature sensor configured to measure a second temperature of exhaust gas produced by the engine at a second location in the exhaust system, and a combustion control module configured to take the following actions when the first exhaust gas temperature is less than a first predetermined temperature: select at least one of a target boost pressure of the engine, a target exhaust gas recirculated (EGR) flow rate of the engine, and a target fuel injection parameter of the engine from a first set of target values when the second exhaust gas temperature is less than or equal to a second predetermined temperature; and select the at least one of the target boost pressure, the target EGR flow rate, and the target fuel injection parameter from a second set of target values when the second exhaust gas temperature is greater than the second predetermined temperature, where the second set of target values is different than the first set of target values.

In one example, the combustion control module is configured to select the target boost pressure from the first set of target values when the first exhaust gas temperature is less than the first predetermined temperature and the second exhaust gas temperature is less than or equal to the second predetermined temperature, the combustion control module is configured to select the target boost pressure from the second set of target values when the first exhaust gas temperature is less than the first predetermined temperature and the second exhaust gas temperature is greater than the second predetermined temperature, and for the same engine speed and the same engine load, the target boost pressure in the first set of target values is greater than the target boost pressure in the second set of target values.

In one example, the combustion control module is configured to select the target EGR flow rate from the first set of target values when the first exhaust gas temperature is less than the first predetermined temperature and the second exhaust gas temperature is less than or equal to the second predetermined temperature, the combustion control module is configured to select the target EGR flow rate from the second set of target values when the first exhaust gas temperature is less than the first predetermined temperature and the second exhaust gas temperature is greater than the second predetermined temperature, and for the same engine speed and the same engine load, the target EGR flow rate in the first set of target values is less than the target EGR flow rate in the second set of target values.

In one example, the combustion control module is configured to select the target fuel injection parameter from the first set of target values when the first exhaust gas temperature is less than the first predetermined temperature and the second exhaust gas temperature is less than or equal to the second predetermined temperature, the combustion control module is configured to select the target fuel injection parameter from the second set of target values when the first exhaust gas temperature is less than the first predetermined temperature and the second exhaust gas temperature is greater than the second predetermined temperature, the target fuel injection parameter includes a target injection quantity, the target injection quantity in the first set of target values has a first variability, and the target injection quantity in the second set of target values has a second variability that is greater than the first variability.

In one example, the first exhaust gas temperature sensor is located at an inlet of a selective catalytic reduction (SCR) catalyst in the exhaust system, the second exhaust gas temperature sensor is located at an inlet of a diesel oxidation catalyst in the exhaust system, and the second predetermined temperature is greater than the first predetermined temperature.

A third system according to the present disclosure includes an exhaust gas temperature sensor configured to measure a temperature of exhaust gas produced by an engine, and a fuel control module configured to adjust a target number of fuel injections for a cylinder of the engine during each combustion cycle of the engine to a first number when the exhaust gas temperature is less than or equal to a predetermined temperature, where the first number is an integer greater than seven.

In one example, the third system further includes a boost error module configured to determine a boost error of the engine, where the boost error is a difference between a target boost pressure of the engine and a current boost pressure of the engine, and where, when the exhaust gas temperature is less than or equal to the predetermined temperature, the fuel control module is configured to: adjust the target number of fuel injections to the first number when the boost error is less than or equal to a predetermined value; and adjust the target number of fuel injections to a second number when the boost error is greater than the predetermined value, where each of the first and second numbers is an integer greater than seven.

In one example, the second number is different than the first number.

DETAILED DESCRIPTION

A system and method according to the present disclosure accelerates engine warmup and reduces emissions during engine warmup by identifying various phases of engine warmup and employing a unique engine control strategy during each phase of engine warmup. The system and method identifies which phase of engine warmup is taking place based on an exhaust gas temperature measured at one or more locations in an aftertreatment system of the engine. The engine control strategy employed optimizes a tradeoff between reducing hydrocarbon emissions and reducing nitrogen oxide emissions while increasing the robustness of the aftertreatment system to rapid changes in exhaust gas temperature. The engine control strategy employed may also reduce carbon dioxide emissions during engine warmup.

In one example, the system and method also identifies whether the engine is completing a dynamic maneuver and, if so, uses a unique engine control strategy for the dynamic maneuver and the engine warmup phase. The system and method identifies whether the engine is completing a dynamic maneuver based on a boost pressure measured in an intake manifold of the engine. The engine control strategy used during the dynamic maneuver increases the robustness of the engine to misfire and hydrocarbon or smoke deterioration.

The system and method uses a unique engine control strategy for each phase of engine warmup and/or during a dynamic maneuver by selecting target combustion control parameters from a unique set of target values based on engine speed and/or engine load. In one example, the system and method selects the target combustion control parameters from a first set of target values when a diesel oxidation catalyst in the aftertreatment system is not yet efficient and the engine is not completing a dynamic maneuver. In addition, the system and method selects the target combustion control parameters from a second set of target values when the diesel oxidation catalyst is not yet efficient and the engine is completing a dynamic maneuver. Further, the system and method selects the target combustion control parameters from a third set of target values when the diesel oxidation catalyst is efficient and the engine is not completing a dynamic maneuver. Moreover, the system and method selects the target combustion control parameters from a fourth set of target values when the diesel oxidation catalyst is efficient and the engine is completing a dynamic maneuver.

The system and method determines whether the diesel oxidation catalyst is efficient based on an exhaust gas temperature measured in or near the diesel oxidation catalyst, such as at the inlet thereof. The target combustion parameters include a target boost pressure, a target EGR flow rate (or percentage), and target fuel injection parameters. The target fuel injection parameters include a target injection quantity, a target injection timing, and/or a target number of injections.

In one example, the system and method increases the number of fuel injections per cylinder for each engine cycle during engine warmup relative to the number of fuel injections per cylinder for each engine cycle during normal engine operation. During engine warmup, the system and method commands at least eight fuel injections, including two pilot injections, one main injection, and at least five after injections (or post injections) for each cylinder during each engine cycle. Increasing the number of fuel injections yields less quantity of fuel per injection, which reduces oil dilution and smoke.

Referring now toFIG. 1, an engine system100includes an engine102. The engine102combusts an air/fuel mixture to produce drive torque for a vehicle based on driver input from a driver input module104. Air is drawn into the engine102through an intake system106. Air flow through the intake system106may be referred to as intake air flow. The intake system106may include an intake manifold108and a throttle valve110. The throttle valve110may include a butterfly valve having a rotatable blade. An engine control module (ECM)112controls a throttle actuator module116, which regulates opening of the throttle valve110to control the amount of air drawn into the intake manifold108.

Air from the intake manifold108is drawn into cylinders of the engine102. While the engine102may include multiple cylinders, for illustration purposes a single representative cylinder114is shown. For example only, the engine102may include 2, 3, 4, 5, 6, 8, 10, and/or 12 cylinders arranged in various configurations such as an inline configuration or a V configuration. The ECM112may deactivate some of the cylinders, which may improve fuel economy under certain engine operating conditions.

The engine102may operate using a four-stroke cycle. The four strokes, described below, are named the intake stroke, the compression stroke, the combustion stroke, and the exhaust stroke. During each revolution of a crankshaft (not shown), two of the four strokes occur within the cylinder114. Therefore, two crankshaft revolutions are necessary for the cylinder114to experience all four of the strokes.

During the intake stroke, air from the intake manifold108is drawn into the cylinder114through an intake valve118. The ECM112controls a fuel actuator module120, which regulates fuel injection in the engine102by adjusting the opening duration and timing of a fuel injector121. Fuel may be injected into the intake manifold108at a central location or at multiple locations, such as near the intake valve118of each of the cylinders. In various implementations, fuel may be injected directly into the cylinders or into mixing chambers associated with the cylinders. The fuel actuator module120may halt injection of fuel to cylinders that are deactivated.

The injected fuel mixes with air and creates an air/fuel mixture in the cylinder114. During the compression stroke, a piston (not shown) within the cylinder114compresses the air/fuel mixture. The engine102may be a compression-ignition engine, in which case compression in the cylinder114ignites the air/fuel mixture. Alternatively, the engine102may be a spark-ignition engine, in which case a spark actuator module122energizes a spark plug124in the cylinder114based on a signal from the ECM112, which ignites the air/fuel mixture. The timing of the spark may be specified relative to the time when the piston is at its topmost position, referred to as top dead center (TDC).

The spark actuator module122may be controlled by a timing signal specifying how far before or after TDC to generate the spark. Because piston position is directly related to crankshaft rotation, operation of the spark actuator module122may be synchronized with crankshaft angle. In various implementations, the spark actuator module122may halt provision of spark to deactivated cylinders.

Generating the spark may be referred to as a firing event. The spark actuator module122may have the ability to vary the timing of the spark for each firing event. The spark actuator module122may even be capable of varying the spark timing for a next firing event when the spark timing signal is changed between a last firing event and the next firing event. The spark actuator module122and the spark plug124may be omitted in implementations where the engine102is a compression-ignition engine.

During the combustion stroke, the combustion of the air/fuel mixture drives the piston down, thereby driving the crankshaft. The combustion stroke may be defined as the time between the piston reaching TDC and the time at which the piston returns to bottom dead center (BDC). During the exhaust stroke, the piston begins moving up from BDC and expels the byproducts of combustion through an exhaust valve126. The byproducts of combustion are exhausted from the vehicle via an exhaust system128.

The engine system100may include a boost device that provides pressurized air to the intake manifold108. For example,FIG. 1shows a turbocharger including a hot turbine130-1that is powered by hot exhaust gases flowing through the exhaust system128. The turbocharger also includes a cold air compressor130-2, driven by the turbine130-1, which compresses air leading into the throttle valve110. In various implementations, a supercharger (not shown), driven by the crankshaft, may compress air from the throttle valve110and deliver the compressed air to the intake manifold108.

A wastegate132may allow exhaust to bypass the turbine130-1, thereby reducing the boost (the amount of intake air compression) of the turbocharger. The ECM112may control the turbocharger via a boost actuator module134. The boost actuator module134may modulate the boost of the turbocharger by controlling the position of the wastegate132. In various implementations, multiple turbochargers may be controlled by the boost actuator module134. The turbocharger may have variable geometry, which may be controlled by the boost actuator module134.

An intercooler (not shown) may dissipate some of the heat contained in the compressed air charge, which is generated as the air is compressed. The compressed air charge may also have absorbed heat from components of the exhaust system128. Although shown separated for purposes of illustration, the turbine130-1and the compressor130-2may be attached to each other, placing intake air in close proximity to hot exhaust.

The engine system100may include an exhaust gas recirculation (EGR) valve136, which selectively redirects exhaust gas back to the intake manifold108. The EGR valve136may be located upstream of the turbocharger's turbine130-1. The EGR valve136may be controlled by an EGR actuator module138.

The exhaust system128includes a diesel oxidation catalyst140, a SCRF catalyst142, and a SCR catalyst144. The exhaust system128may be referred to as an aftertreatment system. The diesel oxidation catalyst140reduces carbon monoxide (CO), hydrocarbons (HC), and particulate matter (PM) emissions. The SCRF catalyst142reduces nitrogen oxide (NOx) emissions and traps soot (PM emissions). The SCR catalyst144simply reduces NOx emissions.

The position of the crankshaft may be measured using a crankshaft position (CKP) sensor146. The ECM112may determine the speed of the crankshaft (i.e., the engine speed) based on the crankshaft position. The temperature of the engine coolant may be measured using an engine coolant temperature (ECT) sensor148. The ECT sensor148may be located within the engine102or at other locations where the coolant is circulated, such as a radiator (not shown).

The pressure within the intake manifold108(i.e., the boost of the engine102) may be measured using a manifold absolute pressure (MAP) sensor150. In various implementations, engine vacuum, which is the difference between ambient air pressure and the pressure within the intake manifold108, may be measured. The mass flow rate of air flowing into the intake manifold108may be measured using a mass air flow (MAF) sensor152. In various implementations, the MAF sensor152may be located in a housing that also includes the throttle valve110. The throttle actuator module116may monitor the position of the throttle valve110using one or more throttle position sensors (TPS)154. The ambient temperature of air being drawn into the engine102may be measured using an intake air temperature (IAT) sensor156.

The temperature of exhaust gas produced by the engine102may be measured at one or more locations in the exhaust system128. The exhaust gas temperature at the inlet of the diesel oxidation catalyst140may be measured using an exhaust gas temperature (EGT) sensor158. The exhaust gas temperature at the inlet of the SCR catalyst144may be measured using an EGT sensor160.

The ECM112uses signals from the sensors to make control decisions for the engine system100. In one example, the ECM112uses the signals from the EGT sensors158,160to determine whether components of the exhaust system128are operating efficiently, and adjusts operating parameters of the engine102based on whether the components of the exhaust system128are operating efficiently. The engine operating parameters adjusted by the ECM112include a target boost pressure of the engine102, a target EGR flow rate of the engine102, and a target fuel injection parameter of the engine102.

Referring now toFIG. 2, an example implementation of the ECM112includes a boost error module202, an aftertreatment system efficiency module204, a diesel oxidation catalyst (DOC) efficiency module206, a boost control module208, an EGR control module210, and a fuel control module212. The boost error module202determines a boost error of the engine102. The boost error of the engine102is the difference between a target boost pressure of the engine102and a current boost pressure of the engine102. The boost error module202receives the current boost pressure of the engine102(i.e., the pressure in the intake manifold108) from the MAP sensor150. The boost error module202receives the target boost pressure of the engine102from the boost control module208.

The aftertreatment system efficiency module204determines whether the aftertreatment system (i.e., the exhaust system128) is operating efficiently. In other words, the aftertreatment system efficiency module204determines whether the aftertreatment system is reducing emissions at a normal rate. The aftertreatment system operates efficiently when the components of the aftertreatment system are at their normal operating temperatures. Thus, when the engine102is initially started after the engine102has been off for an extended period (e.g., hours), the aftertreatment system does not operate efficiently. However, after the exhaust gas from engine102has warmed up the components of the aftertreatment system, the aftertreatment system operates efficiently.

The aftertreatment system efficiency module204may determine that the aftertreatment system is operating efficiently when the exhaust gas temperature at one or more locations in the aftertreatment system has reached a certain temperature. In one example, the aftertreatment system efficiency module204determines that the aftertreatment system is operating efficiently when the exhaust gas temperature at the inlet of the SCR catalyst144is greater than a first predetermined temperature (e.g., a temperature within a range from 110 degrees Celsius (° C.) to 120° C.). The aftertreatment system efficiency module204receives the exhaust gas temperature at the inlet of the SCR catalyst144from the EGT sensor160.

The DOC efficiency module206determines whether the diesel oxidation catalyst140is operating efficiently. In other words, the DOC efficiency module206determines whether the diesel oxidation catalyst140is reducing CO, HC and PM emissions at a normal rate. The DOC efficiency module206may determine that the diesel oxidation catalyst140is operating efficiently when the exhaust gas temperature at one or more locations in or near the diesel oxidation catalyst140has reached a certain temperature. In one example, the DOC efficiency module206determines that the diesel oxidation catalyst140is operating efficiently when the exhaust gas temperature at the inlet of the diesel oxidation catalyst140is greater than a second predetermined temperature (e.g., a temperature within a range from 170° C. to 180° C.). The DOC efficiency module206receives the exhaust gas temperature at the inlet of the diesel oxidation catalyst140from the EGT sensor158.

The boost control module208, the EGR control module210, and the fuel control module212control operating parameters of the engine102that influence the combustion performance of the engine102. Thus, the boost control module208, the EGR control module210, and the fuel control module212may be individually or collectively referred to as a combustion control module. The boost control module208controls the boost pressure of the engine102. The boost control module208accomplishes this by generating the target boost pressure and outputting the target boost pressure to the boost actuator module134. In turn, the boost actuator module134controls the position of the wastegate132to achieve the target boost pressure.

The EGR control module210controls the rate of exhaust gas flow through the EGR valve136, which may be referred to as the EGR flow rate of the engine102. The boost control module208accomplishes this by generating a target EGR flow rate of the engine102and outputting the target EGR flow rate to the EGR actuator module138. In turn, the EGR actuator module138controls the position of the EGR valve136to achieve the EGR flow rate.

The fuel control module212controls fuel injection in the engine102. The fuel control module212accomplishes this by generating one or more target fuel injection parameters and outputting the target fuel injection parameters to the fuel actuator module120. In turn, the fuel actuator module120controls the opening duration and timing of the fuel injector121to achieve the target fuel injection parameters. The fuel injection parameters may include a target fuel injection quantity, a target fuel injection timing, and/or a target number of fuel injections for each cylinder of the engine102during each cycle of the engine102. The engine102completes one cycle when all of the cylinders of the engine complete all four of the strokes discussed above (i.e., the intake stroke, the compression stroke, the combustion stroke, and the exhaust stroke).

Referring now toFIG. 3, an example method of controlling the operating parameters of the engine102during engine warm-up begins at302. The method ofFIG. 3may be performed when the engine102is started. The method is described in the context of the modules ofFIG. 2. However, the particular modules that perform the steps of the method may be different than the modules mentioned below and/or one or more steps of the method may be implemented apart from the modules ofFIG. 2.

At304, the aftertreatment system efficiency module204determines whether the aftertreatment system (i.e., the exhaust system128) is efficient. If the aftertreatment system is efficient, the method continues at306. Otherwise, the method continues at308. As discussed above, the aftertreatment system efficiency module204may determine that the aftertreatment system is efficient if the exhaust gas temperature at the inlet of the SCR catalyst144is greater than the first predetermined temperature. Otherwise, the aftertreatment system efficiency module204may determine that the aftertreatment system is not yet efficient.

At308, the combustion control module (i.e., the boost control module208, the EGR control module210, and/or the fuel control module212) activates a warmup combustion mode. The warmup combustion mode is an operating mode of the combustion control module that is activated during engine warmup. At310, the DOC efficiency module206determines whether the diesel oxidation catalyst140is efficient. If the diesel oxidation catalyst140is efficient, the method continues at312. Otherwise, the method continues at314. As discussed above, the DOC efficiency module206may determine that the diesel oxidation catalyst140is efficient if the exhaust gas temperature at the inlet of the diesel oxidation catalyst140is greater than the first predetermined temperature. Otherwise, the DOC efficiency module206may determine that the diesel oxidation catalyst140is not yet efficient.

At314, the combustion control module determines whether the engine102is completing a dynamic maneuver. If the engine102is completing a dynamic maneuver, the method continues at316. Otherwise, the method continues at318. The combustion control module may determine that the engine102is completing a dynamic maneuver when the boost error is greater than a predetermined value (e.g., a value within a range between 30 kilopascals (kPa) and 60 kPa). Otherwise, the combustion control module may determine that the engine102is not completing a dynamic maneuver. The combustion control module may receive the boost error from the boost error module202.

At318, the combustion control module adjusts a boost pressure of the engine102, an EGR flow rate of the engine102, and/or one or more fuel injection parameters of the engine102based on a first set of target values. In one example, at318, the boost control module208selects a target boost pressure of the engine102from the first set of target values, the EGR control module210selects a target EGR flow rate of the engine102from the first set of target values, and the fuel control module212selects one or more target fuel injection parameters from the first set of target values. The boost control module208, the EGR control module210, and the fuel control module212may select the target boost pressure, the target EGR flow rate, and the target fuel injection parameter(s), respectively, from the first set of target values based on the speed of the engine102and/or the load on the engine102. For example, the boost control module208may select the target boost pressure using a function or mapping that relates engine speed and engine load to a target boost pressure in the first set, the EGR control module210may select the target EGR flow rate using a function or mapping that relates engine speed and engine load to a target EGR flow rate in the first set, and the fuel control module212may select the target fuel injection parameter(s) using a function or mapping that relates engine speed and engine load to target fuel injection parameter(s) in the first set.

The boost control module208, the EGR control module210, and the fuel control module212may determine the speed of the engine102based on the crankshaft position from the CKP sensor146by, for example, determining the change in the crankshaft position with respect to time. Alternatively, the ECM112may include an engine speed module (not shown) that determines the speed of the engine102based on the measured crankshaft position and outputs the engine speed to the boost control module208, the EGR control module210, and the fuel control module212. The boost control module208, the EGR control module210, and the fuel control module212may determine the load the engine102based on the rate of intake air flow from the MAF sensor152using, for example, a function and/or mapping that relates the rate of intake air flow to engine load. Alternatively, the ECM112may include an engine load module (not shown) that determines the load on the engine102based on the measured flow rate of intake air and outputs the engine load to the boost control module208, the EGR control module210, and the fuel control module212.

The target boost pressure is a target value for the pressure within the intake manifold108of the engine102. The target EGR flow rate is a target value for the rate of exhaust gas flow through the EGR valve136(EGR flow). The target EGR flow rate may be expressed as a EGR flow rate or as a ratio or percentage of the EGR flow relative to the total amount of intake air flow and EGR flow entering the intake manifold.

The target fuel injection parameters may include a target fuel injection quantity, a target fuel injection timing, and/or a target number of injections. The target fuel injection quantity may include a target value for the total amount of fuel to be injection in each cylinder of the engine102during each engine cycle and/or a target value for the amount of fuel to be injected during each injection. The target fuel injection timing may be a target value for a crank angle of the engine102at which fuel injection into each cylinder of the engine102is to start. The target number of injections is a target value for the number of fuel injections into each cylinder of the engine102during each engine cycle.

At316, the combustion control module adjusts the boost pressure of the engine102, the EGR flow rate of the engine102, and/or the fuel injection parameter(s) of the engine102based on a second set of target values. In one example, at316, the boost control module208selects the target boost pressure of the engine102from the second set of target values, the EGR control module210selects the target EGR flow rate of the engine102from the second set of target values, and the fuel control module212selects one or more of the target fuel injection parameters from the second set of target values. The boost control module208, the EGR control module210, and the fuel control module212may select the target boost pressure, the target EGR flow rate, and the target fuel injection parameter(s), respectively, from the second set of target values based on the speed of the engine102and/or the load on the engine102. For example, the boost control module208may select the target boost pressure using a function or mapping that relates engine speed and engine load to a target boost pressure in the second set, the EGR control module210may select the target EGR flow rate using a function or mapping that relates engine speed and engine load to a target EGR flow rate in the second set, and the fuel control module212may select the target fuel injection parameter(s) using a function or mapping that relates engine speed and engine load to target fuel injection parameter(s) in the second set.

The second set of target values is different than the first set of target values. For example, the target number of fuel injections and/or the target fuel injection timing in the second set of target values may be different than the target number of fuel injections and/or the target fuel injection timing, respectively, in the first set of target values. In one example, the target number of fuel injections in the first set of target values is a first number (e.g., 10), and the target number of fuel injections in the second set of target values is a second number (e.g., 8) that is less than the first number. In another example, the target fuel injection timing in the second set of target values may be advanced by a predetermined amount (e.g., 5 crank angle degrees) relative to the target fuel injection timing in the first set of target values.

At312, the combustion control module determines whether the engine102is completing a dynamic maneuver. If the engine102is completing a dynamic maneuver, the method continues at320. Otherwise, the method continues at322.

At322, the combustion control module adjusts the boost pressure of the engine102, the EGR flow rate of the engine102, and/or the fuel injection parameter(s) of the engine102based on a third set of target values. In one example, at322, the boost control module208selects the target boost pressure of the engine102from the third set of target values, the EGR control module210selects the target EGR flow rate of the engine102from the third set of target values, and the fuel control module212selects one or more of the target fuel injection parameters from the third set of target values. The boost control module208, the EGR control module210, and the fuel control module212may select the target boost pressure, the target EGR flow rate, and the target fuel injection parameter(s), respectively, from the third set of target values based on the speed of the engine102and/or the load on the engine102. For example, the boost control module208may select the target boost pressure using a function or mapping that relates engine speed and engine load to a target boost pressure in the third set, the EGR control module210may select the target EGR flow rate using a function or mapping that relates engine speed and engine load to a target EGR flow rate in the third set, and the fuel control module212may select the target fuel injection parameter(s) using a function or mapping that relates engine speed and engine load to target fuel injection parameter(s) in the third set.

The third set of target values is different than the first set of target values. For example, for the same engine speed and the same engine load, the target boost pressure in the first set of target values may be greater than the target boost pressure in the third set of target values by a predetermined percentage (e.g., a percentage within a range from 50 percent (%) to 75%). In another example, for the same engine speed and the same engine load, the EGR flow rate in the first set of target values may have a first maximum value (e.g., 10% EGR flow out of total EGR and intake air flow), and the EGR flow rate in the second set of target values may have a second maximum value (e.g., 20% EGR flow out of total EGR and intake air flow). The second maximum value may be greater than the first maximum value. In yet another example, for the same engine speed and the same engine load, the target total amount of fuel injection into each cylinder of the engine102during each engine cycle may be greater in the first set than in the third set.

At320, the combustion control module adjusts the boost pressure of the engine102, the EGR flow rate of the engine102, and/or the fuel injection parameter(s) of the engine102based on a fourth set of target values. In one example, at320, the boost control module208selects the target boost pressure of the engine102from the fourth set of target values, the EGR control module210selects the target EGR flow rate of the engine102from the fourth set of target values, and the fuel control module212selects one or more of the target fuel injection parameters from the fourth set of target values. The boost control module208, the EGR control module210, and the fuel control module212may select the target boost pressure, the target EGR flow rate, and the target fuel injection parameter(s), respectively, from the fourth set of target values based on the speed of the engine102and/or the load on the engine102. For example, the boost control module208may select the target boost pressure using a function or mapping that relates engine speed and engine load to a target boost pressure in the fourth set, the EGR control module210may select the target EGR flow rate using a function or mapping that relates engine speed and engine load to a target EGR flow rate in the fourth set, and the fuel control module212may select the target fuel injection parameter(s) using a function or mapping that relates engine speed and engine load to target fuel injection parameter(s) in the fourth set.

The fourth set of target values is different than the third set of target values. For example, the target number of fuel injections and/or the target fuel injection timing in the fourth set of target values may be different than the target number of fuel injections and/or the target fuel injection timing, respectively, in the third set of target values. In one example, the target number of fuel injections in the third set of target values is a first number (e.g., 10), and the target number of fuel injections in the fourth set of target values is a second number (e.g., 8) that is less than the first number. In another example, the target fuel injection timing in the fourth set of target values may be advanced by a predetermined amount (e.g., 5 crank angle degrees) relative to the target fuel injection timing in the third set of target values.

In addition, the fourth set of target values is different than the second set of target values. For example, for the same engine speed and the same engine load, the target boost pressure in the second set of target values may be greater than the target boost pressure in the fourth set of target values by a predetermined percentage (e.g., a percentage within a range from 50 percent (%) to 75%). In another example, for the same engine speed and the same engine load, the EGR flow rate in the second set of target values may have a first maximum value (e.g., 10% EGR flow out of total EGR and intake air flow), and the EGR flow rate in the fourth set of target values may have a second maximum value (e.g., 20% EGR flow out of total EGR and intake air flow). The second maximum value may be greater than the first maximum value. In yet another example, for the same engine speed and the same engine load, the target total amount of fuel injection into each cylinder of the engine102during each engine cycle may be greater in the second set than in the fourth set.

Further, each of the first, second, third, and fourth sets of target values may specify a target number of fuel injections that is greater than seven injections for each cylinder during each engine cycle, and the variability between the target quantities for the fuel injections may be different in the first and second sets relative to the third and fourth sets. For example, the target fuel injection quantities in the first and second sets of target values may have a first variability, and the target injection quantities in the third and fourth sets of target values may have a second variability that is greater than the first variability. In other words, for the third and fourth sets of target values, there may be greater variation in the target quantities of fuel injections that take place in a single cylinder during a single engine cycle relative to the variation in the corresponding target quantities in the first and third sets of target values.

At306, the combustion control module (i.e., the boost control module208, the EGR control module210, and/or the fuel control module212) activates a normal combustion mode. The normal combustion mode is an operating mode of the combustion control module that is activated during normal operation of the engine102. At324, the combustion control module adjusts the boost pressure of the engine102, the EGR flow rate of the engine102, and/or the fuel injection parameter(s) of the engine102based on a fifth set of target values. In one example, at324, the boost control module208selects the target boost pressure of the engine102from the fifth set of target values, the EGR control module210selects the target EGR flow rate of the engine102from the fifth set of target values, and the fuel control module212selects one or more of the target fuel injection parameters from the fifth set of target values. The boost control module208, the EGR control module210, and the fuel control module212may select the target boost pressure, the target EGR flow rate, and the target fuel injection parameter(s), respectively, from the fifth set of target values based on the speed of the engine102and/or the load on the engine102. For example, the boost control module208may select the target boost pressure using a function or mapping that relates engine speed and engine load to a target boost pressure in the fifth set, the EGR control module210may select the target EGR flow rate using a function or mapping that relates engine speed and engine load to a target EGR flow rate in the fifth set, and the fuel control module212may select the target fuel injection parameter(s) using a function or mapping that relates engine speed and engine load to target fuel injection parameter(s) in the fifth set.

The fifth set of target values is different than each of the first, second, third, and fourth sets of target values. For example, target number of fuel injections in the fifth set of target values may be less than the target number of fuel injections in each of the first, second, third, and fourth sets of target values. The method ends at326.

When one set of target values is referred to herein as being different than another set of target values, the one set includes at least one target value that is different than the corresponding target value in the other set for a given engine speed and a given engine load. However, some of the target values in the one set may be the same as some of the target values in the other set that correspond to a different engine speed and/or a different engine load. In addition, some, but not all, of the target values in the one set may be the same as some of the target values in the other set that correspond to the same engine speed and the same engine load.

Referring now toFIGS. 4-7, example injector command signals and adiabatic heat release rate signals are plotted with respect to an x-axis402that represents crank angle in degrees, a first y-axis404that represents injector command in volts, and a second y-axis406that represents heat release rate in kilojoules per cubic meter times degree (kJ/m3*deg).FIG. 4shows a first injector command signal408and a first adiabatic heat release rate signal410for one cylinder of the engine102during one engine cycle. The first injector command signal408and the first adiabatic heat release rate signal410indicate examples of target fuel injection parameters in the first set of target values. As discussed above, the fuel control module212may select the target fuel injection parameters from the first set of target values when the diesel oxidation catalyst140is not efficient and the engine102is not completing a dynamic maneuver.

Each pulse (or fluctuation) in the first injector command signal408represents a fuel injection pulse. The first injector command signal408includes ten pulses—a first pulse411, a second pulse412, a third pulse413, a fourth pulse414, a fifth pulse415, a sixth pulse416, a seventh pulse417, an eighth pulse418, a ninth pulse419, and a tenth pulse420. Thus, the first injector command signal408indicates that the target number of fuel injections in the first set of target values may be ten. The first and second pulses411and412may be referred to as pilot injections. The third fuel pulse413may be referred to as a main injection. The fourth through tenth pulses414-420may be referred to as after injections or post injections.

The first adiabatic heat release rate signal410has ten spikes—a first spike421, a second spike422, a third spike423, a fourth spike424, a fifth spike425, a sixth spike426, a seventh spike427, an eighth spike428, a ninth spike429, and a tenth spike430. The magnitude of each spike in the first adiabatic heat release rate signal410indicates the quantity of fuel injected during a corresponding one of the pulse411-420in the first injector command signal408. For example, the magnitude of the first spike421in the first adiabatic heat release rate signal410indicates the quantity of fuel injected during the first pulse411in the first injector command signal408, the magnitude of the second spike422in the first adiabatic heat release rate signal410indicates the quantity of fuel injected during the second pulse412in the first injector command signal408, and so on. In one example, the target amount of fuel injection during each of the pilot injections is within a range from 2 to 2.5 millimeters cubed (mm3), the target amount of fuel injection during the main injection and each of the first six after injections is within a range from 5 to 6 mm3, and the target amount of fuel injection during the last after injection is 2 mm3. Notably, the main injection and the first six after injections are all balanced. In other words, there is relatively small variation between the magnitudes of the spikes corresponding to the main injection and the first six after injections, which reflects that there is small variation in the target amount of fuel injection for these seven fuel injections.

FIG. 5shows a second injector command signal508and a second adiabatic heat release rate signal510for one cylinder of the engine102during one engine cycle. The first injector command signal508and the first adiabatic heat release rate signal510indicate examples of target fuel injection parameters in the second set of target values. As discussed above, the fuel control module212may select the target fuel injection parameters from the first set of target values when the diesel oxidation catalyst140is not efficient and the engine102is completing a dynamic maneuver.

Each pulse (or fluctuation) in the second injector command signal508represents a fuel injection pulse. The second injector command signal508includes eight pulses—a first pulse511, a second pulse512, a third pulse513, a fourth pulse514, a fifth pulse515, a sixth pulse516, a seventh pulse517, and an eighth pulse518. Thus, the second injector command signal508indicates that the target number of fuel injections in the second set of target values may be eight. The first and second pulses511and512may be referred to as pilot injections. The third pulse513may be referred to as a main injection. The fourth through eighth pulses514-518may be referred to as after injections or post injections.

The second adiabatic heat release rate signal510has seven spikes—a first spike521, a second spike522, a third spike523, a fourth spike524, a fifth spike525, a sixth spike526, and a seventh spike527. The magnitude of each spike in the second adiabatic heat release rate signal510indicates the quantity of fuel injected during a corresponding one or two of the pulse511-518in the second injector command signal508. For example, the magnitude of the first spike521in the second adiabatic heat release rate signal510indicates the quantity of fuel injected during the first pulse511in the second injector command signal508, the magnitude of the second spike522in the second adiabatic heat release rate signal510indicates the quantity of fuel injected during the second pulse512in the second injector command signal508, and so on. In one example, the target amount of fuel injection during each of the pilot injections is within a range from 2 to 2.5 mm3, the target amount of fuel injection during the main injection and each of the first four after injections is within a range from 5 to 6 mm3, and the target amount of fuel injection during the last after injection is 2 mm3. Notably, the main injection and the first four after injections are all balanced. In other words, there is relatively small variation between the magnitudes of the spikes corresponding to the main injection and the first four after injections, which reflects that there is small variation in the target amount of fuel injection for these five fuel injections.

FIG. 6shows a third injector command signal608and a third adiabatic heat release rate signal610for one cylinder of the engine102during one engine cycle. The third injector command signal608and the third adiabatic heat release rate signal610indicate examples of target fuel injection parameters in the third set of target values. As discussed above, the fuel control module212may select the target fuel injection parameters from the third set of target values when the diesel oxidation catalyst140is efficient and the engine102is not completing a dynamic maneuver.

Each pulse (or fluctuation) in the third injector command signal608represents a fuel injection pulse. The third injector command signal608includes ten pulses—a first pulse611, a second pulse612, a third pulse613, a fourth pulse614, a fifth pulse615, a sixth pulse616, a seventh pulse617, an eighth pulse618, a ninth pulse619, and a tenth pulse620. Thus, the third injector command signal608indicates that the target number of fuel injections in the third set of target values may be ten. The first and second pulses611and612may be referred to as pilot injections. The third pulse613may be referred to as a main injection. The fourth through tenth pulses614-620may be referred to as after injections or post injections.

The third adiabatic heat release rate signal610has nine spikes—a first spike621, a second spike622, a third spike623, a fourth spike624, a fifth spike625, a sixth spike626, a seventh spike627, an eighth spike628, and a ninth spike629. The magnitude of each spike in the third adiabatic heat release rate signal610indicates the quantity of fuel injected during a corresponding one or two of the pulse611-620in the third injector command signal608. For example, the magnitude the first spike621in the third adiabatic heat release rate signal610indicates the quantity of fuel injected during the first pulse611in the third injector command signal608, the magnitude of the second spike622in the third adiabatic heat release rate signal610indicates the quantity of fuel injected during the second pulse612in the third injector command signal608, and so on. In one example, the target amount of fuel injection during each of the pilot injections is 2 mm3, the target amount of fuel injection during the main injection and each of the first six after injections is within a range from 5 to 10 mm3, and the target amount of fuel injection during the last after injection is 2 mm3. Notably, the main injection and the first six after injections are not all balanced. In other words, there is relatively high variation between the magnitudes of the spikes corresponding to the main injection and the first six after injections, which reflects that there is large variation in the target amount of fuel injection for these seven fuel injections.

FIG. 7shows a fourth injector command signal708and a fourth adiabatic heat release rate signal710for one cylinder of the engine102during one engine cycle. The fourth injector command signal708and the fourth adiabatic heat release rate signal710indicate examples of target fuel injection parameters in the fourth set of target values. As discussed above, the fuel control module212may select the target fuel injection parameters from the fourth set of target values when the diesel oxidation catalyst140is efficient and the engine102is completing a dynamic maneuver.

Each pulse (or fluctuation) in the fourth injector command signal708represents a fuel injection pulse. The fourth injector command signal708includes eight pulses—a first pulse711, a second pulse712, a third pulse713, a fourth pulse714, a fifth pulse715, a sixth pulse716, a seventh pulse717, and an eighth pulse718. Thus, the fourth injector command signal708indicates that the target number of fuel injections in the fourth set of target values may be eight. The first and second pulses711and712may be referred to as pilot injections. The third pulse713may be referred to as a main injection. The fourth through eight pulses714-718may be referred to as after injections or post injections.

The fourth adiabatic heat release rate signal710has six spikes—a first spike721, a second spike722, a third spike723, a fourth spike724, a fifth spike725, and a sixth spike726. The magnitude of each spike in the fourth adiabatic heat release rate signal710indicates the quantity of fuel injected during a corresponding one or two of the pulse711-718in the fourth injector command signal708. For example, the first spike721in the fourth adiabatic heat release rate signal710indicates the quantity of fuel injected during the first pulse711in the fourth injector command signal708, the second spike722in the fourth adiabatic heat release rate signal710indicates the quantity of fuel injected during the second pulse712in the fourth injector command signal708, and so on. In one example, the target amount of fuel injection during each of the pilot injections is 2 mm3, the target amount of fuel injection during the main injection and each of the first four after injections is within a range from 5 to 10 mm3, and the target amount of fuel injection during the last after injection is 2 mm3. Notably, the main injection and the first four after injections are not all balanced. In other words, there is relatively high variation between the magnitudes of the spikes corresponding to the main injection and the first four after injections, which reflects that there is large variation in the target amount of fuel injection for these five fuel injections.

The injector command signals and the adiabatic heat release rate signals shown inFIGS. 4-7correspond to a six-cylinder, inline, direct injection, compression-ignition engine. In addition, the injector command signals and the adiabatic heat release rate signals shown inFIGS. 4-7correspond to an engine speed of 1600 revolutions per minute (RPM) and an engine load (or brake mean effective pressure) of 5 bar. While the magnitudes of the spikes in the adiabatic heat release rate signals may be different for different engine applications and different engine speed/load set points, the shape (or variation) in the adiabatic heat release rate signals may be the same.

Referring now toFIGS. 8 and 9, the example injector command signals and adiabatic heat release rate signals ofFIGS. 4 and 6are shown along with corresponding example signals indicating an in-cylinder pressure, an integral of the adiabatic heat release rate, and an average in-cylinder temperature.FIG. 8shows the injector command signal408ofFIG. 4and the adiabatic heat release rate signal410ofFIG. 4, along with an in-cylinder pressure signal802, an adiabatic heat release rate (AHRR) integral signal804and an in-cylinder average temperate signal806.FIG. 9shows the injector command signal608ofFIG. 6and the adiabatic heat release rate signal610ofFIG. 6, along with an in-cylinder pressure signal902, an AHRR integral signal904and an in-cylinder average temperate signal906.

All of the signals are plotted with respect to the x-axis402that represents crank angle in degrees. As withFIGS. 4 and 6, the injector command signals408,608are plotted with respect to the first y-axis404that represents injector command in volts, and the adiabatic heat release rate signals are plotted with respect to the second y-axis406that represents heat release rate in kJ/m3*deg. The in-cylinder pressure signals802,902are plotted with respect to a third y-axis808that represents pressure in kPa. The AHRR integral signals804,904are plotted with respect to a fourth y-axis810that represents AHRR integral in kilojoules per cubic meter (kJ/m3). The in-cylinder average temperature signals806,906are plotted with respect to a fifth y-axis812that represents temperature in kelvin (K).

FIG. 10shows examples of various engine operating parameter signals during a first portion1002of an engine warmup period when the diesel oxidation catalyst140is not yet efficient and during a second portion1004of the engine warmup period when the diesel oxidation catalyst140is efficient. The engine operating parameter signals include combustion mode signals1006,1008, engine speed signals1010,1012, NOx SCR out signals1014,1016, NOx/HC signals1018,1020, NOx engine out signals1022,1024, HC engine out signals1026,1028, ammonia (NH3) SCR out signals1030,1032, EGT SCR inlet signals1034,1036, and EGT SCRF inlet signals1038,1040.

The combustion mode signals1006,1008indicate whether the warmup mode is activated. Each of the combustion mode signals1006,1008indicates that the warmup mode is activated when its value is seven. The engine speed signals1010,1012indicate the speed of the engine102. The NOx SCR out signals1014,1016indicate NOx levels at the outlet of the SCR catalyst144. The NOx/HC signals1018,1020indicate the total levels of NOx and HC in exhaust gas produced by the engine102. The NOx engine out signals1022,1024indicate the NOx levels at the outlet of the engine102. The HC engine out signals1026,1028indicate the HC levels at the outlet of the engine102. The NH3 SCR out signals1030,1032indicate the NH3 levels at the outlet of the SCR catalyst144. The EGT SCR inlet signals1034,1036indicate the EGT at the inlet of the SCR catalyst144. The EGT SCRF inlet signals1038,1040indicate the EGT at the inlet of the SCRF catalyst142.

The combustion mode signal1006, the engine speed signal1010, the NOx SCR out signal1014, the NOx/HC signal1018, the NOx engine out signal1022, the HC engine out signal1026, the NH3 SCR out signal1030, the EGT SCR inlet signal1034, and the EGT SCRF inlet signal1038correspond to a first warmup of the engine102when combustion of the engine102is controlled according to the present disclosure. The combustion mode signal1008, the engine speed signal1012, the NOx SCR out signal1016, the NOx/HC signal1020, the NOx engine out signal1024, the HC engine out signal1028, the NH3 SCR out signal1032, the EGT SCR inlet signal1036, and the EGT SCRF inlet signal1040correspond to a second warmup of the engine102when combustion of the engine102is controlled according to the present disclosure. The emissions signals ofFIG. 10illustrate how the engine control system and method according to the present disclosure yields low emission levels during engine warmup.

The engine operating parameter signals are plotted with respect to an x-axis1042that represents time in seconds. The combustion mode signals1006,1008are plotted with respect to a first y-axis1044that represents signal magnitude (unitless). The engine speed signals1010,1012are plotted with respect to a second y-axis1046that represents engine speed in RPM. The NOx SCR out signals1014,1016are plotted with respect to a third y-axis1048that represents mass per distance in milligrams per kilometer (mg/mi). The NOx/HC signals1018,1020are plotted with respect to a fourth y-axis1050that represents mass per distance in mg/mi. The NOx engine out signals1022,1024are plotted with respect to a fifth y-axis1052that represents mass in grams. The HC engine out signals1026,1028are plotted with respect to a sixth y-axis1054that represents mass in grams. The NH3 SCR out signals1030,1032are plotted with respect to a seventh y-axis1056that represents concentration in particles per million (ppm). The EGT SCR inlet signals1034,1036are plotted with respect to an eight y-axis1058that represents temperature in ° C. The EGT SCRF inlet signals1038,1040are plotted with respect to a ninth y-axis1060that represents temperature in ° C.