Control system and method for preventing hydrocarbon slip during particulate matter filter regeneration

An engine control system includes an injection determination module and an injection regulation module. The injection determination module determines a desired rate of hydrocarbon (HC) injection into exhaust gas produced by an engine for regeneration of a particulate matter (PM) filter. The injection regulation module increases a rate of HC injection from a first rate to the desired rate during a predetermined period before regeneration of the PM filter, wherein the predetermined period is based on a difference between a predetermined temperature and a temperature at an outlet of an oxidation catalyst (OC).

FIELD

The present disclosure relates to internal combustion engines, and more particularly to a control system and method for exhaust gas temperature (EGT) to prevent hydrocarbon (HC) slip during particulate matter (PM) filter regeneration.

BACKGROUND

Internal combustion engines combine air and fuel to create an air/fuel (A/F) mixture that is combusted within a plurality of cylinders. The combustion of the A/F mixture drives pistons which rotatably turn a crankshaft generating drive torque. Specifically, air may be drawn into the cylinders and compressed using the pistons. Fuel may then be combined with (i.e., injected into) the compressed air causing the pressurized A/F mixture to combust (e.g., a compression ignition, or CI engine). For example, CI engines include diesel engines.

Alternatively, the air may be mixed with fuel to create the A/F mixture prior to compression. The A/F mixture may then be compressed until the A/F mixture reaches a critical pressure and/or temperature and automatically ignites (e.g., a homogeneous charge compression ignition, or HCCI engine). HCCI engines, however, may also “assist” ignition of the A/F mixture using spark from spark plugs. In other words, HCCI engines may ignite the A/F mixture using spark assist depending on engine operating conditions. For example, HCCI engines may use spark assist at low engine loads.

Exhaust gas produced during combustion may be expelled from the cylinders into an exhaust manifold. The exhaust gas may include carbon monoxide (CO) and hydrocarbons (HC). The exhaust gas may also include nitrogen oxides (NOx) due to the higher combustion temperatures of CI engines and HCCI engines compared to spark ignition (SI) engines. An exhaust treatment system may treat the exhaust gas to remove CO, HC, and/or NOx. For example, the exhaust treatment system may include, but is not limited to, at least one of an oxidation catalyst (OC), a particulate matter (PM) filter, a selective catalytic reduction (SCR) system, NOx absorbers/adsorbers, and catalytic converters.

SUMMARY

An engine control system includes an injection determination module and an injection regulation module. The injection determination module determines a desired rate of hydrocarbon (HC) injection into exhaust gas produced by an engine for regeneration of a particulate matter (PM) filter. The injection regulation module increases a rate of HC injection from a first rate to the desired rate during a predetermined period before regeneration of the PM filter, wherein the predetermined period is based on a difference between a predetermined temperature and a temperature at an outlet of an oxidation catalyst (OC).

A method includes determining a desired rate of hydrocarbon (HC) injection into exhaust gas produced by an engine for regeneration of a particulate matter (PM) filter, and increasing a rate of HC injection from a first rate to the desired rate during a predetermined period before regeneration of the PM filter, wherein the predetermined period is based on a difference between a predetermined temperature and a temperature at an outlet of an oxidation catalyst (OC).

In still other features, the systems and methods described above are implemented by a computer program executed by one or more processors. The computer program can reside on a tangible computer readable medium such as but not limited to memory, nonvolatile data storage, and/or other suitable tangible storage mediums.

DETAILED DESCRIPTION

As used herein, the term module refers to an Application Specific Integrated Circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or group) and memory that execute one or more software or firmware programs, and/or a combinational logic circuit.

Compression ignition (CI) (e.g., diesel) and homogeneous charge compression ignition (HCCI) engines may include similar exhaust treatment systems. More specifically, exhaust treatment systems for CI and HCCI engines may include an oxidation catalyst (OC) located before (i.e., upstream from) a selective catalytic reduction (SCR) catalyst and a particulate matter (PM) filter. The OC oxidizes carbon monoxide (CO) and hydrocarbons (HC) to form carbon dioxide (CO2) and water (H2O). The SCR catalyst (in conjunction with a dosing agent, such as urea) removes nitrogen oxides (NOx) from the exhaust gas.

The PM filter, on the other hand, removes PM from the exhaust gas. The PM filter may remove PM from the exhaust gas until the PM filter is saturated. In other words, the saturation condition may correspond to when the PM filter is full of PM (e.g., soot), after which a regeneration cycle may begin. The regeneration cycle may introduce HC into the exhaust gas. The HC in the exhaust gas may be catalyzed by the OC in an exothermic reaction that generates heat and increases exhaust gas temperature (EGT). The increased EGT at the outlet of the OC (i.e., at the inlet of the PM) may burn and/or breakdown the PM trapped in the PM filter, thus “regenerating” the PM filter.

Exhaust treatment systems, therefore, may further include one or more HC injectors that inject HC (e.g., fuel) upstream from an OC in an exhaust stream. Alternatively, exhaust treatment systems may perform post-combustion fuel injection to introduce HC into the exhaust gas. Conventional control systems control injection of HC into the exhaust stream during PM filter regeneration based on exhaust flow. The exhaust gas, however, may include HC due to incomplete catalyzation by the OC.

In other words, the OC may not entirely catalyze the injected HC due to insufficient temperature of the OC. The injected HC that passes the OC without being catalyzed may be referred to as “HC slip.” HC slip may poison (i.e., damage) the SCR catalyst, and may further render the SCR catalyst inoperable. Moreover, HC slip may trigger unintentional and/or uncontrolled regeneration cycles of the PM filter. In other words, HC slip may result in increased emissions and/or damage to various components of the exhaust treatment system (e.g., the SCR catalyst, the PM filter, etc.).

Accordingly, a system and method are presented that regulate HC injection to prevent HC slip. The system and method may increase a rate of HC injection based on an outlet temperature of the OC until a desired rate of HC injection is reached. The system and method may determine the desired rate of HC injection based on exhaust gas flow and a speed of the vehicle. For example, the system and method may increase the rate of HC injection according to a time-based ramp function based on the outlet temperature of the OC. Alternatively, the system and method may determine a desired amount of HC injection and control HC injection based on the desired amount of HC injection. In other words, the system and method may gradually increase HC injection based on OC outlet temperature to prevent HO slip, thus decreasing emissions and/or protecting the SCR catalyst and the PM filter.

Referring now toFIG. 1, an engine system10includes a CI engine12. For example only, the engine12may be a diesel engine or an HCCI engine. The engine12combusts an air/fuel (A/F) mixture to produce drive torque. Air is drawn into an intake manifold14through an inlet16. A throttle (not shown) may be included to regulate air flow into the intake manifold14. Air from the intake manifold14is distributed into a plurality of cylinders18. While six cylinders18are shown, it can be appreciated that the engine12may include other numbers of cylinders.

Fuel injectors20correspond to the cylinders18. The fuel injectors20may inject fuel directly into the cylinders18(i.e., direct fuel injection). Alternatively, however, the fuel injectors20may inject fuel via intake ports of the cylinders18(i.e., port fuel injection). A piston (not shown) compresses and combusts the A/F mixture within the cylinder18. The piston drives an engine crankshaft (not shown) during a power stroke to produce drive torque. In one embodiment, the cylinders18may include spark plugs (not shown) (e.g., for spark assist in an HCCI engine). The fuel injectors20may also inject fuel into the cylinders18after combustion of the A/F mixture (i.e., post-combustion injection) to introduce hydrocarbons (HC) into exhaust gas.

The crankshaft (not shown) rotates at engine speed or a rate that is proportional to engine speed. A crankshaft speed (CS) sensor22measures a rotational speed of the crankshaft. For example only, the CS sensor22may be a variable reluctance sensor. Drive torque from the engine crankshaft may be transferred to a driveline of a vehicle (e.g., wheels) via a transmission (not shown). A transmission output shaft speed (TOSS) sensor24measures a rotational speed of the output shaft of the transmission24. In other words, the measurement from the TOSS sensor24may indicate vehicle speed. Both engine speed and vehicle speed, however, may be measured or calculated using other suitable sensors and/or methods.

The exhaust gas resulting from the combustion within the cylinders18is expelled into an exhaust manifold26. An exhaust mass air flow (EMAF) sensor28generates an EMAF signal that indicates a rate of air flowing through the EMAF sensor28. For example, the EMAF signal may be indicate or be used to determine exhaust flow through an exhaust treatment system30. Thus, the EMAF sensor28may be located between the exhaust manifold26and the exhaust treatment system30.

The exhaust treatment system30may treat the exhaust gas. The exhaust treatment system30may include an HC injector32, an OC34, an SCR catalyst38, and a PM filter42. The exhaust treatment system30may also include temperature sensors36,40located at an outlet of the OC34and an inlet of the PM filter42, respectively. Temperature sensor36may measure temperature at the outlet of the OC34, hereinafter referred to as T1. Temperature sensor40may measure temperature at the inlet of the PM filter42, hereinafter referred to as T2. While only two temperature sensors36,40are shown, other numbers of temperature sensors may be implemented. Additionally or alternatively, temperatures at various locations in the exhaust treatment system (including T1and T2) may be modeled based on engine operating parameters.

The HC injector32selectively injects hydrocarbons into an exhaust stream. As previously described, however, the fuel injectors20may perform post-combustion injection to introduce HC into the exhaust gas. The OC34oxidizes CO and HC in the exhaust gas. The SCR catalyst38removes NOx from the exhaust gas. The PM filter42removes PM from the exhaust gas. The exhaust treatment system30may further include one or more NOx sensors (not shown) that measure exhaust gas NOx concentration.

A control module50communicates with and/or controls various components of the engine system10. The control module50may receive signals from the CS sensor22, the TOSS sensor24, the EMAF sensor28, temperature sensor36, and temperature sensor40. The control module50may communicate with the PM filter42to determine when a regeneration cycle is required. Alternatively, the control module50may determine that regeneration of the PM filter42is required based on other parameters and/or modeling. For example, the control module50may determine that regeneration of the PM filter42is required when exhaust flow is less than a predetermined exhaust flow threshold (i.e., the PM filter42is restricted by PM).

The control module50may also control a throttle (not shown), the fuel injectors20, the HC injector32, and an exhaust gas recirculation (EGR) valve48(discussed in more detail below). More specifically, the control module50may actuate the fuel injectors20(i.e., post-combustion injection) or the HC injector32to control EGT and thus may control regeneration of the PM filter42. The control module50may also implement the system and method of the present disclosure to regulate HC injection and prevent HC slip.

The engine system10may further include an EGR system44. The EGR system44includes the EGR valve48and an EGR line46. The EGR system44may introduce a portion of exhaust gas from the exhaust manifold26into the intake manifold14. The EGR valve48may be mounted on the intake manifold14. The EGR line46may extend from the exhaust manifold26to the EGR valve48, providing communication between the exhaust manifold26and the EGR valve48. As previously described, the control module50may actuate the EGR valve48to increase or decrease an amount of exhaust gas introduced into the intake manifold14.

The engine12may also include a turbocharger60. The turbocharger60may be driven by the exhaust gas received through a turbine inlet. For example only, the turbocharger60may include a variable nozzle turbine. The turbocharger60increases airflow into the intake manifold14to cause an increase in intake MAP (i.e., manifold absolute pressure, or boost pressure). The control module50may actuate the turbocharger60to selectively restrict the flow of the exhaust gas, thereby controlling the boost pressure.

Referring now toFIG. 2, the control module50is shown in more detail. The control module50may include an injection determination module70, an injection regulation module80, and a regeneration control module90. The injection determination module70receives signals from the EMAF sensor28and the TOSS sensor24indicating exhaust flow and vehicle speed, respectively. The injection determination module70may determine a desired rate of HC injection required for regeneration of the PM filter42based on the exhaust flow and the vehicle speed. Alternatively, the injection determination module70may determine a desired amount of HC injection for regeneration of the PM filter42based on the exhaust flow and the vehicle speed.

The injection regulation module80receives the desired rate of HC injection from the injection determination module70. The injection regulation module80may also receive a signal from temperature sensor36indicating the temperature T1at the outlet of the OC34. The injection regulation module80generate a regulated rate of HC injection based on the desired rate of HC injection and the outlet temperature T1. Rather, the injection regulation module80may rate limit the desired rate of HC injection based on the measured temperature T1. In other words, the OC34may catalyze merely a portion of the injected HC at a given outlet temperature, and thus the rate of HC injection may be regulated (i.e., rate limited) to prevent HC slip.

For example, the injection regulation module80may include a lookup table that includes a plurality of values relating to various outlet temperatures of the OC34. The plurality of values may be used to rate limit the HC injection. For example only, the plurality of values may include HC injection rates that may be subtracted from the desired rate of HC injection. Alternatively, however, the plurality of values may regulate (i.e., rate limit) the desired HC rate according to other suitable methods. The injection regulation module80may then output a regulated rate of HC injection.

The regeneration control module90is used for controlling injection of HC. Rather, the regeneration control module90receives the regulated rate of HC injection from the injection regulation module80and the regeneration control module90controls injection of HC into the exhaust gas. More specifically, the regeneration control module90may actuate the fuel injectors20(e.g., during a post-combustion period) and/or the HC injector32based on the regulated rate of HC injection. For example, the regeneration control module90may generate control signals for the fuel injectors20and/or the HC injector32. In other words, the control signal may be used to control a rate of HC injected into the exhaust gas during regeneration of the PM filter42while preventing HC slip.

Referring now toFIG. 3, a graph illustrating time-based ramping of HC injection is shown. The temperature T1is shown for both a desired rate of HC injection (i.e., a constant rate) and a time-based ramping to the desired rate of HC injection. More specifically, the desired rate of HC injection is 3.0 milligrams per second (mg/s) and the time-based ramp function increases HC injection from a first rate of HC injection (e.g., zero mg/s) to the desired rate of HC injection (3.0 mg/s) at a rate (e.g., slope) of 0.1 mg/s. For example, the slope of the time-based ramp function may be based on the temperature at the outlet of the OC. As shown in region95, rate limiting the HC injection based on OC outlet temperature decreases HC slip.

Referring now toFIG. 4, a method for regulating HC injection to prevent HC slip begins at100. At100, the control module50determines whether the engine12is on. If true, control may proceed to104. If false, control may return to100. At104, the control module50may determine whether regeneration of the PM filter42is required. If true, control may proceed to108. If false, control may return to100.

At108, the control module50may determine the desired rate of HC injection. At112, the control module50may determine a rate limit for the HO injection based on the measured outlet temperature T1of the OC34. At116, the control module50may determine a regulated rate of HC injection. In other words, the control module50may rate limit the desired rate of HC injection according to the determined rate limit.

At120, the control module50may control HC injection according to the regulated rate of HC injection. At124, the control module50may determine whether the regulated rate of HC injection has reached the desired rate of HC injection. If true, control may proceed128. If false, control may return to112. At128, the control module50may determine whether regeneration of the PM filter42is complete. If true, control may return to100. If false, control may return to120.