Processes And Devices For Regenerating Gasoline Particulate Filters

Abstract

Processes and devices for regenerating a gasoline particulate filter utilized in filtering an exhaust stream of a direct-injection gasoline engine operating at substantially stoichiometric conditions include introducing an amount of oxygen into the exhaust stream downstream of the engine and upstream of the gasoline particulate filter, and regenerating the gasoline particulate filter by passing the exhaust stream enriched with the amount of oxygen through the gasoline particulate filter.

Description

BACKGROUND

1. Field

The present specification generally relates to processes and devices for regenerating gasoline particulate filters that are utilized in filtering exhaust streams of direct-injection gasoline engines operating at substantially stoichiometric conditions.

2. Technical Background

Gasoline engines employing direct-injection technology emit exhaust streams that contain particulates of carbonaceous soot, inorganic ash, and/or liquid aerosols. Such engines may be subject to particulate matter emission regulations. In order to satisfy these emission regulations, an engine may be equipped with a gasoline particulate filter that filters the soot and ash from the exhaust stream. After an amount of soot and ash accumulates in the gasoline particulate filter, the filter may require cleansing through an oxidative regeneration process (i.e., burning off the collected particulates).

However, many gasoline engines employing direct-injection technology are operated at substantially stoichiometric conditions, and thus, all of the oxygen present in the intake air is consumed by fuel combustion within the cylinders. Accordingly, no oxygen is present in the exhaust stream of the engine to support the gasoline particulate filter oxidative regeneration process. Therefore, a continuing need exists for methods of facilitating oxidative regeneration in gasoline particulate filters that are employed in filtering exhaust streams of direct-injection gasoline engines operating at substantially stoichiometric conditions.

SUMMARY

According to one embodiment, a process for regenerating a gasoline particulate filter utilized in filtering an exhaust stream of a direct-injection gasoline engine operating at substantially stoichiometric conditions includes introducing an amount of oxygen into the exhaust stream downstream of the engine and upstream of the gasoline particulate filter, and regenerating the gasoline particulate filter by passing the exhaust stream enriched with the amount of oxygen through the gasoline particulate filter.

In another embodiment, a process for regenerating a gasoline particulate filter utilized in filtering an exhaust stream of a direct-injection gasoline engine includes providing an engine control system for controlling operational parameters of the direct-injection gasoline engine to produce an exhaust stream containing a desired oxygen concentration, and regenerating the gasoline particulate filter by passing the exhaust stream containing the desired oxygen concentration through the gasoline particulate filter.

According to yet another embodiment, a regeneration device for a gasoline particulate filter which traps particulate matter contained in an exhaust gas of a direct-injection gasoline engine includes a mechanism which raises and lowers an oxygen concentration of the exhaust gas in order to facilitate a burning of particulate matter trapped in the filter, at least one sensor selected from a group comprising an oxygen sensor, a temperature sensor and a pressure sensor, and at least one of an engine control system and a pump control system that receives input from the at least one sensor and controls the mechanism to raise and lower the oxygen concentration of the exhaust gas.

Additional features and advantages of the invention will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the embodiments described herein, including the detailed description which follows, the claims, as well as the appended drawings.

It is to be understood that both the foregoing general description and the following detailed description describe various embodiments and are intended to provide an overview or framework for understanding the nature and character of the claimed subject matter. The accompanying drawings are included to provide a further understanding of the various embodiments, and are incorporated into and constitute a part of this specification. The drawings illustrate the various embodiments described herein, and together with the description serve to explain the principles and operations of the claimed subject matter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a schematic representation of a direct-injection gasoline engine and a gasoline particulate filter according to at least one embodiment of the processes and devices described herein; and

FIG. 2 depicts a schematic representation of a direct-injection gasoline engine and a gasoline particulate filter according to at least one embodiment of the processes and devices described herein.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to embodiment(s) of the invention, examples of which are illustrated in the accompanying drawings. Whenever possible, the same reference numerals will be used throughout the drawings to refer to the same or like parts. Embodiments of the processes and devices described herein include a direct-injection gasoline engine and a gasoline particulate filter. Intake air flows into the engine wherein it is utilized in a combustion process and converted into an exhaust gas. The exhaust gas then flows through the gasoline particulate filter.

More specifically, referring to the figures, regeneration processes and devices include a direct-injection gasoline engine 110 and a gasoline particulate filter 120. As illustrated, direct-injection gasoline engine 110 includes four cylinders that each contain an injector 111, 112, 113, 114 (e.g., piezo injectors). However, embodiments of processes and devices may include a direct-injection gasoline engine with any number and type of cylinders and/or injectors. Within each cylinder, an injector 111, 112, 113, 114 distributes fuel (i.e., gasoline, hydrocarbon, etc.) supplied by a fuel pump through a common fuel rail 115. An engine control system 116 may control the sequence, timing, number of fuel injections, and the duration of each fuel injection.

During operation of engine 110, intake air 130 containing oxygen is directed into an intake manifold 140. Because the particular direct-injection gasoline engine 110 depicted in the figures includes four cylinders, intake manifold 140 includes four intakes 141, 142, 143, 144. However, embodiments of processes and devices may include a direct-injection gasoline engine with any number of intakes. The air within intake manifold 140 may then be controlled by a throttle and directed into the cylinders of the engine, wherein the air is mixed with the fuel distributed by the injectors 111, 112, 113, 114. The fuel-oxygen mixture is combusted within the cylinders. Through such combustion, work is extracted and exhaust is produced and directed into an exhaust manifold 150. Again, because the particular direct-injection gasoline engine 110 depicted in the figures includes four cylinders, exhaust manifold 150 includes four exhausts 151, 152, 153, 154. However, embodiments of the processes and devices may include a direct-injection engine with any number of exhausts.

The exhausts are combined to form one exhaust stream 160 which is directed through gasoline particulate filter 120. Gasoline particulate filter 120 operates to filter and capture carbonaceous soot, inorganic ash, and/or liquid aerosols from exhaust stream 160, so that a less toxic exhaust gas stream is released into the surrounding environment.

Regeneration (i.e., burning off the collected soot and ash) of gasoline particulate filter 120 may be necessitated as amounts of carbonaceous soot, inorganic ash, and/or liquid aerosols accumulate on the filter. Regeneration takes place when an exhaust stream containing oxygen is passed over gasoline particulate filter 120 at a temperature higher than a soot burning initiation temperature (i.e., a temperature high enough to support combustion of the soot and ash particulates). As an example, regeneration of a gasoline particulate filter may take place when an exhaust stream heated to a temperature of greater than about 550° C., containing a volumetric concentration of oxygen in a range of about 1.0% to about 5.0%, more specifically about 1.0% to about 2.0%, and even more specifically about 1.5%, is passed over the filter. However, because many gasoline engines that employ direct-injection technology are operated at substantially stoichiometric conditions, substantially all of the oxygen present in the intake air is consumed by fuel combustion within the cylinders. Therefore, many direct-injection gasoline engine exhaust streams lack the oxygen to support a desired regeneration process of a gasoline particulate filter.

In accordance with embodiments described herein, a process for regenerating a gasoline particulate filter utilized in filtering an exhaust stream of a direct-injection gasoline engine operating at substantially stoichiometric conditions includes introducing air (e.g., an amount of oxygen) into the exhaust stream downstream of the engine and upstream of the gasoline particulate filter. The exhaust stream enriched with an amount of oxygen is then passed through the gasoline particulate filter. As shown in FIG. 1, such a process is designated generally throughout by the reference numeral 100.

The air (e.g., an amount of oxygen) introduced into the exhaust stream downstream of the engine and upstream of the gasoline particulate filter may be supplied by any suitable device and/or method. As depicted in FIG. 1, the amount of oxygen may be introduced into exhaust stream 160 ahead of, or upstream from, gasoline particulate filter 120 through employment of an air injection pump 170. Pump 170 can be driven off of engine 110 through a belt or other mechanical means, or alternatively, the pump can be driven electrically. Pump 170 may direct oxygen-containing air from the surrounding environment into exhaust stream 160, or alternatively, may direct a source of concentrated oxygen into the exhaust stream.

The air flow rate of pump 170 may be controlled either by a valve or by direct control of the operating speed of the pump. Further, the amount of air and/or concentration of oxygen introduced into exhaust stream 160 may be controlled in such a manner that the initiation, duration and/or extent of oxidative regeneration are controlled through control of pump 170. Moreover, gasoline particulate filter related thermo-mechanical durability parameters such as maximum oxidation exotherm and temperature distribution in the filter can be controlled through the amount of air and/or concentration of oxygen introduced into exhaust stream 160, together with the inlet temperature to filter 120.

A pump control system 180 may be utilized to control the air flow rate of pump 170 through control of the valve or operating speed of the pump. Because the initiation and progression of oxidative regeneration is dependent in part upon the oxygen concentration supplied across gasoline particulate filter 120, control of the air flow rate of pump 170 may be utilized to control the regeneration process exotherm. Pump control system 180 may receive inputs from oxygen sensors, temperature sensors, and/or pressure sensors associated with intake manifold 140, engine 110, exhaust manifold 150, gasoline particulate filter 120 and/or the exhaust gas leaving the gasoline particulate filter to monitor the soot regeneration process. The sensors may be located anywhere upstream or downstream of gasoline particulate filter 120. For example, an oxygen sensor located upstream of gasoline particulate filter 120 may monitor the oxygen concentration of exhaust gas 160 before entrance into the filter. A temperature sensor located at the exit of the gasoline particulate filter may monitor temperature to evidence or indicate the progress of an exothermic soot burning reaction. A pressure sensor located at the exit of the gasoline particulate filter may monitor a pressure drop that evidences or indicates the completion of an exothermic soot burning reaction. Such inputs may be utilized by pump control system 180 to determine parameters in the control of the operation of pump 170. Thus, pump control system 180 may select and maintain a desired oxygen concentration in the exhaust stream passing through the gasoline particulate filter. Pump control system 180 may also be correlated with engine operational data to control the air flow rate of pump 170, or more simply, may control the air flow rate of pump 170 based on a set of fixed regeneration operating conditions.

Still referring to FIG. 1, air may also be introduced into exhaust stream 160 ahead of gasoline particulate filter 120 through cylinder deactivation. For cylinder deactivation, the fuel supply to one or more cylinders is stopped through control of one or more injectors 111, 112, 113, 114. When the fuel supply is stopped, no combustion occurs in such cylinders and the intake air is passed through to the exhaust stream where it is used to supply oxygen for filter regeneration. For example, injector 111 may be deactivated during operation of engine 110. Intake air is admitted to the cylinder that houses injector 111 during an intake stroke of engine operation, and then passed onto exhaust stream 160 during an exhaust stroke of engine operation. Because no combustion takes place in that cylinder due to the absence of fuel, the same amount of oxygen present in the intake air is supplied to exhaust stream 160. Multi-cylinder deactivation, sequential cylinder deactivation, or other similar deactivation processes may also have applicability in a similar manner. Moreover, cylinder deactivation may work alone in providing an amount of oxygen into exhaust stream 160, or may be utilized together with other processes described herein (e.g., air injection pumps and/or lean burn operations).

Engine control system 116 may be utilized to control cylinder deactivation. As detailed above, because oxidative regeneration is dependent upon the oxygen concentration supplied across gasoline particulate filter 120, control of the concentration of oxygen introduced into exhaust stream 160 may be utilized to control a regeneration process exotherm. Like pump control system 180, engine control system 116 may receive inputs from oxygen sensors, temperature sensors, and/or pressure sensors associated with intake manifold 140, engine 110, exhaust manifold 150, gasoline particulate filter 120 and/or the exhaust gas leaving the gasoline particulate filter to monitor and control the soot regeneration process. The sensors may be located anywhere upstream or downstream of gasoline particulate filter 120. For example, an oxygen sensor located upstream of gasoline particulate filter 120 may monitor the oxygen concentration of exhaust gas 160 before entrance into the filter. A temperature sensor located at the exit of the gasoline particulate filter may monitor temperature to evidence or indicate the progress of an exothermic soot burning reaction. A pressure sensor located at the exit of the gasoline particulate filter may monitor a pressure drop that evidences or indicates the completion of an exothermic soot burning reaction. Such inputs may be utilized by engine control system 116 to determine parameters in the control of the operation of engine 110. Thus, engine control system 116 may select and maintain a desired oxygen concentration in the exhaust stream passing through the gasoline particulate filter. Engine control system 116 may also function on a set of fixed regeneration operating conditions, or may correlate cylinder deactivation with fuel economy functions.

Another embodiment of a process for regenerating a gasoline particulate filter utilized in filtering an exhaust stream of a direct-injection gasoline engine includes providing an engine control system for controlling operational parameters of the direct-injection gasoline engine to produce an exhaust stream containing a desired oxygen concentration. The exhaust stream containing the desired oxygen concentration is then passed through the gasoline particulate filter. As shown in FIG. 2, such a process is designated generally throughout by the reference numeral 200.

Referring to FIG. 2, exhaust stream 160 may be produced to contain a desired oxygen concentration through a lean-burn operation of engine 110. During a lean-burn operation, engine 110 is not operated at stoichiometric conditions, as the fuel supply to one or more cylinders is reduced through control of one or more injectors 111, 112, 113, 114. Accordingly, when the fuel supply is reduced, a high air to fuel ratio is created in the applicable cylinders. Due to this high air to fuel ratio, even when a combustion event occurs in a particular cylinder, excess oxygen in the cylinder is passed through to the exhaust stream. For example, injector 111 may be controlled to burn lean during operation of engine 110. The excess oxygen from injector 111 not used during combustion is passed onto exhaust stream 160, where it is used to supply oxygen for filter regeneration. Multi-cylinder lean-burn operations or other similar lean-burn processes may also have applicability in a similar manner. As with cylinder deactivation above, lean-burn operation may work alone in providing an amount of oxygen into exhaust stream 160, or may be utilized together with other processes described herein (e.g., air injection pumps and/or cylinder deactivation).

Engine control system 116 may be utilized to coordinate a lean-burn operation. As detailed above, because oxidative regeneration is dependent upon the oxygen concentration supplied across gasoline particulate filter 120, control of the concentration of oxygen introduced into exhaust gas stream 160 may be utilized to control a regeneration process exotherm. Engine control system 116 may receive inputs from oxygen sensors, temperature sensors, and/or pressure sensors associated with intake manifold 140, engine 110, exhaust manifold 150, gasoline particulate filter 120 and/or the exhaust gas leaving the gasoline particulate filter to monitor and control the soot regeneration process. The sensors may be located anywhere upstream or downstream of gasoline particulate filter 120. For example, an oxygen sensor located upstream of gasoline particulate filter 120 may monitor the oxygen concentration of exhaust gas 160 before entrance into the filter. A temperature sensor located at the exit of the gasoline particulate filter may monitor temperature to evidence or indicate the progress of an exothermic soot burning reaction. A pressure sensor located at the exit of the gasoline particulate filter may monitor a pressure drop that evidences or indicates the completion of an exothermic soot burning reaction. Such inputs may be utilized by engine control system 116 to determine parameters in the control the operation of engine 110. Thus, engine control system 116 may select and maintain a desired oxygen concentration in the exhaust stream passing through the gasoline particulate filter. Engine control system 116 may also function on a set of fixed regeneration operating conditions for the coordination of a lean-burn operation.

The use of cool regeneration air, either supplied by pump 170 or through the cylinders by cylinder deactivation and/or lean-burn operation, may cause some cooling of exhaust stream 160. If exhaust stream 160 is cooled below the soot burning initiation temperature, some corrective action may need to be taken to facilitate oxidative regeneration. Corrective actions such as spark retard and/or late injection will force selected doses of unburned hydrocarbon (e.g., fuel) into exhaust stream 160. In other words, engine 110 may be controlled by engine control system 116 to burn rich (i.e., operate with a high fuel to air ratio in at least one cylinder) for a determined or predetermined amount of time. When the hydrocarbon in exhaust stream 160 contacts a catalyzed gasoline particulate filter (e.g., a gasoline particulate filter containing an oxidative catalyst such as Pt, Pd, Rh and/or Ce), an exothermic reaction will take place and heat up the gasoline particulate filter to above soot burning initiation temperatures.

A regeneration device utilized in the processes detailed above may contain a mechanism which raises and lowers an oxygen concentration of the exhaust gas in order to facilitate a burning of particulate matter trapped in the gasoline particulate filter. Examples of the mechanism include pump 170 and operational control of the engine. The mechanism may be controlled by an engine control system and/or a pump control system that receives input from at least one sensor located on the device. Suitable sensors include oxygen sensors, temperature sensors and/or pressure sensors.

Example

The embodiments described herein will be further clarified by the following example. Table 1 below provides an example of a mass balance for intake air traveling through engine 110 as detailed in processes 100, 200. The intake air is converted to an exhaust stream by a combustion reaction within the cylinders of a direct-injection gasoline engine operating at stoichiometric conditions. For simplicity in the example, the ppm levels of hydrocarbons, CO and NOX are neglected as the concentration of these species is very low and will not affect the basic process calculations. In addition, it should also be noted that there may be very low levels of oxygen in the exhaust gas from a direct-injection gasoline engine operating at stoichiometric conditions because control of the air to fuel ratio is not perfect, nor is there always 100% complete combustion. However, the low level of oxygen present in the exhaust stream is insufficient for practical oxidative regeneration use.

A quantity of regeneration air is injected into the exhaust stream such that the molar (or volumetric) concentration of oxygen in the combined exhaust stream and air is 1.5%. The injection of air can be done via an air injection pump, cylinder deactivation, or by partial lean-burn operation in one or more cylinders. Regeneration of soot can proceed at a controlled rate when the injection of air, and therefore the oxygen concentration within the exhaust stream, is monitored and controlled. Although a specific amount of oxygen in the exhaust stream is defined in Table 1 below, the amount can be higher or lower depending on the desired application. At lower concentrations, the soot burning rate may be reduced, and at higher concentrations, the rate may be increased. Because the soot regeneration reaction is exothermic [CH_soot+O2→CO+CO₂+H₂O+ΔH_rxn] the possibility for runaway or uncontrolled reaction may exist. However, by monitoring and controlling the oxygen concentration this possibility can be reduced or eliminated, especially where oxygen is made to be the stoichiometrically limiting species in the reaction network. Thus, at least one of an engine control system and a pump control system that can vary the oxygen concentration of the exhaust stream passing through the gasoline particulate filter during regeneration can be used to control the rate of soot burning. As a consequence, the temperature distribution in the filter may also be controlled.

TABLE 1
Fuel Balance
C	H	MW
7.0	13.9	97.9
	MW	Vol %	Mass %
Intake Air Composition
N2	28	79.0	76.7
O2	32	21.0	23.3
H2O	18	0.0	0.0
CO2	44	0.0	0.0
Total		100.0	100.0
Exhaust Gas Composition
N2	28	73.8	71.8
O2	32	0.0	0.0
H2O	18	13.0	8.2
CO2	44	13.1	20.0
Total		100.0	100.0
Injection Air Composition
N2	28	79.0	76.7
O2	32	21.0	23.3
H2O	18	0.0	0.0
CO2	44	0.0	0.0
Total		100.0	100.0
Combined Exhaust + Air
N2	28	74.2	72.2
O2	32	1.5	1.7
H2O	18	12.1	7.6
CO2	44	12.2	18.6
Total		100.0	100.0
Injection Air Percent (Vol % vs. intake)	8%
Fuel Rate, kg/hr	6.4
Intake Air Rate @ stoichiometry, kg/hr	93.6
Intake Air Rate @ 20° C., m3/hr	78.1
Exhaust Gas Flow Rate, kg/hr	100.0
Injection Air Rate, m3/hr @ 20° C.	6.4
Injection Air Rate, kg/hr	7.7
Exhaust Temperature, ° C.	850
Exhaust Flow Rate, m3/hr @ T	92

Table 1 indicates that for an exhaust gas stream of 100 kg/hr at an 850° C. manifold temperature (typical values for a passenger car), an injection of air of about 6.4 m³/hr is needed to provide a 1.5 vol % O₂ concentration in the exhaust stream. An exhaust stream with such an O₂ concentration and temperature should be sufficient for the oxidative regeneration process of a variety of gas particulate filters. Those skilled in the art realize that as exhaust conditions and flow rates vary substantially as a function of vehicle speed and load, the injection air can be varied accordingly through ratio-control or any other method known in the art. Under ratio control the flow rate of the injection air is determined and set by the flow rate of exhaust at a fixed proportion. The exhaust flow rate is a function of vehicle speed and load, fueling rate, and air intake rate.

It will be apparent to those skilled in the art that various modifications and variations can be made to the embodiments described herein without departing from the spirit and scope of the claimed subject matter. Thus, it is intended that the specification cover the modifications and variations of the various embodiments described herein provided such modification and variations come within the scope of the appended claims and their equivalents.

Claims

1. A process for regenerating a gasoline particulate filter utilized in filtering an exhaust stream of a direct-injection gasoline engine operating at substantially stoichiometric conditions, the process comprising:

introducing an amount of oxygen into the exhaust stream downstream of the engine and upstream of the gasoline particulate filter; and

regenerating the gasoline particulate filter by passing the exhaust stream enriched with the amount of oxygen through the gasoline particulate filter.

2. The process of claim 1, further comprising providing an oxygen sensor and at least one of an engine control system and a pump control system that receives an input from the oxygen sensor and selects and maintains a desired oxygen concentration in the exhaust stream passing through the gasoline particulate filter.

3. The process of claim 1, further comprising providing a temperature sensor and at least one of an engine control system and a pump control system that receives an input from the temperature sensor and selects and maintains a desired oxygen concentration in the exhaust stream passing through the gasoline particulate filter.

4. The process of claim 1, further comprising providing a pressure sensor and at least one of an engine control system and a pump control system that receives an input from the pressure sensor and selects and maintains a desired oxygen concentration in the exhaust stream passing through the gasoline particulate filter.

5. The process of claim 1, wherein the exhaust stream passing through the gasoline particulate filter has a volumetric concentration of oxygen in a range of about 1.0% to about 2.0%.

6. The process of claim 5, wherein the volumetric concentration of oxygen is about 1.5%.

7. The process of claim 1, wherein an air injection pump is used to introduce the amount of oxygen into the exhaust stream.

8. The process of claim 7, wherein the amount of oxygen is provided in the form of air from the surrounding environment.

9. The process of claim 1, wherein a cylinder deactivation is used to introduce the amount of oxygen into the exhaust stream.

10. The process of claim of claim 9, wherein the cylinder deactivation is coordinated with a fuel economy function.

11. The process of claim 1, further comprising introducing a selected dose of hydrocarbon into the exhaust stream upstream of the gasoline particulate filter.

12. The process of claim 11, further comprising controlling operational parameters of the engine to introduce the selected dose of hydrocarbon into the exhaust stream.

13. A process for regenerating a gasoline particulate filter utilized in filtering an exhaust stream of a direct-injection gasoline engine, the process comprising:

providing an engine control system for controlling operational parameters of the direct-injection gasoline engine to produce an exhaust stream containing a desired oxygen concentration; and

regenerating the gasoline particulate filter by passing the exhaust stream containing the desired oxygen concentration through the gasoline particulate filter.

14. The process of claim 13, further comprising providing at least one of an oxygen sensor, a temperature sensor and a pressure sensor that provide at least one input to the engine control system.

15. The process of claim 13, wherein the exhaust stream containing the desired oxygen concentration is produced by a partial lean-burn operation.

16. The process of claim 13, wherein the exhaust stream passing through the gasoline particulate filter has a volumetric concentration of oxygen in a range of about 1.0% to about 2.0%.

17. The process of claim 16, wherein the volumetric concentration of oxygen is about 1.5%.

18. A regeneration device for a gasoline particulate filter which traps particulate matter contained in an exhaust gas of a direct-injection gasoline engine, the regeneration device comprising:

a mechanism which raises and lowers an oxygen concentration of the exhaust gas in order to facilitate a burning of particulate matter trapped in the filter;

at least one sensor selected from a group comprising an oxygen sensor, a temperature sensor and a pressure sensor; and

at least one of an engine control system and a pump control system that receives input from the at least one sensor and controls the mechanism to raise and lower the oxygen concentration of the exhaust gas.

19. The regeneration device of claim 18, wherein the mechanism is an air injection pump that is employed to introduce air into the exhaust stream downstream of the engine and upstream of the gasoline particulate filter.

20. The regeneration device of claim 18, wherein the mechanism is an engine operation control.