WO2008106164A2

WO2008106164A2 - Particulate regeneration and engine control system

Info

Publication number: WO2008106164A2
Application number: PCT/US2008/002588
Authority: WO
Inventors: Wade J. Robel; James Joshua Driscoll
Original assignee: Caterpillar Inc.
Priority date: 2007-02-28
Filing date: 2008-02-27
Publication date: 2008-09-04
Also published as: US20080202096A1; WO2008106164A3

Abstract

A particulate regeneration system (26) for an engine (10) is disclosed. The particulate regeneration system may have a particulate filter (28) configured to remove particulate matter from a flow of engine exhaust, and a diesel oxidation catalyst (30) located upstream of the particulate filter to facilitate oxidation of the trapped particulate matter. The particulate regeneration system may further have a regeneration device (32) located upstream of the diesel oxidation catalyst and configured to selectively heat the exhaust above an oxidation temperature of the trapped particulate matter, and a selective catalytic reduction device (36) located downstream of the particulate filter to remove NOx from the engine exhaust. The particulate regeneration system may also have a controller (34) in communication with the regeneration device and the engine. The controller may be configured to modify engine operation in response to initiation of a regeneration event.

Description

PARTICULATE REGENERATION AND ENGINE CONTROL SYSTEM

Technical Field

The present disclosure is directed to a particulate regeneration system and, more particularly, to a particulate regeneration system that implements engine control for improved fuel efficiency.

Background

Engines, including diesel engines, gasoline engines, gaseous fuel power engines, and other engines known in the art, exhaust a complex mixture of air pollutants. These air pollutants include solid material known as particulate matter or soot. Due to increased attention on the environment, exhaust emission standards have become more stringent and the amount of particulate matter emitted from an engine may be regulated depending on the type of engine, size of engine, and/or class of engine. One method implemented by engine manufacturers to comply with the regulation of particulate matter exhausted to the environment has been to remove the particulate matter from the exhaust flow of an engine with a device called a particulate trap. A particulate trap is a filter designed to trap particulate matter and consists of a wire mesh or ceramic honeycomb medium. However, the use of the particulate trap for extended periods of time may cause the particulate matter to build up in the medium, thereby reducing the functionality of the filter and subsequently engine performance.

One method of improving the performance of the particulate trap may be to implement regeneration. Regeneration is the burning away of trapped particulate matter. To initiate regeneration of the filter, the temperature of the particulate matter entrained within the filter must be artificially elevated to a combustion threshold of the particulate matter. The temperature may be artificially elevated through the use of, among other things, fuel powered burners, electric grids, injections of catalysts, and engine control strategies. Generally, these strategies increase the temperature of the exhaust, particulate filter, and/or trapped matter to the highest possible temperature (e.g., as high as 550-700⁰C) without exceeding a degradation temperature of the system. In this manner, the greatest amount of particulate matter may be burned away.

Although increasing the temperature of the exhaust, particulate trap, and/or trapped matter for regeneration purposes may be a successful way to improve the performance of the particulate trap, these high temperatures may be difficult and expensive to attain. One way of adequately regenerating a particulate trap at a lower temperature is disclosed in U.S. Patent No. 4,902,487 (the '487 patent) issued to Cooper et al. on 20 February 1990. In particular, the '487 patent describes a process whereby diesel exhaust gas is passed through a filter to remove particulate matter therefrom before discharge. The particulate matter deposited on the filter is combusted at about 400⁰C with a gas containing NO₂, which may be catalytically generated in the exhaust upstream of the filter. Because the particulate filter may be regenerated at temperatures as low as 400⁰C, the exhaust system may have lower cost components and operate with greater efficiency.

Although the exhaust system of the '487 patent may have improved operating efficiencies, the system may still be less than optimal. That is, at about 400⁰C, other exhaust reducing components within the same system also tend to operate at a greater efficiency (i.e., remove a greater amount of regulated emissions). As a result, engine operation could be altered during such a regeneration event to improve the performance of the engine (e.g., fuel efficiency) during the event, even though the production of the regulated exhaust emissions might increase proportionally. The system of the present disclosure solves one or more of the problems set forth above.

Summary of the Invention

One aspect of the present disclosure is directed to a particulate regeneration system for an engine. The particulate regeneration system may include a particulate filter configured to remove particulate matter from a flow of engine exhaust, and a diesel oxidation catalyst located upstream of the particulate filter to facilitate oxidation of the trapped particulate matter. The particulate regeneration system may further include a regeneration device located upstream of the diesel oxidation catalyst and configured to selectively heat the exhaust above an oxidation temperature of the trapped particulate matter, and a selective catalytic reduction device located downstream of the particulate filter to remove NOx from the engine exhaust. The particulate regeneration system may also include a controller in communication with the regeneration device and the engine. The controller may be configured to modify engine operation in response to initiation of a regeneration event.

Another aspect of the present disclosure is directed to a method of improving fuel efficiency of an engine. The method may include combusting fuel to generate a flow of exhaust, and converting a constituent in the exhaust to an oxidation facilitating constituent. The method may further include removing particulate matter from the exhaust flow, and heating the removed particulate matter above an oxidation threshold temperature. The method may also include changing engine operation in response to a temperature of the particulate matter exceeding the oxidation threshold temperature, and removing NOx from the exhaust flow.

Brief Description of the Drawings

Fig. 1 is a schematic and diagrammatic illustration of an exemplary disclosed power system; and Fig. 2 is a flow chart depicting an exemplary disclosed method of operating the power system of Fig. 1.

Detailed Description

Fig. 1 illustrates a power system 10 having a fuel injection system 12 and an exhaust treatment system 14. For the purposes of this disclosure, power system 10 is depicted and described as a four-stroke diesel engine. One skilled in the art will recognize, however, that power system 10 may embody any other type of internal combustion engine such as, for example, a gasoline or gaseous fuel-powered engine. Power system 10 may include an engine block 16 that at least partially defines a plurality of combustion chambers 18. In the illustrated embodiment, power system 10 includes four combustion chambers 18. However, it is contemplated that power system 10 may include a greater or lesser number of combustion chambers 18 and that combustion chambers 18 may be disposed in an "in-line" configuration, a "V" configuration, or any other suitable configuration.

As also shown in Fig. 1 , power system 10 may include a crankshaft 20 that is rotatably disposed within engine block 16. A connecting rod (not shown) associated with each combustion chamber 18 may connect a piston (not shown) to crankshaft 20 so that a sliding motion of each piston within the respective combustion chamber 18 results in a rotation of crankshaft 20. Similarly, a rotation of crankshaft 20 may result in a sliding motion of the pistons.

Operation of power system 10 may produce power and exhaust. For example, each combustion chamber 18 may mix fuel with air and combust the mixture therein to produce exhaust directed into an exhaust passageway 22. The exhaust may contain carbon monoxide, oxides of nitrogen, carbon dioxide, aldehydes, soot, oxygen, nitrogen, water vapor, and/or hydrocarbons such as hydrogen and methane. It is contemplated that the amount of exhaust and pollutants therein produced by power system 10 may be positively correlated with the amount of power produced by power system 10. That is, as the amount of power produced by power system 10 increases, the amount of exhaust produced by power system 10 may also increase. For example, power system 10 may produce a maximum amount of NOx when it is optimized to produce a maximum amount of power.

Fuel injection system 12 may include components that cooperate to deliver injections of pressurized fuel into each combustion chamber 18. Specifically, fuel injection system 12 may include a plurality of fuel injectors 24 connected to receive a supply of fuel. Each fuel injector 24 may be associated with one of combustion chambers 18 to inject an amount of pressurized fuel into the combustion chamber 18 at predetermined timings, fuel pressures, and quantities. Each fuel injector 24 may embody any type of electronically controlled fuel injection device such as, for example, an electronically actuated - electronically controlled injector, a mechanically actuated - electronically controlled injector, a digitally controlled fuel valve associated with a high pressure common rail, or any other type of fuel injector known in the art. It is contemplated that some or all operational parameters of fuel injectors 24 may be electronically regulated. For example, the timings, pressures, quantities, and/or velocities of the injections may be electronically controlled in response to one or more input. Although illustrated as a common rail injection system, it is contemplated that fuel injection system 12 may alternatively embody any other type of injection system such as, for example, a high-pressure unit injection system.

Exhaust treatment system 14 may direct exhaust from combustion chambers 18 to the atmosphere and may include a particulate regeneration system 26 in fluid communication with exhaust passageway 22. Although not shown, it is contemplated that exhaust treatment system 14 may include other components such as, for example, a turbocharger, or any other component for treating or handling exhaust known in the art. Particulate regeneration system 26 may include components that cooperate to remove or reduce constituents of the exhaust, and periodically reduce the buildup of particulate matter within exhaust treatment system 14. These components may include, among other things, a particulate filter 28, a diesel oxidation catalyst 30, a catalyst injector 32 communicatively coupled with a controller 34, and a selective catalytic reduction device 36. It is contemplated that particulate regeneration system 26 may include additional or different components such as, for example, an air injection system, a pressure sensor, a temperature sensor, a flow sensor, a flow blocking device, and other components known in the art.

Particulate filter 28 may include a wire mesh or ceramic honeycomb filtration media utilized to remove particulate matter from the exhaust. In particular, as exhaust from power system 10 flows through particulate regeneration system 26, particulate matter may be removed from the exhaust flow by particulate filter 28. Over time, the particulate matter may build up in particulate filter 28 and, if left unchecked, the particulate matter buildup could be significant enough to restrict or even block the flow of exhaust through exhaust treatment system 14, allowing for backpressure within power system 10 to increase. An increase in the backpressure of power system 10 could reduce the system's ability to draw in fresh air, resulting in decreased performance, increased exhaust temperatures, and poor fuel consumption.

Diesel oxidation catalyst 30 may be a device with a porous ceramic honeycomb-like or metal mesh structure coated with a material that catalyzes a chemical reaction to reduce pollution. For example, diesel oxidation catalyst 30 may oxidize NO constituents into NO₂, which is more susceptible to catalytic treatment. Diesel oxidation catalyst 30 may be located upstream of particulate filter 28. It is contemplated that diesel oxidation catalyst 30 may alternatively embody a catalyst coating applied to an upstream portion of particulate filter 28, if desired. Catalyst injector 32 may be disposed within a housing of particulate regeneration system 26 upstream of diesel oxidation catalyst 30, and connected to a catalyst line. In one example, the catalyst may be diesel fuel. In this example, it is contemplated that catalyst injector 32 may be connected to the same fuel supply as fuel injectors 24. Catalyst injector 32 may be operable to inject an amount of pressurized fuel into particulate regeneration system 26 at predetermined timings, pressures, and flow rates. The timing of catalyst injection into particulate regeneration system 26 may be synchronized with sensory input received from a temperature sensor (not shown), one or more pressure sensors (not shown), a timer (not shown), or any other similar sensory devices such that the injections of catalyst substantially correspond with a buildup of particulate matter within particulate filter 28. For example, catalyst may be injected as a pressure of the exhaust flowing through particulate regeneration system 26 exceeds a predetermined pressure level or a pressure drop across particulate filter 28 exceeds a predetermined differential value. Alternatively or additionally, catalyst may be injected as the temperature of the exhaust flowing through particulate regeneration system 26 deviates from a desired temperature by a predetermined value. It is further contemplated that catalyst may also be injected on a set periodic basis, in addition to or regardless of pressure or temperature conditions, if desired.

In order to accomplish these specific injection events, controller 34 may control operation of catalyst injector 32 in response to one or more inputs. In particular, controller 34 may regulate a fuel injection timing, pressure, and/or amount by directing a predetermined current waveform or sequence of predetermined current waveforms to catalyst injector 32. For the purposes of this disclosure, the combination of current levels directed to catalyst injector 32 that produce the desired injections during a single regeneration event may be considered a current waveform. Controller 34 may embody a single microprocessor or multiple microprocessors that include a means for controlling an operation of catalyst injector 32 and/or power system 10. Numerous commercially available microprocessors can be configured to perform the functions of controller 34. It should be appreciated that controller 34 could readily embody a general power system microprocessor capable of controlling numerous different functions of power system 10. Controller 34 may include components required to run an application such as, for example, a memory, a secondary storage device, and a processor, such as a central processing unit or any other means known in the art. Various other known circuits may be associated with controller 34, including power supply circuitry, signal-conditioning circuitry, solenoid driver circuitry, communication circuitry, and other appropriate circuitry. It is contemplated that controller 34 may further be communicatively coupled with fuel injectors 24 to similarly control the timings, pressures, and fuel flow rates of injections of fuel into combustion chambers 18. It is further contemplated that controller 34 may communicate with other components of power system 10 to change the operation thereof.

Selective catalytic reduction device 36 may be disposed within a housing of particulate regeneration system 26 downstream of particulate filter 28. Selective catalytic reduction device 36 may chemically reduce NOx into N₂. In a lean gas flow, selective catalytic reduction device 36 may require reductants for the chemical reaction and may utilize a reductant injector (not shown) to introduce the reductant into the lean gas flow. Reductants employed may be diesel fuel, ethanol, blended fuels, or any other reductant known in the art. Efficiency of NOx reduction by selective catalytic reduction device 36 may be at least partially dependent on the ratio OfNO₂ to NOx in the exhaust. In particular, NOx reduction by selective catalytic reduction device 36 may be most efficient when the ratio of NO₂ to NOx in the exhaust is about 50%. The ratio of NO₂ to NOx in the exhaust may be at least partially influenced by the temperature of the exhaust. In particular the ratio of NO₂ to NOx may occur optimally when the temperature of the exhaust is about 400⁰C. That is, when the temperature of the exhaust is about 400⁰C, the ratio of NO₂ to NOx may be about 50%. Those skilled in the art will appreciate that NO₂-based regeneration of particulate filter 28 may be particularly active at about 400⁰C.

Although the temperature of the exhaust may not be 400⁰C during a normal operation of power system 10, controller 34 may be operable to control catalyst injector 32 to inject diesel fuel or another catalyst into particulate regeneration system 26 to artificially increase the temperature of the exhaust to about 400⁰C. More specifically, as a catalyst is injected into particulate regeneration system 26, it may be caused to burn and raise the temperature of the exhaust to about 400⁰C.

Because the ratio of NO2 to NOx may be about 50% when the temperature of the exhaust is about 400⁰C, NOx reduction by selective catalytic reduction device 36 may be most efficient when the temperature of the exhaust is about 400⁰C. As a result, when the temperature of the exhaust is about 400⁰C, an operation of power system 10 may be optimized even though the optimization may maximize the production of NOx. The increased amount of NOx exhausted by power system 10 may be optimally reduced by selective catalytic reduction device 36 to remain compliant with exhaust emission standards, because of the unique conversion characteristics at 400⁰C. It is contemplated that controller 34 may further be configured to optimize an operation of power system 10 when the temperature of the exhaust is about 400⁰C. For example, controller 34 may modify a fuel injection characteristic of fuel injectors 24, such as a fuel pressure, timing, or rate of injection, to optimize a fuel economy of power system 10. When optimizing the fuel economy of power system 10, the production of NOx by power system 10 may be maximized while the power output of power system 10 may increase or remain the same as during normal operation of power system 10.

Industrial Applicability

The particulate regeneration system of the present disclosure may be applicable to a variety of power system configurations that include at least an engine and an exhaust treatment system. The disclosed particulate regeneration system may improve engine performance by taking advantage of exhaust temperatures available during a regeneration event. In particular, during a regeneration event, exhaust temperatures may be increased to a level at which NOx can be removed from the exhaust most efficiently. Further, engine operation may be modified during the regeneration event to increase power output, which may in turn increase the engine's NOx output. Since NOx may be removed most efficiently at the increased exhaust temperature level, the particulate regeneration system may remove or reduce the increased NOx output by the engine such that compliance with government regulations is maintained. The operation of power system 10 will now be explained.

Referring to Fig. 1 , air and fuel may be drawn into combustion chambers 18 of power system 10 for subsequent combustion. Specifically, fuel from fuel injection system 12 may be injected into combustion chambers 18, mixed with the air therein, and combusted by power system 10 to produce a mechanical work output and an exhaust flow of hot gases. The exhaust flow may contain a complex mixture of air pollutants composed of gaseous and solid material, including NOx and particulate matter. This particulate-laden exhaust flow may be directed from combustion chambers 18 to exhaust treatment system 14 via exhaust passageway 22. As the particulate-laden exhaust flow is directed through exhaust treatment system 14, particulate matter may be strained from the exhaust flow by particulate filter 28. Over time, the particulate matter may build up in particulate filter 28 and, if left unchecked, the buildup could be significant enough to restrict, or even block the flow of exhaust through exhaust treatment system 14. As indicated above, the restriction of exhaust flow from power system 10 may increase the backpressure of power system 10 and reduce the system's ability to draw in fresh air, resulting in decreased performance of power system 10, increased exhaust temperatures, and poor fuel consumption. To prevent the undesired buildup of particulate matter within exhaust treatment system 14, particulate filter 28 may be regenerated. Regeneration may be periodic or based on a triggering condition such as, for example, a lapsed time of engine operation, a pressure differential measured across particulate filter 28, a temperature of the exhaust flowing from power system 10, or any other condition known in the art.

Controller 34 may regulate regeneration events. Fig. 2 illustrates an exemplary operation of controller 34. In particular, controller 34 may determine whether a regeneration event is required, as discussed above (Step 200). If a regeneration event is required, controller 34 may elevate the temperature of the exhaust and alter operation of power system 10 to improve engine efficiency (Step 202). For example, if a regeneration event is required, controller 34 may artificially increase the temperature of the exhaust by controlling catalyst injector 32 to inject, for example, diesel fuel into particulate regeneration system 26 upstream of diesel oxidation catalyst 30. As the exhaust passes through diesel oxidation catalyst 30, NO constituents of the exhaust may be oxidized to NO₂, as discussed above. As the injected fuel reaches particulate filter 28, the fuel may burn to heat particulate filter 28 to about 400⁰C, thus heating the newly-oxidized NO₂. As the oxygen of the newly-oxidized NO₂ heats to about 400⁰C, it may burn the particulate matter trapped in particulate filter 28. At the elevated temperature of about 400⁰C, the ratio of NO₂ to

NOx in the exhaust may be about 50%, which may be the ratio at which selective catalytic reduction device 36 most efficiently reduces NOx, as disclosed above. That is, as the exhaust passes through selective catalytic reduction device 36, NOx may be chemically reduced to N₂ before being released to the atmosphere. During the regeneration event, controller 34 may further control fuel injectors 24 to advance the timings of fuel injection into combustion chambers 18. These advanced timings may improve the combustion of the fuel within combustion chambers 18, thus improving the fuel efficiency of power system 10 as well as increasing the amount of NOx exhausted by power system 10. The increased amount of NOx exhausted by power system 10 may then be reduced by selective catalytic reduction device 36, as discussed above. It is contemplated that the advanced timings may also increase the power output of power system 10.

Controller 34 may periodically check the conditions discussed above to determine whether or not regeneration is complete (Step 204). For example, controller 34 may monitor a pressure differential measured across particulate filter 28, a temperature of the exhaust flowing from power system 10, or a predetermined elapsed time interval of the regeneration event, or any other condition known in the art. When one of these conditions has met a predetermined threshold stored in the memory of controller 34, controller 34 may return power system 10 to normal operation (Step 206). More specifically, controller 34 may control catalyst injector 32 to stop injecting fuel into particulate regeneration system 26 and fuel injectors 24 to inject fuel into combustion chambers 18 at a retarded timing substantially the same as the timing of fuel injection into combustion chambers 18 before the regeneration event.

The disclosed particulate regeneration system may increase fuel efficiency while maintaining NOx emissions at a tolerable level. More specifically, because the temperature of the exhaust passing through the particulate filter may be elevated to about 400⁰C, the selective catalytic reduction device may perform at an optimized rate to reduce total NOx emissions into the atmosphere during regeneration events. Engine power output may therefore be increased along with an increase in NOx emissions from the engine during regeneration events, the increased NOx emissions being offset by the optimized NOx reduction. Thus, the particulate filter may be regenerated while engine operation may be optimized.

It will be apparent to those skilled in the art that various modifications and variations can be made to the system of the present disclosure without departing from the scope of the disclosure. Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the system disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope of the disclosure being indicated by the following claims and their equivalents.

Claims

1. A particulate regeneration system (26) for an engine (10), comprising: a particulate filter (28) configured to remove particulate matter from a flow of engine exhaust; a diesel oxidation catalyst (30) located upstream of the particulate filter to facilitate oxidation of the trapped particulate matter; a regeneration device (32) located upstream of the diesel oxidation catalyst and configured to selectively heat the exhaust above an oxidation temperature of the trapped particulate matter; a selective catalytic reduction device (36) located downstream of the particulate filter to remove NOx from the engine exhaust; and a controller (34) in communication with the regeneration device and the engine, the controller being configured to modify engine operation in response to initiation of a regeneration event.

2. The particulate regeneration system of claim 1, wherein changing engine operation results in improved fuel efficiency of the engine.

3. The particulate regeneration system of claim 2, wherein changing engine operation also results in increased NOx production.

4. The particulate regeneration system of claim 3, wherein the effectiveness of the selective catalytic reduction device increases at the oxidation temperature to accommodate the increased NOx production.

5. The particulate regeneration system of claim 1, wherein the diesel oxidation catalyst includes a coating applied to an upstream portion of the particulate filter.

6. A method of improving fuel efficiency of an engine (10), comprising: combusting fuel to generate a flow of exhaust; converting a constituent in the exhaust to an oxidation-facilitating constituent; removing particulate matter from the exhaust flow; heating the removed particulate matter above an oxidation threshold temperature; changing engine operation in response to a temperature of the particulate matter exceeding the oxidation threshold temperature; and removing NOx from the exhaust flow.

7. The method of claim 6, wherein changing engine operation results in improved fuel efficiency of the engine.

8. The method of claim 7, wherein changing engine operation also results in increased NOx production.

9. The method of claim 8, wherein a NOx removal effectiveness increases at the oxidation threshold temperature to accommodate the increased NOx production.

10. A power system, comprising the particulate regeneration system as in any one of claims 1-5, wherein: the diesel oxidation catalyst is configured to convert NO to NO2 to facilitate oxidation of the trapped particulate matter; the oxidation temperature is about 400⁰C; modifying engine operation includes changing a fuel injection characteristic; and the engine is an internal combustion engine configured to combust fuel and generate the flow of exhaust.