WO2006093574A1

WO2006093574A1 - Particulate trap regeneration control system

Info

Publication number: WO2006093574A1
Application number: PCT/US2006/001408
Authority: WO
Inventors: Cornelius N. Opris
Original assignee: Caterpillar Inc.
Priority date: 2005-02-28
Filing date: 2006-01-13
Publication date: 2006-09-08
Also published as: CN1834418A; US20060191258A1

Abstract

A particulate trap regeneration control system (100) may include one or more filter sections (202, 204, 206) within the exhaust element (114). The regeneration control system may also include a controller (104) configured to determine an amount of soot accumulated in the exhaust. The controller may also be configured to determine an amount of ash accumulated in the exhaust element. The controller may also be configured to determine the accumulated particulate matter in the exhaust element based on the accumulated soot and the accumulated ash in the exhaust element.

Description

PARTICULATE TRAP REGENERATION CONTROL SYSTEM

Technical Field

The present disclosure is directed to controlling regeneration of exhaust system components and, more particularly, to systems and methods for regenerating exhaust system components based on an amount of particulate matter accumulated in the exhaust element.

Background

Engines, including diesel engines, gasoline engines, natural gas engines, and other engines in the art, may exhaust air pollutants. The air pollutants may be composed of both gaseous materials and solid particulate matter. Particulate matter may include carbon particles called soot. In addition, particulate matter may contain ash, which is a material that can be used in engine oils to reduce the acidity of the oil. The particulate matter generated by an engine may be filtered from an exhaust stream. Various technologies may be used to filter particulate matter from an exhaust stream. One of these technologies includes the use of an exhaust element, such as a particulate filter. Particulate filters trap particles contained in the exhaust stream, so the exhaust stream is cleaner when it enters the air. Various types of particulate filters have been developed. Some filters may include porous filter material, and others may include wire mesh filters. The pores or wire meshes of these filters may trap at least a portion of the particulate matter in the exhaust stream as the exhaust stream flows from the input to the output of the filter. Particulate matter trapped by the filter can accumulate in the filter and reduce the operating efficiency of the engine. As particulate matter in the filter accumulates, the back pressure to the engine can increase. Therefore, the engine may consume more fuel to produce the same amount of power as compared to when the filter is free of particulates.

These and other problems may be avoided by periodic cleaning of the filter. Various methods of cleaning filters exist in the art. One method of cleaning the filter includes heating the particulate matter trapped in the filter to a temperature at which it combusts or vaporizes. This type of filter cleaning may be referred to as regeneration.

Various regeneration systems have been proposed to determine when to regenerate a particulate trap filter. Many of these systems involve using the value of the pressure differential across the exhaust element to determine when to commence regeneration of the exhaust element. For example, U.S.

Patent No. 6,622,480 to Tashiro et al ("the '480 patent"), which issued on 23

September 2003, describes a method that determines the time to regenerate a particulate trap based solely on a comparison between the estimated differential pressure across the exhaust element and the measured differential pressure across the exhaust element. If the measured differential pressure exceeds the estimated differential pressure, the system initiates regeneration.

While the method of the '480 patent may be used to determine the time to start regeneration of an exhaust element, the method has several shortcomings. The system uses pressure differential measurements across the exhaust element as the sole basis to determine the time to regenerate an exhaust element. Because the need for regeneration is related to the amount of particulate matter accumulated in the exhaust element, and because the pressure differential measurement method of the '480 patent may be inadequate for accurately determining the amount of particulate matter accumulated in the exhaust element, the method of the '480 patent may be unsuited for accurately determining when to regenerate.

The present disclosure is directed to overcoming one or more of the problems associated with the prior art regeneration method. Summary of the Invention

One aspect of the present disclosure includes a regeneration control system for an exhaust element. The regeneration control system may include one or more filter sections within the exhaust element. The regeneration control system may also include a controller configured to determine an amount of soot accumulated in the exhaust. The controller may also be configured to determine an amount of ash accumulated in the exhaust element. The controller may also be configured to determine the accumulated particulate matter in the exhaust element based on the accumulated soot and the accumulated ash in the exhaust element.

Another aspect of the present disclosure includes a method of controlling regeneration in an engine exhaust element. The method may include flowing exhaust through one or more filter sections of the exhaust element. The method may also include estimating an amount of soot accumulated in the exhaust. The method may include estimating an amount of ash accumulated in the exhaust element. The method may also include estimating the accumulated particulate matter in the exhaust element based on the accumulated soot and the accumulated ash in the exhaust element.

Brief Description of the Drawings Fig. 1 is a pictorial representation of a work machine according to an exemplary disclosed embodiment.

Fig. 2 is block diagram of a regeneration system according to an exemplary disclosed embodiment.

Fig. 3 is a diagrammatic illustration of an exhaust element according to an exemplary disclosed embodiment.

Detailed Description

Fig. 1 provides a pictorial illustration of a work machine 10. Work machine 10 may include engine 12. Work machine 10 may also include a frame 14 and a work implement 16. Engine 12 may be operably connected to an exhaust system 18. Engine 12 may include a diesel engine, a gasoline engine, or any other power-producing device. Work machine 10 may also include a traction device 20. While work machine 10 is shown as a track type tractor, work machine 10 may include various types of machines. For example, work machine 10 may be a truck, wheeled tractor, dump truck, automobile, on-highway vehicle, off-highway vehicle, skid-steer, stationary generator, or any other device that includes an engine that generates an exhaust stream. Exhaust system 18 may include components used to transfer exhaust produced by engine 12 or other exhaust producing devices to the atmosphere. For example, exhaust system 18 may include an exhaust manifold (not shown), a particulate filter or any other filtration device, a catalytic converter or any other catalytic device, a muffler, a tailpipe (not shown), and one or more exhaust conduits (e.g., exhaust pipes).

Fig. 2 provides a block diagram representation of a particulate regeneration control system 100 according to an exemplary disclosed embodiment. Regeneration system 100 may include engine 12, exhaust system 18, and a controller 104. Regeneration system 100 may also include a regeneration device 106, an exhaust conduit 108, a forward pressure sensor 110, and an aft pressure sensor 112. In addition, regeneration system 100 may also include an exhaust element 114. Exhaust conduit 108 may carry an exhaust stream 122.

Exhaust conduit 108 may be used to transfer exhaust stream 122 from engine 12 to exhaust element 114. Exhaust conduit 108 may include pipes or other components that facilitate the movement of exhaust stream 122 from engine 12 to exhaust element 114.

Various types of pressure sensors known in the art may be used in regeneration system 100. For example, pressure sensors 110 and 112 may include differential pressure sensors or gage pressure sensors. Pressure sensors 110 and 112 may be placed in any desired location on work machine 10. In the exemplary embodiment, as shown in Fig. 2, pressure sensor 110 may be placed upstream, and pressure sensor 112 may be placed downstream of exhaust element 114.

Exhaust element 114 may include any device (e.g., a particulate trap) that traps at least a portion of the particulate matter carried by exhaust stream 122. Exhaust element 114 may include any type of structure suitable for trapping particulates in exhaust stream 122. In one embodiment, exhaust element 114 may include a porous ceramic structure that may be configured to trap particulate matter contained in exhaust stream 122. This ceramic structure may include compounds such as alumina, calcia and silicon nitride. In another embodiment, exhaust element 114 may use a mesh configured to trap particulate matter contained in exhaust stream 122. The mesh may be made of electrically conductive materials such as, for example, aluminum and copper or any other such material.

Fig. 3 is a diagrammatic illustration of an exhaust element according to an exemplary disclosed embodiment. Exhaust element 114 may include one or more filter sections. For example, as shown in Fig. 3, exhaust element 114 includes filter sections 202, 204 and 206. Each filter section 202, 204 and 206 may be capable of being regenerated individually, as a group including all of the filter sections, or as a subgroup containing any number of filter sections. Various mechanisms may be used to regenerate each filter section individually or as a group. For example, a valve assembly (not shown) may be used to selectively block exhaust stream 122 from flowing into one or more filter sections 202, 204 or 206. Regeneration device 106 may be configured to regenerate some or all of the filter sections from which exhaust stream 122 has been blocked. While only three filter sections 202, 204 and 206 are shown in Fig. 3, it should be noted that exhaust element 114 may include any number of filters sections.

Returning to Fig. 2, regeneration device 106 may be used to regenerate exhaust element 114 and may include any type of device capable of providing sufficient heat for regenerating at least a portion of exhaust element 114. Regeneration devices may include one or more heat exchangers, burners or resistive heating elements. In the exemplary embodiment, one or more resistive heating elements may be included in regeneration device 106. Power provided to the resistive heating element may be used to heat the element. The heat dissipated by the resistive heating element may be used for the regeneration of exhaust element 114. Specifically, heat dissipated from the resistive heating element may raise the temperature of the particulate matter accumulated in exhaust element 114 to a temperature at which the particulate matter combusts or vaporizes. Alternatively, especially where exhaust element 114 includes a wire mesh made of electrically conductive material, regeneration device 106 may include a current source that delivers current to the wire mesh. Heat dissipated by the mesh due to resistive heating may by used to regenerate at least a portion of the particulate matter trapped in the mesh. Controller 104 may include any suitable devices associated with running a software application. For example, controller 104 may include a CPU, RAM, I/O modules, etc. In one embodiment, controller 104 may constitute a unit dedicated to controlling the regeneration of exhaust element 114. Alternatively, controller 104 may be integrated with and/or correspond to an electronic control unit (ECU) of work machine 10. Controller 104 may also include sensors suitable for the regeneration process. These sensors may include temperature sensors, soot sensors or any other such sensors.

Controller 104 may control the operations of various components of work machine 10. In one embodiment, controller 104 may be configured to control the operation of regeneration device 106. For example, controller 104 may determine the time to start the regeneration process. At that time, controller 104 may cause regeneration device 106 to begin a regeneration cycle. Further, controller 104 may determine the time to stop the regeneration process. At that time, controller 104 may halt the operation of regeneration device 106.

In order to control the operation of regeneration device 106, controller 104 may determine an amount of particulate matter accumulated in exhaust element 114. When the particulate matter accumulated in exhaust element 114 exceeds a predetermined threshold value, controller 104 may begin operation of regeneration device 106. When the particulate matter accumulated in exhaust element 114 becomes less than or equal to a predetermined threshold value, controller 104 may halt operation of regeneration device 106.

Controller 104 may monitor the effectiveness of the operation of regeneration device 106 by comparing the observed pressure drop across exhaust element 114 with an estimated pressure drop across exhaust element 114. It should be noted that the estimated pressure drop is the expected pressure drop that may be calculated based on, for example, one or more engine operating conditions of engine 12 and one or more known characteristics associated with exhaust element 114. It should also be noted that while the observed and estimated pressure drop across exhaust element 114 may be used to monitor the effectiveness of the regeneration operation, the decision to begin and halt operation of regeneration device 106 may be based solely on the particulate matter accumulation level in exhaust element 114. Thus, the use of the estimated and observed pressure drop values across exhaust element 114 may be optional. The accumulated particulate matter in exhaust element 114 may be determined based on the amount of soot accumulated in the exhaust element, hi addition, the amount of ash accumulated in the exhaust element may also be used in determining the accumulated particulate matter in exhaust element 114. The amount of soot accumulated in the exhaust element may be determined based on an amount of filtered soot entering exhaust element 114 and an amount of soot oxidized in exhaust element 114. In one embodiment, the difference between the amount of filtered soot entering exhaust element 114 and the amount of soot oxidized in exhaust element 114 may be used to compute the total soot accumulated in exhaust element 114.

Controller 104 may determine the amount of filtered soot entering exhaust element 114 based on one or more engine operating conditions. For example, the air flow rate, fuel flow rate, engine speed, engine torque and any other appropriate parameters may be used to determine the amount of soot entering exhaust element 114. Li one embodiment, controller 104 may be configured to determine an estimated soot accumulated in exhaust element 114 during any time period (Δt) by using the following equation:

(ξ) -C_1n(ξ) -Q(ξ) -_eχ_V(-RR₀(ξ) -ξ)]dξ [1]

where m₀ is the mass of the soot present in exhaust element 114 at t = to, and the integration limits X_\ and t₂ are related to the time period Δt = t₂ -t_1} η is the filtration efficiency of the exhaust element, ξ is the porosity of the filter sections in exhaust element 114, Cj_n is the concentration of soot in the exhaust upstream of exhaust element 114, Q is the exhaust volumetric flow rate, and RR₀ is the overall reaction rate of combustion in the engine. It should be noted that while equation [1] is one method for calculating the soot accumulation in exhaust element 114, any other suitable equations may be used for calculating an amount of soot accumulated in exhaust element 114.

Controller 104 may also be configured to determine the amount of soot oxidized in exhaust element 114. The amount of soot oxidized may be determined based on an overall reaction rate. This overall reaction rate may be determined based on one or more engine operating conditions, one or more regeneration techniques, and one or more factors associated with regeneration. The engine operating conditions may include, for example, the oxygen concentration in exhaust stream 122 and a temperature of the exhaust stream 122. The regeneration techniques may include, for example, electric heaters and burners. The presence of fuel additives and catalyzed filters may be examples of factors associated with regeneration. For example, if a fuel additive (a) is used to aid regeneration, then the overall reaction rate RR₀ (1/s) of an oxidation process can be described as the sum of the reaction rate contributions provided by (1) oxidation of the soot (s) (e.g., the quantity represented by RR_s(x,y,t) that depends on the engine operating conditions and the type of regeneration technique used and (2) catalyst action of fuel additive (a) (e.g., the quantity RR_a(x,y,t) may represent the effects of various factors associated with regeneration). This reaction rate may be obtained from the following equation: RRo(^χ,y,t) = RRs(^χ,y,t) + RR_a(^χ,y,t)

RRo(x,y,t) - A_s [O₂] " exp ^E> — +

R -T(x,y,t - At)

A₃[O₂] ^m exp ^E" [2]

R - T(x,y,t- At) where A (m³/g S) is the pre-exponential factor, m is assumed to be one for this type of oxidation process, O₂ (g/m ) is the oxygen mole fraction in the exhaust gas, E (kJ/kmol) is the soot activation energy, R (kJ/kmol-K) is the universal gas constant, and T(xyt - Δt) (K) is the local temperature at the previous time iteration level (t - Δt). The oxidized mass traction is related to the reaction rate as follows: dm __.,_.

-— = -ni RRo [3] at

It should be noted that while equations [2] and [3] provide one method for calculating the amount of oxidized soot in exhaust element 114, any other suitable equations may be used for calculating an amount of oxidized soot in exhaust element 114.

Controller 104 may be further configured to determine the amount of ash accumulated in exhaust element 114. The amount of ash accumulated in exhaust element 114 may be determined based on at least one of the type of oil used in engine 12 and one or more operating conditions associated with engine 12. For example, if the type of oil used is known, the ash content in the oil may be determined based on the predetermined ash content of the oil, which may correspond to a manufacturer-supplied numerical value indicating the amount of ash contained per unit of oil. Further, if the speed of engine 12 is known at a particular time, the oil flow rate may be determined based on laboratory tests which determine the oil flow rate for a given engine speed. Controller 104 may be configured to determine the ash accumulated in exhaust element 114 based on the predetermined ash content of the oil and the oil flow rate.

Controller 104 may be configured to determine the total particulate matter accumulation in exhaust element 114. Controller 104 may obtain the total particulate matter accumulation by adding the amount of ash accumulated in exhaust element 114 and the amount of soot accumulated in exhaust element 114. Thus, controller 104 may be configured to determine the particulate matter accumulated in exhaust element 114 based on both the ash and the soot accumulated in exhaust element 114.

As an option, controller 104 can monitor the operation of regeneration control system 100 by determining the estimated pressure drop across exhaust element 114 and the observed pressure drop across exhaust element 114. The estimated pressure drop may be determined based on one or more operating conditions of engine 12. Further, the estimated pressure drop may be determined based on one or more characteristics associated with exhaust element 114, which may include, for example, the length, width, permeability, and/or porosity of exhaust element 114. For example, the estimated pressure drop ΔP may be obtained from the following equation:

NH^Aγ(e^r -V) where L = length of a filter section of exhaust element 114, Q = volumetric flow rate of the exhaust from engine 12, N = number of filter sections, H = width of each filter section, μ is the dynamic viscosity of the gas, and

where w is the wall thickness of a filter section of exhaust element 114, and k₀ is the wall permeability of the filter section. It should be noted that while equation [4] represents one method for determining the estimated pressure drop across exhaust element 114, any other suitable equation may also be used.

The operation of regeneration control system 100 may be monitored with the help of the observed pressure drop obtained from forward pressure sensor 110 and aft pressure sensor 112. For example, the difference between the pressure measured by forward pressure sensor 110 and aft pressure sensor 112 may be used to determine an observed pressure drop across exhaust element 114. Controller 104 may also be configured to receive output signals from pressure sensors 110 and 112 indicative of this observed pressure drop. If controller 104 determines that the observed pressure drop is different than the estimated pressure drop, it may be configured to vary one or more operations of regeneration control system 100 to protect exhaust element 114. For example, controller 104 may be configured to do at least one of the following: maintain a regeneration cycle for a longer or shorter duration; adjust one or more parameters used in determining particulate matter accumulation; and warn the user that the exhaust element needs servicing. These actions may further increase the accuracy and effectiveness of the disclosed regeneration system.

Industrial Applicability

The disclosed regeneration system may be adapted for use in any system that may benefit from regeneration of an exhaust element. By basing the decision to regenerate exhaust element 114 on the total particulate matter accumulated in the exhaust element, rather than on a pressure drop across the exhaust element, the disclosed regeneration system may offer a more accurate method of regeneration than those available in the prior art.

Use of the disclosed system may help increase the reliability of the exhaust element. It may be important to control the amount of particulate matter accumulated in an exhaust element in order to avoid failure of the exhaust element. By increasing the accuracy of determining the particulate matter accumulation in the exhaust element, the disclosed system may accurately determine (1) the time to commence regeneration and (2) the duration of the regeneration. This feature of the disclosed system may help reduce the risk of ^• failure of the exhaust element due to over-heating because of an increased regeneration duration.

The accumulation of ash, not just soot, in an exhaust element can adversely affect the operation of the exhaust element. Because the disclosed regeneration system accounts for both soot and ash accumulated in the exhaust element, the disclosed system may be more accurate than a system that monitors only ash or only soot accumulated in the exhaust element.

Further, the use of the observed and estimated pressure differential to monitor the operation of the disclosed regeneration system may enhance the reliability of the disclosed system by providing a built-in check on the regeneration system. If the system is not operating as expected, the disclosed system can proactively takes steps to further improve the accuracy of the particulate matter accumulation calculation and the effectiveness of the regeneration system.

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

Claims

1. A regeneration control system (100) for an exhaust element (114) comprising: one or more filter sections (202, 204, 206) within the exhaust element; a controller (104) configured to: determine an amount of soot accumulated in the exhaust element; determine an amount of ash accumulated in the exhaust element; and determine the accumulated particulate matter in the exhaust element based on the accumulated soot and the accumulated ash in the exhaust element.

2. The regeneration system of claim 1 , wherein the amount of soot accumulated in the exhaust element is based on an amount of soot entering the exhaust element and an amount of soot oxidized in the exhaust element

3. The regeneration control system of claim 2, wherein the controller is configured to determine the amount of soot entering the exhaust element based on one or more engine operating conditions.

4. The regeneration control system of claim 2, wherein the controller is configured to determine the amount of soot oxidized in the exhaust element based on one or more engine operating conditions and one or more regeneration techniques.

5. The regeneration control system of claim 1 , wherein the controller is configured to determine the amount of ash accumulated in the exhaust element based on at least one of a type of oil used in an engine, an engine speed and oil flow rate.

6. The regeneration control system of claim 1 , wherein if a measured pressure drop across the exhaust element is greater than an estimated pressure drop, the controller is configured to perform at least one of the following steps: maintain a regeneration cycle for a period of time after the accumulated particulate matter in the exhaust element falls below a predetermined threshold; adjust one or more parameters used to determine the accumulated particulate matter; and issue a warning that the exhaust element needs servicing.

7. A method of controlling regeneration in an exhaust element (114), the method comprising: flowing exhaust (122) through one or more filter sections (202,

204, 206) of the exhaust element; estimating an amount of soot accumulated in the exhaust element; estimating an amount of ash accumulated in the exhaust element; and estimating the accumulated particulate matter in the exhaust element based on the amount of accumulated soot and the amount of accumulated ash in the exhaust element.

8. The method of claim 7, wherein the amount of soot accumulated in the exhaust element is based on an amount of soot entering the exhaust element and an amount of soot oxidized in the exhaust element

9. The method of claim 8, wherein estimating the amount of soot oxidized in the exhaust element is based on one or more engine operating conditions and one or more regeneration techniques.

10. The method of claim 8, wherein estimating the amount of ash accumulated in the exhaust element is based on at least one of a type of oil used in an engine, a speed of the engine, and an engine oil flow rate.