U.S. patent application number 13/943474 was filed with the patent office on 2014-05-08 for ammonia slip detection.
The applicant listed for this patent is International Engine Intellectual Property Company, LLC. Invention is credited to Paul Boon Charintranond, Michael James Miller, Navtej Singh.
Application Number | 20140123629 13/943474 |
Document ID | / |
Family ID | 49518755 |
Filed Date | 2014-05-08 |
United States Patent
Application |
20140123629 |
Kind Code |
A1 |
Singh; Navtej ; et
al. |
May 8, 2014 |
AMMONIA SLIP DETECTION
Abstract
A method of detecting ammonia in the exhaust system includes
detecting a predetermined engine operating condition. Upon
detecting the predetermined operating condition, the method
determines a first NO.sub.x conversion efficiency of a catalyst at
a first time T1. The method then injects a reactant into the
exhaust upstream of the catalyst and determines a second NO.sub.x
conversion efficiency at a second time T2. The method then
processes the first and second NO.sub.x conversion efficiencies to
determine whether an ammonia slip condition exists.
Inventors: |
Singh; Navtej; (Arlington
Heights, IL) ; Charintranond; Paul Boon; (Elmhurst,
IL) ; Miller; Michael James; (Mt. Prospect,
IL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
International Engine Intellectual Property Company, LLC |
Lisle |
IL |
US |
|
|
Family ID: |
49518755 |
Appl. No.: |
13/943474 |
Filed: |
July 16, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61722123 |
Nov 2, 2012 |
|
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|
Current U.S.
Class: |
60/274 ;
60/286 |
Current CPC
Class: |
F01N 2900/1621 20130101;
F01N 3/208 20130101; Y02T 10/12 20130101; B01D 53/9409 20130101;
F01N 11/00 20130101; F01N 2560/14 20130101; F01N 2900/08 20130101;
F01N 2560/026 20130101; Y02T 10/40 20130101; Y02T 10/47 20130101;
B01D 53/9495 20130101; B01D 2251/2062 20130101; Y02T 10/24
20130101; F01N 2550/02 20130101; F01N 2900/1616 20130101; F01N
3/2066 20130101; F01N 2900/1402 20130101 |
Class at
Publication: |
60/274 ;
60/286 |
International
Class: |
F01N 3/20 20060101
F01N003/20 |
Claims
1. A method of detecting ammonia slip across a catalyst in an
exhaust system of an internal combustion engine comprising;
detecting a preselected operating condition of the engine;
determining a first NO.sub.x conversion efficiency of the catalyst
at a first time; injecting a reductant into the exhaust upstream of
the catalyst; thereafter detecting a second NO.sub.x conversion
efficiency of the catalyst at a second time; and processing the
first and second NO.sub.x conversion efficiencies to determine
whether an ammonia slip condition exists.
2. The method of claim 1, wherein the reductant comprises
ammonia.
3. The method of claim 1, wherein the preselected engine operating
condition comprises a steady state condition.
4. The method of claim 1, wherein the step of determining a first
NO.sub.x conversion efficiency of the catalyst at a first time
further comprises: detecting a first upstream NO.sub.x level
relative to the catalyst at the first time; and detecting a first
downstream NO.sub.x level relative to the catalyst at the first
time.
5. The method of claim 1, wherein the step of determining a second
NO.sub.x conversion efficiency of the catalyst at a second time
further comprises: detecting a second upstream NO.sub.x level
relative to the catalyst at the second time; and detecting a second
downstream NO.sub.x level relative to the catalyst at the second
time.
6. The method of claim 1, wherein NO.sub.x conversion efficiency is
determined in accordance with the following formula: Eff = NO x -
upstream - NO x - downstream NO x - upstream 100 ##EQU00004## where
Eff is NO.sub.x conversion efficiency, NO.sub.x-upstream is the
upstream NO.sub.x level and NO.sub.x-downstream is the downstream
NO.sub.x level.
7. The method of claim 1, further comprising signaling an ammonia
slip condition in response to the NO.sub.x conversion efficiency
increasing between the first and second times.
8. A method of detecting ammonia slip across a catalyst in an
exhaust system of an internal combustion engine comprising:
detecting a preselected operating condition of the engine;
thereafter detecting a first upstream NO.sub.x level relative to
the catalyst at a first time; detecting a first downstream NO.sub.x
level relative to the catalyst at a first time; injecting a
reductant into the exhaust upstream of the catalyst; thereafter
detecting a second upstream NO.sub.x level relative to the catalyst
at a second time; detecting a second downstream NO.sub.x level
relative to the catalyst at a second time; and determining a first
NO.sub.x conversion efficiency based on the first upstream and
first downstream NO.sub.x levels; determining second NO.sub.x
conversion efficiency based on the second upstream and second
downstream NO.sub.x levels; and processing the first and second
NO.sub.x conversion efficiencies to determine whether an ammonia
slip condition exists.
9. The method of claim 8, wherein NO.sub.x conversion efficiency is
determined in accordance with the following formula: Eff = NO x -
upstream - NO x - downstream NO x - upstream 100 ##EQU00005## where
Eff is NO.sub.x conversion efficiency, NO.sub.x-upstream is the
upstream NO.sub.x level and NO.sub.x-downstream is the downstream
NO.sub.x level.
10. The method of claim 9, wherein the reductant comprises
ammonia.
11. The method of claim 10, wherein the preselected engine
operating condition comprises a steady state condition.
12. A system for detecting ammonia in an exhaust system of an
internal combustion engine, the exhaust system including a catalyst
and an injector upstream of the catalyst for injecting a reductant
into the exhaust system, the system comprising: an upstream
NO.sub.x sensor positioned to detect the level of NO.sub.x in the
exhaust stream at a location upstream of the catalyst and produce a
responsive upstream NO.sub.x signal; a downstream NO.sub.x sensor
positioned to detect the level of NO.sub.x in the exhaust stream at
a location downstream of the catalyst and produce a responsive
downstream NO.sub.x signal; a controller configured to receive the
upstream and downstream NO.sub.x signals; detect a preselected
engine operating condition; determine a first NO.sub.x conversion
efficiency based on the upstream and downstream NO.sub.x levels at
a first time; signal the injector to inject reductant into the
exhaust system; determine a second NO.sub.x conversion efficiency
based on the upstream and downstream NO.sub.x levels at a second
time following injection of the reluctant; and process the first
and second NO.sub.x conversion efficiencies to determine whether an
ammonia slip condition exists.
13. The system of claim 12, wherein the preselected engine
operating condition comprises a steady state operating
condition.
14. The method of claim 12, wherein NO.sub.x conversion efficiency
is determined in accordance with the following formula: Eff = NO x
- upstream - NO x - downstream NO x - upstream 100 ##EQU00006##
where Eff is NO.sub.x conversion efficiency, NO.sub.x-upstream is
the upstream NO.sub.x level and NO.sub.x-downstream is the
downstream NO.sub.x level.
15. The method of claim 12, wherein the reductant comprises
ammonia.
Description
BACKGROUND
[0001] Selective catalytic reduction (SCR) is commonly used to
remove NO.sub.x (i.e., oxides of nitrogen) from the exhaust gas
produced by internal engines, such as diesel or other lean burn
(gasoline) engines. In such systems, NO.sub.x is continuously
removed from the exhaust gas by injection of a reductant into the
exhaust gas prior to entering an SCR catalyst capable of achieving
a high conversion of NO.sub.x.
[0002] Ammonia is often used as the reductant in SCR systems. The
ammonia is introduced into the exhaust gas by controlled injection
either of gaseous ammonia, aqueous ammonia or indirectly as urea
dissolved in water. The SCR catalyst, which is positioned in the
exhaust gas stream, causes a reaction between NO.sub.x present in
the exhaust gas and a NO.sub.x reducing agent (e.g., ammonia) to
convert the NO.sub.x into nitrogen and water.
[0003] Proper operation of the SCR system involves precise control
of the amount (i.e., dosing level) of ammonia (or other reductant)
that is injected into the exhaust gas stream. If too little
reductant is used, the catalyst will convert an insufficient amount
of NO.sub.x. If too much reductant is used, a portion of the
ammonia will pass unreacted through the catalyst in a condition
known as "ammonia slip." Thus, it is desirable to be able to detect
the occurrence of "ammonia slip" conditions in order to, among
other things, regulate dosing levels.
SUMMARY
[0004] Aspects and embodiments of the present technology described
herein relate to one or more systems and methods for detecting
ammonia slip across a catalyst in the exhaust system of an internal
combustion engine. According to at least one aspect of the present
technology, a method of detecting ammonia in the exhaust system of
an internal combustion engine includes detecting a predetermined
engine operating condition. Upon detecting the predetermined
operating condition, the method determines a first NO.sub.x
conversion efficiency of the catalyst at a first time T1. The
method then injects a reactant into the exhaust upstream of the
catalyst and determines a second NO.sub.x conversion efficiency at
a second time T2. The method then processes the first and second
NO.sub.x conversion efficiencies to determine whether an ammonia
slip condition exists. In particular, the method may include
determining that an ammonia slip condition exists when the second
NO.sub.x conversion efficiency is greater than the first NO.sub.x
conversion efficiency. According to some embodiments, the reductant
is ammonia. In some embodiments, the preselected engine operating
condition may be a steady state condition. In some embodiments, the
steady state condition may correspond to a condition where engine
speed or load is constant.
[0005] In some embodiments, the method may determine the first
NO.sub.x conversion efficiency by detecting a first upstream
NO.sub.x level relative to the catalyst at the first time and
detecting a first downstream NO.sub.x level relative to the
catalyst at the first time. Likewise, the method may determine the
second NO.sub.x conversion efficiency by detecting a second
upstream NO.sub.x level relative to the catalyst at the second time
and detecting a second downstream NO.sub.x level relative to the
catalyst at the second time. In at least some embodiments, the
method may determine NO.sub.x conversion efficiency in accordance
with the following formula:
Eff = NO x - upstream - NO x - downstream NO x - upstream 100
##EQU00001##
where Eff is NO.sub.x conversion efficiency, NO.sub.x-upstream is
the upstream NO.sub.x level and NO.sub.x-downstream is the
downstream NO.sub.x level.
[0006] Certain aspects of the present technology relate to a system
for detecting ammonia in an exhaust system of an internal
combustion engine. The exhaust system including an SCR catalyst and
an injector upstream of the catalyst for injecting a reductant into
the exhaust system. An upstream NO.sub.x sensor is positioned to
detect the level of NO.sub.x in the exhaust stream at a location
upstream of the catalyst and produce a responsive upstream NO.sub.x
signal. A downstream NO.sub.x sensor is positioned to detect the
level of NO.sub.x in the exhaust stream at a location downstream of
the catalyst and produce a responsive downstream NO.sub.x signal. A
controller is configured to receive the upstream and downstream
NO.sub.x signals; detect a preselected engine operating condition;
determine a first NO.sub.x conversion efficiency based on the
upstream and downstream NO.sub.x at a first time T1; signal the
injector to inject reductant into the exhaust system; determine a
second NO.sub.x conversion efficiency based on the upstream and
downstream NO.sub.x levels at a second time T2 following injection
of the reductant; and process the first and second NO.sub.x
conversion efficiencies to determine whether an ammonia slip
condition exists. In at least some embodiments, the reductant may
be ammonia. In some embodiments, the preselected engine operating
condition comprises a steady state operating condition. In some
embodiments, the controller may determine NO.sub.x conversion
efficiency in accordance with the following formula:
Eff = NO x - upstream - NO x - downstream NO x - upstream 100
##EQU00002##
where Eff is the NO.sub.x conversion efficiency, NO.sub.x-upstream
is the upstream NO.sub.x level and NO.sub.x-downstream is the
downstream NO.sub.x level. The system may be configured to identify
an ammonia slip condition in response to the second NO.sub.x
conversion efficiency being greater than the first NO.sub.x
conversion efficiency.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1 is a schematic illustration of an internal combustion
engine with an exhaust gas SCR system.
[0008] FIG. 2 is a graph illustrating an exemplary relationship
between NO.sub.x conversion and NO.sub.x storage by a catalyst.
[0009] FIG. 3 is a graph illustrating an exemplary relationship
between NO.sub.x conversion and NO.sub.x storage by a catalyst.
[0010] FIG. 4 is a flow chart of an exemplary method for detecting
ammonia slip in an engine exhaust system according to certain
embodiments of the present technology.
DETAILED DESCRIPTION
[0011] Various examples of embodiments of the present technology
will be described more fully hereinafter with reference to the
accompanying drawings, in which such examples of embodiments are
shown. Like reference numbers refer to like elements throughout.
Other embodiments of the presently described technology may,
however, be in many different forms and are not limited solely to
the embodiments set forth herein. Rather, these embodiments are
examples representative of the present technology. Rights based on
this disclosure have the full scope indicated by the claims.
[0012] FIG. 1 shows an exemplary schematic depiction of an internal
combustion engine 10 and an SCR system 12 for reducing NO.sub.x
from the engine's exhaust. The engine 10 can be used, for example,
to power a vehicle such as an over-the-road vehicle (not shown).
The engine 10 can be a compression ignition engine, such as a
diesel engine, for example. Generally speaking, the SCR system 12
includes a catalyst 20, a reductant supply 22, a reductant injector
24, an electronic control unit ("ECU") 26, an upstream NO.sub.x
detector 30 and a downstream NO.sub.x detector 32.
[0013] The ECU 26 controls delivery of a reductant, such as
ammonia, from the reductant supply 22 and into an exhaust system 28
through the reductant injector 24. The reductant supply 22 can
include canisters (not shown) for storing ammonia in solid form. In
most systems, a plurality of canisters will be used to provide
greater travel distance between recharging. A heating jacket (not
shown) is typically used around the canister to bring the solid
ammonia to a sublimation temperature. Once converted to a gas, the
ammonia is directed to the reductant injector 24. The reductant
injector 24 is positioned in the exhaust system 28 upstream from
the catalyst 20. As the ammonia is injected into the exhaust system
28, it mixes with the exhaust gas and this mixture flows through
the catalyst 20. The catalyst 20 causes a reaction between NO.sub.x
present in the exhaust gas and a NO.sub.x reducing agent (e.g.,
ammonia) to reduce/convert the NO.sub.x into nitrogen and water,
which then passes out of the tailpipe 34 and into the environment.
While the SCR system 12 has been described in the context of solid
ammonia, it will be appreciated that the SCR system 12 could
alternatively use a reductant such as pure anhydrous ammonia,
aqueous ammonia or urea, for example.
[0014] The upstream NO.sub.x sensor 30 is positioned to detect the
level of NO.sub.x in the exhaust stream at a location upstream of
the catalyst 20 and produce a responsive upstream NO.sub.x signal.
As shown in FIG. 1, the upstream NO.sub.x sensor 30 may be
positioned in the exhaust system 28 between the engine and the
injector 24. The downstream NO.sub.x sensor 32 may be positioned to
detect the level of NO.sub.x in the exhaust stream at a location
downstream of the catalyst 20 and produce a responsive downstream
NO.sub.x signal. The ECU 26 is connected to receive the upstream
and downstream NO.sub.x signals from the sensors 30 and 32. The ECU
26 may be configured to control reductant dosing from the injector
24 in response to the upstream and/or downstream NO.sub.x signals
(and other sensed parameters). The present technology is not
limited to any particular dosing strategy. Accordingly, the
particulars of the dosing strategy are not detailed herein.
[0015] In addition to controlling the dosing or metering of
ammonia, the ECU 26 can also store information such as the amount
of ammonia being delivered, the canister providing the ammonia, the
starting volume of deliverable ammonia in the canister, and other
such data which may be relevant to determining the amount of
deliverable ammonia in each canister. The information may be
monitored on a periodic or continuous basis. When the ECU 26
determines that the amount of deliverable ammonia is below a
predetermined level, a status indicator (not shown) electronically
connected to the controller 26 can be activated.
[0016] FIGS. 2 and 3 are graphs illustrating exemplary
relationships between NO.sub.x conversion and NO.sub.x storage by a
catalyst, where NO.sub.x storage represents the percentage of
storage capacity of the catalyst that is being used. The NO.sub.x
conversion efficiency of a catalyst is generally a function of
stored NO.sub.3, temperature and space velocity. As can be seen in
FIGS. 2 and 3, NO.sub.x conversion generally increases as NO.sub.x
storage increases. However, when the catalyst reaches a certain
capacity, e.g., 90% in the illustrated embodiment, its efficiency
stops increasing. As a result, the catalyst will stop converting
all of the ammonia and some of the ammonia will pass ("slip")
through the catalyst and into the environment. NO.sub.x sensors are
typically cross-sensitive to ammonia. More specifically, NO.sub.x
sensors typically cannot discriminate between these two compounds.
Accordingly, ammonia that slips through the catalyst will be sensed
as NO.sub.x by a downstream NO.sub.x. As a result, the ammonia
slippage may cause more ammonia to be injected, which will, in
turn, compound the slippage problem. Thus, it is desirable to be
able to detect the occurrence of "ammonia slip" in order to
regulate dosing levels.
[0017] FIG. 4 is a flow chart of an exemplary method 400 for
detecting ammonia slip in an SCR system according to certain
aspects of the present technology. The method 400 begins in step
405. Control is then passed to the step 410 where the method checks
to see if the engine is in a preselected engine operating
condition. In at least some embodiments, the preselected engine
operating condition may be a "steady state" operating condition
where the NO.sub.x produced by the engine is substantially
constant. For example, a steady state operating condition may
correspond to a condition where a vehicle is motoring, e.g., engine
speed or load is substantially constant. The method continues to
loop through step 410 until the preselected operating condition is
detected.
[0018] Once the condition is detected, control is passed to step
415, where the method 400 determines a first NO.sub.x efficiency at
a first time T1. In particular, the method determines the upstream
NO.sub.x level, e.g., by reading the upstream NO.sub.x signal from
the upstream NO.sub.x sensor 30 and a downstream NO.sub.x level,
e.g., by reading the downstream NO.sub.x signal from the downstream
NO.sub.x sensor 32. The method 400 then uses the upstream and
downstream NO.sub.x values to determine the NO.sub.x efficiency in
accordance with the following formula:
Eff = NO x - upstream - NO x - downstream NO x - upstream 100
##EQU00003##
where Eff is NO.sub.x conversion efficiency, NO.sub.x-upstream is
the upstream NO.sub.x level and NO.sub.x-downstream is the
downstream NO.sub.x level.
[0019] Control is then passed to step 420, where the method 400
injects a test dose of reductant, e.g., ammonia, into the exhaust
system upstream of the catalyst 20. For example, the method 400 may
involve having the ECU 26 actuate the injector 24 to inject a
predetermined amount of reductant into the exhaust system 28.
[0020] Control is then passed to the step 425, where the method
determines a second NO.sub.x conversion efficiency at a second time
T2. As above, the method 400 may determine NO.sub.x conversion
efficiency by reading the signals from the upstream and downstream
NO.sub.x sensors 30, 32 at the second time and calculating NO.sub.x
conversion efficiency based on these values.
[0021] Control is then passed to step 430, where the method 400
processes the first and second NO.sub.x conversion efficiency
values to determine if an ammonia slip condition exists.
Specifically, the method compares the first and second NO.sub.x
conversion efficiency values to see if the NO.sub.x efficiency
increases following injection of the test dose in step 420. If the
NO.sub.x conversion efficiency value increased, control is passed
to step 435, where the method indicates that an ammonia slip
condition may exist. Conversely, if the NO.sub.x conversion
efficiency value did not increase, control is passed to step 440,
where the method indicates that an ammonia slip condition does not
exist. Specifically, since the engine is operating in a steady
state condition where NO.sub.x production is substantially
constant, the NO.sub.x reading from the upstream NO.sub.x sensor 30
will remain substantially constant between the first and second
times T1, T2. If the ammonia dose, which is injected downstream of
the sensor 32, is not fully converted by the catalyst 20, it will
be sensed by the downstream NO.sub.x sensor 32. Accordingly, when
ammonia slip occurs, the second NO.sub.x conversion efficiency
value will be higher than the first NO.sub.x conversion
efficiency.
[0022] In sum, the method 400 initially checks to see if the engine
10 is operating in a steady state condition where the NO.sub.x
produced by the engine is substantially constant. Upon detecting a
steady state condition, the method 400 determines a first NO.sub.x
conversion efficiency of the catalyst at a first time T1. The
method 400 then injects a dose of reactant into the exhaust
upstream of the catalyst 20 and determines a second NO.sub.x
conversion efficiency at a second time T2. The method 400 then
determines if the NO.sub.x conversion efficiency has increased
between the first and second times. An increasing NO.sub.x
conversion efficiency indicates the presence of an ammonia slip
condition.
[0023] At least some embodiments of the present technology relate
to a system 12 for detecting an ammonia slip across an SCR catalyst
in the exhaust system of an internal combustion engine. Referring
again to FIG. 1, the system 12 may generally include the injector
24, the reductant supply 22, the upstream NO.sub.x sensor 30, the
downstream NO.sub.x sensor 32 and a controller such as the ECU 26.
The ECU 26 may be configured to receive the upstream and downstream
NO.sub.x signals and to control operation of the injector 24. The
ECU 26 may be configured to detect a preselected operating
condition in the engine, such as a steady state operating
condition. Upon detecting the steady state operating condition, the
ECU 26 determines a first NO.sub.x conversion efficiency at a first
time T1. The ECU 26 then signals the injector 24 to inject a dose
of reductant into the exhaust system 28. The ECU 26 then determines
a second NO.sub.x conversion efficiency based on the upstream and
downstream NO.sub.x levels at a second time following injection of
the reductant. The ECU 26 then processes the first and second
NO.sub.x conversion efficiencies to determine whether an ammonia
slip condition exists. In particular, the ECU 26 may be configured
to signal that an ammonia slip condition is present when NO.sub.x
conversion efficiency increases between the first and second
times.
[0024] While this disclosure has been described as having exemplary
embodiments, this application is intended to cover any variations,
uses, or adaptations using the general principles set forth herein.
It is envisioned that those skilled in the art may devise various
modifications and equivalents without departing from the spirit and
scope of the disclosure as recited in the following claims.
Further, this application is intended to cover such departures from
the present disclosure as come within the known or customary
practice within the art to which it pertains.
* * * * *