Patent Application
20180223712
Some existing vehicles have exhaust gas aftertreatment systems to reduce the amounts of carbon monoxide, unburned hydrocarbons, and nitrogen oxides (collectively, NOx) that are discharged to the atmosphere in the exhaust from internal combustion engines that power the vehicles. Existing exhaust gas aftertreatment systems may be most effective in treating the exhaust from a warmed-up engine because the catalyst materials have been heated to temperatures (e.g., 200° C. and above) at which the catalyst materials serve to effectively oxidize carbon monoxide and incompletely burned fuel constituents to carbon dioxide and water, and to reduce nitrogen oxides to nitrogen gas. The existing exhaust gas aftertreatment systems have been effective for both gasoline engines operating at or around the stoichiometric air-to-fuel ratio and diesel engines (and other lean-burn engines) operating with excess air (sometimes called “lean burn” engines).
It has been difficult to treat exhaust emissions immediately following a cold engine start, before the exhaust has heated the catalytic converter or converters to the effective temperatures for designated catalytic reactions. Lean-burn engines, such as diesel engines, tend to produce cooler exhaust streams because of the excess air used in the combustion mixtures charged to the cylinders of the diesel engine. Untreated cold start emissions may make-up a significant portion of the total regulated emissions at a tailpipe of a vehicle. Mixed nitrogen oxides in the exhaust of diesel engines have been difficult to reduce. These nitrogen oxides include nitric oxide (NO) and nitrogen dioxide (NO2); the mixture may be typically referred to as NOx.
A vehicle includes a NOx storage converter to receive exhaust gases from a diesel engine, store at least a minimum amount of the NOx at a temperature below a storage threshold, release the NOx at a temperature above a releasing threshold, oxidize hydrocarbon, and oxidize carbon monoxide. An input temperature sensor at an entrance to the NOx storage converter determines an input temperature of the exhaust gases. An output temperature sensor is at an output of the NOx storage converter to determine an output temperature of the exhaust gases. A control module receives the input temperature and the output temperature, determines a magnitude of an exotherm in the NOx storage converter, and stores an electronic fault code in a computer memory in response to the magnitude of the exotherm being below a minimum temperature. The fault code indicates a reduction in a NOx storage capacity of the NOx storage converter.
Features of examples of the present disclosure will become apparent by reference to the following detailed description and drawings, in which like reference characters correspond to similar, though perhaps not identical, components. For the sake of brevity, reference characters or features having a previously described function may or may not be described in connection with other drawings in which they appear.
Selective Catalytic Reduction (SCR) of NOx using ammonia (NH3) as a reductant is used to reduce NOx emissions from diesel engines that power existing vehicles and stationary machines. In the existing SCR process, NOx reacts with a reductant, such as pure anhydrous ammonia, aqueous ammonia, and/or ammonia generated by urea decomposition. The reductant (e.g., urea) is injected into the exhaust gas stream before a mixer (e.g., a urea mixer) placed upstream of an SCR catalytic converter. The existing ammonia SCR technologies are considered an effective way to reduce diesel NOx emissions when the exhaust system is warmed up and the SCR catalyst has reached an SCR operating temperature.
In examples of the vehicle 2 as depicted in
The exhaust gas treatment system 10 includes one or more exhaust gas conduits 14, and one or more exhaust treatment devices. In the example illustrated in
In
The NOx storage converter 18 contains a NOx storage catalyst together with a DOC for HC and CO oxidation. In examples of the present disclosure, the NOx storage converter 18 also contains a HC storage material. Close coupled with the diesel engine 12, the NOx storage converter 18 passively stores NOx emissions until the stored NOx emissions are released at a higher temperature. The downstream SCR converter 22 (or SCRF converter 22′) then reduces the released NOx using ammonia. In the aftertreatment system 10, most of NOx is reduced to nitrogen gas.
Examples of the NOx storage converter 18 may include a dual-layer catalyst. In other examples of the present disclosure, the NOx storage converter 18 may have a NOx storage catalyst and a DOC catalyst mixed into one single layer catalyst washcoat. An example of the dual-layer catalyst includes a substrate, a NOx storage layer disposed on the substrate and a DOC layer disposed on top of the NOx storage layer. The substrate may be any material suitable for a diesel emissions control catalyst, examples of which include ceramic substrates (e.g., cordierite) or a metallic alloy (e.g., stainless steel containing Cr, Al or Ti), and combinations thereof.
The NOx storage layer includes a NOx storage catalyst for storing NOx. The NOx storage catalyst is to release the stored NOx when the NOx storage catalyst is heated to an active temperature of the NOx storage catalyst. The DOC layer may include the DOC for HC and CO oxidation. The dual-layer catalyst may be achieved with a double catalyst washcoating of the two layers, with the DOC layer formed on top of the NOx storage layer.
The NOx storage layer and the DOC layer may be applied sequentially onto the substrate by any suitable method. In an example, the NOx storage layer and the DOC layer are sequentially applied by multiple washcoating (e.g., dual washcoating). Depending on the type of a given substrate, suitable NOx storage layer and DOC layer thicknesses are sufficient to maintain a predetermined pressure drop in order to control engine back pressure.
In an example, the thickness of each of the NOx storage layer and the DOC layer, individually, ranges from about 5 micrometers to about 150 micrometers. In a further example, the thickness of each of the NOx storage layer and the DOC layer, individually, ranges from about 20 micrometers to about 100 micrometers. It is to be understood that the thickness of the NOx storage layer may be the same as, or different from the thickness of the DOC layer.
In an example, “cold start” may refer to a period of time under conditions defined in 40 CFR § 86.137-94 (a), included by reference herein in its entirety. As stated in 40 CFR § 86.137-94 (a), the cold start test is divided into two periods. The first period, representing the cold start “transient” phase, terminates at about 505 seconds of the driving schedule referred to in 40 CFR § 86.137-94. The second period, representing the “stabilized” phase, consists of the remainder of the cold start driving schedule (including engine shutdown).
Examples of the NOx storage catalyst of the present disclosure store NOx between about 10 degrees Celsius (° C.) and about 160° C. In an example, the storage threshold temperature may be above 160 degrees Celsius (° C.).
The NOx storage converter 18 is to release the stored NOx at a temperature above a releasing threshold temperature. In an example the releasing threshold temperature may be above 140° C. In an example, the storage threshold temperature may be within 20° C. of the releasing threshold temperature. The NOx storage converter 18 is further to oxidize HC, and to oxidize CO.
As depicted in
Examples of the vehicle 2 of the present disclosure include a control module 50 to receive the input temperature from the input temperature sensor 52 and the output temperature from the output temperature sensor 54. The control module 50 includes circuits and/or logic to determine a magnitude of an exotherm in the NOx storage converter 18 based on the input temperature and the output temperature. The control module 50 is to store an electronic fault code in a computer memory 36 in response to the magnitude of the exotherm being below a minimum temperature. The electronic fault code indicates a reduction in a NOx storage capacity of the NOx storage converter.
In an example of the vehicle 2 depicted in
The SCR 22 may include, for example, a flow-through ceramic or metallic monolith substrate that may be packaged in a stainless steel shell or canister having an inlet and an outlet in fluid communication with the exhaust gas conduit 14. The substrate may include an SCR catalyst composition applied thereto. The SCR catalyst composition may contain a mesoporous material (e.g., zeolite, SSZ-13, SAPO (silico-alumino-phosphate)) and one or more base metal components such as iron (Fe), cobalt (Co), copper (Cu) or vanadium (V) which can operate efficiently to reduce NOx constituents in the exhaust gas 15 to nitrogen and water in the presence of a reductant 26 such as NH3. In examples of the present disclosure, an SCRF converter 22′ may be substituted for the SCR converter 22. In examples with an SCRF converter 22′, both ceramic and metallic filter substrates can be used.
An NH3 reductant, (e.g., DEF) may be supplied from a reductant supply source (not shown) and may be injected into the exhaust gas conduit 14 at a location upstream of the SCR converter 22 (or the SCRF converter 22′) using a DEF injector 46, or other suitable method of delivery of the reductant to the exhaust gas 15. The reductant may be in the form of a gas, a liquid, or an aqueous urea solution and may be mixed with air in the DEF injector 46 to aid in the dispersion of the injected spray.
With further reference to
The control module 50 includes control logic to activate a HC/fuel injector 40 when the control module 50 determines that a threshold hydrocarbon value has not been met. Upon activation, the HC/fuel injector 40 introduces unburned HC into the exhaust gas stream. If the control module 50 determines that the threshold hydrocarbon value has been met, then the control module 50 further includes control logic for deactivating the HC/fuel injector 40. Alternatively, the HC/fuel injector 40 may be omitted, and the control module 50 may modify operating parameters of the engine 12 to control the hydrocarbon levels in the exhaust gases 15. Specifically, the control module 50 adjusts the engine timing and rate/frequency of fueling to deliver excess, unburned fuel into the exhaust gas conduit 14 for mixing with the exhaust gas 15.
In examples according to the present disclosure, control module 50 may operate on-board the vehicle 2 by a method 100 as depicted in
In
In the box with the dashed outline at reference numeral 126 is “storing at least a minimum amount of the NOx by adsorption in the NOx storage converter at a monolith temperature below a storage threshold temperature; releasing the NOx when the monolith temperature is above a releasing threshold temperature; oxidizing hydrocarbon in the NOx storage converter; and oxidizing carbon monoxide in the NOx storage converter.”
In the box with the dashed outline at reference numeral 128, “the minimum amount of the NOx stored is 10 percent of the NOx received from the diesel engine. In the box with the dashed outline at reference numeral 130 “the storage threshold temperature is above 160 degrees Celsius.” In an example of the present disclosure that includes the element depicted at reference numeral 132, “the releasing threshold temperature is above 140 degrees Celsius.” At reference numeral 134, the method of the present disclosure includes the optional element wherein “the storage threshold temperature is within 20 degrees Celsius of the releasing threshold temperature.”
As depicted in the box with the dashed outline at reference numeral 136, “the determining the exothermic activity value indicative of exothermic activity of the NOx storage converter includes determining a temperature change by subtracting the input temperature from the output temperature; the exothermic activity value is the temperature change; and a positive temperature change is indicative of the exothermic activity of the NOx storage converter.”
As depicted in the box with the dashed outline at reference numeral 138, “the determining the diagnostic value includes subtracting a predetermined temperature threshold from the temperature change; and a positive diagnostic value indicates the operational state of both the NOx storage function and the HC oxidation function of the NOx storage converter.” For example, a positive diagnostic value may indicate that the operational state of both the NOx storage function and the HC oxidation function of the NOx storage converter is “good”. In other words, a “good” operational state may mean that NOx storage converter is operating within specified limits for both the NOx storage function and the HC oxidation function. Conversely, a negative diagnostic value may indicate that the operational state of both the NOx storage function and the HC oxidation function of the NOx storage converter is “malfunctioning”. A “malfunctioning” operational state may mean that NOx storage converter is not operating within specified limits for both the NOx storage function and the HC oxidation function.
As depicted in the box with the dashed outline at reference numeral 124, the method may include the step of “injecting a predetermined amount of the HC into the exhaust gases to chemically react in the NOx storage converter.”
An existing catalytic converter diagnostic method is disclosed in U.S. Pat. No. 5,630,315 by inventor Joseph R. Theis, referred to herein as “Theis”. Theis is included by reference herein in its entirety. Theis discloses steps in a catalytic converter diagnostic method wherein exothermic activity of the catalytic converter is monitored to determine if the catalytic converter is operating properly. However, Theis does not contemplate a NOx storage converter 18 as disclosed herein. Further, the steps in the method disclosed by Theis would not be capable of diagnosing the NOx storage functionality of the NOx storage converter because the method disclosed by Theis checks for a warmed-up engine and exits if the engine is not warmed up. Theis discloses at step 114 in Theis' FIG. 4A that the diagnostic method is not attempted until the engine has been run for greater than 200 seconds. Further, at step 112, Theis discloses that the coolant must have a temperature indicating that the engine is running at the normal operating temperature. Since Theis does not contemplate a catalytic converter with both DOC and low temperature NOx storage functions, Theis does not contemplate a NOx storage converter 18 according to the present disclosure. Further, Theis does not disclose that exothermic activity of a NOx storage converter 18 that has both a low temperature NOx storage layer and a DOC layer could be used to indicate the operative status of both the NOx storage layer and the DOC layer as disclosed in the present disclosure.
The discussion of the SCR converter has been presented above, in some examples, in terms of urea as the reductant that is injected into the exhaust system for reaction with the SCR converter to reduce NOx to nitrogen and water. However, other reductants, such as anhydrous ammonia and aqueous ammonia, may also be used in lieu of the DEF (aqueous urea solution). If urea is used, the reduction reaction also produces carbon dioxide.
Reference throughout the specification to “one example”, “another example”, “an example”, and so forth, means that a particular element (e.g., feature, structure, and/or characteristic) described in connection with the example is included in at least one example described herein, and may or may not be present in other examples. In addition, it is to be understood that the described elements for any example may be combined in any suitable manner in the various examples unless the context clearly dictates otherwise.
It is to be understood that the ranges provided herein include the stated range and any value or sub-range within the stated range. For example, a range of from about 5 micrometers to about 150 micrometers should be interpreted to include not only the explicitly recited limits of from about 5 micrometers to about 150 micrometers, but also to include individual values, such as 12 micrometers, 50.7 micrometers, etc., and sub-ranges, such as from about 40 micrometers to about 80 micrometers, etc. Furthermore, when “about” is utilized to describe a value, this is meant to encompass minor variations (up to +/−10 percent) from the stated value.
In describing and claiming the examples disclosed herein, the singular forms “a”, “an”, and “the” include plural referents unless the context clearly dictates otherwise.
While several examples have been described in detail, it is to be understood that the disclosed examples may be modified. Therefore, the foregoing description is to be considered non-limiting.
