EXHAUST SYSTEM FOR A VEHICLE
An exhaust system for a vehicle includes a passageway, a selective catalytic reduction system, a diesel particulate filter, a urea injection system, and a hydrolysis catalyst. The passageway is operable to direct a flow of exhaust gas emitted from an engine of the vehicle. The selective catalytic reduction system and the diesel particulate filter are positioned along the passageway spaced from one another. The urea injection system includes an injection port positioned along the passageway upstream of the selective catalytic reduction system. The urea injection system is operable to inject urea into the passageway. The hydrolysis catalyst coats at least a portion of the diesel particulate filter. Urea injected into the passageway through the injection port decomposes into ammonia and carbon dioxide upon contact with the hydrolysis catalyst. Thus, the decomposition of the urea is not dependent on mixing the urea with the exhaust gases.
The present disclosure relates generally to an exhaust system for a vehicle, such as an exhaust system operable to remove nitrogen oxides and particulate matter from exhaust gases.
BACKGROUNDIt is desirable to eliminate nitrogen oxides (NOx) and particulate matter (PM) contained in exhaust gas emitted from internal combustion engines. One of the methods for purifying exhaust gas includes the step of injecting aqueous urea into the exhaust passageway to generate ammonia by hydrolysis. The urea decomposes into ammonia and carbon dioxide by being intermixed with the relatively hot and moisture-rich exhaust gas. The ammonia is then utilized with a nitrogen oxide catalyst, such as a selective catalytic reduction (SCR) type catalyst. The nitrogen oxide is decomposed into nitrogen and water. Effective decomposition of the urea often requires that the system includes a mixer, or that the system provides sufficient time for mixing, resulting in increased system length. In medium-duty applications, the temperature of the exhaust gas can fall below 200° C. and compromise urea decomposition. For example, the water component of the aqueous urea evaporates before the urea decomposes. The urea then crystallizes and forms undesirable deposits within the system. Thus, while current exhaust systems work for their intended purpose, there remains a need for improvement in the relevant art.
SUMMARYIn one form, an exhaust system for a vehicle is provided in accordance with the teachings of the present disclosure. In an exemplary implementation, the exhaust system includes a passageway, a selective catalytic reduction system, a diesel particulate filter, a urea injection system, and a hydrolysis catalyst. The passageway is operable to direct a flow of exhaust gas emitted from an engine of the vehicle. The selective catalytic reduction system and the diesel particulate filter are positioned along the passageway spaced from one another. The urea injection system includes an injection port positioned along the passageway upstream of the selective catalytic reduction system. The urea injection system is operable to inject urea into the passageway. The hydrolysis catalyst coats at least a portion of the diesel particulate filter. An injector portion of the urea system will be located downstream or upstream of the coated portion of the diesel particulate filter to inject urea into the diesel particulate filter passageways. Urea injected into the passageway through the injection port decomposes into ammonia and carbon dioxide upon contact with the hydrolysis catalyst. Thus, the decomposition of the urea is not dependent on mixing the urea with the exhaust gases.
In another form, a method of treating exhaust from an engine is provided in accordance with the teachings of the present disclosure. In an exemplary implementation, the method includes providing a passageway to direct the flow of exhaust. The method also includes providing a selective catalytic reduction system and a diesel particulate filter along the passageway to treat the exhaust. An injection port of a urea injection system is provided along the passageway to inject urea into the passageway upstream of the selective catalytic reduction system. The method also includes providing a hydrolysis catalyst coating on at least a portion of the diesel particulate filter. Urea injected into the passageway through the injection port decomposes into ammonia and carbon dioxide upon contact with the hydrolysis catalyst. As a result, the decomposition of the urea is not dependent on mixing the urea with the exhaust gases.
In some implementations, the positioning of the hydrolysis catalyst can be varied. For example, the hydrolysis catalyst can be arranged on the diesel particulate filter proximate to the injection port rather than on the entire diesel particulate filter. As a result, a quantity of hydrolysis catalyst applied to the diesel particulate filter can be minimized. In addition, the position of the injection port can be arranged such that the urea is injected at least partially against the flow of exhaust. This can enhance the distribution of urea about the coated portion of the diesel particulate filter.
In some implementations, the exhaust system includes a diesel oxidation catalyst positioned along the passageway upstream of and spaced from the diesel particulate filter. In some implementations, the urea injection system is positioned between the diesel oxidation catalyst and the diesel particulate filter.
Further areas of applicability of the teachings of the present disclosure will become apparent from the detailed description, claims and the drawings provided hereinafter, wherein like reference numerals refer to like features throughout the several views of the drawings. It should be understood that the detailed description, including disclosed embodiments and drawings referenced therein, are merely exemplary in nature, intended for purposes of illustration only and are not intended to limit the scope of the present disclosure, its application or uses. Thus, variations that do not depart from the gist of the present disclosure are intended to be within the scope of the present disclosure.
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Effective decomposition of the urea in current exhaust systems requires that the urea sufficiently mix with the exhaust gas. Sufficient mixing in current exhaust systems is achieved by extending the length of the system in order to increase the amount of time that the urea and the exhaust intermix prior to encountering the selective catalytic reduction system. The extended length increases costs and compromises packaging efficiency of current exhaust systems. Some current systems include a mixer to reduce the amount of extended length. However, the mixer does not eliminate the need for extended length and also increases the cost and complexity of current exhaust systems. Another challenge associated with effective intermixing of urea and exhaust arises in medium-duty applications. In these applications, the temperature of the exhaust gas can fall below 200° C., which compromises urea decomposition. In such medium-duty systems, the water component of the aqueous urea evaporates. Urea decomposes at around 100° C., but if the temperature of the exhaust gas drops below 180° C., urea injection is generally stopped because the SCR catalyst is not at a preferred temperature to use the ammonia derived from the urea. In previous systems, if high levels of urea are injected there will not be enough thermal energy (even at 200° C.) to evaporate and decompose the urea that is injected. Further, water would be evaporated before the urea is decomposed and deposit formations would arise. The present teachings overcome this deficiency.
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In exemplary implementations of the present disclosure where the injection port 26 is upstream of the diesel particulate filter 20, the full length of the diesel particulate filter 20 can be coated with the hydrolysis coating 30. In exemplary implementations of the present disclosure where the injection port 26 is downstream of the diesel particulate filter 20, coating only a portion of the diesel particulate filter is sufficient. In the case where the injection port 26 is upstream of the diesel particulate filter 20, it may not be desirable to place an oxidizing washcoat on any portion of the diesel particulate filter 20 since it will oxidize the ammonia formed from the reaction between the urea and the hydrolysis coating. Thus, it may be desirable to coat the whole length of the diesel particulate filter 20. If the injector is downstream of the diesel particulate filter 20, a forward portion of the diesel particulate filter 20 may be coated with oxidation catalyst and a rearward portion with hydrolysis catalyst, since urea spray will likely not penetrate deep into the diesel particulate filter 20.
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It should be understood that the mixing and matching of features, elements, methodologies and/or functions between various examples may be expressly contemplated herein so that one skilled in the art would appreciate from the present teachings that features, elements and/or functions of one example may be incorporated into another example as appropriate, unless described otherwise above.
Claims
1. An exhaust system for a vehicle comprising:
- a passageway operable to direct a flow of exhaust gas emitted from an engine of the vehicle;
- a selective catalytic reduction system positioned along the passageway;
- a diesel particulate filter positioned along the passageway spaced from the selective catalytic reduction system;
- a urea injection system including an injection port positioned along the passageway upstream of the selective catalytic reduction system, the urea injection system operable to inject urea into the passageway; and
- a hydrolysis catalyst coating on at least a portion of the diesel particulate filter, wherein urea injected into the passageway through the injection port decomposes into ammonia and carbon dioxide upon contact with the hydrolysis catalyst.
2. The exhaust system of claim 1, wherein the hydrolysis catalyst coating coats less than a full length of the diesel particulate filter along the passageway.
3. The exhaust system of claim 2, wherein the hydrolysis catalyst coating coats a leading edge of the diesel particulate filter along the passageway.
4. The exhaust system of claim 3, wherein the urea injection system is positioned upstream of and adjacent to the leading edge of the diesel particulate filter.
5. The exhaust system of claim 4, wherein the exhaust system further comprises a diesel oxidation catalyst positioned along the passageway upstream of and spaced from the diesel particulate filter, and wherein the urea injection system is positioned between the diesel oxidation catalyst and the diesel particulate filter.
6. The exhaust system of claim 2, wherein the hydrolysis catalyst coating coats less than one quarter of the full length of the diesel particulate filter along the passageway.
7. The exhaust system of claim 1, wherein the injection port directs urea into the passageway in a direction transverse to a direction of exhaust flow.
8. The exhaust system of claim 7, wherein the direction of the injection port is perpendicular to the direction of the exhaust flow.
9. The exhaust system of claim 2, wherein the hydrolysis catalyst coating coats a trailing edge of the diesel particulate filter along the passageway.
10. The exhaust system of claim 9, wherein the urea injection system is positioned downstream of and adjacent to the trailing edge of the diesel particulate filter.
11. The exhaust system of claim 10, wherein a direction of the injection port is at least partially opposite to a direction of exhaust flow.
Type: Application
Filed: Jun 11, 2014
Publication Date: Dec 17, 2015
Inventors: Homayoun Ahari (Bloomfield, MI), Michael G. Zammit (White Lake, MI), Luis Cattani (Aurora, IL)
Application Number: 14/301,707