EXHAUST AFTERTREATMENT SYSTEM WITH IN-ELBOW REDUCTANT INJECTION
An exhaust aftertreatment system, such as for a diesel engine, includes a reductant dosing system with an injector positioned in an elbow pipe of an exhaust conduit. A tubeless mixer is positioned in the exhaust conduit between the injector nozzle outlet and an SCR catalyst. The tubeless mixer includes a plurality of rings, all of which are distributed with increasing size as distance from the nozzle outlet increases. The tubeless mixer aides in more uniformly distributing reductant in the exhaust flow prior to arrival at the SCR catalyst.
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The present disclosure relates generally to mixing of reductant and exhaust in an aftertreatment system, and more particularly to a tubeless mixer that includes a plurality of stacked rings distributed with increasing size as a distance from a reductant injector increases.
BACKGROUNDIn many exhaust aftertreatment systems, a reductant, such as liquid urea, is injected into exhaust flow. The urea droplets go through a vaporization and hydrolysis reactions to form ammonia gas. The ammonia adsorbs onto an SCR catalyst and then reacts with NOx in the exhaust flow, with the end result being water and nitrogen at the tailpipe after the selective catalytic reduction. In general, the urea injection site can be located at various positions, such as in the center of a straight segment of an exhaust conduit or at an elbow pipe in the exhaust conduit.
Those skilled in the art will appreciate that a successful mixing strategy of the urea droplets with the exhaust flow can be evaluated based upon the uniformity of ammonia gas distribution at the SCR catalyst combined with minimal or no urea deposits in the exhaust conduit upstream from the catalyst. One of the main issues associated with urea injection, especially in elbow pipe injection locations, are urea deposits. The occurrence of a deposit in the flow path may create severe issues related with performance, such as back pressure increases, reductions in ammonia distribution uniformity and maybe even structural damage if a deposit build up separates from the wall and hits a key component, such as the SCR catalyst itself. The problem is further complicated by the fact that spray distribution may be very dependent upon exhaust conditions, such as low flow conditions associated with idle versus high exhaust flow conditions associated with the engine operating at a rated condition. The main issues faced with in-elbow pipe injection include spray distribution variation with exhaust flow conditions, deposit issues due at an elbow bend, and deposit risk at the injector tip during low exhaust flow conditions.
The present disclosure is directed toward improved performance for in-elbow urea injection of exhaust aftertreatment systems.
SUMMARYIn one aspect, an exhaust aftertreatment system includes an exhaust conduit with an elbow pipe positioned between an engine end and a tailpipe end. An SCR catalyst is positioned in the exhaust conduit between the elbow pipe and the tailpipe end. A reductant dosing system with a nozzle outlet of an injector is positioned in the elbow pipe of the exhaust conduit. A tubeless mixer is positioned in the exhaust conduit between the nozzle outlet and the SCR catalyst. The tubeless mixer includes a plurality of rings, all of which are distributed with increasing size as distance from the nozzle outlet increases.
In another aspect, an elbow pipe of an exhaust conduit includes a pipe with an inlet and an outlet. A centerline of the inlet is angled, at an angle greater than zero, with respect to a centerline of the outlet. The pipe defines an injector opening therethrough. A tubeless mixer is attached to an inner surface of the pipe and includes a plurality of rings, all of which are distributed with increasing size as distance from the injector opening increases.
In still another aspect, a method of operating an exhaust aftertreatment system includes moving exhaust in an exhaust conduit from an engine end toward a tailpipe end. Reductant is injected from an injector into an elbow pipe of the exhaust conduit. The reductant is mixed with exhaust at least in part by passing the exhaust and the reductant through a tubeless mixer that includes a plurality of rings distributed with increasing size as a distance from the injector increases. NOx is reacted in the exhaust with the reductant at an SCR catalyst positioned in the exhaust conduit.
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The tubeless mixer 50 shown in
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When the exhaust flow is high as in
As used in this disclosure, the tubeless mixer 50 is characterized as having a plurality of rings 51, all of which are distributed with increasing size as distance from the nozzle outlet 44 of injector 41 increases. Also, tubeless mixer 50 also includes no structure that could be fairly characterized as a tube consistent with the definition set forth earlier in this disclosure. Thus, a tubeless mixer 50 according to the present disclosure means something other than a mixed flow guiding device of the type shown in Chinese Patent CN 202021015 that includes a central tube 7.
The present description is for illustrative purposes only, and should not be construed to narrow the breadth of the present disclosure in any way. Thus, those skilled in the art will appreciate that various modifications might be made to the presently disclosed embodiments without departing from the full and fair scope and spirit of the present disclosure. Other aspects, features and advantages will be apparent upon an examination of the attached drawings and appended claims.
Claims
1. An exhaust aftertreatment system comprising:
- an exhaust conduit with an elbow pipe positioned between an engine end and a tailpipe end;
- an SCR catalyst positioned in the exhaust conduit between the elbow pipe and the tailpipe end;
- a reductant dosing system with a nozzle outlet of an injector positioned in the elbow pipe of the exhaust conduit;
- a tubeless mixer positioned in the exhaust conduit between the nozzle outlet and the SCR catalyst; and
- the tubeless mixer includes a plurality of rings, all of which are distributed with increasing size as distance from the nozzle outlet increases.
2. The exhaust aftertreatment system of claim 1 wherein the rings share a common centerline.
3. The exhaust aftertreatment system of claim 2 wherein the exhaust conduit immediately adjacent the elbow pipe shares the common centerline.
4. The exhaust aftertreatment system of claim 3 wherein leading edges of consecutively increased size rings are located at distances that increase along the common centerline from the nozzle outlet.
5. The exhaust aftertreatment system of claim 4 wherein trailing edges of consecutively increased size rings are located at distances that increase along the common centerline from the nozzle outlet.
6. An elbow pipe of an exhaust conduit comprising:
- a pipe with an inlet and an outlet;
- a centerline of the inlet being angled, at an angle greater than zero, with respect to a centerline of the outlet;
- the pipe defining an injector opening therethrough;
- a tubeless mixer attached to an inner surface of the pipe and including a plurality of rings, all of which are distributed with increasing size as distance from the injector opening increases.
7. The elbow pipe of claim 6 wherein the rings share a common centerline.
8. The elbow pipe of claim 7 wherein the outlet of the pipe shares the common centerline.
9. The elbow pipe of claim 8 wherein leading edges of consecutively increased size rings are located at distances that increase along the common centerline from the injector opening.
10. The elbow pipe of claim 9 wherein trailing edges of consecutively increased size rings are located at distances that increase along the common centerline from the injector opening.
11. The elbow pipe of claim 10 wherein each of the rings has a circular cross section.
12. The elbow pipe of claim 11 wherein the plurality of rings includes five rings.
13. A method of operating an exhaust aftertreatment system, comprising the steps of:
- moving exhaust in an exhaust conduit from an engine end toward a tailpipe end;
- injecting reductant from an injector into an elbow pipe of the exhaust conduit;
- mixing the reductant with the exhaust at least in part by passing the exhaust and the reductant through a tubeless mixer that includes a plurality of rings distributed with increasing size as a distance from the injector increases;
- reacting NOx in the exhaust with the reductant at an SCR catalyst positioned in the exhaust conduit.
14. The method of claim 13 wherein the mixing step includes:
- dispersing the reductant toward an inside wall of the elbow pipe responsive to an exhaust flow being high; and
- inhibiting impingement of the reductant on the inside wall responsive to the exhaust flow being low.
15. The method of claim 14 wherein the mixing step includes orienting the rings to share a common centerline.
16. The method of claim 15 wherein the mixing step includes orienting the common centerline colinear with a centerline of the exhaust conduit immediately adjacent the elbow pipe.
Type: Application
Filed: Jan 13, 2014
Publication Date: Jul 16, 2015
Applicant: Caterpillar, Inc. (Peoria, IL)
Inventors: Arvind Jujare (Peoria, IL), Jinhui Sun (Dunlap, IL), Yong Yi (Dunlap, IL), Jason Wesley Hudgens (Washington, IL), David Gorisek (Granville, IL)
Application Number: 14/153,596