Patent Application
20110219745
The present invention relates to an apparatus and method for treating and mixing diesel exhaust in a diesel exhaust system. Particularly, the present invention provides methods and apparatus for injecting reagent into a diesel exhaust stream to reduce nitrogen oxides (NOx) without increasing the packing space of the exhaust system.
Diesel engines are efficient, durable and economical. Diesel exhaust, however, can harm both the environment and people. To reduce this harm, governments, such as the United States and the European Union, have proposed stricter diesel exhaust emission regulations. These environmental regulations require diesel engines to meet the same pollution emission standards as gasoline engines.
Typically, to meet such regulations and standards, systems require equipment additions and modifications. Additional equipment can often lead to additional weight and/or additional packaging length.
For example, a lean burning engine provides improved fuel efficiency by operating with an amount of oxygen in excess of the amount necessary for complete combustion of the fuel. Such engines are said to run “lean” or on a “lean mixture.” However, the increase in fuel efficiency is offset by the creation of undesirable pollution emissions in the form of nitrogen oxides (NOx). One method used to reduce NOx emissions from lean burn internal combustion engines is known as selective catalytic reduction. When used to reduce NOx emissions from a diesel engine, selective catalytic reduction involves injecting atomized urea into the exhaust stream of the engine in relation to one or more selected engine operational parameters and running the stream through a reactor containing a catalyst. However, selective catalytic reduction and the use of aqueous urea involve many disadvantages, including added packaging weight and added packaging length to the exhaust system, as well as the highly corrosiveness and poor lubricity of aqueous urea.
It would be advantageous to provide methods and apparatus for addressing the regulations and standards without adding weight or length to an already complex diesel exhaust system. Accordingly, it would be advantageous to provide methods and apparatus for injecting a NOx reducing reagent into the diesel exhaust stream of a lean burn engine where little or no added weight or packaging length is required. Further, it would be advantageous to provide a mixing system which creates a more homogenous mixture in a limited length. It would also be advantageous to provide an injector which is capable of distributing the reagent more uniformly throughout a cross-section of the treatment area. Accordingly, it would be advantageous to provide multiple injection points within a diesel exhaust stream.
The methods and apparatus of the present invention provide the foregoing and other advantages.
There is disclosed herein an improved diesel exhaust treatment system and method which avoid disadvantages of prior devices and methods, while affording additional structural and operating advantages.
Generally speaking, a mixing device for a diesel exhaust system is disclosed having a chamber, a mixer within the chamber, and an injection tube supported on the mixer within the chamber. The mixer is positioned within the chamber adjacent an inlet and includes a plurality of angled blades to effect turbulent flow in a diesel exhaust stream entering the chamber through the inlet.
In specific embodiments of the system, the injection tube includes a plurality of injection points (e.g., openings) for discharging a reagent into the exhaust stream. The injection tube is curved, and more specifically it is coiled with the injection points spread along the length of the tube in order to deliver reagent across a section of the chamber perpendicular to the exhaust stream flow.
The disclosed method for mixing gaseous ammonia in a diesel exhaust system begins with a diesel exhaust stream from a diesel engine passing from the engine through a conduit in fluid communication with the engine. The exhaust stream is directed to flow through the conduit into a housing having a mixer, an injection tube and an exit disposed therein. Turbulent flow in the diesel exhaust stream is created within the housing as the stream passes through the mixer. A continuous injection of gaseous NH3 from the injection tube into the diesel exhaust stream is made as the stream moves from the mixer toward the housing exit to create a treated homogenous exhaust stream. Finally, the treated exhaust stream is discharged through the housing exit.
These and other aspects of the invention may be understood more readily from the following description and the appended drawings.
For the purpose of facilitating an understanding of the subject matter sought to be protected, there are illustrated in the accompanying drawings embodiments thereof, from an inspection of which, when considered in connection with the following description, the subject matter sought to be protected, its construction and operation, and many of its advantages should be readily understood and appreciated.
While this invention is susceptible of embodiments in many different forms, there is shown in the drawings and will herein be described in detail a preferred embodiment of the invention with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention and is not intended to limit the broad aspect of the invention to embodiments illustrated.
Referring to
The mixer/treatment canister 116 is shown to include a connection pipe 120 with an injector 122 at the upstream end where NH3—or an NH3 containing reagent—is injected into a laminar diesel exhaust flow as it is discharged from the DOC 112 and DPF 114. The ammonia/exhaust stream then passes through a mixer 124 to effect mixing of the NH3 and the diesel exhaust. A substantial length of pipe 120 is needed to allow for adequate mixing of the two components before the flow enters the NSC 118. As such, the mixer/injector system adds packaging length and weight to the diesel exhaust system 100 which might otherwise be used for other after-treatment substrates.
Referring to
Regardless of the specific configuration, it is clear from examination of
Generally speaking, system 10 is comprised of a housing 20 defining a mixing chamber 25, an injection tube 22 fed by an exterior injector boss 30 coupled to a supply (not shown), and a mixer 24.
The tube 22 may be configured in several alternative shapes, including circular and serpentine, so long as a distribution of the injection points 23 throughout a cross-section of the chamber is provided. Further, the injection points 23 comprise small openings in the tube 22 to allow discharge of the reagent from the tube 22. To effect a uniform or even discharge from all the injection points 23, the first opening has a very small diameter and successive opening diameters increase toward the tube end 27—i.e., the smallest diameter openings are positioned at the beginning of the tube where the fluid pressure is the greatest. The purpose, again, is to achieve even distribution of reagent across the entire cross-section of the mixing chamber 25.
Also shown in
Another feature of the mixer 24 is that it supports the injection tube 22. That is, the tube 22, which is positioned on the downstream side of the mixer 24, attaches to, by way of welds or any other suitable attachment means, each of the mixer blades 37 for simple structural support. Attachment may be achieved, for example, at the areas 39 where the tube 22 crosses each blade 37. The securing of the coiled tube 22 alleviates damage which might otherwise be caused by the more violent vibration of the tube 22 during operation of the vehicle. Reagent (e.g., gaseous NH3) discharged from injection points 23 immediately enters the turbulent diesel exhaust stream as it moves toward the chamber exit 35 (
The homogenous mixture is then exited from the mixing chamber 25 into one of either the NSC 18 (
The matter set forth in the foregoing description and accompanying drawings is offered by way of illustration only and not as a limitation. While particular embodiments have been shown and described, it will be apparent to those skilled in the art that changes and modifications may be made without departing from the broader aspects of applicants' contribution. The actual scope of the protection sought is intended to be defined in the following claims when viewed in their proper perspective based on the prior art.
