Exhaust aftertreatment device, including chemical mixing and acoustic effects

This application is a Continuation-in-part of U.S. patent application Ser. No. 09/981,171, filed Oct. 17, 2001, incorporated herein by reference.

The invention relates to aftertreatment devices for internal combustion engine exhaust, and more particularly to combined chemical mixing and acoustic effects.

To address engine emission concerns, new standards continue to be proposed for substantial reduction of various emissions, including NO X and particulate emissions. Increasingly stringent standards will require installation of aftertreatment devices in engine exhaust systems. Some of the aftertreatment technologies require certain chemical species to be injected into the exhaust system. For example, HC or fuel is injected in some active lean NO X systems, and additives such as cerium and iron are injected for diesel particulate filter regeneration, and urea solution is injected in selective catalytic reduction (SCR) systems for NO X reduction. These injected chemical species need to be well mixed with exhaust gas before reaching catalysts or filters for the systems to perform properly.

Perforated tubes are widely used in engine exhaust systems for noise reduction. If designed properly, perforated tubes can also create high intensity turbulent flow. The turbulent flow will promote turbulent diffusion of the chemical species and therefor enhance the mixing process.

In one aspect of the present invention, improved chemical mixing is provided.

In another aspect, the invention integrates a turbulent mixing tube with an acoustic tube into an engine exhaust system.

In another aspect, the invention provides an engine exhaust system with two-stage perforated tubes. The system is designed not only to reduce the noise level, but also to enhance the mixing processes of chemical species which are injected into the exhaust system, including for regeneration of diesel particulate filters and for controlling engine NO X emissions.

FIG. 1 is a side schematic sectional view of an exhaust aftertreatment device in accordance with the invention.

FIG. 2 is like a portion of FIG. 1 and shows another embodiment.

FIG. 3 is like a portion of FIG. 1 and shows another embodiment.

FIG. 1 shows an exhaust aftertreatment device 10 including a housing 12 extending axially along an axis 14 , and having an upstream inlet 16 for receiving engine exhaust as shown at arrow 18 , and having a downstream outlet 20 for discharging the exhaust as shown at arrow 22 . An aftertreatment element 24 , for example an SCR catalyst and/or an oxidation catalyst and/or a particulate filter, is provided in the housing for treating the exhaust. An injector 26 is provided in the housing for injecting chemical species as shown at 28 mixing with the exhaust prior to reaching aftertreatment element 24 . For example, in one embodiment, aqueous urea solution is injected from reservoir or tank 30 through tubular conduit 32 and is injected at nozzle or tip 34 , though other chemical species may be used.

A turbulator 36 is provided in the housing upstream of aftertreatment element 24 and turbulating the exhaust to enhance the noted chemical mixing upstream of aftertreatment element 24 . The turbulator is provided by a perforated mixing tube 38 . Also provided in the housing is a perforated acoustic tube 40 quieting the exhaust.

It has been found that improved performance results from providing the tubes 36 and 40 with different perforation hole sizes, namely by providing the mixing tube 36 with larger perforation hole sizes than acoustic tube 40 . In a particular situation, it has been found that improved performance results when mixing tube 36 has a perforation hole size greater than or equal to one-quarter inch, and when acoustic tube 40 has a perforation hole size less than one-quarter inch, preferably less than or equal to one-eighth inch. It has been found that the noted perforation hole size greater than or equal to one-quarter inch for mixing tube 36 creates improved turbulent diffusion and mixing of the injected chemical species, and that the noted perforation hole size less than one-quarter inch for acoustic tube 40 minimizes aeroacoustic effects. In preferred form, perforation holes 48 of turbulator 36 are square shaped as shown at 47 for generating homogenous and isotropic turbulence, though circular holes are also acceptable as optionally shown at 49 . Perforation holes 52 and 54 of acoustic tube are preferably circular.

In the preferred embodiment, mixing tube 36 is conical, preferably frustoconical with a closed nonperforated downstream end 42 . Further in the preferred embodiment, acoustic tube 40 is cylindrical, with a closed nonperforated downstream end 44 . Conical mixing tube 38 has a tapered sidewall 46 with uniform porosity as shown at perforations 48 . Cylindrical acoustic tube 40 has a sidewall 50 with varied porosity, for example as shown at upstream perforations 52 having a higher density than downstream perforations 54 . The varied porosity along a cylindrical sidewall has been found to provide a more even flow therealong. Porosity may also be varied by varying the size, distance, and number of perforation holes. Mixing tube 38 is disposed in acoustic tube 40 and concentrically surrounded thereby. Each of tubes 38 and 40 is upstream of aftertreatment element 24 . In preferred form, mixing tube 38 is upstream of acoustic tube 40 , and mixing tube 38 is within acoustic tube 40 .

Mixing tube 38 has an upstream end 56 and a downstream end 58 , and the noted perforated sidewall 46 extending therebetween. Sidewall 46 is perforated at perforations 48 with a porosity selected to provide substantially uniform resistance and even flow along mixing tube 38 . In preferred form, the noted substantially uniform resistance and even flow is provided in combination by a conically tapered sidewall 46 perforated with uniform porosity. The conical shape points downstream such that mixing tube 38 narrows to smaller cross-sectional areas as mixing tube 36 extends from upstream end 56 to downstream end 58 . As above noted, the conical shape is truncated at 42 at downstream end 58 .

FIG. 2 uses like reference numerals from above where appropriate to facilitate understanding. In FIG. 2, a screen 60 extends from injector 26 at nozzle or tip 34 and is disposed in mixing tube 38 . Injector 26 at nozzle 34 injects the chemical species along a spray pattern as shown at 28 , FIG. 1, having an injection boundary 62 . Screen 60 , FIG. 2, extends from the injector along injection boundary 62 . As above noted, mixing tube 38 has a conical shape pointing downstream. Screen 60 has a conical shape pointing upstream, namely to an apex or truncated apex at injector tip or nozzle 34 . Conical mixing tube 38 at its tapered sidewall 46 convergingly tapers as it extends downstream. Screen 62 divergingly tapers as it extends downstream.

FIG. 3 uses like reference numerals from above where appropriate to facilitate understanding. In FIG. 3, conical screen 60 of FIG. 2 is replaced by a spherical screen 64 around injector tip 34 and extending therefrom.

As is known, the injected chemical species undergoes chemical processes in mixing with the exhaust, including chemical decomposition, chemical reaction, and phase change. In a further embodiment, injector 26 is heated by a heat source in addition to heating by the exhaust. In one embodiment, the heat source is provided by a voltage source 70 external of the housing and a pair of electrical conductors 72 , 74 connecting the voltage source to the injector. Heater 70 is provided for heating the injector and accelerating the noted chemical processes.

Also as known, the injected chemical species is subject to coagulation and coalescence. In a further embodiment, a screen such as 60 or 64 is provided, extending from the injector, and a heater is provided for heating the screen to minimize the noted coagulation and coalescence. In one embodiment, such heat source is provided by the same voltage source 70 noted above, and a pair of electrical conductors 76 , 78 connecting the voltage source to screen 60 or 64 .

It is recognized that various equivalents, alternatives, and modifications are possible within the scope of the appended claims.