Fluid entrainment apparatus

A fluid entrainment apparatus is provided which operates to mix a first fluid stream with a second fluid stream. The apparatus includes first and second fluid flow conduits. The first fluid flow conduit includes a nozzle portion having a converging bore through which the first fluid is accelerated. Additionally, the second fluid flow conduit includes a nozzle portion having a converging bore, a duct portion having a generally cylindrical bore, and a diffuser portion having a diverging bore. The nozzle portion of the second fluid flow conduit is mounted with respect to the nozzle portion of the first fluid flow conduit such that an annular port is formed through which the second fluid passes to mix with the first fluid. Additional fluid mixing occurs in the duct portion and the diffuser portion. The fluid entrainment apparatus may be configured for use within a vehicle exhaust system.

TECHNICAL FIELD

The present invention relates to a fluid entrainment apparatus and, more specifically, to a fluid entrainment apparatus to cool the exhaust stream of a vehicular engine.

BACKGROUND OF THE INVENTION

Manufacturers of vehicles that employ internal combustion engines, more particularly diesel engines, are under increased pressure to comply with current and future emission standards for the release of oxides of nitrogen (NOX), particularly nitrogen monoxide (NO), as well as unburned and partially oxidized hydrocarbons (HC), carbon monoxide (CO), particulate matter, and other emissions, such as hydrogen sulfide (H2S) and ammonia (NH3). In order to reduce the previously mentioned emissions of a diesel engine, the latter are typically operated with exhaust gas after-treatment systems through which the exhaust gas from the diesel engine flows.

Exhaust gas after-treatment systems typically include one or more after-treatment devices, such as oxidation catalysts, NOXabatement devices, diesel particulate filters (DPFs) and sulfur traps. These after-treatment devices generally require certain conditions to exist in the engine exhaust gas in order to perform optimally. More specifically, NOXabatement devices and oxidation catalysts, for example, have a relatively narrow temperature window within which the devices are activated, regenerated, or operate with high conversion efficiency. Periodically, after-treatment devices require heating beyond that provided by the exhaust gas to achieve the desired operating temperature, such as in the case of DPFs.

Additionally, DPFs periodically require a relatively high concentration of oxygen in the exhaust gas to facilitate regeneration of the particulate filter. Often, the required exhaust gas conditions cannot always be achieved during normal operation of the engine. More particularly, the exhaust gas temperature can only be influenced to a certain degree by the combustion process without the use of a source of supplemental heat, such as an electric heater in the exhaust-gas stream. The particulate matter can generally be characterized as soot that is captured and reduced by DPF. Present DPFs contain a separation medium with tiny pores that capture particles. Resistance to exhaust flow in the DPF increases as trapped material accumulates in the DPF, thereby generating an increase in exhaust backpressure. The DPF must then be regenerated to burn off the particulate matter/soot in the particulate trap to reduce the exhaust backpressure and increase exhaust flow through the DPF. A typical method of regenerating a DPF utilizes an energy source such as a burner or electric heater to encourage combustion of the particulate matter. Particulate combustion in a DPF has been found to increase the exhaust gas temperature within the vehicles exhaust system, downstream from the DPF.

SUMMARY OF THE INVENTION

A fluid entrainment apparatus is provided which operates to mix a first fluid stream with a second fluid stream. The fluid entrainment apparatus includes a first fluid flow conduit and a second fluid flow conduit. The first fluid flow conduit may include a nozzle portion having a converging bore through which the first fluid is accelerated. Additionally, the second fluid flow conduit may include a nozzle portion having a converging bore, a duct portion having a generally cylindrical bore, and a diffuser portion having a diverging bore. The nozzle portion of the second fluid flow conduit is mounted with respect to the nozzle portion of the first fluid flow conduit such that a generally annular port is formed through which the second fluid passes to mix with the first fluid. Additional mixing occurs in the duct portion and the diffuser portion.

The first flow conduit may be sufficiently configured for attachment to a tailpipe of the vehicular exhaust system. In this configuration the first fluid is exhaust gas and said second fluid is ambient air, such that the ambient air operates to cool the exhaust gas as it passes through the fluid entrainment apparatus. A vehicular exhaust system incorporating the disclosed fluid entrainment apparatus is also provided.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the figures wherein like reference numbers represent like characters, there is shown inFIG. 1a fluid entrainment apparatus10having a first fluid flow conduit12and a second fluid flow conduit14. The first fluid flow conduit12includes a nozzle portion16having a generally frusto-conical shape, thereby defining a generally converging bore18through which a first fluid may flow.

The second fluid flow conduit14includes a nozzle portion20, duct portion22, and diffuser portion24. The nozzle portion20has a generally frusto-conical shape, thereby defining a generally converging bore26. The duct portion22is generally cylindrical in shape and defines a generally cylindrical bore28, shown inFIG. 2. The diffuser portion24has a generally frusto-conical shape, thereby defining a generally diverging bore30, shown inFIG. 2. The nozzle portion16and the nozzle portion20are spaced concentrically from one another by a plurality of gussets32. The nozzle portion16and the nozzle portion20cooperate to form a generally annular orifice or port34through which a second fluid may flow. The first and second fluid may be the same fluid or different fluids. Those skilled in the art will recognize that various other methods of attaching the nozzle portion16to the nozzle portion20may be employed while remaining within the scope of that which is claimed, such as straps, brackets, posts, etc.

In its simplest form, the fluid entrainment apparatus10can include the first fluid flow conduit12discharging a first fluid into the second fluid flow conduit14. The first fluid flow conduit12and the second fluid flow conduit14cooperate to form the orifice or port34through which a second fluid may flow and operates to influence the mass flow rate of the second fluid. Those skilled in the art will recognize that the cross-sectional shape of the first and second fluid flow conduits12and14may be of any shape such as, for example, oval, square, rectangular, etc, while remaining within the scope of that which is claimed.

Referring now toFIG. 2, there is shown a schematic diagrammatic cross-sectional view of the fluid entrainment apparatus10. The fluid entrainment apparatus10may be installed near a tailpipe36of a vehicular exhaust system37. In this application, the fluid entrainment apparatus10operates to cool the exhaust stream33flowing through the tailpipe36by the entrainment of an ambient air stream35. The cooling of the exhaust stream33is often desired when there is an emission control device such as a diesel particulate filter, or DPF,38mounted upstream of the tailpipe36. To maintain efficiency, the DPF38must periodically regenerate by oxidizing and burning of the accumulated soot or particulate matter contained within the DPF38. In doing so, the temperature of the exhaust stream33exiting the tailpipe36increases.

As the higher temperature exhaust stream33flows from the tailpipe36into the nozzle portion16, the reduction in cross-sectional area due to the converging bore18causes the speed of the exhaust stream33to increase. By accelerating the exhaust stream33, an increased amount of ambient air35can enter the fluid entrainment apparatus10through the annular port34. The ambient air stream35partially mixes, shown at39, with the exhaust stream33in the nozzle portion20. The combined ambient air stream and the exhaust stream41then flows to the duct portion22where further mixing occurs. At the exit of the duct portion22, the combined ambient air stream and exhaust gas stream41enter the diffuser portion24and continue to mix while decelerating as a result of the increasing cross-sectional area of the diverging bore30. The diffuser portion24partially compensates for the pressure drop across the fluid entrainment apparatus10when high exhaust stream gas flow is present, such as at high load engine operating conditions. By entraining an ambient air stream35into the exhaust stream33, the temperature of the exhaust stream33may be reduced.

The principle under which the fluid entrainment apparatus10operates is that a faster moving fluid, i.e., the exhaust stream33, entrains or draws along a slower moving fluid, i.e. the ambient air stream35. In the fluid entrainment apparatus10, shown inFIG. 2, the exhaust gas stream33flows along the central axis of the fluid entrainment apparatus10surrounded by a relatively slower moving ambient air stream35, which is entrained through the annular port34. High radial velocity gradients tend to form at the generally annular boundary between the ambient air stream35and the exhaust stream33, thereby enhancing the entrainment rate of the ambient air stream35and improving the mixing between the ambient air stream35and the exhaust stream33.

The dimensions of an exemplary fluid entrainment apparatus10for a vehicle exhaust system37include a nozzle portion16having an upstream opening of four inches in diameter that gradually tapers to a three inch diameter downstream opening over an axial length of two inches. Alternately, for vehicles with a tailpipe36diameter of 3.5 inches, an upstream opening of 3.5 inches in diameter that gradually tapers to a three inch diameter downstream opening over an axial length of one inch is appropriate. The nozzle portion20, of this exemplary embodiment, will have an upstream opening of five inches in diameter and a downstream opening of four inches in diameter over an axial length of nine inches. The duct portion22will have a continuous inside diameter of four inches over a two inch axial length. The diffuser portion24has an upstream opening of four inches in diameter and a downstream opening of five inches in diameter over an axial length of nine inches. Additionally, the nozzle portion20and the nozzle portion16may be spaced axially away from each other to increase the mass flow rate of ambient air stream35through the annular port34. As discussed hereinabove, the various design attributes of the fluid entrainment apparatus10, shown inFIGS. 1 and 2, include the upstream opening diameter and axial length of the nozzle portion16, the upstream opening diameter and axial length of the nozzle portion20, the internal diameter and axial length of the duct portion22, and the downstream opening diameter and axial length of the diffuser portion24.

Those skilled in the art will recognize that the dimensions given above are only exemplary in nature and are in no way intended to limit the scope of that which is claimed. Those skilled in the art will recognize that the dimensions stated above may be varied to balance the entrainment of the ambient air with packaging constraints, exhaust backpressure constraints, pass-by noise requirements, mixing efficiency of the exhaust and ambient air streams and various other design constraints of the fluid entrainment apparatus10. Additionally, although the above exemplary fluid entrainment apparatus10has a generally circular cross section for the first and second fluid flow conduit12and14, respectively, those skilled in the art will recognize other cross sections that may be appropriate, such as box sections and oval sections.

InFIG. 3there is shown a portion of a cross section of the second fluid flow conduit14illustrating a plurality of generally outwardly radiating cooling fins40disposed about the periphery of the second fluid flow conduit14. The cooling fins40operate to increase the heat transfer from the fluid entrainment apparatus10to the atmosphere. The cooling fins40may vary in size, number, and shape as a result of design considerations. That is, the cooling fins40may have any shape or configuration while remaining within the scope of that which is claimed. The cooling fins40operate to increase the thermal performance of the fluid entrainment apparatus10; however, those skilled in the art will recognize that the cooling fins40are not a necessary element for the proper functioning of the fluid entrainment apparatus10. Additionally, the emissivity of the outer surface of the second fluid flow conduit14may be enhanced to improve radiation heat transfer to the atmosphere. Noise absorbers may be provided on the second fluid flow conduit14to reduce the noise emissions of the fluid entrainment apparatus10.

FIG. 4illustrates a partial cross section of the nozzle portion16having a plurality of radially inwardly projecting flow vanes42disposed on the converging bore18. The flow vanes42may be oriented parallel to the flow stream of the first fluid such as, for example, the exhaust stream33discussed hereinbefore. Similarly, the flow vanes42to may oriented at a predetermined angle to the flow stream of the first fluid to induce motion thereby increasing the mixing effectiveness within the second fluid flow conduit14. Additionally, flow vanes42may be placed within the converging bore26, near the annular port34, to induce motion of the second fluid, thereby increasing to the mixing of the two fluids. Likewise, the flow vanes42may be disposed on the cylindrical bore28of the duct portion22and/or the diverging bore30of the diffuser portion24to induce fluid motion. The flow vanes42may vary in size, number, and shape as a result of design considerations. That is, the flow vanes42may have any shape or configuration while remaining within the scope of that which is claimed. The flow vanes42operate to increase the performance of the fluid entrainment apparatus10; however, those skilled in the art will recognize that the flow vanes42are not a necessary element for the proper functioning of the fluid entrainment apparatus10.

Although the function of the fluid entrainment apparatus10has been discussed with reference to the vehicular exhaust system37, those skilled in the art will recognize that the fluid entrainment apparatus10may be used in other applications involving both gaseous and liquid flows. Additionally, the fluid entrainment apparatus10may be viewed as both a heater and a cooler depending on the desired function of the fluid entrainment apparatus10.