Fluid handling – With heating or cooling of the system – With diversion of part of fluid to heat or cool the device...
Reexamination Certificate
1998-10-01
2001-08-28
Knode, Marian C. (Department: 1764)
Fluid handling
With heating or cooling of the system
With diversion of part of fluid to heat or cool the device...
C060S274000, C123S472000, C137S340000, C239S125000, C251S129150, C422S177000
Reexamination Certificate
active
06279603
ABSTRACT:
FIELD OF INVENTION
This invention relates to injectors and especially to fluid-cooled injectors wherein the fluid is a liquid reagent and a portion of the reagent is injected as an atomized liquid reagent into the exhaust gas stream of an internal combustion engine.
BACKGROUND OF INVENTION
Improved fuel efficiency for vehicles having internal combustion engines can be achieved by using diesel engines or gasoline engines operated with an excess of oxygen over the amount necessary for complete combustion of the fuel. Such engines are said to run “lean” or on a “lean mixture.” The increase in fuel economy, however, is offset by undesired pollution emissions, specifically in the form of oxides of nitrogen (NOx).
One method used to reduce NOx emissions from internal combustion engines is known as selective catalytic reduction (SCR). SCR, when used, for example, to reduce NOx emissions from a diesel engine, involves injecting an atomized reagent into the exhaust stream of the engine in relation to one or more selected engine operational parameters, such as exhaust gas temperature, engine rpm or engine load as measured by engine fuel flow, turbo boost pressure or exhaust NOx mass flow. The reagent/exhaust gas mixture is passed through a reactor containing a catalyst, such as, for example, activated carbon, or metals, such as platinum, vanadium or tungsten, which are capable of reducing the NOx concentration in the presence of the reagent. An SCR system of this type is disclosed in U.S. patent application Ser. No. 08/1831,209, issued as U.S. Pat. No. 5,976,475 hereby incorporated by reference.
An aqueous solution of urea is known to be an effective reagent in SCR systems for diesel engines but suffers several disadvantages. Urea is highly corrosive and tends to attack mechanical components of the SCR system, such as the injectors used to inject the urea mixture into the exhaust gas stream. Urea also tends to solidify upon prolonged exposure to elevated temperatures, such as encountered in diesel exhaust systems. Solidified urea tends to accumulate in the narrow passageways and orifice openings typically found in injectors. The solidified urea fouls moving parts of the injector and clogs any openings, thus, rendering the injector unusable.
Furthermore, if the urea mixture is not finely atomized, urea deposits will form in the catalytic reactor, inhibiting the action of the catalyst and thereby reducing the SCR system effectiveness. High injection pressures are one way of dealing with the problem of insufficient atomization of the urea mixture, but high injection pressures often result in over-penetration of the injector spray plume into the exhaust stream, causing the plume to impinge on the inner surface of the exhaust pipe opposite the injector. Over-penetration leads to inefficient use of the urea mixture and reduces the range over which the vehicle can operate with reduced NOx emissions. Like fuel for the vehicle, only a finite amount of aqueous urea can be carried and what is carried should be used efficiently to maximize vehicle range and reduce the need for frequent fill ups of the reagent.
Additionally, aqueous urea is a poor lubricant. This characteristic adversely affects moving parts within the injector and requires that special fits, clearances and tolerances be employed between relatively moving parts within an injector.
SUMMARY AND OBJECTS OF INVENTION
The invention provides an injector for delivery of a fluid into a stream of hot gas, the injector being designed to operate effectively with a corrosive, temperature-sensitive reagent, such as aqueous urea. When used in a system for reducing NOx emissions, the injector is mounted on an exhaust conduit of an internal combustion engine where it injects the reagent into the exhaust gas stream.
The injector comprises a valve and a means for actuating the valve between a closed position and an open position. Acceptable actuating means include, for example, a solenoid-type actuator. Preferably the components of the valve exposed to extreme heat or corrosive reagents like urea are made of a corrosion resistant material such as stainless steel.
The valve includes an orifice through which the reagent is expelled when the valve is in the open position. Regardless of the state of the valve (i.e., open or closed), the reagent is continuously circulated through it when the system is in operation, at least a portion of the circulating reagent being expelled when the valve is opened. The circulation of the reagent cools the valve and minimizes the dwell time of the reagent within the valve, thereby minimizing exposure of the reagent to heat and the creation of urea deposits. Thus, aqueous urea, for example, can be effectively used with such an injector without the characteristic fouling and clogging of the injector. Means independent of the valve actuating means are provided for continuously circulating the reagent through the valve, as described in detail below.
Preferably the valve comprises a valve body which has an elongated cylindrical chamber therein in fluid communication with the orifice. A valve seat is positioned within the chamber surrounding the orifice. An elongated valve plunger is slidably mounted within the chamber. One end of the plunger is sealingly interengagable with the valve seat to close the orifice. The plunger is connected with the actuating means and is movable from the closed position where the plunger end sealingly engages the valve seat and the open position where the plunger end is removed from sealing interengagement with the valve seat to open the orifice.
The means for independently circulating fluid through the valve comprises a portion of the plunger which is arranged adjacent to the plunger end. This portion of the plunger has a diameter less than the chamber diameter and forms an annular fluid space or passageway within the valve adjacent to the valve seat and the orifice. The annular passageway, thus, allows for both the continuous circulation of fluid through the valve and the expelling of a portion of the fluid through the orifice when the valve is in the open position.
Preferably, the independent fluid circulating means further comprises a fluid inlet and a fluid outlet arranged within the valve body in fluid communication with the annular passageway. Fluid, such as the aqueous urea reagent, is supplied from a reservoir and flows into the valve through the inlet, continues through the annular passageway and exits the valve via the outlet, thereby cooling the injector. When the valve is opened by the actuator, the valve plunger is moved to the open position, and a portion of the fluid is expelled from the chamber through the orifice.
In order to provide additional heat protection for the injector, a heat shield is preferably interposed between the valve and the stream of hot gas. The heat shield has an aperture which is aligned with the orifice. The heat shield aperture allows fluid expelled from the valve to pass through the heat shield and into the hot gas stream. The heat shield preferably comprises a metal plate and a layer of insulating material interposed between the plate and the valve. The heat shield aperture passes through both the layer of insulating material, as well as the metal plate.
To improve atomization of liquid reagents, especially at relatively low injection pressures, an atomizing hook is preferably mounted on the valve. The atomizing hook has an end surface which is positioned in a spaced apart relation with the orifice. Liquid reagent expelled through the orifice impinges on the hook end surface where further atomization of the reagent occurs. The shape and position of the hook end surface directly affect the dispersion characteristics of the injected reagent.
It is an object of the invention to provide an injector for injecting a fluid into a stream of hot gas.
It is another object of the invention to provide an injector useable with corrosive liquids such as aqueous urea.
It is yet another object of the invention to provide an injector in which aqueous urea will not solidi
Czarnik Richard J.
DiCarlo Jeffrey P.
Knapper Curtis J.
Simard Thomas C.
Tarabulski Theodore J.
Ambac International
Knode Marian C.
Synnestvedt & Lechner LLP
Varcoe Frederick
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