Abstract:
A fluid injection system includes a mixing chamber locatable in an exhaust gas conduit upstream of a selective catalytic reduction device for providing an exhaust gas flow path and space for receiving injected fluid, an injector with a plurality of bundled capillary tubes each having an inlet configured to receive a fluid for injection into the chamber and an outlet wherein the injector is mounted on the chamber with the tube outlets in fluid communication with the chamber space, a base plate disposed in the chamber spaced from and aligned with the bundled tubes, a voltage supply connected to the tubes and to the base plate for providing a charge to the tubes and to the base plate to create an electric field to the fluid in the tubes, and a valve disposed on a wall of the chamber for at least one of priming and purging of the tubes.

Description:
BACKGROUND 
       [0001]    The present disclosure relates to vehicle exhaust systems for treating exhaust gas and more particularly, to systems and methods for improving the NOx reduction of exhaust gas. 
         [0002]    In vehicles such as trucks, exhaust gas (which is a combination of gas and particulate matter) is processed in multiple stages prior to being released to the atmosphere as illustrated in  FIG. 1 . Exhaust from an engine  110  may be processed by a diesel oxidation catalyst (DOC)  120  to remove hydrocarbons, by a diesel particulate filter (DPF)  130  to remove particulate matter, and by a selective catalytic reduction device (SCR)  140  to reduce NOx to Nitrogen gas and water vapor. For the SCR  140  stage, diesel exhaust fluid (DEF) is injected into and mixed with the exhaust upstream of the SCR device  140 . 
         [0003]    Currently, trucks have an onboard tank that contains DEF. DEF is composed of approximately 32.5% Urea and 67.5% demineralized water. In most DEF injection systems, DEF is delivered through an injector. DEF delivering injectors can be of a plurality of designs which rely on a pressure gradient across an orifice (high pressure in the injector, low pressure on the outside) to atomize the fluid. DEF is injected by applying approximately nine bar pressure to the fluid. The pressure forces the fluid through the orifices into the exhaust where it is then atomized. In other systems, DEF is mixed with compressed air before it enters the injection nozzle to improve atomization. 
         [0004]    It is desirable to have smaller droplet sizes (of the DEF) during atomization to increase the efficiency and effectiveness of the after treatment process of the exhaust gas or fluid. 
       SUMMARY 
       [0005]    In accordance with an exemplary embodiment, a fluid injection system comprises: a mixing chamber locatable in an exhaust gas conduit upstream of a selective catalytic reduction device (SCR), the chamber providing a flow path for exhaust gas and a space for receiving an injected fluid; an injector having a plurality of bundled capillary tubes each having an inlet and an outlet wherein the inlet is configured to receive a fluid for injection into the chamber, the injector being mounted on the chamber with the tube outlets in fluid communication with the space in the chamber; a base plate disposed in the chamber spaced from and aligned with the bundled capillary tubes; a voltage supply connected to the tubes and to the base plate wherein the voltage supply provides a charge to the tubes and to the base plate to create an electric field to the fluid in the tubes; and a valve disposed on a wall of the chamber for at least one of priming and purging of the tubes. 
         [0006]    In accordance with another exemplary embodiment, a fluid injection method is comprises the steps of: keying on a diesel engine; opening an exit valve and a prime/purge valve of an exhaust chamber associated with the engine; priming a plurality of capillary tubes that inject diesel exhaust fluid (DEF) into the chamber; closing the prime/purge valve; opening an entry valve of the exhaust chamber; cranking the engine on; applying a voltage to the tubes to electrically charge the fluid in the tubes; and drawing the electrically charged fluid into the chamber. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    The several features, objects, and advantages of exemplary embodiments will be understood by reading this description in conjunction with the drawings. The same reference numbers in different drawings identify the same or similar elements. In the drawings: 
           [0008]      FIG. 1  illustrates schematically a typical exhaust treatment system of a vehicle; 
           [0009]      FIGS. 2A and 2B  illustrate schematically injection systems in accordance with exemplary embodiments; 
           [0010]      FIG. 3  illustrates an atomization process in accordance with exemplary embodiments; 
           [0011]      FIG. 4  illustrates exemplary states of a plurality of valves used in exemplary embodiments; and 
           [0012]      FIG. 5  illustrates a method in accordance with exemplary embodiments. 
       
    
    
     DETAILED DESCRIPTION 
       [0013]    In the following description, numerous specific details are given to provide a thorough understanding of embodiments. The embodiments can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the exemplary embodiments. 
         [0014]    Reference throughout this specification to an “exemplary embodiment” or “exemplary embodiments” means that a particular feature, structure, or characteristic as described is included in at least one embodiment. Thus, the appearances of these terms and similar phrases in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. The headings provided herein are for convenience only and do not interpret the scope or meaning of the embodiments. 
         [0015]    According to exemplary embodiments, an injector having a plurality of capillary tubes is disclosed. An exemplary arrangement of an injector  200  is illustrated in  FIG. 2A . Injector  200  may include or consist of a plurality of capillary tubes  202  arranged as a bundle. A capillary tube is a thin walled conduit made partly or entirely of conductive material. The tubes are arranged parallel to each other. Each tube  202  may have an inlet  204  and an outlet  206 . The inner diameter of the capillary tube may be approximately 0.25 mm but not more than 2.5 mm to utilize capillary action. The term “injector” may be used interchangeably with the terms “bundle” or “capillary tube bundle” within this disclosure. 
         [0016]    Diesel exhaust fluid (DEF) may be delivered to an inlet end  204  of each of the capillary tubes  202  from a DEF reservoir or tank  250 . An exhaust gas path chamber  280  is located downstream of a DPF  290  and upstream of an SCR  295 . The injector  200  is mounted on the chamber  280  with the outlet end  206  of each of the capillary tubes  202  in the chamber  280 . The outlets are in fluid communication with an inner portion or interior space of the chamber  280 . The diameter of the chamber  280  may vary according to the application under which the aftertreatment system is needed. For example, the inner diameter of the chamber for a large engine (such as that of a truck, for example) will be greater than the inner diameter of the chamber for a passenger vehicle (such as sedan, for example). 
         [0017]    A base plate  248  is mounted in the exhaust gas path chamber  280  spaced from and aligned with the tube outlets  206 . The base plate  248  may be made of a conductive material and located on an interior surface of the chamber opposite to the outlets. A voltage source  240  may be connected between the base plate  248  and the capillary tube bundle  200 . Voltage may be applied to the capillary tube bundle and to the base plate such that the tube bundle forms anode  244  and the base plate becomes a cathode  248 . The voltage supply circuit is also grounded as illustrated. 
         [0018]    As the liquid enters (and passes through) the tubes  202 , the fluid becomes electrically charged and is subjected to the electric field. Coulombic attraction between the anode  244  and cathode  248  draws the charged fluid from the anode through outlets  206  toward the cathode base plate  248 . The fluid from outlets  206  becomes atomized within chamber  280  as described below with reference to  FIG. 3 . 
         [0019]    The atomization of the fluid is illustrated in  FIG. 3 . As described above, due to coulombic attraction between cathode  348  and anode  344 , the charged fluid in tube  302  flows through outlet  306 . Due to surface tension, electrostatic and hydrodynamic forces at outlet  306  of capillary tube  302 , above a threshold voltage the fluid may form a Taylor cone  380  from which an electrostatic jet of charged fluid  382  emanates. 
         [0020]    As the jet  382  gets closer to the cathode, it becomes unstable and atomizes into a plume  386  of charged fluid. The atomized fluid mixes with the exhaust gas flowing through the exhaust gas path chamber (i.e. exhaust gas path chamber  280  of  FIG. 2A ). 
         [0021]    Referring to  FIG. 2A , flow of exhaust gas through chamber  280  may be controlled by butterfly valves (BVs)  210  and  220 . A first butterfly valve  210  (BV 1 ) upstream of the injector  200  regulates exhaust gas flow from DPF  290  into chamber  280 . A second butterfly valve  220  (BV 2 ) downstream of the injector  200  regulates exhaust gas flow which contains exhaust gas mixed with atomized DEF out of mixing chamber  280  into SCR  295 . Upon exposure to the heat of the exhaust, the atomized DEF breaks down into CO 2  and NH 3 . 
         [0022]    A third butterfly valve  230  (BV 3 ) disposed on a wall of the mixing chamber  280  can regulate flow of air into the mixing chamber. BV 3    230  may be connected to a pressure modifying device, which may be vacuum source or a pump  260  that is connected to an air tank or air compressor  265 . 
         [0023]    BV 3    230  may selectively prime or purge injector  200  by altering the pressure in chamber  280 . BV 3    230  may prime injector  200  by lowering the air pressure in chamber  280  with respect to the atmosphere. Conversely, BV 3    230  may purge injector  200  by raising the air pressure in chamber  280  with respect to the atmosphere. 
         [0024]    In other embodiments, the injector can also be primed by using air tank  265  to pressurize DEF tank  250  as illustrated in  FIG. 2B . This would have the same effect as lowering the pressure in mixing chamber  280 . A fourth butterfly valve  235  (BV 4 ) may regulate flow between air tank  265  and DEF tank  250  in this exemplary embodiment. 
         [0025]    Referring back to  FIG. 2A , when the engine is keyed off and is not cranking (i.e. ignition off and engine off), BV 1 , BV 2  and BV 3  are all in a “close” position (i.e. not permitting gas or air flow). This may be referred to as Phase 1. 
         [0026]    When the engine is keyed on but is not cranking (i.e. ignition on and engine off), BV 1  remains in a “close” position while BV 2  is changed to an “open” position. BV 3  is changed to an “open” position to prime the injector  200 . This may be referred to as Phase 2. The injector  200  may be primed by adjusting the pressure in chamber  280  to a level that is lower than the pressure in the DEF holding tank  250 . Priming results in the DEF being drawn from DEF tank  250  into each of the tubes  202  that form injector (or bundle)  200 . 
         [0027]    As the engine starts cranking and is keyed on (i.e. ignition on and engine on), BV 1  is changed to an open position. BV 2  remains in the “open” position. BV 3  is changed to a “close” position as the injector  200  is primed. This may be referred to as Phase 3. Exhaust from DPF  290  enters chamber  280  and mixes with atomized DEF from injector  200  and exits chamber  280  to SCR  295 . 
         [0028]    When the engine is not cranking and is still keyed on (i.e. ignition on and engine off), BV 1  and BV 2  are changed to a “close” position. BV 3  is changed to an “open” position to purge the injector  200 . This may be referred to as Phase 4. The injector may be purged by adjusting the pressure in chamber  280  to a level that is higher than the pressure in the DEF holding tank  250 . Purging results in evacuating the tube bundle  200  of DEF from each of the capillary tubes  202  and forcing it back into DEF tank  250 . The removal of DEF from the tubes eliminates the freezing or crystallization of the urea in the tubes. 
         [0029]    When the engine is turned off and keyed off (i.e. ignition off and engine off), BV 1  and BV 2  remain in “close” position and BV 3  changes to “close” position. This may be referred to as Phase 5 which is identical to Phase 1. 
         [0030]    The position of each of the butterfly valves BV 1 , BV 2  and BV 3  as well as the state of engine ignition and engine crank for each phase described above with reference to  FIG. 2A  is illustrated in table  400  of  FIG. 4 . 
         [0031]    The number of capillary tubes  202  included within a bundle that forms the injector  200  may depend on the amount of DEF needed to effectively treat the exhaust gas as well as packaging constraints. For example, the tube bundle as described herein may include one hundred and sixty (160) individual capillary tubes assuming an optimized circle packing constant of 0.9069 is achieved in order to meet a required DEF flow rate of 2 grams per second for example. A packing constant may be defined as the area used divided by the area available (packing constant=area used/area available). 
         [0032]    Other factors that may affect the number of tubes include, but are not limited to, the temperature, pressure, electric field potential (i.e. voltage applied), fluid contaminants, and fluid viscosity. The voltage is applied after the injector has been primed and the injection of DEF is needed or desired. 
         [0033]    A method in accordance with exemplary embodiments may be described with reference to  FIG. 5 . For purposes of describing an exemplary method  500 , valve BV 1  may be referred to as entry valve, BV 2  may be referred to as exit valve and BV 3  may be referred to as prime/purge valve. 
         [0034]    An engine may be keyed on at step  510  (Phase 2). Exit valve  220  (BV 2 ) and prime/purge valve  230  (BV 3 ) may open at step  512 . This allows tubes  200  to be primed at step  514  by reducing air pressure in exhaust chamber  280 . The tubes may be primed by drawing fluid from DEF tank  250 . The prime/purge valve  230  (BV 3 ) may be closed at step  516 . The entry valve  210  (BV 1 ) may be opened at step  518  (BV 2    220  remains open). 
         [0035]    The engine may start cranking at step  520  (i.e. Phase 3). A voltage  240  may be applied to injector  200  to charge the fluid at step  524 . The charged fluid may be drawn to chamber  280  at step  528 . 
         [0036]    The engine may be shut off or stop cranking at step  530  (Phase 4). Voltage supply to the tubes  200  may be switched off step  532 . Entry valve  210  (BV 1 ) and exit valve  220  (BV 2 ) may be closed at step  534 . Prime/purge valve  230  (BV 3 ) may be opened at step  535 . Tubes  200  may be purged at step  536 . After the injector (made up of the tubes) is purged, prime/purge valve  230  (BV 3 ) may be closed at step  538 . The engine may be keyed off at step  540  (Phase 5). 
         [0037]    Exemplary embodiments as described herein facilitate the production of an advantageously small droplet size of the atomized diesel exhaust fluid that facilitates the DEF being mixed with the exhaust gas. Droplets having a size (i.e. diameter) of 1 to 100 micrometers may be formed. Existing systems are not believed capable of producing droplets having such a size. The voltage supply may range between 5 volts (V) to 200 kilovolts (kV). An airless urea dosing system may also be realized utilizing exemplary embodiments. An airless system refers to not using compressed air to facilitate the pressure drop across the injector orifice, i.e. atomization. 
         [0038]    Although exemplary embodiments have been disclosed, it will be apparent to those skilled in the art that various changes and modifications can be made which will achieve some of the advantages of embodiments without departing from the spirit and scope of the disclosure. Such modifications are intended to be covered by the appended claims in which the reference signs shall not be construed as limiting the scope. 
         [0039]    In the description and the appended claims the meaning of “comprising” is not to be understood as excluding other elements or steps. Further, “a” or “an” does not exclude a plurality, and a single unit may fulfill the functions of several means recited in the claims. 
         [0040]    The above description of illustrated embodiments, including what is described in the Abstract, is not intended to be exhaustive or to limit the embodiments to the precise forms disclosed. Although specific embodiments of and examples are described herein for illustrative purposes, various equivalent modifications can be made without departing from the spirit and scope of the disclosure, as will be recognized by those skilled in relevant art. 
         [0041]    The various embodiments described above can be combined to provide further embodiments. Aspects of the embodiments can be modified, if necessary to employ concepts of the various patents, applications and publications to provide yet further embodiments. 
         [0042]    These and other changes can be made to the embodiments in light of the above-detailed description. In general, in the following claims, the terms used should not be construed to limit the claims to the specific embodiments disclosed in the specification and the claims, but should be construed to include all possible embodiments along with the full scope of equivalents to which such claims are entitled. Accordingly, the claims are not limited by the disclosure.