Abstract:
An ammonia producing device for an exhaust system of an engine is provided. It includes a pressure vessel having a cavity for storage of pressurized gases. The pressure vessel includes insulation located at least partially about the cavity for limiting heat transfer from within the cavity. A flash heater is disposed within the cavity and adjacent a solid ammonia gas producing material. An outlet port extends from the pressure vessel and has a valve located therein for providing egress of pressurized gases from within the pressure vessel.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to U.S. Provisional Application No. 61/182,968, filed Jun. 1, 2009, the contents of which are incorporated by reference herein. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    Exhaust emission control has been and will continue to be of interest as effects of emissions from stationary and transient emission generating devices are continually being understood. This, along with government mandates, have caused manufacturers of emission generating devices, particularly internal combustion engines, to develop methods and devices for controlling the content of emissions emanating from such devices. In one particular sector, due to the advantages of diesel burning engines over gasoline burning engines, advancements of emission control for diesel engines are continuingly being sought. These advancements include emission control devices configured for removing particulate matter from an exhaust gas stream and Selective Catalyst Reduction (SCR) technology that converts certain exhaust gases, such as NO x  to specific exhaust gas outputs such as nitrogen and water. 
         [0003]    One particular advancement in the reduction of emissions from diesel and gasoline burning engines is the application of a urea solution to an exhaust gas stream prior to treatment by one or more components of an SCR treatment system. Specifically, current SCR systems employ a 32% aqueous solution of urea which is injected in liquid form into the exhaust ahead of the SCR catalyst where it is hydrolyzed and ultimately thermo-hydrolyzed into NH3 and CO2. The addition of ammonia and/or urea solution improves efficiency of the conversion of the NO x . 
         [0004]    Increased effectiveness of the ammonia or urea is achieved at higher temperatures. During certain operating conditions, such as extreme cold temperatures, the ammonia or urea solution may become frozen, particularly below the freezing temperature of urea solution, e.g., −12° C., thereby losing the ability to inject the solution into the exhaust gas stream. In order to maintain effectiveness of the urea injection system, the use of heating systems for thawing the urea solution have been employed. The use of cool urea solution leads to the development of crystallized urea on the urea injector, exhaust components or exhaust treatment device, also reducing the efficiency of the urea injection system. 
         [0005]    In addition, the use of aqueous urea solution contains a relatively low quantity of NH3 on a volume basis especially when compared with a solid ammonia transport material such as urea, ammonium carbamate and ammonium carbonate. As such, in order to maintain efficiency over long periods of time, a significant urea solution must be contained on board a vehicle. This adds both weight and cost to the vehicle. 
         [0006]    In view of the foregoing, there is a need for improved delivery systems capable of providing ammonia to an exhaust treatment device, such as a SCR device, that minimizes power consumption and storage requirements. 
       SUMMARY OF THE INVENTION 
       [0007]    An ammonia producing device for an exhaust system of an engine is provided. It includes a pressure vessel having a cavity for storage of pressurized gases. The pressure vessel includes insulation located at least partially about the cavity for limiting heat transfer from within the cavity. A flash heater is disposed within the cavity and adjacent a solid ammonia gas producing material. An outlet port extends from the pressure vessel and has a valve located therein for providing egress of pressurized gases from within the pressure vessel. 
         [0008]    In another embodiment, an exhaust system of an engine is provided. It includes a pressure vessel including a flash heater and a solid ammonia gas producing material disposed therein. The solid ammonia gas producing material is in contact with the flash heater. It generates a heat suitable for decomposition of the solid ammonia gas producing material. A manifold having an ammonia gas inlet is in fluid communication with the pressure vessel and has an exhaust gas inlet and an exhaust gas outlet in fluid communication with a main exhaust supply line. A control valve regulates the flow of ammonia gas between the pressure vessel and the manifold. A controller is in communication with the flash heater and the control valve, the controller causes actuation of the flash heater upon a pressure drop signal from within the pressure vessel and causes opening of the control valve to allow stored ammonia gas to enter the manifold and the exhaust gas stream. 
         [0009]    In yet another embodiment, a method of generating ammonia gas for use by a selective catalytic reduction device is provided. It comprises fluidly coupling a cavity of a pressure vessel to an exhaust gas stream of an engine and providing a flash heater and a solid ammonia gas producing material within the cavity of the pressure vessel. Heating of the flash heater to a temperature suitable for causing decomposition of the solid ammonia gas producing material generates an ammonia gas. The ammonia gas is stored within the pressure vessel between successive heating cycles of the flash heater and is provided to the exhaust gas stream upon the initiation of a new heating cycle. 
         [0010]    These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
           [0012]      FIG. 1  is a perspective view, in cross-section, of an ammonia producing device in accordance with the present invention; 
           [0013]      FIG. 2  is a top view of the ammonia producing device in accordance with the present invention; 
           [0014]      FIG. 3  is an elevation view of the ammonia producing device in accordance with the present invention; 
           [0015]      FIG. 4  is a first side elevation view of the ammonia producing device in accordance with the present invention; 
           [0016]      FIG. 5  is a second side elevation view of the ammonia producing device in accordance with the present invention; 
           [0017]      FIG. 6  is a top view of the flash heater; 
           [0018]      FIG. 7  is a functional flow diagram showing another aspect of the present invention; 
           [0019]      FIG. 8  is functional diagram showing the ammonia producing device in accordance with the present invention; 
           [0020]      FIG. 9  is a graphical illustration showing an aspect of the present invention; and 
           [0021]      FIG. 10  is a graphical illustration showing another aspect of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0022]    Referring now to the Figures and the Appendix (the entirety of which is incorporated by reference herein), where the invention will be described with reference to specific embodiments, without limiting same, a cross section through an ammonia generator pressure vessel reactor  10  is shown in  FIGS. 1 ,  2  and  3 . Additional details are shown in the Appendix. The ammonia generator is comprised of side walls  11 ,  12 ,  13  and  14 , with end walls  15  and  16  to form a rectangular configuration. 
         [0023]    As shown in  FIG. 1 , side walls  11 ,  12 ,  13 , and  14  fit into notches  21  and  22  located within end walls  15  and  16  to form a cavity  23  within ammonia generator  10 . End walls  11 ,  12 ,  13  and  14  are retained within notches  21  by threaded screw stock  31  that spans the length of ammonia generator  10  and is retained in opposing end walls  15  and  16  by extending through holes  32  and retained in compression by nuts  33  and washers  34 . In this way, a pressure vessel  10  having a rectangular cross-section is created for purposes that will be described later. It will be appreciated that there are numerous ways to create a pressure vessel  10 , and the aforementioned is intended only as a non-limiting exemplary embodiment. 
         [0024]    End wall  15  includes a pressure relief valve  45  which extends through the end wall  15  from the exterior side  40  to the interior and cavity  23 . Two heaters  42  and  43  are located on the exterior side  40  of end wall  15  for the purpose of heating cavity  23  of pressure vessel  10 . In the embodiment shown, heaters  42  and  43  are 200 W resistors that act as heaters. Obviously other heater types may be used for the purposes described herein. End wall  15  also includes an NPT plug  44  extending therethrough. 
         [0025]    End wall  16  includes a pressure transducer  54  for the purpose of measuring and maintaining pressure within cavity  23 . Pressure sensor  54  extends from the exterior side  51 , through end wall  16 , to the interior and cavity  23 . In an exemplary embodiment, pressure within cavity  23  is maintained at about 5 psi to 40 psi and more particularly at about 25 psi when in a working mode. Obviously, the dynamic characteristics of the reactor, as will be described hereinafter, can cause the pressure to vary significantly. Two additional heaters  46  and  47  are located on the exterior side  51  of end wall  16  for the purpose of heating cavity  23  of pressure vessel  10 . Like heaters  42  and  43 , heaters  46  and  47  are 200 W resistors that act as heaters. Other types of heaters could be substituted for the resistor heaters shown. A thermistor and temperature sensor  55  is located on end wall  16  for determining and maintaining a working temperature within pressure vessel  10 . In an exemplary embodiment, the working temperature is of cavity  23  is maintained at about 60 to about 100 degrees C. and more particularly at about 70 degrees C. 
         [0026]    A normally closed solenoid valve  61  is in fluid communication with cavity  23  of pressure vessel  10  through an orifice within solenoid retainer  62 . A manifold  63  is in fluid communication with cavity  23  through solenoid valve  61 . As shown, manifold  63  has an exhaust gas inlet  64  and an exhaust gas outlet  65 . Located between inlet  64  and outlet  65  is a plenum chamber  67  through which exhaust gas passes and is mixed with pressurized ammonia injected from cavity  23  through solenoid valve  61 . Adjacent inlet  64  is an ammonia inlet  71  through which ammonia gas is injected into plenum chamber  67 . The flow of exhaust through the plenum chamber  67  aids mixing &amp; provides a continuous transport media preventing re-composition of solid ammonium carbamate. Advantageous flow of heat from the exhaust to the reactor is assisted by multiple vanes  72  thus reducing energy required to decompose &amp; improving decomposition efficiency. 
         [0027]    As best seen in  FIG. 8 , pressure cavity insulation  73  is disposed on the interior side of walls  11 ,  12 ,  13  and  14 , while end wall insulation  74  is disposed on the interior side of end walls  15  and  16 . Teflon is a preferred insulating material as in addition to limiting heat loss, it prevents recomposed ammonium carbamate from attaching to the interior walls. Insulation  73  and  74  keep heat within cavity  23 , as discussed above at about 60 degrees C. to about 100 degrees C., for purpose described herein. Alternatively, insulation  73  and  74  may be disposed about the entirety of the interior of pressure vessel  10 , in selected locations throughout the interior of pressure vessel  10 , along the exterior of pressure vessel  10  or any number of subcombinations that efficiently achieve the target temperature ranges. A flash heater  75  is located within cavity  23  and is disposed adjacent a flash heater insulation layer  76  that is disposed between end wall  14  and flash heater  75 . In the embodiment shown, flash heater insulation layer  76  is glass insulation. In the exemplary embodiment shown, flash heater  75  is a thin sheet aluminum 300 W thick film flash heater. Flash heater  75  includes electrical contact pads  77  and an NTC thermistor  78  for controlling temperature. 
         [0028]    An ammonium carbamate block  81  is disposed within cavity  23  and adjacent to flash heater  75 . In the embodiment shown, carbamate block  81  rests directly upon flash heater  75  so that there is face to face contact, and an interface  84  therebetween. A buffer space  82  is located about block  81  and occupies the space in cavity  23  not occupied by block  81 . Block  81  is retained in the position of face to face contact with the force of gravity, and thus relies on proper orientation of pressure vessel  10  to form interface  84 . While other types of methods of retaining positioning of block  81  against flash heater  75 , such as springs or piston devices, each add additional weight and complexity to the system. Other types of solid ammonium salts such as ammonium carbonate may also be used. In another embodiment, ammonium carbamate block may actually be composed of multiple discrete blocks within cavity  23 , instead of the single solid block shown. 
         [0029]    The invention allows NH3 to be released from the solid form for subsequent injection into the exhaust stream  101 , shown in  FIG. 7 , produced by engine  102 . The NH3 enhanced exhaust stream is introduced into an SCR  103  for the reduction of NOX. The decomposition described herein maximizes NH3 release rate while minimizing power consumption and required storage pressure. 
         [0030]    Ammonium salts such as ammonium carbamate and ammonium carbonate decompose into ammonia at rates that increase exponentially as a function of temperature. The equilibrium vapor pressures of these ammonium salts also increase exponentially as a function of temperature. Therefore, achieving useful NH3 production rates is complicated in that the resulting vapor pressures are generally difficult in an automotive environment, usually greater that 10 Bars. By application of multiple heat paths, the invention allows NH3 production rate to be de-coupled from the associated vapor pressure. 
         [0031]    The generation of NH3 is directed by controller  104  and is achieved by first heating pressure vessel  10  using exterior heaters  42 ,  43  and  46 ,  47 . Specifically, the cavity  23  is heated to a working temperature of about 60 degrees C. to about 100 degrees C. and is generally held to about 70 degrees C. Thereafter, power is applied to flash heater  75 , sandwiched between insulation layer  76  and ammonium carbamate block  81 . Insulation layer minimizes heat loss such that a very high percentage of applied electrical energy results in solid to gas decomposition. 
         [0032]    The generation of heat from flash heater  75  results in a high temperature, generally up to about 110 degrees C. at full power, between block  81  and insulation layer  76 . The temperature from flash heater  75  will cause a rapid decomposition of transport material local to interface  84  between flash heater  75  and block  81 . The decomposition reaction converts ammonium carbamate NH4CO2NH2 to 2NH3+CO2 (the transport material) at interface  84 . It will be appreciated that the decomposition reaction is bi-directional, but the invention contemplates preventing significant recombination of the products. The decomposition reaction causes internal pressure of cavity  23 , and specifically buffer space  82 , to rise at a rate far greater than that induced by the relatively low temperature induced by heaters  42 ,  43 ,  46 ,  47 . 
         [0033]    Controller  104  is constantly monitoring pressure sensor  54 , thermistor and temperature sensor  55 . When the internal pressure of buffer space  82  is generally equal to the equilibrium vapor pressure sustainable by the pressure vessel reactor  10 , specifically wall  11 ,  12 ,  13 ,  14  temperature, controller  104  directs that power is removed from flash heater  75 . At this point, the internal temperature and pressure of the pressure vessel  10  are in equilibrium. Further decomposition or recombination of the transport material is limited. Therefore, 2NH3+CO2 formed after decomposition remains in quantity within buffer space  82 , with heat from heaters  42 ,  43 ,  46  and  47  maintaining the transport material and generally preventing significant recombination of the products. As shown in  FIG. 9 , the decomposition rate of block  81  to transport material is generally linear with respect to power output, and shows a decomposition efficiency in excess of 90%. 
         [0034]    At such time as NH3 injection into SCR  103  is required, the normally closed solenoid valve  61  is opened, allowing stored NH3 and CO2 to enter plenum chamber  67  and mix with exhaust gas which has been diverted by an exhaust loop  105 , having an inlet portion  106  and an outlet portion  107 , from exhaust stream  101 . The NH3 and CO2 mix with the exhaust stream in manifold  63  and continue to mix in outlet portion  107  and exhaust stream  101 . A corresponding reduction in the internal pressure within pressure vessel reactor  10  occurs. This triggers controller  104  to immediately apply sufficient power to flash heater  75  to maintain internal pressure at between about 5 psi to about 40 psi. 
         [0035]    As shown in  FIG. 10 , until decomposition reaches a steady state, shown at node  110 , supply of NH3 to exhaust stream  101  will be insufficient. Thus the exhaust system  100 , shown in  FIG. 7 , can rely on a stored supply of NH3 within buffer space  82  of pressure vessel  10 . The maintenance of both temperature and pressure within pressure vessel reactor  10  prevents recombination of the transport material back to ammonium carbamate and thus provides an immediate supply of NH3, without a time lag until the steady state condition at node  110 . Once the steady state is reached at time past node  110 , the transport material can be injected into the exhaust stream at the same rate that block  81  is decomposing. In addition, the rectangular configuration of pressure vessel reactor  10  assures that buffer space  82  is maximized for a given volume required to house pressure vessel  10  within exhaust system  100  of vehicle. 
         [0036]    The invention allows flash heating of ammonium carbonate in which the reactor  10  is held at a sufficient working temperature to prevent significant recombination. As such, the two stage process contemplates decomposing block  81 , regulating pressure and sustaining temperature to provide an immediate source of NH3 for exhaust system  100  while achieving a decomposition efficiency of solid ammonium that has a higher density than liquid urea and weighs less. 
         [0037]    While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description.