Abstract:
A method for heating solid ammonia (NH 3 ) in a main unit ( 12 ) to deliver gaseous ammonia into the exhaust gas (EG) downstream of an engine ( 16 ) includes the steps of diverting at least a portion of the exhaust gas from the exhaust gas passageway ( 14 ), fluidly communicating the exhaust gas on a delivery line ( 28 ) from the exhaust gas passageway to the main unit, heating the solid ammonia with the exhaust gas, and fluidly communicating the exhaust gas on a return line ( 30 ) from the main unit to the exhaust gas passageway.

Description:
BACKGROUND 
       [0001]    Embodiments described herein relate to methods for heating a cartridge of ammonia salts to release ammonia into an exhaust aftertreatment system. 
         [0002]    Diesel engine combustion results in the formation of nitrogen oxides, (NO x ), in the exhaust gas. An aftertreatment system is used to reduce oxides of Nitrogen (NO x ) emitted from the diesel engine. Nitrogen oxides can be reduced by ammonia (NH 3 ), which is injected into the exhaust gas stream, yielding N 2 , H 2 O and CO 2 . 
         [0003]    Typically, NH 3  is molecularly bonded to a solid host salt that is placed inside of a vessel called a main unit. The main unit is heated by hot engine coolant that is circulated around the main unit in a surrounding heating mantle. When heated, the host salt releases NH 3  molecules as gas, and the gaseous NH 3  is delivered to the exhaust gas stream where the nitrogen oxides are reduced. 
         [0004]    The engine needs to provide an adequate amount of thermal energy for the host salt to release the gaseous NH 3 . Some engines may need to operate for a period of time to heat up the coolant. To decrease the NH 3  delivery time, an electrically heated start-up unit is often used to provide NH 3  to the exhaust gas stream until the engine coolant is hot enough to provide adequate thermal energy to the main unit. 
         [0005]    Even when there is sufficient thermal energy for a reaction to occur, often only seven of the eight NH 3  molecules are released from the host salt because the engine coolant does not have adequate thermal energy to remove the eighth molecule. The eighth molecule often goes unused. 
         [0006]    Some engines may not provide sufficient thermal energy for the exothermic NH 3  reaction to occur at all. Further, with developments in engine technology directed at increased efficiency, future engines may not run hot enough to support the exothermic NH 3  reaction. 
         [0007]    Additionally, diverting engine coolant from other engine systems can cause a flow imbalance in the other engine systems. A flow imbalance of engine coolant can lead to engine system failures. 
       SUMMARY 
       [0008]    A method for heating solid ammonia (NH 3 ) in a main unit to deliver gaseous ammonia into the exhaust gas downstream of an engine includes the steps of providing engine coolant that is dedicated only to heating the ammonia, heating the dedicated engine coolant at a heater, and fluidly communicating the engine coolant on a delivery line from the heater to the main unit. The method also includes the steps of heating the solid ammonia with the heated engine coolant, and fluidly communicating the engine coolant on a return line from the main unit to the heater. 
         [0009]    Another method for heating solid ammonia (NH 3 ) to deliver gaseous ammonia into the exhaust gas downstream of an engine includes the steps of diverting at least a portion of the exhaust gas from the exhaust gas passageway, fluidly communicating the exhaust gas on a delivery line from the exhaust gas passageway to the main unit, heating the solid ammonia with the exhaust gas, and fluidly communicating the exhaust gas on a return line from the main unit to the exhaust gas passageway. 
         [0010]    In another method for heating ammonia (NH 3 ) in a main unit to deliver gaseous ammonia into exhaust gas downstream of an engine, the method includes the steps of providing engine oil or transmission oil, fluidly communicating the oil on a delivery line from the engine or the transmission to the main unit, and heating the solid ammonia with the heated oil. The method also includes the step of fluidly communicating the oil on a return line from the main unit to the engine or the transmission. 
         [0011]    Another method for heating solid ammonia (NH 3 ) to deliver gaseous ammonia into exhaust gas downstream of an engine includes the steps of embedding an electric coil into the solid ammonia, heating the electric coil with an electrical heater, and attaching the electric coil to the electric heater with at least one wire. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  is a schematic showing the method of heating ammonia in a main unit with diverted exhaust gas. 
           [0013]      FIG. 2  is a schematic showing the method of heating ammonia in the main unit with engine oil or transmission oil. 
           [0014]      FIG. 3  is a schematic showing the method of heating ammonia in the main unit with dedicated coolant and an electric heater. 
           [0015]      FIG. 4  is a schematic showing the method of heating ammonia in the main unit with dedicated coolant and a Peltier module. 
           [0016]      FIG. 5  is a schematic showing the method of heating ammonia in the main unit with embedded electrical coils. 
       
    
    
     DETAILED DESCRIPTION 
       [0017]    Referring to  FIGS. 1-5 , a method of heating a main unit  12  for delivering gaseous ammonia (NH 3 ) into an exhaust gas passageway  14  of a diesel engine  16  is indicated generally at  10 ,  110 ,  210 ,  310  and  410 . The exhaust gas (EG) flows from the engine  16  to an outlet  18  through the exhaust gas passageway  14  in the direction indicated by the arrow. One or more aftertreatment devices  20  may be disposed on the exhaust gas passageway  14  between the engine  16  and the outlet  18  to treat the exhaust gas EG before being emitted at the outlet. 
         [0018]    When the engine  16  combusts diesel, nitrogen oxides form and are released with the exhaust gas (EG). Nitrogen oxides, NOx, are a pollutant that are reduced in the aftertreatment system by gaseous ammonia (NH 3 ) resulting in the emission of less harmful nitrogen, N 2 , water, H 2 O, and carbon dioxide, CO 2 . The NH 3  is stored in a solid state in a NH 3  cartridge  22  inside of the main unit  12 . When there is sufficient thermal energy, an exothermic reaction occurs, releasing gaseous NH 3  that can be delivered to the exhaust gas. 
         [0019]    The delivery of NH 3  may be implemented by software on the vehicle, such as at a control unit  24 , however other controllers are possible. At least one sensor  26  may sense the NH 3  gas outlet pressure at or near the NH 3  cartridge  22 , such as at the outlet or downstream of the main unit  12 . If the sensor  26  senses that the system requires NOx reduction, the control unit  24  may increase the amount of thermal energy from an alternative source of thermal energy, as will be discussed below. The system will dose NH 3  to the exhaust passageway  14  as long as the main unit  12  NH 3  outlet pressure is in the range of about 1.8-2.5 bar abs. The exhaust gas EG pressure is typically in the range of 1.4-1.5 bar abs. 
         [0020]    The methods  10 ,  110 ,  210 ,  310  and  410  of  FIGS. 1-5  all use alternative sources of thermal energy to heat the main unit  12  as compared to the conventional source, which is engine coolant that is shared with other engine systems to heat the main unit  12 . Although the following description will be directed to a method for heating the main unit  12  in a vehicle aftertreatment system, the method  10 ,  110 ,  210 ,  310  and  410  of  FIGS. 1-5  can be used with any diesel engine  16  that emits NOx. 
         [0021]    Referring to  FIG. 1  and the method of heating  10 , the alternative source of thermal energy is exhaust gas EG diverted from the exhaust gas passageway  14 . The exhaust gas EG may be diverted downstream of the aftertreatment device  20  so that the exhaust gas is less corrosive and free of unburned hydrocarbons and other particulate matter relative to the exhaust gas upstream of the aftertreatment device. The exhaust gas EG flows through a delivery line  28  to the main unit  12 . 
         [0022]    At the main unit  12 , the exhaust gas EG surrounds the NH 3  cartridge  22  and heats the ammonia salt contained in the cartridge. The temperature of the NH 3  cartridge  22  may exceed the minimum temperature to release gaseous ammonia NH 3 , and may be about 150-degrees Celsius, which is sufficient thermal energy to release the eighth molecule of gaseous NH 3  from the ammonia salt. After circulating around the NH 3  cartridge  22 , the exhaust gas EG is cooled and flows back to the exhaust gas passageway  14  on a return line  30 . The gaseous NH 3  may also flow to the exhaust gas passageway  14  on the return line  30 , or alternatively, may be delivered to the exhaust gas passageway on a separate NH 3  line  31 . Using exhaust gas EG as the thermal source, engine coolant systems are not affected. 
         [0023]    Referring to  FIG. 2 , the method of heating  110  employs engine oil or transmission oil (oil) as the alternative source of thermal energy. The heated oil is delivered from the engine or transmission  16  and flows through a delivery line  128  to the main unit  12 , where the oil flows around the NH 3  cartridge  22 . The oil heats the ammonia salt contained in the NH 3  cartridge  22  to release gaseous ammonia. The cooled oil flows from the main unit  12  back to the engine or transmission  16  on the return line  130 . The gaseous ammonia NH 3  released from the NH 3  cartridge  22  is delivered to the aftertreatment device  20  on the exhaust gas passageway  14 . 
         [0024]    It is possible that transmission oil may be used in applications where the engine is not hot enough to provide adequate thermal energy, or where diverting engine coolant may lead to system imbalances. Further, since oil is used as the thermal source, engine coolant systems are not affected by the method  110  of heating the NH 3  cartridge  22 . It is possible that both engine oil and transmission oil can be used. 
         [0025]    Referring now to the method of heating  210  of  FIG. 3 , the alternative source of energy is coolant (CL) provided on a dedicated coolant circuit. The coolant CL is coolant that is not used for other engine systems, but is coolant that is used only to heat the NH 3  cartridge. The dedicated coolant CL is not connected to the engine&#39;s  16  coolant circuit, however the hardware to circulate the coolant may be mounted on the engine, the chassis, or anywhere else. The coolant CL is heated at a heater  232 , such as an electrical heater, and from the heater, the coolant is in fluid communication with the main unit  12  on a delivery line  228 . Temperatures may exceed about 150-degrees Celsius at the main unit  12 , which may release the eighth molecule of NH 3  from the NH 3  cartridge  22 . The cooled coolant CL flows back to the heater  232  on a return line  230 . The gaseous NH 3  released from the cartridge  22  is delivered to the exhaust gas passageway  14  on line  31 . 
         [0026]    The method of heating  310  of  FIG. 4  employs dedicated engine coolant (CL) that is heated thermoelectrically. The coolant CL is coolant that is not used for other engine systems, but is used only to heat the NH 3  cartridge. The coolant CL is heated thermoelectrically at a thermo-module  332 , for example a thermo-module that uses the Peltier Effect to heat the coolant CL. The heated coolant CL is in fluid communication with the main unit  12  on a delivery line  328  from the thermo-module  332  to the main unit. The heated coolant provides sufficient thermal energy for gaseous ammonia to be released and to be delivered to the exhaust gas passageway  14 . A return line  330  provides the fluid communication of the coolant CL from the main unit  12  back to the thermo-module  332 . 
         [0027]    Referring now to  FIG. 5 , the method of heating  410  employs electrical coils  434  embedded in the host salt of the NH 3  cartridge  22 . The electrical coils  434  are electrically connected with at least two wires  436 ,  438  to an electric heating source  432 . The embedded coils  434 , heated by the heating source  432 , provide sufficient thermal energy to release gaseous ammonia NH 3 , which is deliverable to the exhaust gas passageway  14 . 
         [0028]    The methods of  FIGS. 1-5  may allow the size of the main unit  12  to be reduced since the alternative sources of thermal energy may be more efficient than the conventional engine coolant. Further, the methods of  FIGS. 1-5  may release the eighth molecule of the NH 3  to which can be used to convert NOx. Further still, the start-up unit that is often used with the conventional engine coolant can be eliminated.