Thermal Stability for Exhaust Emissions Treatment Materials

Abstract

A storage vessel for emission control liquids such as aqueous solutions of urea is equipped with phase change materials that are calibrated to help maintain the liquid within a proper temperature range. Multiple phase change materials having phase transition temperatures of fifty to seventy degrees Celsius and seventy to one hundred degrees Celsius provide staged high-temperature stability for the urea solutions. Phase change materials can be included that also provide low temperature stability by changing from liquids to solids when freezing of the aqueous solution is threatened. Containers of phase change materials are applied to the interior or exterior surfaces of the storage vessel. Alternatively the storage vessel is included within and surrounded by a housing that forms an annular space with the storage vessel, and phase change materials are installed within the annular space. A method for using the storage vessel in an emissions control system also is presented.

1 . A storage vessel with improved thermal stability for liquids used to reduce engine exhaust emissions comprising an inlet for admitting a liquid into the storage vessel, an outlet for providing liquid to exhaust emissions equipment of the engine, and phase change material in heat transfer relationship with the liquid, said phase change material being calibrated with a phase transition temperature within an identified temperature range to exchange its heat of fusion with the liquid and thereby stabilize the temperature of the liquid within the identified temperature range. 
   
   
       2 . The storage vessel of  claim 1  in which the phase change material is calibrated to undergo a phase change and absorb thermal energy when the temperature of the liquid increases above the phase transition temperature of the phase change material. 
   
   
       3 . The storage vessel of  claim 2  in which the liquid is an aqueous solution of urea and the phase change material is calibrated with a phase transition temperature within a range of fifty to one hundred degrees Celsius. 
   
   
       4 . The storage vessel of  claim 3  in which the phase change material is high-temperature phase change material, said high-temperature phase change material being calibrated with a phase transition temperature within a range of seventy to one hundred degrees Celsius. 
   
   
       5 . The storage vessel of  claim 4  comprising low-temperature phase change material in heat transfer relationship with the liquid, said low-temperature phase change material being calibrated with a phase transition temperature within a range of fifty to seventy degrees Celsius. 
   
   
       6 . The storage vessel of  claim 5  comprising additional phase change material in heat transfer relationship with the liquid, said additional phase change material being calibrated with a phase transition temperature within a range of zero to minus ten degrees Celsius to release thermal energy when the temperature of the liquid is within the range of zero to minus ten degrees Celsius. 
   
   
       7 . The storage vessel of  claim 1  comprising a sealed container positioned on an interior surface of the storage vessel and in heat transfer relationship with the liquid, said sealed container containing said phase change material, said phase change material being calibrated with a phase transition temperature within a range of fifty to one hundred degrees Celsius to absorb thermal energy. 
   
   
       8 . The storage vessel of  claim 1  comprising a first sealed container in heat transfer relationship with the liquid, said sealed container containing said phase change material, said phase change material being calibrated with a phase transition temperature within a range of seventy to one hundred degrees Celsius to absorb thermal energy, and a second sealed container in heat transfer relationship with the liquid, said second sealed container containing phase change material calibrated with a phase transition temperature within a range of fifty to seventy degrees Celsius to absorb thermal energy. 
   
   
       9 . The storage vessel of  claim 1  in which the phase change material is calibrated with a phase transition temperature within a range of zero to minus ten degrees Celsius to release thermal energy when the temperature of the liquid is within the range of zero to minus ten degrees Celsius. 
   
   
       10 . A storage vessel with improved thermal stability for liquids used to reduce engine exhaust emissions comprising an inlet for admitting a liquid into the storage vessel, an outlet for providing liquid to exhaust emissions equipment of the engine, an outer housing surrounding the storage vessel and forming an annular space with the storage vessel, and phase change material installed in the annular space and in heat transfer relationship with the liquid. 
   
   
       11 . The storage vessel of  claim 10  in which the liquid is an aqueous solution of urea and the phase change material is calibrated with a phase transition temperature within a range of fifty to one hundred degrees Celsius to absorb thermal energy when the temperature of the liquid is within a range of fifty to one hundred degrees Celsius. 
   
   
       12 . The storage vessel of  claim 11  comprising a partition that extends through the annular space and divides the annular space into more than one compartment, each of said compartments being suitable for containing phase change material. 
   
   
       13 . The storage vessel of  claim 12  in which one compartment contains phase change material calibrated with a phase transition temperature within a range of fifty to one hundred degrees Celsius to undergo a phase change and absorb thermal energy when the temperature of the liquid is within a range of fifty to seventy degrees Celsius, and another compartment contains phase change material calibrated with a phase transition temperature within a range of seventy to one hundred degrees Celsius to absorb thermal energy when the temperature of the liquid is within a range of seventy to one hundred degrees Celsius. 
   
   
       14 . The storage vessel of  claim 13  comprising additional phase change material is calibrated with a phase transition temperature within the range of zero to minus ten degrees Celsius to release thermal energy when the temperature of the liquid is within the range of zero to minus ten degrees Celsius. 
   
   
       15 . A method for injecting an exhaust treatment liquid into engine exhaust gases generated by an engine and having an exhaust conduit for conducting the exhaust gases to a catalytic unit comprising providing a storage vessel for the exhaust treatment liquid, introducing exhaust treatment liquid into the storage vessel, stabilizing the exhaust treatment liquid with phase change material being calibrated with a phase transition temperature within an identified temperature range to exchange its heat of fusion with the liquid and thereby stabilize the temperature of the liquid within the identified temperature range, and conducting the exhaust treatment liquid to the engine emissions gases. 
   
   
       16 . The method of  claim 15  comprising calibrating the phase change material with a phase transition temperature of seventy to one hundred degrees Celsius to undergo a phase change and absorb thermal energy when the temperature of the exhaust treatment liquid within the storage vessel is seventy to one hundred degrees Celsius. 
   
   
       17 . The method of  claim 16  comprising placing second phase change material within the storage vessel and in heat transfer relationship with the exhaust treatment liquid, and calibrating said second phase change material with a phase transition temperature of fifty to seventy degrees Celsius to undergo a phase change and absorb thermal energy when the temperature of the exhaust treatment liquid within the storage vessel is fifty to seventy degrees Celsius. 
   
   
       18 . The method of  claim 17  in which dosing equipment for spraying exhaust treatment liquid into the engine exhaust gases is located in the exhaust conduit upstream of the catalyst, and comprising transporting extra exhaust treatment liquid to the dosing equipment, returning excess exhaust treatment liquid to the storage vessel via a return line, and stabilizing the temperature of the returning exhaust treatment liquid within the return line with phase change material. 
   
   
       19 . The method of  claim 15  in which dosing equipment for spraying exhaust treatment liquid into the engine exhaust gases is located in the exhaust conduit upstream of the catalyst, and comprising transporting extra exhaust treatment liquid to the dosing equipment, returning excess exhaust treatment liquid to the storage vessel via a return line, and stabilizing the temperature of the returning exhaust treatment liquid within the return line with phase change material. 
   
   
       20 . The method of  claim 15  comprising calibrating the phase change material to undergo a phase change and release thermal energy when the temperature of the exhaust treatment liquid is zero to minus ten degrees Celsius.