Abstract:
The use of a solution of salt within ammonia as a fuel. The preferred ammonia/salt solution is an ammonium nitrate solute (NH 4 NO 3 ) within the solvent anhydrous ammonia (NH 3 ). The solution may also contain a small amount of water (H 2 O).

Description:
RELATED APPLICATIONS 
       [0001]    This application claims the benefit of US Provisional Application No. 61297587, filed Jan. 22, 2010. 
     
    
     TECHNICAL FIELD 
       [0002]    This invention relates to carbon-free fuels. More specifically, this invention relates to the use of an ammoniacal, ammonia salt solution as a fuel. 
       BACKGROUND OF THE INVENTION 
       [0003]    In 2005, the United States Department of Energy (DOE) updated its goals for hydrogen production. The DOE noted that one kilogram of hydrogen contains approximately the same energy as one gallon of gasoline, termed as a gallon of “gasoline equivalent,” or “gge.” The DOE therefore set the goal for the DOE&#39;s hydrogen program to develop methods and techniques capable of producing hydrogen for between $2-$3 per gge by 2015. In the intervening three years, the DOE has funded millions of dollars of research at DOE owned federal laboratories to attain this goal. To date, no one has reported any results that have done so. 
         [0004]    The reason that the DOE is interested in hydrogen is because when burned hydrogen produces no carbon dioxide effluent. As such, hydrogen is a potential fuel that does not generate so-called greenhouse gasses, including carbon dioxide. Unfortunately, hydrogen is costly, and is difficult to store and transport. 
         [0005]    A better alternative to hydrogen is anhydrous ammonia. Like hydrogen, ammonia contains no carbon. As such, when burned, ammonia does not produce carbon dioxide. Ammonia has also long been shown to be a useful fuel. Both turbine and internal combustion engines have been shown to run effectively on ammonia. However, the use of ammonia as an engine fuel is not without drawbacks. 
         [0006]    One such drawback is related to the fact that at room temperature and atmospheric pressure, ammonia exists as a vapor. However, the critical temperature of ammonia (T c =132.6° C.) is much greater than standard room temperature. As such, ammonia may be stored as a non-cyrogenic liquid (in contrast with liquid hydrogen, T c =−240° C.) at elevated pressure. 
         [0007]    An additional drawback related to the use of ammonia as a combustion fuel is its limited flammability (16-25% ammonia by volume in air, compared to 4-74% hydrogen in air), as well as its low flame speed (ca. 0.11 m/s for ammonia, compared to ca. 3.8 m/s for hydrogen), which limits its utility for high-speed engines and burners. 
         [0008]    Accordingly, there is a need by those having ordinary skill in the art to devise alternative fuels to ammonia that provide the benefits of ammonia while escaping some of the drawbacks. The present invention provides such an alternative. 
       SUMMARY OF THE INVENTION 
       [0009]    One aspect of the invention is the use of a solution of salt within ammonia as a fuel. The preferred ammonia/salt solution is an ammonium nitrate solute (NH 4 NO 3 ) within the solvent anhydrous ammonia (NH 3 ). The solution may also contain a small amount of water (H 2 O), although water is neither necessary nor desirable. 
         [0010]    The preferred application for this fuel solution is for use in internal combustion engines and gas combustion turbines. The invention improves on prior art ammonia-based fuel mixtures because the addition of salts reduces the vapor pressure of ammonia, allowing it to be stored in tanks at pressures closer to or at atmospheric pressure. The invention also improves on prior art ammonia-based fuel mixtures because it does not contain carbon, which if present would produce undesired carbon dioxide or carbon monoxide upon combustion. The invention also improves on prior art ammonia-based fuel mixtures because it does contain molecularly-fixed oxygen, which increases the combustibility of the mixture relative to pure ammonia when burned in air. The oxygen in the fuel solution also enhances the combustion flame speed relative to pure ammonia, which is of benefit to its use in piston-based and rotary combustion engine applications. 
         [0011]    Ammonium nitrate may be dissolved in ammonia at room temperature (the desired temperature for the storage and use of the fuel solution) up to a concentration of at least 3.62 grams of ammonium nitrate per gram of ammonia. 
         [0012]    As increasing amounts of ammonium nitrate are added to liquid ammonia, the vapor pressure of the mixture is reduced, reaching a vapor pressure of nearly atmospheric pressure at saturation. Thus, one aspect of the present invention is that the fuel solution&#39;s vapor pressure may be tuned as appropriate for the intended combustion device by the addition of a specific amount of ammonium nitrate solute to the ammonia solvent. In this manner, the fuel of the present invention may be configured to provide a specific vapor pressure to an engine or other combustion device at a given fuel storage temperature. 
         [0013]    The salt/ammonia solution will also have an increased internal oxygen content when compared to pure ammonia, and increasing amounts of ammonium nitrate within the solution will aid the oxidation of the fuel during its combustion in air. Therefore, the combustibility and flame speed of a fuel solution may also be tuned as appropriate for the intended combustion device by the addition of a specific amount of ammonium nitrate solute to the ammonia solvent. In this manner, the fuel of the present invention may be configured to provide a fuel having a specific combustibility and flame speed for an intended combustion device. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0014]    For the purposes of promoting an understanding of the principles of the invention, a series of experiments were conducted reducing the present invention to practice. 
         [0015]    A salt/ammonia fuel mixture was created by measuring 24.0 grams of ammonium nitrate salt crystals into a stainless steel jar with a usable volume of approximately 100 cubic centimeters. The container was then sealed and connected to a gas line providing gaseous anhydrous ammonia from a small cylinder at room temperature. The stainless steel jar was then immersed in an ice water bath while ammonia was allowed to flow into the jar, where it condensed within as a liquid. The amount of ammonia transferred to the jar was determined by weighing. The final solution had a density of approximately 0.8 grams per milliliter and comprised a solution of approximately 30 weight percent ammonium nitrate in liquid ammonia. The stainless steel jar, which was also fitted with a dip tube, was connected to a small automotive liquid fuel injector. The injector was triggered by intermittent connection to an automotive 12 volt lead acid battery. Liquid salt/ammonia solution was sprayed through the injector into a free-burning propane flame, where the solution was ignited, burning with an orange-yellow flame. In contrast, a spray consisting of pure anhydrous ammonia (with no added ammonium nitrate salt) did not visibly ignite within the flame. 
         [0016]    While the invention has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character. Only certain embodiments have been shown and described, and all changes, equivalents, and modifications that come within the spirit of the invention described herein are desired to be protected. Any experiments, experimental examples, or experimental results provided herein are intended to be illustrative of the present invention and should not be considered limiting or restrictive with regard to the invention scope. Further, any theory, mechanism of operation, proof, or finding stated herein is meant to further enhance understanding of the present invention and is not intended to limit the present invention in any way to such theory, mechanism of operation, proof, or finding. 
         [0017]    Thus, the specifics of this description and the attached drawings should not be interpreted to limit the scope of this invention to the specifics thereof Rather, the scope of this invention should be evaluated with reference to the claims appended hereto. In reading the claims it is intended that when words such as “a”, “an”, “at least one”, and “at least a portion” are used there is no intention to limit the claims to only one item unless specifically stated to the contrary in the claims. Further, when the language “at least a portion” and/or “a portion” is used, the claims may include a portion and/or the entire items unless specifically stated to the contrary. Likewise, where the term “input” or “output” is used in connection with an electric device or fluid processing unit, it should be understood to comprehend singular or plural and one or more signal channels or fluid lines as appropriate in the context. Finally, all publications, patents, and patent applications cited in this specification are herein incorporated by reference to the extent not inconsistent with the present disclosure as if each were specifically and individually indicated to be incorporated by reference and set forth in its entirety herein.