Patent Publication Number: US-6210504-B1

Title: Tertiary amine azides in liquid or gel fuels in gas generator systems

Description:
BACKGROUND OF THE INVENTION 
     A liquid or gel bipropellant rocket propulsion system consists of gas generators, oxidizer and fuel propellant tanks, plumbing, oxidizer and fuel valves, and an engine. This propulsion unit begins operation when the gas generators have been initiated and the gases from the gas generator pressurize oxidizer and fuel propellant tanks. When the oxidizer and fuel valves open, the pressurized oxidizer and fuel tanks then force the propellants through the plumbing into the engine where the propellants are mixed and ignited. The propellants can be ignited by either ignition aids or by hypergolic chemical reaction. Ignition aids can take up valuable space in the propulsion system so a hypergolic chemical reaction is the preferred ignition method. Inhibited Red Fuming Nitric Acid (IRFNA) type IIIB and monomethyl hydrazine (MMH) ignite when contacted with each other because of a hypergolic chemical reaction and are the preferred oxidizer and fuel for bipropellant rocket propulsion systems. These propellants can deliver a specific impulse of 284 lbf sec/Ibm and density impulse of 13.36 lbf sec/cubic inch when the engine operating pressure is 2000 psi. Special precautions must be used when handling because of its toxic properties. 
     If a liquid gas generator is used excess pressurizing gases do not have to be dumped overboard to prevent overpressurization that can result from a solid gas generator formulation. A solid gas generator formulation once ignited cannot be stopped; however, a liquid gas generator system supplies gas pressure only when it is needed. Hydrazine and hydrazine blends have been considered for liquid gas generators because of their ability to decompose at ambient conditions on an iridium catalyst preheated to above 350° F. to form warm (1000° F. to 1500° F.) gases. Hydrazine is undesirable because of its toxicity and high melting point (34° F.). 
     An object of this invention is to provide a less toxic liquid/gas generator propellant that is a suitable replacement for hydrazine or hydrazine blends. 
     Another object of this invention is to provide less toxic fuel gel propellants which are good candidates for gas generators because of their exothermic decomposition. 
     A further object of this invention is to provide an alternate less toxic fuel gel propellant which decomposes exothermically to release enough heat to sustain decomposition in a thermal reactor bed. 
     A further object of this invention is to provide gas generators as alternative fuels selected from tertiary amine azides that can function also as hypergolic fuels in a bipropellant propulsion system to meet the above conditions as further described hereinbelow. 
     SUMMARY OF THE INVENTION 
     The tertiary amine azides which are defined below are non-carcinogenic alternatives to hydrazine in liquid gas generator systems or monopropellant thruster propulsion systems. The tertiary amine azides which are defined below are non-carcinogenic alternative for use with a thermal reactor bed where exothermic reaction releases enough heat to sustain decomposition for furnishing gases for gas generator systems employed. Calorimetry methods have been used to determine the heat of formation of these compounds since this information has not been published in the open literature. The heat of formation data has been used to determine the specific impulse and density impulse of the respective formulations. A tertiary amine typically has three hydrocarbon moieties attached to the nitrogen atom. The tertiary amine azides of this invention can have no more than seven carbon atoms in the molecules. 
     Further, these tertiary amine azides can contain no more than two azide moieties which are attached at the opposite end of the hydrocarbon portions from the amine nitrogen atom. A special case that still meet these requirements is a pyrollidine moiety (five atom cyclic structure wherein each end of a linear four carbon atom structure is attached to a common nitrogen atom), and the common nitrogen atom has an attached ethyl azide moiety. 
     Pyrollidinylethylazide (PYAZ) has the following structure:                    
     wherein R 3  is as 
     previously defined and wherein R 4  is —CH 2 . 
     Three compounds meeting the specified requirements have been synthesized and their physical and ballistic properties are evaluated herein as shown in Table 1. The chemical names for these compounds are dimethylaminoethylamine (DMAZ), pyrollidinylethylazide (PYAZ), and bis(ethyl azide)methylamine (BAZ). The structural formulae for these compounds are defined hereinbelow. 
     Dimethylaminoethylamine (DMAZ) has the following structure:                    
     wherein R 1 =—CH 3 , 
     R 2 =—CH 3 , 
     R 3 =—CH 2 CH 2 N. 
     Bis(ethylazide)methylamine (BAZ) has the following structure:                    
     and wherein 
     R 1  and R 3  are as previously defined. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 of the Drawing depicts the temperature of the gas generator reactor during operation using hydrazine and DMAZ, curve a and curve b respectively. 
     FIG. 2 of the Drawing depicts the pressure of the gas generator reactor during operation using hydrazine and DMAZ, curve a and curve b respectively. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT(S) 
     Where there exists bipropellant liquid or gel propulsion systems which use fuel gel as one of the components, (this would include NASA systems which uses nitrogen tetroxide and MMH for reactive control systems, and the Army and Air Force of the components, (this would include NASA systems which uses nitrogen tetroxide and MMH for reactive control systems, and the Army and Air Force systems which use IRFNA and MMH for tactical systems) DMAZ fuel could be used as a no-carcinogenic alternative to MMH. The tertiary amine azide gel can have from 0.5-10% gellant. The gellant can be silicon dioxide, clay, carbon, or any polymeric gellant. The tertiary amine azide gel can also include additives to improve the specific impulse and density impulse. These solid additives can include but would not be limited to amine-nitrate salts, quaternary ammonium salts, or triaminotrinitrobenzene. The formulation can contain 1%-90% solid additive, 98.5%-10% tertiary amine azide and 0.5%-10% gellant. 
     The tertiary amine azides used as hypergolic liquid or gel fuels in accordance with this invention have the requirement specified in Table 1 which are responsible for their superior fuel characteristics. The inclusion of an azide moiety into the tertiary amine molecule, improves the density and energy content. The effect that the azide moiety had on ignition delay was unexpected. In the propulsion literature tertiary amines typically have a 20-30 millisecond ignition delay while the hydrazines have a 3-10 millisecond ignition delays. The presence of the azide moiety reduces the ignition delay of tertiary amines to the hydrazine levels. Testing of dimethylaminoethylazide (DMAZ) was tested and had a 6 millisecond ignition delay. Calorimetry methods were used to determine the heats of formation of the tertiary amine azides. The freezing points have been verified using DSC (differential scanning calorimetry) method. The boiling points have been determined by observation. The heat of formation data has been used to determine the specific impulse and density specific impulse for each of the tertiary amines. 
     In existing bipropellant liquid/gel gas generator systems that use hydrazine or hydrazine blends, a tertiary amine azide of this invention is used as a non-carcinogenic alternative to hydrazine or hydrazine blends. In a gel formulation the tertiary amine azide gel can be 0.5%-10% gellant. The gellant can be silicon dioxide, clay, carbon, or any polymeric gellant. The tertiary amine azide gel can also include additives that could improve the specific impulse and density specific impulse. These solid additives could include but is not limited to carbon, aluminum, silicon, boron, tungsten, triaminotrinitrobenzene or tetramethylammoniumazide. The formulation can be 1%-90% solid additive, 98.5%-10% tertiary amine azide and 0.5%-10% gellant. 
     Table 1 (below) displays the physical and ballistic properties of the tertiary amine azide fuels. PYAZ has a considerably broader boiling point to freezing point range. All of the fuels have large densities. 
     
       
         
           
               
               
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                 COMPOUND 
                 UNITS 
                 MMH 
                 DMAZ 
                 PYAZ 
                 BAZ 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Boiling Point 
                 (0° F.) 
                 188 
                 276 
                 d−310 
                 d−316 
               
               
                 Freezing Point 
                 (0° F.) 
                 63 
                 −92 
                 −176 
                 61 
               
               
                 Density 
                 (g/cc) 
                 0.88 
                 0.933 
                 0.986 
                 1.06 
               
               
                 Heat of Formation 
                 (cal/g) 
                 276 
                 580 
                 520 
                 828 
               
               
                   
               
               
                 d = Compound decomposes before boiling  
               
            
           
         
       
     
     The gel can have 0.5%-10% gellant. The gellant can be selected from the group of gellant consisting of silicon dioxide, clay, carbon or any polymeric gellant. The DMAZ gel can also include additives for improving the specific impulse and density impulse. These additives can include but are not be limited to carbon, aluminum, silicon or boron. These additives can be in a formulation comprised of about 1%-70% boron, carbon, silicon or aluminum; 98.5%-20% DMAZ; and 0.5%-10% gellant. 
     The tertiary amine as hypergolic fuel can be employed with a common pressurization source which can be employed to expel an oxidizer into a combustion chamber as illustrated in commonly assigned U.S. Pat. No. 5,133,183. The described features can be within the spirit and scope of this invention. 
     It is to be understood, therefore, that while the present invention has been described by means of specific examples, it should not be limited thereto, for obvious variations and modifications may occur to those skilled in the art and such variations and modifications may be adhered to without departing from the spirit of the invention or the scope of the appended claims.