Title of Invention	"GELLED UDMH FUEL COMPOSITION CONTAINING HYDRAZINE HYDRATE AND THE METHOD OF PREPARATION THEREOF"
Abstract	The invention relates to a gelled-fuel composition and a method of preparation thereof. The gelled fuel composition comprises UDMH (unsymmetrical dimethyl hydrazine) 88-94% by weight; Hydrazine Hydrate in the range of 3-6% by weight; and Methyl Cellulose 3-6% by weight. The gelled fuel of the invention provides overcomes the problems of prior art gelled-fuels i.e., in-homogeneity, reduced propellant mass to the thrusters, reduced volumetric loading and further oxidation of UDMH (unsymmetrical dimethyl hydrazine). The invention also provides for a method to prepare UDMH gel completely devoid of air bubbles, and less prone to oxidation.

Title of Invention

"GELLED UDMH FUEL COMPOSITION CONTAINING HYDRAZINE HYDRATE AND THE METHOD OF PREPARATION THEREOF"

Abstract

The invention relates to a gelled-fuel composition and a method of preparation thereof. The gelled fuel composition comprises UDMH (unsymmetrical dimethyl hydrazine) 88-94% by weight; Hydrazine Hydrate in the range of 3-6% by weight; and Methyl Cellulose 3-6% by weight. The gelled fuel of the invention provides overcomes the problems of prior art gelled-fuels i.e., in-homogeneity, reduced propellant mass to the thrusters, reduced volumetric loading and further oxidation of UDMH (unsymmetrical dimethyl hydrazine). The invention also provides for a method to prepare UDMH gel completely devoid of air bubbles, and less prone to oxidation.

Full Text	GELLED UDMH FUEL COMPOSITION CONTAINING HYDRAZINE HYDRATE AND THE METHOD OF PREPARATION THEREOF FIELD OF THE INVENTION The invention relates to a gelled-fuel composition and a method of preparation thereof. The invention provides for a gelled fuel which overcomes the problems of prior art gelled-fuels i.e., in-homogeneity, reduced propellant mass to the thrusters, reduced volumetric loading and further oxidation of UDMH (unsymmetrical dimethyl hydrazine). The invention also provides for a simple and inexpensive method to prepare UDMH gel completely devoid of air bubbles, and less prone to oxidation. BACKGROUND AND PRIOR ART OF THE INVENTION The aeration problem of unsymmetrical dimethyl hydrazine gel [hereinafter referred to as "UDMH", having the chemical formula N(CH3)2NH2] has not been reported in publications which discuss about UDMH Gellation. The two references mentioned below discuss about the aeration problem in RP-1 Gels, and oxidation of UDMH. J. W. Morodosky et al. (J. W. Morodosky, B. Q. Zhang, K. K. Kuo, F. Tepper, L.A. Kaledin, "Spray Combustion of Gelled RP-1 Propellants Containing Nano-sized Aluminum Particles in Rocket Engine conditions", AIAA-2001-3274) have reported the aeration problem with RP-1 Gels and a method to degas the trapped air bubbles. The method of degassing here is done by preparing samples of RP-1 Gels [composition: RP-1, Aluminum Powder, Fumed silica, and Surfactant] were and placing them in a vacuum chamber at a pressure of 125 mm Hg [abs.] for several hours. The samples obtained were free of air bubbles after the applications of vacuum. The method of degassing discussed in J. W. Morodosky et al. has the following disadvantages: (i) Additional equipments like the vacuum chamber, Vacuum pumps and associated hardware needs to be employed. (ii) The process time for realization of the final product increases significantly. (iii) This method cannot be employed for high vapor pressure liquids like UDMH. (iv) Bulk quantities of gelled propellant are very difficult to degas by this process and may be suited for lab scale application. An attempt was made to remove the air bubbles entrapped in the gels by the application of vacuum up to 100 m Hg [abs.] but it failed to de-gas the UDMH gels. The UDMH Gel samples were subjected to more than 10 Hours of Vacuum but the air bubbles were still present in the samples. This process causes loss of UDMH from the Gel samples and changes characteristics of the gels significantly which is undesirable from the performance aspect. Gellation and rheological characterization of metallized-UDMH and kerosene gels was reported by T. L. Varghese and co-workers (Varghese, T. L., Gaindhar, S. C., John, D. Josekutty, J. Muthiah, Rm., Rao, S. S.., Ninan, K. N., and Krishnamurthy, V.N., "Developmental studies on Metallized UDMH and Kerosene Gels, Defence science Journal, Vol. 45, No. 1, January 1995, pp. 25-30) They discussed a method to avoid the oxidation of UDMH Gels. Performance evaluation and hypergolicity tests of those fuel gels with ^0*4 were also conducted. This process uses Nitrogen blanket to avoid oxidation of UDMH in the initial and final stages of gellation. This method has the following disadvantages: (i) Increases the complexity of the gellation equipment since it calls for additional sealing design. (ii) This method is suitable for lab scale application. This process to reduce oxidation when employed during the gellation of UDMH leaves bubbles in the gels. Munjal et al. [Munjal, N. L., Gupta, B. L., and Mohan Varma, "Preparative and Mechanistic Studies on Unsymmetrical dimethyl Hydrazine-Red Fuming Nitric Acid Liquid Propellant, Explosives, Pyrotechnic 10, 1985, pp. 111-117] studied the effects of various parameters on the gellation process of unloaded and metallized unsymmetrical dimethyl hydrazine (UDMH) and red-fuming nitric acid (RFNA) using optical and photomicrographic techniques. Varma et al. [Varma, M., Gupta, B. L., Panday, M. "Formulation and Storage Studies on Hydrazine based Gelled Propellants", Defence Science Journal, vol. 46, No. 5, 1996, pp. 435-442] experimentally investigated the ability to prepare thixotropic gels of hydrazine-based fuels using various gellants. They also studied critical gellant concentrations, gellation times, the effect of metal additives, and storage characteristics. The rheological properties of gels were found to vary with temperature, and in general, viscosity decreases with increasing temperature. The effect of temperature has been investigated by Gupta et al. and Rahimi and Natan. Gupta et al. indicate that for virgin UDMH-MC gel, for temperatures between 0°C-30°C, the rate index increased from 0.655 to 0.897 and the consistency index decreased from 22.7 to 3 Pa s"n. Doule C.F., ["Gelled Fuel Compositions", US 3,343,931 (1967)] teaches novel means for preparing gelled liquid fuel compositions by admixing finely divide polyoxymethylene polymer e.g. UDMH (1 to ~ 10 wt. %) with a liquid fuel composition. Fujiyoshi Hironobu et. o/.[JP: 09249047 (1997), Publication No. 11082172 A (1999): "Gelling Propellant, its Manufacture and its Cleaning Method"] describes preparation of a gel propellant by adding polyacrylic acid (preferably 0.1-1.0 wt.%) to hydrazine anhydride, and thereby make handling of liquid fuel easy. Kuboto Nobuhiko et. al.[W: 09006990 (1997), Publication No. 10203890 A (1998): "Gelled Propellant Containing Metal"] discloses the method of preparation of a metal-added gel propellant containing fine alloy particles (e.g. Mg-Al) for good ignition ability, improvement in specific impulse and securing the stability of the propellant owing to the gellation. The rheological properties of gel propellants affect several processes in rocket motor operation. This particular character of gels causes various problems that should be addressed. The properties that need to be addressed are: (i) Rheological characterization: Definition of the gel type, measurement of the rheological properties, identification of the parameters that affect their behavior, (ii) Processing. Preparation of gel propellants, gellants, compatibility of the ingredients, (iii) Flow behavior. Flow of shear-thinning fluids in pipes and injectors, thixotropic effect. (iv) Combustion behavior. Measurement of gel fuel droplet burning rates, theoretical modeling (characterization of secondary atomization of metallized slurry/gel fuel droplets), combustion of gel fuels in small motors, ignition. (v) Performance evaluation. Theoretical or experimental evaluations of the performance of different gel propellant formulations for various missions. (vi) Feeding process. In comparison to liquids, increased feed pressures are required for the same propellant mass flow rate. (vii) Atomization process. Atomization of gels is more difficult due to their non-Newtonian character. This can also result in reduced performance, and a longer combustion chamber (increased weight) is required. (viii) Burning process. Gel fuel droplets burn at a lower burning rate than the same fuel liquid-state droplets. This, in addition to the probably coarser spray, may also reduce the combustion efficiency. Moreover, increasing the gellant content results in increased burning residue and performance may decrease76 by 2%-5%. (ix) Particle sedimentation, phase separation and physical instabilities. These may occur during storage or under in-flight acceleration. Although in comparison to slurries particle sedimentation is significantly lower, at high acceleration levels the solid particles and even the solid phase gellant may separate from the liquid. (x) Cost. Gels are more expensive than both conventional liquids and solid propellants. The price of a gel propellant can be 30% higher or more than the price of a solid propellant. Considering these problems, research has been conducted in several areas. The present invention theoretically evaluates the performance UDMH gel in terms of Isp (due to the addition of Hydrazine Hydrate), the rate of exudation of air bubbles in UDMH gel (higher with higher concentrations of Hydrazine Hydrate) thereby also increasing the shelf life of the gelled fuel. OBJECTS OF THE INVENTION The primary object of the invention is to provide for a UDMH gelled fuel composition devoid of air bubbles and prone to less oxidation. Another object of the invention is to provide for a method for the preparation of homogenous UDMH gelled fuel composition devoid of air bubbles and prone to less oxidation. SUMMARY OF THE INVENTION The present invention relates to a gelled fuel composition comprising: UDMH (unsymmetrical dimethyl hydrazine) 88-94% by weight; Hydrazine Hydrate in the range of 3-6% by weight; and Methyl Cellulose 3-6% by weight. In a preferred embodiment of the invention the gelled fuel composition comprises UDMH is 91% by wt, Hydrazine Hydrate is 5% by wt. and Methyl Cellulose is 4% by wt. In accordance with the embodiments of the invention Methyl Cellulose in the gelled fuel composition is in the range of 3-6% by weight, more preferably 4% by weight. The invention also relates to a method for the preparation of homogeneous gelled fuel composition comprising: (a) mixing UDMH and Hydrazine Hydrate; (b) cooling the reaction mixture of step (a) to 0-4°C; (c) adding methyl cellulose to the cooled mixture of step (b) with continuous stirring; (d) leaving the resulting product of step (c) undisturbed till the formation of a clear gel devoid of air bubbles. In accordance with the various embodiments of the invention the reaction mixture of step (a) is cooled preferably for at least 2 hours, the cooled mixture of step (b) is stirred preferably for 30 minutes and/or the product of step (c) is left undisturbed preferably for a period of 2-4 hours. BRIEF DESCRIPTION OF DRAWINGS: Fig. 1 Specific Impulse (Isp) v/s Mixture Ratio (MR). Fig. 2 Rheogram of Viscosity v/s Shear Rate UDMH/HH (5%)/MC(4%). Fig. 3 Effect of adding Hydrazine Hydrate to UDMH Gel on aeration pattern of the gelled fuel. DETAILED DESCRIPTION OF THE INVENTION The primary rocket engine technology at the present time is the chemical rocket engine, and it is likely to remain the dominant technology for some time to come. All rocket vehicles work on the principle of reaction, or "recoil", which is a consequence of the law of conservation of momentum. When a cannon fires a cannonball, the cannonball flies away with a momentum equal to the mass of the cannonball times its velocity. The shot gives the cannon the same momentum in the opposite direction, and if it were free to move without interference from friction or other constraint, it would fly backward, with a velocity less than that of the cannonball by the same factor that the cannon's mass is greater than the cannonball. There's a popular misconception that a rocket vehicle "pushes against the air", but that's not the case. It pushes against itself, using the recoil of the hot gases shot out the rocket engine exhaust to drive itself forward, and the air just gets in the way, causing drag and friction. Heavier the mass of the exhaust flow and greater the velocity of that flow, greater would be the recoil generated by the rocket engine and therefore greater the thrust. There are various ways to generate this thrust, though in all cases the result is the same, to expel a gas at high velocity. Nuclear rocket engines run a fluid through a nuclear reactor. Electric rocket engines accelerate ions to high velocities using electrified grids. Chemical rocket engines, burn a "fuel" and an "oxidizer", either in a solid mixture or stored as liquids in separate tanks, and blast the exhaust out a usually bell-shaped ("convergent-divergent" or "con-di") nozzle. Rocket engine thrust is formally measured in newtons (N) in the metric system; in pounds force (Ibf) in the English system; and sometimes in kilograms force (kgp, where the "p" stands for the French "puissance / force"). Efficiency of a rocket engine can be measured in terms of exhaust velocity, but since the actual thrust is also dependent on the mass of the exhaust gas, a more useful measure is "specific impulse (Isp)", or thrust produced by a unit mass of propellant per second. In metric units, Isp is defined as "Newtons per kilogram of propellant per second", and in English units it is defined as "pounds thrust per pound of propellant per second". The second definition, by the way, evaluates to "seconds", and that's normally how specific impulse is described. Specific impulse can be taken as an index of the "mass ratio" of a rocket vehicle, or the ratio of payload to vehicle mass: the higher the specific impulse, the greater the efficiency in terms of the amount of payload per fuel mass. When the thrust and the flow rate remain constant throughout the burning of the propellant, the specific impulse is the time for which the rocket engine provides a thrust equal to the weight of the propellant consumed. Gelled propellant systems offer a number of advantages in comparison to neat-liquid-propellant systems. These benefits include improved safety in storage and handling; better compliance with insensitive munitions (IM) requirements; lower toxicity and fire hazards; reduced leakage, spillage, and slosh problems; and higher energy density (when solids loaded). In addition, their inherent thrust-modulation capability provides excellent application flexibility for utilization in smart tactical missiles, divert and attitude-control systems, advanced launch-vehicle boosters and upper stages, sustainer engines for endo/exoatmospheric interceptors, pilot-seat ejection systems and air-breathing propulsion systems. The key to gel propellant science and technology is rheology. The rheological properties of a gel control its combustion, atomization and flow characteristics. These properties depend on the chemical structure of the gel. Gel propulsion systems employ gelled propellants for generating hot gases which in turn imparts propulsive power to the missile/launch vehicles. Gellation of fuels can be achieved with a suitable polymeric gellant at lower concentrations. UDMH gellation with Methyl Cellulose has been reported in prior art. It is observed that the Methyl Cellulose gels UDMH but is prone to severe aeration which worsens with time. The effects of aeration are: 1. non-homogeneous propellant formulation, 2. reduced propellant mass to the thrusters, 3. reduced volumetric loading of the propellant, which has direct bearing on the volume limited propulsion systems, 4. further oxidation of UDMH results in depletion of available UDMH in the propellant. The subject matter of the invention discloses a gelled fuel composition to achieve UDMH gel devoid of air bubbles, which eliminates the problems mentioned above. Gelled-fuel Composition (UDMH/MC/HH) The gelled fuel composition of the invention is prepared by incorporating Hydrazine Hydrate to the UDMH before the addition of Methyl cellulose (as depicted on Table-1 below): Table-1 (Table Remove) Method for the preparation of Gelled-fuel Composition (UDMH/MC/HH) UDMH [91% w/w] and Hydrazine Hydrate [5% w/w] are mixed in a three necked round bottom glass vessel, with slow and steady purging of nitrogen. The vessel and its contents are cooled to 0-4°C to reduce evaporation loss. The contents are stirred by using mechanical stirrer with a marine impeller and addition of methyl cellulose [4% w/w] is carried out sequentially with continuous stirring for 30 minutes. This mixture is left undisturbed for a period of 2-4 hours (preferably 2 hours) which resulted in formation of a clear gel devoid of air bubbles. The rate of oxidation is drastically reduced by addition of Hydrazine Hydrate which increases the storage life of the gel. With reference to Fig. 1 it can be seen that the addition of Hydrazine Hydrate 2.5% reduces the lsp by approximately 2sec. which has been theoretically evaluated. The rate of exudation of air bubbles is higher with higher concentrations of Hydrazine Hydrate. Higher concentrations of Hydrazine Hydrate in UDMH gel results in marginal decrease in performance which can be seen in the Fig. I. The Rheogram in Fig. 2 shows the pseudoplastic behavior of the UDMH/HH/MC gel. Rheological studies on unsymmetrical dimethyl hydrazine-methyl cellulose gelled system have been conducted under varying shear rates in order to establish its flow characteristics. The gel is found to behave as a pseudoplastic thixotrop. An increase in shear rate decreases the apparent viscosity significantly. The Viscosity of the Gel drops from 11000 cP to 3000 cP over a shear rate range of 1-100 sec"1. The effect of adding Hydrazine Hydrate to UDMH Gel on aeration pattern of the gelled fuel is apparent in Fig. 3. Tube-A which does not contain Hydrazine Hydrate shows severe oxidation and aeration problem. Other tubes (B, C and D) contain increasing amounts of Hydrazine Hydrate (2.5, 5 and 7.5% by wt. respectively). The following examples and experiments are provided to illustrate the invention in detail and are not to limit the scope of the claims of the invention. Example 1 The gelled fuel composition of the invention is prepared by incorporating Hydrazine Hydrate to the UDMH before the addition of Methyl cellulose (as depicted in Table-2 below): (Table Remove) Example 2 Method for the preparation of Gelled-fuel Composition (UDMH/MC/HH) UDMH and Hydrazine Hydrate are mixed in a three necked round bottom glass vessel, with slow and steady purging of nitrogen. The vessel and its contents are cooled to 0-4°C to reduce evaporation loss. The contents are stirred by using mechanical stirrer with a marine impeller and addition of methyl cellulose is carried out subsequently with continuous stirring for 30 minutes. This mixture is left undisturbed for a period of 2-4 hours (preferably 2 hours) which results in formation of a clear gel devoid of air bubbles. The rate of oxidation is drastically reduced by addition of Hydrazine Hydrate which increases the storage life of the gel. MAIN ADVANTAGES OF THE INVENTION 1. The addition of Hydrazine Hydrate (HH) to the gelled fuel composition (UDMH/MC) drastically reduces the rate of oxidation, as shown in Fig. 3. 2. The reduction in the rate of oxidation in turn increases the shelf life of the gelled fuel. 3. Using UDMH gel as fuel is beneficial over other gel-based fuels as it is economic (i.e. less expensive) and has more availability in India. References: 1. J. W. Morodosky, B. Q. Zhang, K. K. Kuo, F. Tepper, L.A. Kaledin, "Spray Combustion of Gelled RP-1 Propellants Containing Nano-sized Aluminum Particles in Rocket Engine conditions", A1AA-2001-3274. Varghese, T. L., Gaindhar, S. C., John, D. Josekutty, J. Muthiah, Rm., Rao, S. S.., Ninan, K. N., and Krishnamurthy, V.N., "Developmental studies on Metallized UDMH and Kerosene Gels, Defence science Journal, Vol. 45, No. 1, January 1995, pp. 25-30. Munjal, N. L., Gupta, B. L., and Mohan Varma, "Preparative and Mechanistic Studies on Unsymmetrical dimethyl Hydrazine-Red Fuming Nitric Acid Liquid Propellant, Explosives, Pyrotechnic 10, 1985, pp. 111-117. Varma, M., Gupta, B. L., Panday, M. "Formulation and Storage Studies on Hydrazine based Gelled Propellants", Defence Science Journal, vol. 46, No. 5, 1996, pp. 435-442. Doyle, C.F., "Gelled Fuel Compositions", US 3343931, Sept 26, 1967. Atkins, B. L., and Harper, B. J. "Gelled Hydrazine", US 3359144, Dec. 19, 1967. Vander Wall, E. M., "Gelation of Hydrazine and Hydrazine-Type Rocket Fuels", US 3751311, Aug. 7, 1973. Burdette, G.W, Couch, D. H., "Gelled Amine Rocket Fuels", US 3650857, Mar. 21, 1972. Rau, E., and Warren, D., "Pseudo-plastic Rocket Propellants Containing Hydrazines with Hydroxypropyl Cellulose Ether", US 3492177, Jan. 27, 1970. Hodge, K. Crofoot, T., and Nelson, S., "Gelled Propellants for Tactical missile Applications," AIAA Paper 99-2976, 1999. Natan, B., Rahimi, S., "The Status of Gel Propellant in the Year 2000", Kuo, K. K., DeLuca, L. T., eds., combustion of Energetic Materials, Begell House, 2002. We Claim: 1. A gelled fuel composition comprising: UDMH (unsymmetrical dimethyl hydrazine) 88-94% by weight; Hydrazine Hydrate in the range of 3-6% by weight; and Methyl Cellulose 3-6% by weight. 2. The composition as claimed in claim 1, wherein UDMH is 91% by wt., Hydrazine Hydrate is 5% by wt. and methyl cellulose is 4% by wt. 3. The composition as claimed in claim 1, wherein Methyl Cellulose is present in an amount of 4% by weight. 4. A method for the preparation of homogeneous gelled fuel composition comprising: a. mixing UDMH and Hydrazine Hydrate; b. cooling the reaction mixture of step (a) to 0-4°C; c. adding methyl cellulose to the cooled mixture of step (b) with continuous stirring; d. leaving the resulting product of step (c) undisturbed till the formation of a clear gel devoid of air bubbles. 5. The method as claimed in claim 4, wherein the reaction mixture of step (a) is cooled for at least 2 hours. 6. The method as claimed in any preceding claims, wherein the cooled mixture of step (b) is stirred for about 30 minutes. 7. The method as claimed in any preceding claims, wherein the product of step (c) is left undisturbed for a period of 2-4 hours. 8. A gelled fuel composition substantially as hereinbefore described and with reference to the foregoing examples and accompanying drawings 9. A method for the preparation of homogeneous gelled fuel composition substantially as hereinbefore described and with reference to the foregoing examples and accompanying drawings.

Full Text

GELLED UDMH FUEL COMPOSITION CONTAINING HYDRAZINE HYDRATE AND THE METHOD OF PREPARATION THEREOF FIELD OF THE INVENTION
The invention relates to a gelled-fuel composition and a method of preparation thereof. The invention provides for a gelled fuel which overcomes the problems of prior art gelled-fuels i.e., in-homogeneity, reduced propellant mass to the thrusters, reduced volumetric loading and further oxidation of UDMH (unsymmetrical dimethyl hydrazine). The invention also provides for a simple and inexpensive method to prepare UDMH gel completely devoid of air bubbles, and less prone to oxidation. BACKGROUND AND PRIOR ART OF THE INVENTION
The aeration problem of unsymmetrical dimethyl hydrazine gel [hereinafter referred to as "UDMH", having the chemical formula N(CH3)2NH2] has not been reported in publications which discuss about UDMH Gellation. The two references mentioned below discuss about the aeration problem in RP-1 Gels, and oxidation of UDMH.
J. W. Morodosky et al. (J. W. Morodosky, B. Q. Zhang, K. K. Kuo, F. Tepper, L.A. Kaledin, "Spray Combustion of Gelled RP-1 Propellants Containing Nano-sized Aluminum Particles in Rocket Engine conditions", AIAA-2001-3274) have reported the aeration problem with RP-1 Gels and a method to degas the trapped air bubbles. The method of degassing here is done by preparing samples of RP-1 Gels [composition: RP-1, Aluminum Powder, Fumed silica, and Surfactant] were and placing them in a vacuum chamber at a pressure of 125 mm Hg [abs.] for several hours. The samples obtained were free of air bubbles after the applications of vacuum. The method of degassing discussed in J. W. Morodosky et al. has the following disadvantages:
(i) Additional equipments like the vacuum chamber, Vacuum pumps and associated hardware needs to be employed.
(ii) The process time for realization of the final product increases significantly.
(iii) This method cannot be employed for high vapor pressure liquids like UDMH.
(iv) Bulk quantities of gelled propellant are very difficult to degas by this process and may be suited for lab scale application.

An attempt was made to remove the air bubbles entrapped in the gels by the application of vacuum up to 100 m Hg [abs.] but it failed to de-gas the UDMH gels. The UDMH Gel samples were subjected to more than 10 Hours of Vacuum but the air bubbles were still present in the samples. This process causes loss of UDMH from the Gel samples and changes characteristics of the gels significantly which is undesirable from the performance aspect.
Gellation and rheological characterization of metallized-UDMH and kerosene gels was reported by T. L. Varghese and co-workers (Varghese, T. L., Gaindhar, S. C., John, D. Josekutty, J. Muthiah, Rm., Rao, S. S.., Ninan, K. N., and Krishnamurthy, V.N., "Developmental studies on Metallized UDMH and Kerosene Gels, Defence science Journal, Vol. 45, No. 1, January 1995, pp. 25-30) They discussed a method to avoid the oxidation of UDMH Gels. Performance evaluation and hypergolicity tests of those fuel gels with ^0*4 were also conducted. This process uses Nitrogen blanket to avoid oxidation of UDMH in the initial and final stages of gellation. This method has the following disadvantages:
(i) Increases the complexity of the gellation equipment since it calls for additional sealing design.
(ii) This method is suitable for lab scale application.
This process to reduce oxidation when employed during the gellation of UDMH leaves bubbles in the gels.
Munjal et al. [Munjal, N. L., Gupta, B. L., and Mohan Varma, "Preparative and Mechanistic Studies on Unsymmetrical dimethyl Hydrazine-Red Fuming Nitric Acid Liquid Propellant, Explosives, Pyrotechnic 10, 1985, pp. 111-117] studied the effects of various parameters on the gellation process of unloaded and metallized unsymmetrical dimethyl hydrazine (UDMH) and red-fuming nitric acid (RFNA) using optical and photomicrographic techniques.
Varma et al. [Varma, M., Gupta, B. L., Panday, M. "Formulation and Storage Studies on Hydrazine based Gelled Propellants", Defence Science Journal, vol. 46, No. 5, 1996, pp. 435-442] experimentally investigated the ability to prepare thixotropic gels of hydrazine-based fuels using various gellants. They also studied critical gellant concentrations, gellation times, the effect of metal additives, and storage characteristics.
The rheological properties of gels were found to vary with temperature, and in general, viscosity decreases with increasing temperature. The effect of temperature has

been investigated by Gupta et al. and Rahimi and Natan. Gupta et al. indicate that for virgin UDMH-MC gel, for temperatures between 0°C-30°C, the rate index increased from 0.655 to 0.897 and the consistency index decreased from 22.7 to 3 Pa s"n.
Doule C.F., ["Gelled Fuel Compositions", US 3,343,931 (1967)] teaches novel means for preparing gelled liquid fuel compositions by admixing finely divide polyoxymethylene polymer e.g. UDMH (1 to ~ 10 wt. %) with a liquid fuel composition.
Fujiyoshi Hironobu et. o/.[JP: 09249047 (1997), Publication No. 11082172 A (1999): "Gelling Propellant, its Manufacture and its Cleaning Method"] describes preparation of a gel propellant by adding polyacrylic acid (preferably 0.1-1.0 wt.%) to hydrazine anhydride, and thereby make handling of liquid fuel easy.
Kuboto Nobuhiko et. al.[W: 09006990 (1997), Publication No. 10203890 A (1998): "Gelled Propellant Containing Metal"] discloses the method of preparation of a metal-added gel propellant containing fine alloy particles (e.g. Mg-Al) for good ignition ability, improvement in specific impulse and securing the stability of the propellant owing to the gellation.
The rheological properties of gel propellants affect several processes in rocket motor operation. This particular character of gels causes various problems that should be addressed. The properties that need to be addressed are:
(i) Rheological characterization: Definition of the gel type, measurement of the
rheological properties, identification of the parameters that affect their behavior, (ii) Processing. Preparation of gel propellants, gellants, compatibility of the
ingredients, (iii) Flow behavior. Flow of shear-thinning fluids in pipes and injectors,
thixotropic effect.
(iv) Combustion behavior. Measurement of gel fuel droplet burning rates, theoretical modeling (characterization of secondary atomization of metallized slurry/gel fuel droplets), combustion of gel fuels in small motors, ignition.
(v) Performance evaluation. Theoretical or experimental evaluations of the
performance of different gel propellant formulations for various missions.

(vi) Feeding process. In comparison to liquids, increased feed pressures are
required for the same propellant mass flow rate.
(vii) Atomization process. Atomization of gels is more difficult due to their non-Newtonian character. This can also result in reduced performance, and a longer combustion chamber (increased weight) is required.
(viii) Burning process. Gel fuel droplets burn at a lower burning rate than the same fuel liquid-state droplets. This, in addition to the probably coarser spray, may also reduce the combustion efficiency. Moreover, increasing the gellant content results in increased burning residue and performance may decrease76 by 2%-5%.
(ix) Particle sedimentation, phase separation and physical instabilities. These may occur during storage or under in-flight acceleration. Although in comparison to slurries particle sedimentation is significantly lower, at high acceleration levels the solid particles and even the solid phase gellant may separate from the liquid.
(x) Cost. Gels are more expensive than both conventional liquids and solid propellants. The price of a gel propellant can be 30% higher or more than the price of a solid propellant.
Considering these problems, research has been conducted in several areas. The present invention theoretically evaluates the performance UDMH gel in terms of Isp (due to the addition of Hydrazine Hydrate), the rate of exudation of air bubbles in UDMH gel (higher with higher concentrations of Hydrazine Hydrate) thereby also increasing the shelf life of the gelled fuel. OBJECTS OF THE INVENTION
The primary object of the invention is to provide for a UDMH gelled fuel composition devoid of air bubbles and prone to less oxidation.
Another object of the invention is to provide for a method for the preparation of homogenous UDMH gelled fuel composition devoid of air bubbles and prone to less oxidation. SUMMARY OF THE INVENTION
The present invention relates to a gelled fuel composition comprising: UDMH (unsymmetrical dimethyl hydrazine) 88-94% by weight; Hydrazine Hydrate in the range of 3-6% by weight;

and Methyl Cellulose 3-6% by weight.
In a preferred embodiment of the invention the gelled fuel composition comprises UDMH is 91% by wt, Hydrazine Hydrate is 5% by wt. and Methyl Cellulose is 4% by wt.
In accordance with the embodiments of the invention Methyl Cellulose in the gelled fuel composition is in the range of 3-6% by weight, more preferably 4% by weight.
The invention also relates to a method for the preparation of homogeneous gelled fuel composition comprising:
(a) mixing UDMH and Hydrazine Hydrate;
(b) cooling the reaction mixture of step (a) to 0-4°C;
(c) adding methyl cellulose to the cooled mixture of step (b) with
continuous stirring;
(d) leaving the resulting product of step (c) undisturbed till the formation of
a clear gel devoid of air bubbles.
In accordance with the various embodiments of the invention the reaction mixture of step (a) is cooled preferably for at least 2 hours, the cooled mixture of step (b) is stirred preferably for 30 minutes and/or the product of step (c) is left undisturbed preferably for a period of 2-4 hours. BRIEF DESCRIPTION OF DRAWINGS: Fig. 1 Specific Impulse (Isp) v/s Mixture Ratio (MR). Fig. 2 Rheogram of Viscosity v/s Shear Rate UDMH/HH (5%)/MC(4%). Fig. 3 Effect of adding Hydrazine Hydrate to UDMH Gel on aeration pattern of the
gelled fuel. DETAILED DESCRIPTION OF THE INVENTION
The primary rocket engine technology at the present time is the chemical rocket engine, and it is likely to remain the dominant technology for some time to come. All rocket vehicles work on the principle of reaction, or "recoil", which is a consequence of the law of conservation of momentum. When a cannon fires a cannonball, the cannonball flies away with a momentum equal to the mass of the cannonball times its velocity. The shot gives the cannon the same momentum in the opposite direction, and if it were free to move without interference from friction or other constraint, it would

fly backward, with a velocity less than that of the cannonball by the same factor that the cannon's mass is greater than the cannonball.
There's a popular misconception that a rocket vehicle "pushes against the air", but that's not the case. It pushes against itself, using the recoil of the hot gases shot out the rocket engine exhaust to drive itself forward, and the air just gets in the way, causing drag and friction. Heavier the mass of the exhaust flow and greater the velocity of that flow, greater would be the recoil generated by the rocket engine and therefore greater the thrust.
There are various ways to generate this thrust, though in all cases the result is the same, to expel a gas at high velocity. Nuclear rocket engines run a fluid through a nuclear reactor. Electric rocket engines accelerate ions to high velocities using electrified grids. Chemical rocket engines, burn a "fuel" and an "oxidizer", either in a solid mixture or stored as liquids in separate tanks, and blast the exhaust out a usually bell-shaped ("convergent-divergent" or "con-di") nozzle.
Rocket engine thrust is formally measured in newtons (N) in the metric system; in pounds force (Ibf) in the English system; and sometimes in kilograms force (kgp, where the "p" stands for the French "puissance / force").
Efficiency of a rocket engine can be measured in terms of exhaust velocity, but since the actual thrust is also dependent on the mass of the exhaust gas, a more useful measure is "specific impulse (Isp)", or thrust produced by a unit mass of propellant per second. In metric units, Isp is defined as "Newtons per kilogram of propellant per second", and in English units it is defined as "pounds thrust per pound of propellant per second". The second definition, by the way, evaluates to "seconds", and that's normally how specific impulse is described. Specific impulse can be taken as an index of the "mass ratio" of a rocket vehicle, or the ratio of payload to vehicle mass: the higher the specific impulse, the greater the efficiency in terms of the amount of payload per fuel mass. When the thrust and the flow rate remain constant throughout the burning of the propellant, the specific impulse is the time for which the rocket engine provides a thrust equal to the weight of the propellant consumed.
Gelled propellant systems offer a number of advantages in comparison to neat-liquid-propellant systems. These benefits include improved safety in storage and handling; better compliance with insensitive munitions (IM) requirements; lower toxicity and fire hazards; reduced leakage, spillage, and slosh problems; and higher

energy density (when solids loaded). In addition, their inherent thrust-modulation capability provides excellent application flexibility for utilization in smart tactical missiles, divert and attitude-control systems, advanced launch-vehicle boosters and upper stages, sustainer engines for endo/exoatmospheric interceptors, pilot-seat ejection systems and air-breathing propulsion systems.
The key to gel propellant science and technology is rheology. The rheological properties of a gel control its combustion, atomization and flow characteristics. These properties depend on the chemical structure of the gel.
Gel propulsion systems employ gelled propellants for generating hot gases which in turn imparts propulsive power to the missile/launch vehicles. Gellation of fuels can be achieved with a suitable polymeric gellant at lower concentrations. UDMH gellation with Methyl Cellulose has been reported in prior art. It is observed that the Methyl Cellulose gels UDMH but is prone to severe aeration which worsens with time. The effects of aeration are:
1. non-homogeneous propellant formulation,
2. reduced propellant mass to the thrusters,
3. reduced volumetric loading of the propellant, which has direct bearing on the
volume limited propulsion systems,
4. further oxidation of UDMH results in depletion of available UDMH in the
propellant.
The subject matter of the invention discloses a gelled fuel composition to achieve UDMH gel devoid of air bubbles, which eliminates the problems mentioned above. Gelled-fuel Composition (UDMH/MC/HH)
The gelled fuel composition of the invention is prepared by incorporating Hydrazine Hydrate to the UDMH before the addition of Methyl cellulose (as depicted on Table-1 below):
Table-1 (Table Remove)
Method for the preparation of Gelled-fuel Composition (UDMH/MC/HH)
UDMH [91% w/w] and Hydrazine Hydrate [5% w/w] are mixed in a three necked round bottom glass vessel, with slow and steady purging of nitrogen. The vessel and its contents are cooled to 0-4°C to reduce evaporation loss. The contents are stirred by using mechanical stirrer with a marine impeller and addition of methyl cellulose [4% w/w] is carried out sequentially with continuous stirring for 30 minutes. This mixture is left undisturbed for a period of 2-4 hours (preferably 2 hours) which resulted in formation of a clear gel devoid of air bubbles. The rate of oxidation is drastically reduced by addition of Hydrazine Hydrate which increases the storage life of the gel.
With reference to Fig. 1 it can be seen that the addition of Hydrazine Hydrate 2.5% reduces the lsp by approximately 2sec. which has been theoretically evaluated. The rate of exudation of air bubbles is higher with higher concentrations of Hydrazine Hydrate. Higher concentrations of Hydrazine Hydrate in UDMH gel results in marginal decrease in performance which can be seen in the Fig. I.
The Rheogram in Fig. 2 shows the pseudoplastic behavior of the UDMH/HH/MC gel. Rheological studies on unsymmetrical dimethyl hydrazine-methyl cellulose gelled system have been conducted under varying shear rates in order to establish its flow characteristics. The gel is found to behave as a pseudoplastic thixotrop. An increase in shear rate decreases the apparent viscosity significantly. The Viscosity of the Gel drops from 11000 cP to 3000 cP over a shear rate range of 1-100
sec"1.
The effect of adding Hydrazine Hydrate to UDMH Gel on aeration pattern of the gelled fuel is apparent in Fig. 3. Tube-A which does not contain Hydrazine Hydrate shows severe oxidation and aeration problem. Other tubes (B, C and D) contain increasing amounts of Hydrazine Hydrate (2.5, 5 and 7.5% by wt. respectively).
The following examples and experiments are provided to illustrate the invention in detail and are not to limit the scope of the claims of the invention.
Example 1
The gelled fuel composition of the invention is prepared by incorporating Hydrazine Hydrate to the UDMH before the addition of Methyl cellulose (as depicted in Table-2 below):
(Table Remove)
Example 2
Method for the preparation of Gelled-fuel Composition (UDMH/MC/HH)
UDMH and Hydrazine Hydrate are mixed in a three necked round bottom glass vessel, with slow and steady purging of nitrogen. The vessel and its contents are cooled to 0-4°C to reduce evaporation loss. The contents are stirred by using mechanical stirrer with a marine impeller and addition of methyl cellulose is carried out subsequently with continuous stirring for 30 minutes. This mixture is left undisturbed for a period of 2-4 hours (preferably 2 hours) which results in formation of a clear gel devoid of air bubbles. The rate of oxidation is drastically reduced by addition of Hydrazine Hydrate which increases the storage life of the gel. MAIN ADVANTAGES OF THE INVENTION
1. The addition of Hydrazine Hydrate (HH) to the gelled fuel composition
(UDMH/MC) drastically reduces the rate of oxidation, as shown in Fig. 3.
2. The reduction in the rate of oxidation in turn increases the shelf life of the
gelled fuel.
3. Using UDMH gel as fuel is beneficial over other gel-based fuels as it is
economic (i.e. less expensive) and has more availability in India.
References:
1. J. W. Morodosky, B. Q. Zhang, K. K. Kuo, F. Tepper, L.A. Kaledin, "Spray Combustion of Gelled RP-1 Propellants Containing Nano-sized Aluminum Particles in Rocket Engine conditions", A1AA-2001-3274.
Varghese, T. L., Gaindhar, S. C., John, D. Josekutty, J. Muthiah, Rm., Rao, S.
S.., Ninan, K. N., and Krishnamurthy, V.N., "Developmental studies on
Metallized UDMH and Kerosene Gels, Defence science Journal, Vol. 45, No. 1,
January 1995, pp. 25-30.
Munjal, N. L., Gupta, B. L., and Mohan Varma, "Preparative and Mechanistic
Studies on Unsymmetrical dimethyl Hydrazine-Red Fuming Nitric Acid Liquid
Propellant, Explosives, Pyrotechnic 10, 1985, pp. 111-117.
Varma, M., Gupta, B. L., Panday, M. "Formulation and Storage Studies on
Hydrazine based Gelled Propellants", Defence Science Journal, vol. 46, No. 5,
1996, pp. 435-442.
Doyle, C.F., "Gelled Fuel Compositions", US 3343931, Sept 26, 1967.
Atkins, B. L., and Harper, B. J. "Gelled Hydrazine", US 3359144, Dec. 19,
1967.
Vander Wall, E. M., "Gelation of Hydrazine and Hydrazine-Type Rocket
Fuels", US 3751311, Aug. 7, 1973.
Burdette, G.W, Couch, D. H., "Gelled Amine Rocket Fuels", US 3650857, Mar.
21, 1972.
Rau, E., and Warren, D., "Pseudo-plastic Rocket Propellants Containing
Hydrazines with Hydroxypropyl Cellulose Ether", US 3492177, Jan. 27, 1970.
Hodge, K. Crofoot, T., and Nelson, S., "Gelled Propellants for Tactical missile
Applications," AIAA Paper 99-2976, 1999.
Natan, B., Rahimi, S., "The Status of Gel Propellant in the Year 2000", Kuo, K.
K., DeLuca, L. T., eds., combustion of Energetic Materials, Begell House, 2002.

We Claim:
1. A gelled fuel composition comprising:
UDMH (unsymmetrical dimethyl hydrazine) 88-94% by weight; Hydrazine Hydrate in the range of 3-6% by weight; and Methyl Cellulose 3-6% by weight.
2. The composition as claimed in claim 1, wherein UDMH is 91% by wt., Hydrazine
Hydrate is 5% by wt. and methyl cellulose is 4% by wt.
3. The composition as claimed in claim 1, wherein Methyl Cellulose is present in an
amount of 4% by weight.
4. A method for the preparation of homogeneous gelled fuel composition comprising:
a. mixing UDMH and Hydrazine Hydrate;
b. cooling the reaction mixture of step (a) to 0-4°C;
c. adding methyl cellulose to the cooled mixture of step (b) with
continuous stirring;
d. leaving the resulting product of step (c) undisturbed till the formation of
a clear gel devoid of air bubbles.
5. The method as claimed in claim 4, wherein the reaction mixture of step (a) is cooled
for at least 2 hours.
6. The method as claimed in any preceding claims, wherein the cooled mixture of step
(b) is stirred for about 30 minutes.
7. The method as claimed in any preceding claims, wherein the product of step (c) is
left undisturbed for a period of 2-4 hours.
8. A gelled fuel composition substantially as hereinbefore described and with
reference to the foregoing examples and accompanying drawings
9. A method for the preparation of homogeneous gelled fuel composition substantially
as hereinbefore described and with reference to the foregoing examples and
accompanying drawings.

Documents:

http://ipindiaonline.gov.in/patentsearch/GrantedSearch/viewdoc.aspx?id=eblp30Iubb2WprsdukmiHw==&loc=+mN2fYxnTC4l0fUd8W4CAA==

« Previous Patent

Next Patent »

Patent Number

268644

Indian Patent Application Number

7/DEL/2007

PG Journal Number

37/2015

Publication Date

11-Sep-2015

Grant Date

09-Sep-2015

Date of Filing

02-Jan-2007

Name of Patentee

THE DIRECTOR GENERAL, DEFENCE RESEARCH AND DEVELOPMENT ORGANIZATION

Applicant Address

MINISTRY OF DEFENCE, GOVERNMENT OF INDIA, WEST BLOCK-8, WING -1, R.K. PURAM, NEW DELHI-110066, INDIA

Inventors:

#	Inventor's Name	Inventor's Address
1	WARAD SHSRIKANT MAHADEV .	DRDL, HYDERABAD, INDIA
2	D. JAYARAMAN	DRDL, HYDERABAD, INDIA
3	S. SESHADRI	DRDL, HYDERABAD, INDIA
4	M. SAMBASIVA RAO	DRDL, HYDERABAD, INDIA
5	M. S. RAJU	DRDL, HYDERABAD, INDIA

PCT International Classification Number

C06B33/00; C06B45/02; C06B47/08

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA