Metallised gel propellants offer higher specific impulse and volumetric loading, reduced vaporisation loss, spillage and slosh problems and easy storage in comparison to the conventional liquid propellants. Theoretical performance analysis of gel propellant containing Al in unsymmetrical dimethyl hydrazine-dinitrogen tetroxide (UDMH-N/sub 2/O/sub 4} system shows peak Isp (vacuum condition) of 316.7 s and 318.3 s at oxidiser/fuel (O/f) ratios of 1.5 and 1.0, respectively for 30 per cent and 40 per cent UDMH-Al gel propellants, under standard conditions. The effect of other parameters like area ratio and chamber pressure on performance has been brought out in view of mission oriented applications. Aluminium has been found to be a better choice over magnesium in metallised gel propellants. Experimental studies on UDMH gellation using propellant grade (15 micrometer)and pyrotechnic grade (1.5 micrometer)Al in 500g batch level show that gellant(methyl cellulose) concentration could be reduced by 50 percent using pyrotechnic grade Al. The pseudoplastic-thixotropic behaviour, flow rate through die holes, burst pressure tests and bulk density are studied. UDMH -25 to 30 per cent Al gels with both grades of Al are found to be stable, pseudoplastic (shear thinning) and thixotropic (time-dependent shear thinning), but their flow pattern through die holes differ in nature

Krishnamurthy, V. N.

Ninan, K. N.

Prabhakaran, N.

Rao, S. S.

Subramanian, S.

Thanki, K. P.

Varghese, T. L.

English

Defence Science Journal

Defence Science Journal, Vol49, No 1, January 1999, pp. 71-78 Q 1999, DESIDOC Performance Evaluation and Experimental Studies on Metallised Gel Propellants T. L. Varghese, N. Prabhakaran, K. P. Thanki, S. Subramanian S. S. Rao, K. N. Ninan and V. N. Krishnamurthy Vikram Sarabhai Space Centre, Thiruvananthapuram - 695 022. ABSTRACT Metallised gel propellants offer higher specific impulse and volumetric loading, reduced vaporisation loss, spillage and slosh problems and easy storage in comparison to the conventional 'liquid propellants. Theoretical performance analysis of gel propellant containing A1 in unsymmetrical dimethyl hydrazine-dinitrogen tetroxide (UDMH-N204) system shows peak Isp (vacuum condition) of 3 16.7 s and 3 18.3 s at oxidiser /fuel (OR) ratios of 1.5 and 1 .O, respectively for 30 per cent and 40 per cent UDMH-AIgel propellants, under standard conditions. The effect of other parameters like area ratio and chamber pressure on performance has been brought out in view of mission oriented applications. Aluminium has been found to be a better choice over magnesium in metallised gel propellants. Experimental studies on UDMH gellation using propellant grade (15 pm) and pyrotechnic grade (1.5 pm) A1 in 500 g batch level show that gellant (methyl cellulose) concentration could be reduced by 50 per cent using pyrotechnic grade AI. The pseudoplastic-thixotropic behaviour, flow rate through die holes, burst pressure tests and bulk density are studied. UDMH - 25 to 30 per cent Al gels with both grades of A1 are found to be stable, pseudoplastic (shear thinning) and thixotropic (time-dependent shearthinning), but their flow pattern through die holes differ in nature. 1. INTRODUCTION fuel Al has been found to be a better choice over Mg, The axiomatic fact of the propulsion based on its higher performance, easy system is always a demand for high performance. and low cost. As one moves from solids to storable liquids and then to cryogenic propellants, the performance The Srst part of this paper presents the results increases but the storage and handling requirements of detailed thermochemical analysis using Gordon and safety imposes high restrictions. Metallised gel and McRride computer pr~gram4.5 for the calculation propellants belong to a new class of storable liquid of complex chemical equilibrium compositions propellants',2 and offer higher specific impulse with free-energy rninirnisation considerations. (Isp) and volumetric loading, reduced vaporisation program using equilibrium flow loss, spillage and slosh problems and easy storage, in comparison to  the conventional liquid conditions is used for computations. These results are propellants'. They are emerging as a choice used to find the impact of payload on operational candidate for future liquid engines. The metallic launch vehicles. The experimental part details the Received 16 June 1997, revised 21 April 1998 7 1 DEF SCI J, VOL 49, NO 1 ,  JANUARY 1999 development and characterisation of metallised unsymmetrical dimethyl hydrazine (UDMH) gel propellant using propellant grade (15 pm) A1 and pyrotechnic grade (1.5 pm) Al. 2. MATERIALS & METHODS UDMH Unsymmetrical dimethyl hydrazine. Purity: minimum, 98.5 per cent; moisture content: maximum, 0.3 per cent. (Source- Andhra Sugars (P) Ltd., Tanuku , A.P). Dinitrogen tetroxide. Purity: minimum, 99.9 per cent; Fe content: maximum 2 ppm; moisture content: maximum, 0.17 per cent. (Source: Hindustan Organic Chemicals, Bombay). Agar-Agar Sea weed carbohydrate (powder form) having the structure of alternating copolymer 3-linked beta-D-galacto pyranose and 4-linked 3,6, anhydro-alpha-L-galacto pyranose units.(Source: CDH (P) Ltd., Bombay). Cab-o-sil (M5) Trade name of fused silica containing 99 per cent Si02, 1 per cent volatile matter and with particle size of 8 pm. (Source: Cabot Corp., USA). MC Methyl cellulose. Viscosity of 2 per cent aqueous solution at 20 OC is 4000 cps. (Source: SISCO Chemical Industries, Bombay). EC Ethyl cellulose with degree of substitution 2.42 to 2.50. (Source: CDH (P) Ltd., Delhi). HMC Hydroxy methyl cellulose. (Source: CDH (P) Ltd., Delhi). CMC Carboxy methyl celIuIose (sodium salt), assay 99 per cent with degree of substitution 0.7 to 0.8. (Source: CDH (P) Ltd., Delhi. OPC Complex Organophilic clay complex (smectone clay) passing through 200 specific BSS 95 per cent, specific gravity 1.7. (Source: David & Co (P) Ltd., Gujarat). Silicone oil Metroark DM Silicone fluid of viscosity 1000 centistocks (Source: Metroark (P) Ltd., Calcutta). The heat of formation used for the equilibrium flow condition is +12.7 kcallmole for UDMH (C2H$V2), - 4.676 kcallmole for N204 and zero for Al. NASA-SP-273 program using equilibrium flow conditions is used for theoretical computations. 3. PERFORMANCE EVALUATION The actual performance of gel propellant can only be evaluated by static test firing in a liquid engine using small thrustors. However, thennochemical analysis would give a clear picture on the energetics of the gel propellant. A typical UDMH-A1 gel propellant with N204 is analysed under equilibrium conditions. The effect of A1 loading (0-40 %) and oxidiserlfuel (OIF) ratio (0.5 - 4.0) on (Isp) of UDMH-A1 gel with N204 under standard conditions [PJP, = 70, area ratio (AR) =lo] is shown in Fig. 1. When A1 is introduced in UDMH fuel, the maximum performance in Isp is 3 18.3 s with 40 per cent A1 and 3 16.6 s with 30 per cent A1 at OIF ratio of 1.0 and 1.5, respectively as against 263.0 and 287.4 s for virgin UDMH-N204 system. Figure 2 shows that increase in AR from 10 to 500 increases Isp with a marginal shift in OIF ratio. The AR for stage motors differ with altitude for a particular mission. For example, the AR of liquid engine for PSLV second stage and GSLV cryo stage are 30 and 200, respectively. The effect of chamber pressure on Isp shown in Fig. 3 is found to be only marginal over 10 to 60 ksc beyond which the Isp gain is negligible. The combined effect of enhanced Isp and improved density of the gel propellant can boost the payload capability of launch vehicles. Data analysis has shown that for an operational launch vehicle like PSLV which has, earth storable liquid propellant in the second stage of 37.5 tonnes, VARGHESE, et al: PERFORMANCE EVALUATION OF METALLISED GEL PROPELLANTS u STANDARD CONDITIONS O/F = 0.5 250 (PC / Pe =lo, A.R=101 0 5 10 15 20 25 30 35 40 ALUMINIUM LOADING (%I Figure 1. Effect of O/F ratio and A1 loading on the performance of UDMH-N204 propellant. substituted with UDMH-A1 gel propellant, the payload gain is 20 per cent (260 kg). 4. GELATION EXPERIMENTS Gelation experiments6 were conducted at 15-20 "C in a sealed reaction kettle fitted with high speed emulsifier. UDMH was charged to the kettle and then cooled to 15-20 "C in a water bath using immersion cooler. Methyl cellulose (MC) gellant was added pinch by pinch under mechanical agitation. This was followed by the addition of surfactant (silicone oil) and stepwise addition of A1 powder. The system was kept undisturbed and gelation was found to occur within 30-60 min for propellant grade (15 pm) A1 and 15-30 min for pyrotechnic grade (1.5 pm) AI. Nitrogen gas was purged in the initial and final phase of gelation to avoid air oxidation. The gelation experiments were conducted in 500 g batch level. Table 1. Characteristics of aluminium powder Properties Propellant Pyrotechnic grade grade Purity (96) 99.30 95.00 Volatile matter (%) 0.05 0.25 Coating agent (96) 0.00 1.00 Particle size (pm) 15.00 1.50 Specific surface area (m2/g) 0.10-0.20 2-3 3404 CHAMBER PRESSURE = 70 KSC 330 A1 LOADING 30% n 300 I I 1 1 1.5 2 2.5 OXIDIZER FUEL RATIO Figure 2. Effect o b r e a  ratio and O/F ratio on Isp of UDMH-30 % AI-N204 propellant. Propellant grade (15 pm) A1 and pyrotechnic grade (1.5 pm) A1 were used and the properties of both grades are given in Table 1. The pseudoplastic and thixotropic behaviour of the gels was studied using Brookfield viscometer at different rpm and time intervals. The flow rate of the gel was measured using 500 ml pressure vessel and die holes of 0.45 to 2 mm under nitrogen pressure of 1 to 3 kg f/cm2. Burst pressure tests were also carried out using different diaphragm materials like mylar film, kapton film, copper foil, - - A( LOADING 40 % - + - _.__.-.-.-.-- //- .@-@. A1 LOADING 30 % - / .' O/F = t5 10 20 30 40 50 60 70 80 90 100 CHAMBER PRESSURE (KSC) Figure 3. Effect of chamber pressure on Isp of metallised UDMH-N20d propellant. DEF SCI J, VOL 49, NO 1, JANUARY 1999 SHEAR RATE (rpr) Figure 4. Effect of rpm on viscosity of UDMH-A1 gel etc., as a step for controlling the flow during testing of liquid engine. 5. RESULTS & DISCUSSION Among the hydrocolloid ( Agar-agar, ethyl cellulose, carboxymethyl cellulose (CMC), hydroxymethyl cellulose (HMC)) and particulate (cab-o-sil, organophilic clay complex) gellants, MC was found to be the most suitable gellant for UDMH gelation. The influence of the above gellants on UDMH gelation was detailed earlier6. Small concentration of silicone oil was found to improve the flow characteristics of UDMH-A1 gel. The composition details are given in Table 2. The gellant concentration could be reduced by the use of pyrotechnic grade A1 (1.5 pm) which has larger surface area compared to propellant grade A1 (1 5 pm). 5.1 Pseudoplastic Behaviour The pseudoplastic behaviour of UDMH-A1 gel is shown in Fig. 4. The drastic reduction in viscosity with increase in rpm (a shear rate) is indicative of pseudoplasticity. This is more pronounced in the gel with pyrotechnic grade A1 than the one with propellant grade Al. However, the viscosity values are higher with pyrotechnic' grade A1 and hence, proper consistency and stability of the gel was achieved with 25 per cent metal loading. mEw Figure 5. Time dependency and rpm on viscosity of UDMH-A1 gel. 5.2 Thixotropic Behaviour The time dependency on viscosity of UDMH-A1 gel is shown in Fig. 5. Here also the reduction in viscosity is more distinct with the gel containing pyrotechnic grade Al. The changes in viscosity with time is more at lower rpm than at higher rpm. These results show that UDMH-A1 gel with pyrotechnic grade A1 is more pseudoplastic and thixotropic than the one with propellant grade Al. 5.3 Gel Flow Rate The flow rate data of UDMH-A1 gel is shown in Table 3. Die hole diameters of 0.45 to 2 mm were used at applied pressure range 0.5-2.0 kg f/cm2. Though the gel with pyrotechnic grade A1 was expected to give higher flow rate due to smaller particle size, flow rate was found to be very poor. While the gel with propellant grade A1 flows through 0.75 mm die hole at 2 kg f/cm2, the gel with pyrotechnic grade AZ shows a slower rate even through 2 mm die hole at the same pressure. This could be attributed to the flat nature of the particles of pyrotechnic grade A1 even though that have low Table 2. Compostions of UDMH-A1 gel Composition - UDMH-A1 gel With propellant With pyrotechnic grade A1 grade A1 1 2 UDMH (%) 67.2 68.2 73.0 MC (%) 2.1 0.7 1 .O Silicone oil (%) 0.7 1 .O 1.0 A1 powder (%) 30.0 30.0 25.0 VARGHESE, et al: PERFORMANCE EVALUATION OF MlXALLISED GEL PROPELLANTS Table 3. Flow rate of UDMH-A1 gel Flow rate (gtmin) Applied pressure Die hole Number of holes (kg flcm2) (mm) 30 % (propellant grade) 25 5% (pyrotechnic grade) 15 prn AI 1.5 pm A1 0.5-3.0 0.45 1 0 0 0.5- 1 .O 0.75 1 0 0 2.0 0.75 1 27 0 0.5 1 .O 3 72 0 1 .O 1 .O 3 224 0 1.0 2.0 3 720 0 2.0 2.0 3 1 40 average particle size (expressed as that of the which is higher by 37 per cent over UDMH fuel. equivalent sphere), compared to propellant grade For the same tankage volume of UDMH-N204, this Al. Hence UDMH gel with propellant grade Al is higher bulk density of metallised system enhances superior to the one with pyrotechnic grade A1 wrt the propellant loading by 20 per cent and density flow characteristics. impulse by 17 per cent. 5.4 Burst Pressure Tests 6. CONCLUSIONS Diaphragm burst pressure tests were carrid out to find a suitable diaphragm material for use in the flow path. The results are shown in Table 4. Even though the burst pressure for copper foil is 3 kg f/cm2, copper was getting tarnished with UDMH gel. Kapton and mylar films do not burst even at 6 kg f/cm2. Kapton film with a larger opening diameter of 24 mm bursts at 5.5 kg f/cm2, and hence, may be a suitable diaphragm material. Performance evaluation of metallised UDMH-A1 gel propellant with N2O4 showed peak Isp values of 3 18.3 and 3 16.7 for 40 per cent and 30 per cent Al at O/F ratio of 1 and 1.5, respectively. Specific impluse increased with increase in AR. For peak performance, O/F ratio shifted from 1.5 to 2 and 1 to 1.5 for 30 per cent and 40 per cent Al, respectively, when the AR was increased from 10 to 500. Marginal Isp gain was seen when the chamber pressure was increased 5.5 Bulk Density from 10 to 60 kg f/cm2 beyond which the Isp gain The experimental value of density of was negligible. UDMH-30 per cent A1 gel system is 1.074 g/cc Metallised UDMH gel propellants containing Table 4. Burst pressure test with UDMH-AI-gel 25-30 per cent propellant grade and pyrotechnic grade A1 were prepared in 500 g level. Gellant Thickness Hole opening Results material concentration could be reduced when pyrotechnic (mm) (mm) Mylar film 0.04 12 No bursting grade Al was used. Both systems were found to be uv to pseudoplastic and thixotropic. However, the gel 6'kg f/cm2 flow characteristics were superior with propellant A1 sheet 0.09 12 Bursting at sandwitched 6 kg f/cm2 with polythene Copper foil 0.04 12 Bursting at 3 kg f/cm2 Kapton film 0.06 12 No bursting up to 6 kg f/crn2 Kapton film 0.06 24 Bursting at 5.5 kg f/cm2 grade Al. Actual firing of UDMH-A1 gel propellant with N204 is planned with suitable modification of solenoid valve, injector design and nozzle. REFERENCES 1. Palaszewki, B.A. Upper stages using liquid propulsion and metallised propellants. National Aeronautics & Space Administration, USA, 1992. NASA-TP-3 1 9 1. DEF SCI J, VOL 49, NO 1, JANUARY 1999 2. Munjal, N.L. Prop. Explos. Pyrotech., 1985, 10, 11 1-17. 3. Green, J.M. Flow visualisation of rocket injector spray using gelled propellant simulants. American Institute of Aeronautics & Astronautics. AIAA- 91-2198. 4. Gordon, S. & McBride, B.J. Computer program for complex chemical equilibrium composition rocket performance and applications., National Aeronautics & Space Administration, USA, 1976. NASA-SP-273. 5. Glassman, I. & Sawyer, R.F. The performance of chemical propellants. Technivision Services Slough, England, January 1969. 6. Varghese, T.L.; Gaindhar, S.C.; John, David.; Josekutty, Jose.; Muthiah, Rm.; Rao, S.S.; Ninan, K.N. & Krishnamurthy, V.N. Developmental studies on metallised UDMH and kerosene gels. DeJ Sci. J., 1995,45 ( I ) ,  25-30. Contributors Dr TL Varghese is heading Formulation and Experimentation Section of Vikram Sarabhai Space Centre (VSSC), Thiruvananthapuram. He obtained his PhD in Chemistry from Kerala University. He joined VSSC in 1971 and has been engaged in the research and development of solid propellant for launch vehicles and gel propellants. He has 37 papers to his credit. He is a member of the High Energy Materials Society of India and the Society of India and the Society for Polymer Science, (India). Mr N Prabhakaran obtained his MSc (Chemistry) from University of Poona, Pune. He joined VSSC in 1969. Since then, he has been engaged in the development of composite propellant. He has 18 papers to his credit. He is a member of the High Energy Materials Society of India, Society for Polymer Science (India) and Indian Society for Non-Distructive Testing. Ms KP Thanki obtained her BSc (Mathematics) from Kerala University. She joined at the VSSC in 1970. Since then, she has been engaged in the performance analysis of solid propellants, gel propellants and statistical analysis of data on rheological, mechanical and ballistic properties of various propellant formulations. She has many papers to her credit. She is a member of the High Energy Materials Society of India. VARGHESE, et al: PERFORMANCE EVALUATION OF METALLISED GEL PROPELLANTS M r  S Subramanian obtained his AMIE from Institute of Engineers in 1984 and MTech in Mechanical Engineering from Indian Institute of Technology, Madras, in 1986. He joined at the VSSC in 1989 and has been engaged in software development for the design of thermal energy conversion devices and performance prediction of solid and liquid motors of launch uehicle. Presently, he is engaged in the modelling of various subsystems like combustion chamber, nozzle and liquid stage of rocket. He is a member of the Aeronautical Society of India. Dr SS Rao obtained his BTech (Chem Engg.) from Osmania University, Hyderabad, in 1965, ME from Indian Institute of Science, Bangalore, in 1967 and PhD from University of Birmingham, UK, in 1978. He joined at the VSSC in 1972 and has been engaged in R & D of propellants, polymers and chemicals. Presently, he is heading Propellant Engineering Division at VSSC. He is the recipient of Commonwealth Scholarship Award (1975) and NRDC Award (1986). He is Founder-Secretary of Thiruvananthapuram Regional Centre of Indian Institute of Chemical Engineers and Thiruvananthapuram Regional Chapter of High Energy Materials Society of India and is a member of Society of Polymer Science (India). He has published several papers and guided research students in the areas of transfer processes, propellant, polymer and rubber technology and safety. Recently, he has received Distinguished Leadership Award from the American Biographical Institute (ABI), USA. Dr KN Ninan is Group Director of Propellant & Special Chemicals Group of VSSC. He did his PhD (Chemistry) from the University of Kerala. He joined at the VSSC in 1968 and has made significant contributions in the development of propellants, polymers and chemicals. He has setup a modern integrated analytical facility at VSSC. Besides being a member of several scientific and professional bodies, he is the Chairman, Education Committee, India Region of International Confederation of Thermal Analysis and the Vice-President of Society for Polymer Science (India), Thiruvananthapuram Chapter. He has published more than 200 research papers in nationaUintemationa1 journals. He was given the Netzch-ITAS Award (1987) for his outstanding contributions in the field of thermal analysis. DEF SCI J, VOL 49, NO 1, JANUARY 1999 Dr VN Krishnamurthy obtained his PhD from Indian Institute of Science, Bangalore. He joined at theVSSC in 1968 and was responsible for the development and productionisation of a variety of propellants, polymers and chemicals. He retired as Dy Director in 1997. He has guided PhD students and published a number of papers in nationaYintemational journals. He is the recipient of N R D C d  FIE Awards. He had been President, Indian Thermal Analysis Society, Founder-Chairman of the Thimvananthapuram Chapter of High Energy Materials Society of India. Society for Polymer Science (India), Materials Research Society of India and also a member of a few other professional societies. Presently, he is Honorary Director, ~ R D O / I S R O - P U ~ ~  niversity Interactive Cell at Pune. 

Performance Evaluation and Experimental Studies on Metallised Gel Propellants

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Performance Evaluation and Experimental Studies on Metallised Gel Propellants

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