Defence Science Journal, Vol51, No 2, April 2001, pp. 147-153 O 2001, DESIDOC Ballistic Evaluation of LOVA Propellant in High Calibre Gun A.G.S. Pillai, R.R. Sanghavi, C.R. Dayanandan, M.M. Joshi and J.S. Karir High Energy Materials Research Laboratory, Pune - 41 1 021 ABSTRACT This paper presents the data obtained on dynamic firing ofacellulose acetate binder-based low vulnerability ammunition (LOVA) propellant using 120mmfin-stabilised armour piercingdiscarding sabot (FSAPDS) kinetic energy ammunition. An optimised propellant composition formulated using fine RDX as an energetic ingredient andamixtweofcelluloseacetate and nitrocelluloseas binderwasqualified fit for firing in a high calibregun by its successful static evaluation for absolute ballistics using high pressure closed vessel technique. Dynamic firing of the propellant processed in heptatubular geometry was undertaken to assess the propellant charge mass. This . . . . . oronellant achieved hieher muzzle velocitv as comoared to the standard NOMI 19 hiole-base orooellant while u meeting the non-vulnerability characteristics convincingly. Keywords: LOVA propellants, ball~st~evca luat~onF, SAPDS ammunltlon, b~nder-basedL OVA propellant promising inert binders in LOVA propellant 1. INTRODUCTION formulations3. To compensate the energy loss The development of low vulnerability caused by the replacement of nitroglycerine (NG) ammunition (LOVA) gun propellant has gained and partially of nitrocellulose (NC) by CA, the high importance from the fact that accidental initiation energy nitramines like RDX in fine particulate of onboard ammunition happened to be the cause of form4 is used as the energetic ingredient. This paper major catastrophy, resulting in casualty of tank highlights the thermochemical data of a promising crew and loss of costly equipment1. Ammunition LOVA formulation and its ballistic properties by vulnerability is mainly due to the sensitivity of static evaluation using high pressure closed vessel conventional nitricesters-based propellantsz. The (HPCV) technique and actual dynamic firing concept of LOVA gun propellant is evolved by results. formulating a propellant which is least sensitive to impact, friction and heat stimuli and meeting the 2. EXPERIMENTAL PROCEDURE ballistic requirements satisfactorily at par with the conventional propellants. Cellulose derivatives, 2.1 Formulation & Processing such as cellulose acetate (CA), cellulose acetate Exhaustive evaluation stud~ews ere carr~edo ut butyrate (CAB), cellulose acetate Propionate on cellulosic binder-based LOVA propellant5. In (CAP), ethyl cellulose (EC) are reported as the present study, the authors have selected a Revised 09 September 2000 , . I47 .&i. DEF SCI J, VOL 51, NO 2, APRIL 2001 propellant formulation containing 10 parts CA, 11 parts NC of 12.2 per cent nitrogen content, 5.5 parts triacetin, 71 parts fine RDX,2 parts dinitrotoluene, 0.5 parts ethyl centralite and 1 part over 100 parts of basic composition, KN03. The processing of the propellant formulation was carried out by solvent method to get the finished propellant in heptatubular geometry with 2.3 lengh'diameter and 10 external diametdinternal diameter ratio. 2.1.1 Vulnerability Study Vulnerability aspects of LOVA propellant were evaluated by carrying out the test for determining impact and friction sensitivity, ignition dPcal:200 MPa/ms Pcal:550 HPa temperature, hot fragments 'conductive ignition temperaturezs6e,t c. (a) 2.1.2 Ignition Study ~arne~".'e, t al. reported that the ignition energy requirement of LOVA propellant is twice as that of conventional single-base propellant. Accordingly, the necessity for evaluating the ignitability of the LOVA propellant under development was felt before going for the dynamic firings. Different igniter materials, such as gun powder, borodKNO3, magnesium, teflon, viton and magnesium-based igniters were tried. Based on the analysis of ignition delay, conventional gun powder n I I I I I t t I I was selected as the promising igniter material. Lap b1: i 2.0 Log [PI: 3.0 (b) 3. BALLISTIC EVALUATION 1 3.1 Static Evalnation Static evaluation by HPCV technique was carried out and HPCV (700 ml) was used for this purpose. Propellant was subjected to static firing at various loading densities from 0.2 glml to 0.32 g/ml. Since the propellant was planned to be dynamically tested in the gun up to 500 MPa, HPCV firing was carried out by gradually raising the - - loading density till the pressure reahsed in HPCV closely matched with the expected pressure in the gun. Absolute ballistic values were then calculated Pcal: 550 MPa Tcal:40ms from the HPCV output using the internal ballistic solutiong. dpldt versus P, log r versus log P and the (c) pressure versus time profiles as obtained from FLgorr 1. Static EPCV ruing oiLOVA propellant conditioned HPCV at the maximum loading density of 0.32 g/ml at 2PC at 0.32 ghnl loading density, (a) &/dl versus P, (b) lag r versus log P, and (c) pressure versus time are given in Figs l(a), I(b) and I(c). profiles. PILLAI. ri nl BALLISTIC EVALUATION OF LOVA PROPELLANT IN HIGH CALIBRE GUN Table 1. Charge assessment dynamic gun firing of LOVA Table 2. Propellant formulations, their theoretical propelldnt thermochemical values and ballistic data from CV-firing Propellant Chamber pressure P,,,, Muzzle velocity charge (MPa) (mls) Che~nicaflo rnlulafion mass Predicted Achieved Cellulose acetate (CA) 10.0 parts (kg) Crusher Piezo Predicted Achieved Nitrocellulose (NC) 1 1.0 parts gauge gauge (Nitrogen content 12.2 %) 6.5 220 197 201 1179 1180 Triacetin (TA) 5.5 parts 7.0 247 232 223 1262 1263 Dinitrotoluene (DNT) 2.0 parts 7.5 276 279 NR 1344 1353 RDX 71.0 8.0 347 368 340 1426 i499 Carbamite 0.5 8.1 370 396 405 1531 NR KNO, 1 part over 100 parts 8.2 372 400 398 1533 1572 Thermochemical values 8.3 419 437 405 1548 1578 Flame temperature (K) 2853 8.4 449 457 467 1564 NR Force constant (Ilg) 1081 8.5" 463 470 482 1643 1645 Cal. val (callg) 815 8.6* 486 485 495 1666 1661 Ballistic data from closed vessel * Average of the five rounds fired NR - Not recorded firing (loading density 0.2 glml) Force constant (Ilg) 1070 3.2 Dynamic Evaluation P.,., (MPa) 263.5 ward'', et al. have reported the dynamic firing B,(cmlslMPa) 0.082 of different types of LOVA propellant in 105 mm Pressure exponent (a) 0.8153 tank gun. The propellant mass used was 4.98 kg. Ulrike ~eck-~rbschr"e ported the gun firing of conventional triple-base propellant are given in LOVA propellant in 40 mm and 120 mm simulator Figs 2 and 3. and based on their findings they have concluded that LOVA propellant must be proved in original 4. RESULTS & DISCUSSION ammunition Thermochemical data for the selected formulation and the ballistic data obtained from A 120 mm gun barrel with its kinetic energy closed vessel evaluation at 0.2 glrnl loading density ammunition belonging to fin-stabilised armour are given in Table 2. The studies carried on the piercing discarding sabot (FSAPDS) category was selected formulation under evaluation and the selected for the dynamic evaluation of the LOVA detailed vulnerability test results are given in propellant 'under development. The ballistic Table 3. Linear burn rate coefficient (PI) for gun prediction of this propellant in 120 mm FSAPDS propellants is generally considered as a constant for ammunition was carried out using the absolute the composition. HPCV evaluation of LOVA ballistic parameters of this propellant achieved by propellant under development indicated that the HPCV evaluation. The chamber pressure value of PI changes according to the loading density measurement carried out using copper crusher and this change is quite significant in predicting the gauge and piezoelectric gauge during the dynamic firing, using the FSAPDS projectile of 6.85 kg with Table 3. Vulnerability properties 7.5 kg-8.6 kg propellant charge mass are given in Table 1. Control firings were also carried out Impact sensitivity Ht. of 50% explosion (cm) 58 using conventional triple-base propellant to Friction sensitivity comparatively evaluate the performance of the (insensitive up to) (kg) 36 LOVA propellant. Pressure-time profile obtained Ignition temperature > 220 by piezoelectric gauge for LOVA propellant and (OC) DEF SCI J, VOt 51, NO 2, APRIL 2001 I , I 20 40 60 80 TIME ins) Figure 2. Pressure versus time profiles obtained by Figure 3. Pressure versus time profiles obtained by piezoelectric gauge during dynahic gun firings for piezoelectric gauge during dynamic gun firings for LOVA propellant. triple-base propellant NQM 119. gun pressure. For reliable and correct prediction of cm/s/MPa and at 0.32 glml loading density, the the chamber pressure during dynamic firing, the PI same was 0.108 cmIslMPa, whereas the PI value value from HPCV of matching Pressure levels have of 0.14 cm/s/MPa for triple-base NQ/M propellant to be applied in the computation. As seen from the had increased to only 0,147 cm,slMPa, this closed vessel profiles, the burning of LOVA PI difference in change of value according to propellant is quite normal, almost at par with the loading density is considered to be due to the higher conventional propellants. Pressure-time profile obtained during the dynamic firings indicated that Pressure sensitivity of =OVA propellant. the combustion behaviour of this propellant is more Similarly, the pressure exponent value for or less similar to the conventional propellants. conventional propellant remained almost constant while for LOVA propellant, it has shown a linear From the results of HPCV carried out for both increase in the pressure exponent (a) value. It is LOVA propellant (Table 4) and the conventional triple-base propellant (Tables), it is seen that pI for also observed that the achieved force constant is both the propellants shows increasing trend as the considerably more than the theoretical force loading density increases. However, this change constant. The change in force constant at higher (increasing loading density) is more in the case of loading densities may be due to the inaccuracy of LOVA propellant. PI value at 0.25 glml loading the cooling correction applied for computing the density for LOVA propellant recorded was 0.0965 force constant. Results of dynamic firing as glven Table 4. High pressure closed vessel results of LOVA propellant Propellant results Parameters (1) (2) (3) (4) (5) , Loading dcnsity (glml) 0.2500 027.50 0.3000 0.3100 0.3200 Pm."( MPa) 350.2300 . 399.1600 448. 1300 470.4600 49 1.7600 dp/dr (MPaIms) 90.0900 1 19.6900 153.1900 170.5 I00 188.1000 Force constant (Jlg) 1085.5000 1097 7000 1102 7600 1 109 8000 l I13 0000 a 0 8635 0 8775 0 8899 09120 09172 PILLAI, er 01: BALLISTIC EVALUATION OF LOVA PROPELLANT IN HIGH CALIBRE GUN Table 5. Hieh oressure closed vessel results of conventional NOIM rooe ell ant Pnrameters Propellant results (1) (2) (3) (4) (5) Loading density (glcc) 0.250 0.275 0.300 0.310 0.320 Force constant (Jlg) 1032.0M) 1057.000 1054.000 1053.000 1064.000 a 0.738 0.710 0.721 0.700 0.712 (cmlslMPa) 0.141 0.142 0.144 0.146 0.147 Composition NQ has NC (Nz 96 13.1). 20.8; NG, 20.6; Picrite, 55.00; Carbamite, 3.6; Potassium cryolite, 0.3 (parts). in Table I indicate that the, chamber pressure 2. Kirshenbaum, MS.; Avaromi, L. & Strauss, B. realised by crusher gauge and piezoelectric gauge Sensitivity characterisation of low vulnerable (LOVA) propellants. Journal of Ballistics, 1983, are in close agreement. Moreover, the predicted 7(2), 1701-40. chamber pressure calculated using the PI value at the appropriate pressure level from HPCV have 3. Strauss, B.; Hui, P.; Beardell, A! & Costa, E. Burning rate performance of insensitive closely matched with the realised pressure during propellants as a function of ageing. 19" JANNAF dynamic firing. Pressure-time profile of LOVA Combustion Meeting, 4-7 October 1982, Vol. 1. propellant and conventional propellant shown in NASA Godard Space Flight Centre, Maryland, Figs 2 and 3 indicate the smooth burning USA. CPIA Publication-1, 1982. pp. 367-81. characteristic on the expected lines. The muzzle velocity realised for the LOVA propellant at the 4. Pillai, A.G.S.; Dayanandan, C.R.; Joshi, M.M.; adjusted charge mass (8.6 kg) on matching pressure Patgaonkar, S.S. & Karir, J.S. Studies on the effects of RDX particle size on the burning rate of level (490 MPa) has been superior in comparison to gun propellants, Def Sci. J., 1996,46(2), 83-86. conventional propellant adjusted charge mass (8.46 kg). This is due to the improved energy 5. Pillai, A.G.S.; Joshi, M.M.; Barve, A.M.; Velapure, S.P. & Karir, J.S. Cellulose acetate output of LOVA propellant. binder-based LOVA gun propellant for tank guns. Def Sci. J., 1999,49(2), 141-49. 5. CONCLUSION LOVA gun propellant based on RDX as the 6. Dayanandan, C.R.; Sanghavi, R.R.; Dhulekar, energetic ingredient is found to be slightly higher K.M.; Joshi, M.M. & Pillai, A.G.S. Studies on pressure sensitive as compared to conventional cellulose acetate binder-based low vulnerability propellant. However, this will not seriously affect gun propellant. 2nd International High Energy the smooth performance of the propellant in the Materials Conference and Exhibition (MEMCE), gun. LOVA propellant with RDX as energetic Indian Institute of Technology, Madras, Chennai, ingredient can satisfactory meet the ballistic 8-10 December 1988. requirement of high performance kinetic energy ammunition. 7. Vamey, A.M.; Martino, J. & Henry, R. Ignition effectiveness tests of selected igniter materials REFERENCES with navy gun propellant. 19'~J ANNAF 1. Zimmer, M.F. US efforts in munition Combustion Meeting, 4-7 October 1982, Vol. 1. survivability. International Jahrestagung, 1982, NASA Godard Space Flight Centre, Maryland, 527-38. USA. CPIA Publication-1, 1982,535-46. DEF SCI J, VOL 51, NO 2, APRIL 2001 8. Vamey, A.M.; Martino, J. &Henry, R. Ignitability pellants. JANNAF Propulsion Meeting, Vol. 2, studies of LOVA propellant. 20Ih JANNAF 1981,359-78. Combustion Meeting. 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