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Effect of addition of carbon in the form of graphite and carbolac on the combustion characteristics of Magnesium‐Sodium nitrate propellant has been studied. Results indicated that the burning rate of the propellant increased significantly by the addition of graphite upto 2%. Thermal decomposition studies revealed that the graphite particles in addition to its absorption of thermal energy being an inert material react with the decomposed products of the sodium nitrate just above the burning surface of the propellant for the exothermic heat release. This heat release which is high at low concentration of graphite is seen causing high burning rate. Any further increase in graphite concentration beyound 2% reduces the burning rate as the thermal energy absorption exceeds the heat release at the burning surface. When carbon in the form of carbolac was used in the composition reactive species diffuse out prior to the sample ignition without participating in the combustion thus reduces the burning rate. The heat of reaction data supported the suggested mechanism.

A BSTRA CTThe combustion phenomena of Mg-NaNO3 propellants have been studied. Results of burning rate at different mixture ratios and particle sizes indicate that the compositions containing finer particle size (50 Jlm) NaN°3 give higher burning rate at high fuel content of the mixture than at the stoichiometric ratio; whereas the compositions with coarser particle size (250 Jlm) NaNO3 show increased burning rate with increasing oxidiser content and give a maximum at stoicbiometric point. Thermal decomposition results indicate that the condensed phase heat release at the propellant surface and the reactions in the vapour phase are responsible for variations in the burning rate. The decomposition products of finer size NaNO3, react with Mg before Mg particles acquire sufficient energy for ignition, and lead to condensed phase heat release. This heat is maximum at high fuel content and causes high burning rate with low pressure and temperature sensitivity. The increase in the oxidiser content reduces the condensed phase heat due to formation of metal agglomerates and causes lower burning rate with high pressure and temperature sensitivity. After the Mg particles acquire sufficient energy for ignition the decomposition products of coarser size NaNOl diffuse out along with Mg and react in the vapour phase. This causes an increase of burning rate with increase in the oxidiser content of the mixture up to the stoichiometric ratio with a pressure and telflperature dependence.parameters 'controlling the bumming rate characteristics, Attempts have been made to evolve a suitable combustion mechanism to explain the results obtained, EXPERIMENT ALTo determine the burning rate characteristics, Mg-NaNOJ propellant grains of 100 mm dia and 200 mm length were processed by pressure moulding using the Mg-NaNOJ compositions of different mixture ratios and particle sizes. Samples for measurement of heat of combustion were prepared in the form of 10 mm dia pellets by compacting to the same density level. Samples for thermal decomposition studies were taken from the pellets.Burning rates of the propellant at different chamber pressures were determined in a test motor of 114 mm dia by static firing. The different chamber pressures

Agglomeration phenomenon of magnesium particles during combustion of MgNaNO3 propellant has been studied. High speed photographs of combustion zones and the burning surface temperature data indicate that the metal particles form agglomerates on the burning surface in varying degree depending on the mass fraction of NaNO3. It is found that the increase of oxidizer content increases the metal agglomeration and the agglomerate size depends on the initial particle size of the ingredients. An attempt has been made to predict the size of the agglomerates based on the consideration that the agglomerate size depends on the thickness of the molten oxidizer layer enveloping the metal particles in the condensed phase and surface heat flux providing local temperature environment to agglomerate the metal particles and to eject from the burning surface for the vapour phase combustion. The results were compared with the experimental data. The prediction describes fairly well the observed effects of the concentration and particle size.

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