A Combustion Study of Metal Powders in Contact with Sodium Nitrate

• Published in: Combustion science and technology 1995-12, Vol.110-111 (1), p.185-195
• Main Authors: RAO, R. BHASKARA, SINGH, HARIHAR, RAO, P. NAGESWARA
• Format: Article
• Language: English
• Subjects: Applied sciences; burning rate; combustion; Combustion of solid fuels; Combustion. Flame; effect of NaNO; Energy; Energy. Thermal use of fuels; Exact sciences and technology; metal agglomeration; Metal-Oxidiser propellants; Theoretical studies. Data and constants. Metering; thermal decomposition
• ISSN: 0010-2202; 1563-521X
• DOI: 10.1080/00102209508951922

Combustion phenomena of metal powders in contact with NaNO 3 used as propellants have been studied in order to find out burning rate variations at different oxidiser levels. Commonly used metals like Mg, Al, Zr and B (a metalloid) have been considered for the present study. It is found that the burning rate of the propellants largely depends on mixture ratio of the fuel and oxidiser. The burning rate of Mg-NaNO 3 and Zr-NaNO 3 propellants decreases with increasing concentration of NaNO 3 in contrast to the energy content of the propellants, On the otherhand the burning rate as well as the energy content of Al-NaNO 3 and B-NaNO 3 propellants increases with increasing NaNO 3 concentration. Thermal decomposition results indicate that propellants containing Mg and Zr at low oxidiser content have higher condensed phase/surface heat release before the metal particles acquire sufficient energy for ignition and hence provide surface mode of combustion leading to high burning rates. At higher oxidiser contents, they have a lower heat release in the condensed phase and at the surface with a delay in ignition due to the oxide coating of the metal particles in presence of higher concentration of molten oxidiser, thus provide vapour phase combustion leading to low burning rates. In contrast, decomposition of the propellants containing Al and B occurring after the metal particles acquire sufficient energy for ignition due to the presence of protective nature of their oxide layers around the metal particles leading to vapour phase combustion at all mixture ratios. This causes an increase of burning rates with increasing oxidiser content of the mixture upto the stoichiometric ratio. The burning surface temperature data and the photographs of partially burnt samples also support the suggested mechanism.