Studies on the role of iron oxide and copper chromite in solid propellant combustion
Introduction
A composite solid propellant burning rate is often modified by the addition of burn rate modifiers to its composition in small quantities (<∼3%) [1]. Iron oxide (IO) and copper chromite (CC) are known burn rate modifiers, which are employed in a composite solid propellant when enhancement in the burning rate is desired. In general, much of the literature has been dedicated to understanding the mechanism and location of the burn rate modifiers in the combustion of solid propellants. Table 1, gives a broad overview of the mechanism/action site of these burn rate modifiers, as proposed by various earlier studies. The table should be read as follows. The proposed action site, corresponding to a burn rate modifier, is presented in column one, with the details of the burn rate modifier discussed in the study (whether IO or CC or both IO and CC) themselves given in columns three to five. Column two further elaborates on the proposed mechanism of action for these burn rate modifiers. Again, some of the studies disagree with the proposed action site/mechanism by other studies. To bring out these contradictions among the studies, each of the columns from three to five are divided into two.
A glance at Table 1 and at the review paper by Kishore and Sunitha [43] showed that the proposed mechanisms for IO and CC in the combustion of a composite solid propellant are too varied. In addition to the above discussion, it has been noticed that, IO and CC when added in a composite solid propellant enhances the burn rate pressure index. This increase in burn rate pressure index is greater with IO than with CC [44]. This is despite the fact (refer Table 1) that, a large portion of the literature proposes the same mechanism of action for both CC and IO. Thus, the main aim of this paper is to explain this aspect of composite propellant combustion. It will also throw more light on the possible location of action of these catalysts in the propellant combustion. For this purpose, experimental studies have been carried out, which are presented further in this paper.
Section snippets
Experiments
A typical composite solid propellant (non-metalized) has AP as oxidizer and HTPB as, both fuel and binder. Firstly, experiments are performed to understand the effect of IO and CC on the individual components (AP and HTPB, here) that constitute a composite solid propellant. Then experiments are conducted on sandwich propellants, which is a two-dimensional analog of a composite propellant. Lastly, experiments are carried out with IO and CC in the composite propellants, to bring in the complex
Results and discussions
The pellet, sandwich propellant and composite propellant samples are maintained at a temperature of 300 K in an oven for 24 h before the experiments are conducted. Thus, all the burning rate results obtained correspond to an initial temperature of 300 K. All the experiments are conducted in the pressure range of 20–70 bar. Experiments are repeated to obtain at least three burning rate readings at each pressure. This establishes the repeatability of the burning rate values.
All the burning rates
Conclusions
Experiments are performed to study the behavior of iron oxide and copper chromite when present in AP and binder of a composite solid propellant, individually. Experiments are extended to both sandwich propellants and composite propellants to understand the mechanism/location of action of these burning rate modifiers. From all these experiments it is concluded that both IO and CC are proposed to be acting by modifying AP condensed phase reactions and thus the reactants entering into the gas
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