Elsevier

Combustion and Flame

Volume 161, Issue 10, October 2014, Pages 2717-2728
Combustion and Flame

Studies on the role of iron oxide and copper chromite in solid propellant combustion

https://doi.org/10.1016/j.combustflame.2014.03.015Get rights and content

Abstract

Iron oxide and copper chromite are the known burn rate enhancers used in a composite solid propellant. Lot of research has been carried out to understand the mechanism or location of action of the burn rate modifiers so as to better tailor the burning rate of a composite propellant. The literature is still very confusing in affirming the mechanism. Here, a systematic study has been carried out, by undertaking experiments at varying levels of combinations of the individual components (ammonium perchlorate, which is oxidizer and hydroxyl terminated poly butadiene, which is both fuel and binder) of composite solid propellant. Firstly, thermal gravimetric analysis, differential scanning calorimetry and burning rate measurements on the individual components are carried out to study the effect of iron oxide and copper chromite on the components themselves. It has been noticed that though both iron oxide and copper chromite are effective on ammonium perchlorate, iron oxide is slightly more effective than copper chromite. Also, copper chromite enhanced the binder melt flow, while iron oxide reduced it. These are followed-up by experiments on sandwich propellants, which give greater insight and enables better understanding of the behavior of iron oxide and copper chromite in composite propellants, as these are simple two-dimensional analogue of the composite solid propellants. Finally, experiments are carried out on the composite solid propellants to obtain a holistic understanding of the behavior/location of action of iron oxide and copper chromite in them. These studies are used to explain certain unexplained but observed phenomena, at the same time elucidating the location of action of these burn rate modifiers in composite solid propellant combustion. Based on these observations, it has been proposed that both iron oxide and copper chromite are primarily acting on the condensed phase. These studies are further complimented with experiments to analyze the thermal conductivity measurements of various propellant samples. This is pursued to understand the reason for the differences in burn rate pressure index for the composite propellants with iron oxide and with copper chromite. It has been understood from these studies that the thermal conductivity of a composite propellant is a key parameter, which affects the burn rate pressure index. Literature has never addressed it from this perspective.

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

References (60)

  • K. Kishore et al.

    Combust. Flame

    (1978)
  • N.N. Bakhman et al.

    J. Catal.

    (1974)
  • P.W.M. Jacobs et al.

    Combust. Flame

    (1969)
  • F. Solymosi et al.

    Proc. Combust. Inst.

    (1971)
  • N.N. Bakhman et al.

    Combust. Flame

    (1974)
  • H.E. Jones et al.

    Proc. Combust. Inst.

    (1973)
  • S. Krishnan et al.

    Combust. Flame

    (1990)
  • S.H. Inami et al.

    Combust. Flame

    (1971)
  • P.W.M. Jacobs et al.

    Proc. Combust. Inst.

    (1967)
  • S.H. Inami et al.

    Combust. Flame

    (1968)
  • J. Powling

    Proc. Combust. Inst.

    (1967)
  • J.R. Ward

    Combust. Flame

    (1975)
  • C.W. Fong et al.

    Combust. Flame

    (1986)
  • F. Solymosi et al.

    Combust. Flame

    (1968)
  • S. Verma et al.

    Acta Astronaut.

    (2014)
  • J.D. Hightower et al.

    Proc. Combust. Inst.

    (1967)
  • T.B. Brill et al.

    Combust. Flame

    (1993)
  • R. Friedman et al.

    Proc. Combust. Inst.

    (1957)
  • K. Jayaraman et al.

    Combust. Flame

    (2009)
  • N. Kubota

    Propellants and Explosives

    (2002)
  • V.F. Komarov

    Combust. Explo. Shock Waves

    (1999)
  • O.P. Korobeinichev et al.

    Combust. Explo. Shock Waves

    (1973)
  • S.A. Vorob’eva et al.

    Combust. Explo. Shock Waves

    (1995)
  • O.P. Korobeinichev et al.

    Combust. Explo. Shock Waves

    (1972)
  • K. Kishore

    Colloid Polym. Sci.

    (1979)
  • V.K. Bobolev et al.

    Combust. Explo. Shock Waves

    (1971)
  • C.U. Pittman

    AIAA J.

    (1969)
  • B.S. Ermolaev et al.

    Combust. Explo. Shock Waves

    (1969)
  • K. Kishore et al.

    AIAA J.

    (1980)
  • S.R. Chakravarthy et al.

    J. Propul. Power

    (1997)
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