M.Sc Thesis | |
M.Sc Student | Greenfeld Hagit |
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Subject | Prediction of the Burning Rate of a Multi-Modal Oxdizer Composite Propellant |
Department | Department of Aerospace Engineering | Supervisor | PROF. Benveniste Natan |
Full Thesis text | ![]() |
A typical composite solid propellant is a mixture of a crystalline
oxidizer and a polymeric fuel binder. Conventional crystalline oxidizers
include ammonium perchlorate (AP), ammonium nitrate (AN) and potassium
perchlorate, whereas among the fuels there are hydrocarbon-structured binders, e.g.,
polybutadiene or polyurethane. Modern propellants consist of several more
chemical ingredients, such as metal particles added as fuel, burning rate
modifiers, processing aids, anti-aging agent, combustion instability
suppressant and curatives. The selection of the ingredients is based on the
desired combustion characteristics and mechanical properties. The combustion of
such a heterogeneous mixture is understandably complex since the solid
components are usually blended in three or four discrete sizes to aid in
processing and control burning rate. In developing an analytical model for
composite propellant combustion, these complexities are further limited by the
incomplete understanding of the various possible reactions present in composite
propellants. There is need for mathematical tractability in representing these
reactions as well as those that are more understood. This study presents a
computerized code, based on the BDP model and the Cohen at el. analytical model
of composite propellant combustion. In the first stage, the model results of
the burning rate were compared with the Miller and Foster experimental results.
The goal was to examine the model accuracy and correct the thermochemical constants
to match materials used in the Israeli industries. Once the values for these
constant parameters were established, they were not changed during the
calculations for burning rate and burning rate exponent. After the
determination of the model constants, the model burning rate results were
compared with experiments for several propellant compositions produced in
Rafael. The model showed good prediction for low coarse/fine particle size
ratio compositions but had a large deviation from the experiments for high
ratio compositions. Trying to overcome this problem, the model was modified and
the improvement was implemented in the basic model. This improvement includes a
new approach of calculating the O/F ratio with respect to the AP size fractions
in the propellant. This new approach of calculating the O/F ratio affects the
characteristic surface dimension that is used in determining the diffusion
height and also the parameter
of the BDP model. After the implementation, the prediction for high coarse/fine
particle size ratio compositions was improved significantly and the predictions
for "fast" (low C/F ratio) propellants were still very good, all
within15-20% deviation from the experimental results.
It may be concluded that the current work improved the BDP model with a new approach for various calculations, resulting in a very good burning rate prediction of all reduced-smoke; bi-modal; AB-10; IPDI propellant compositions. Most probably, it can also predict well the burning rate for tri-modal propellants of the same kind; however, this was not tested methodically.