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Combustion of non-catalyzed cyclotrimethylenetrinitramine-composite modified double-base propellants (Part II)
Radislav Stojanović, Miloš Filipović
The burning rate and the burning rate law of non-catalyzed reference double-base (DB) and cyclotrimethyl-enetrinitramine-composite modified double-base (RDX-CMDB) propellants were studied in order to elucidate the effect of the RDX addition on burning rate characteristics of these propellants. The burning rate characteristics were measured using a particular small-scale ballistic evaluation motor. It was found that the burning rates of RDX-CMDB propellants decrease with the increase of the RDX concentration, with the burning rate relatively independent of the RDX particle size. Also, it was established that the pressure exponent in the burning rate law increases, while the combustion index decreases linearly with the increase of the RDX concentration. The burning rate activity decreases slowly as the pressure increases. The temperature sensitivity of burning rate at a constant pressure of RDX-CMDB propellants is slightly lower than that of the conventional nitrocellulose and nitroglycerin based double-base propellant and for both propellants it decreases slowly and exponentially as the pressure increases. Since the mole fraction of NO2 produced by the initial decomposition of RDX is lower than that of NO2 produced by the initial decomposition of DB propellant, and because the ratio of NO2/aldehydes of a DB propellant as an initial decomposition product is decreased by the addition of RDX, the addition of RDX shifts the equivalence ratio of NO2/aldehydes towards fuel rich. As a result, the reaction rate in the fizz zone decreases and the heat feedback from the gas phase to the burning surface decreases when RDX is mixed within double-base propellants. Consequently, the burning rate of RDX-CMDB propellants decreases comparing to the double-base propellants, used as the base matrix of RDX-CMDB propellants.
Key words: cyclotrimethylenetrinitramine-composite modified double-base propellant, burning rate, temperature sensitivity, flame structure, the surface and gas phase reactions, burning rate characteristics.
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