Sustainer propellant

Fuel-rich propellants - Sustainers of Kvadrat (Russian) and Akash (Indian)... 

Heterogeneous solid propellants possess additional mechanisms with potentials for producing oscillatory burning. For example, certain metalized composite propellants have been observed to burn in the laboratory with identifiable ranges of frequencies of oscillation [118] in this case, the mechanism may involve chemical interactions between the metal and the oxidizer. It was indicated in Section 9.1.5.5 that heterogeneities introduce at least local periodicities and that, in the presence of a mechanism for synchronizing the phases of the oscillations over the surface of the propellant, sustained coherent oscillations of the combustion will occur. A review is... 

At very high water speeds cavitation-damage (Section 8.8) is sustained by any meti high-speed bronze propellers, for instance, may suffer seriously. This form of attack is mainly mechanical, although an element of true corrosion may be present, and is not specifically associated with sea water. 

The basic approach taken in the analytical studies of composite-propellant combustion represents a modification of the studies of double-base propellants. For composite propellants, it has been assumed that the solid fuel and solid oxidizer decompose at the solid surface to yield gaseous fuel and oxidizing species. These gaseous species then intermix and react in the gas phase to yield the final products of combustion and to establish the flame temperature. Part of the gas-phase heat release is then transferred back to the solid phase to sustain the decomposition processes. The temperature profile is assumed to be similar to the situation associated with double-base combustion, and, in this sense, combustion is identical in the two different types of propellants. 

Another contributing mechanism is the direct cooling of hot propellant surface by contact with the injected fluid. The fluid should cause the decomposing surface to reduce its pyrolysis rate to a point where combustion cannot be sustained. In addition, the presence of water on the surface would obstruct heat transfer from the gas-phase reaction zones to the solid surface, thus augmenting the cooling of the surface. Proponents of these two approaches have correlated the injection data on the basis of mass of fluid required per unit area of surface, but theoretical justifications for the use of this particular correlating parameter have not been presented. 

Other than possibly for the insensible perspiration they absorb, transdermal patches tend to operate as thermodynamically static systems, meaning as com-positionally fixed systems, from the moment they are applied until their removal. Marketed ethanol-driven estradiol and fentanyl patches are exceptions because they meter out ethanol and drive it into the stratum corneum to propel the absorption process. Compositional steadfastness is still the rule, however, and it is this feature that bestows the zero-order delivery attribute on the ordinary transdermal patch. Drug is present within the patches in reservoir amounts whether or not the reservoir compartment is easily distinguished, for there must be enough drug to sustain delivery over the full course of patch wear. 

The burning mechanism of composite propellants differs from that described above. There is no exothermic reaction which can lead to a self-sustaining fizz zone. Instead, the first process appears to be the softening and breakdown of the organic binder/fuel which surrounds the ammonium perchlorate particles. Particles of propellant become detached and enter the flame. The binder is pyrolysed and the ammonium perchlorate broken down, initially to ammonia and perchloric acid. The main chemical reaction is thus in the gas phase, between the initial dissociation products. 

Nike-Ajax Tandem separating boost. Internal liquid-propellant rocket sustainer. 

Combustion Self-sustained, exothermic, rapid oxidation reaction of explosive substance and propellant. 

Fig. 14.13 shows a typical example of a propellant grain for which the burning surface area ratio of the booster stage and sustainer stage is 2.18. The relahonship... 

Fig. 14.18 A pair of photographs of the cross-section of propellant 2 (a) before combustion, and (b) after combustion interruption at the transition from booster stage to sustainer stage.

The mere presence of the ash seems responsible for the ability of the LP3—AP propellant to undergo self-sustained combustion to pressures as low as 0.005 atm., an order of magnitude less than PBAA-AP and PB(CT)-AP propellants, and to maintain a relatively high burning rate at such low pressures. Two questions are of interest why does it form, and how does it sustain the burning rate It is not clear why the ash forms. It may be related to Bircumshaw and Newman s (14,15) discovery that only 30% of the original AP decomposes when the temperature is below ca. 350 °C. and that the remaining 70% is unreacted solid AP, and to the fact that the surface temperature and the temperature in the ash were measured by Most (60) as 250° 300°C. (The GDF theory with a collapsed A/PA flame indeed predicts a low surface temperature, ca. 400°C. below 0.01 atm.)... 

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