Propellants plateau

There are plateau propellants that exhibit an intermediate range of pressure over which m is practically independent of p and mesa propellants for which m(p) achieves a maximum at a particular value of p then a minimum at a higher value. These effects may be produced in conventional double-base propellants by suitable addition of burning-rate catalysts (typically certain metal-organic salts) to the propellant formulation. It has been shown experimentally that these catalysts usually operate by modifying the interaction between the condensed-phase and dispersed-phase reaction zones [57], [58]. Thus dispersion phenomena are of importance to the deflagration of homogeneous propellants in a number of ways. 

It was soon realized that platonized propellants, with their reduced temperature sensitivity in the plateau- and mesa-burning range, could be effectively used to minimize the sensitivity of the performance of a rocket to the temperature of the environment. Much work has been devoted to understanding the mechanism of plateau and mesa burning, with a view to optimizing the performance characteristics of rocket motors. 

Fig. 6.21 Definition of super-rate, plateau, and mesa burnings of a catalyzed double-base propellant.

NG and NC-TMETN are not quite the same due to small differences in chemical structure and in the energy levels of the propellants, the burning characteristics of NC-NG and NC-TMETN propellants are broadly similar and the action of the catalysts in terms of producing super-rate, plateau, and mesa burning is the same for both propellants. 

Kubota, N., Determination of Plateau Burning Effect of Catalyzed Double-Base Propellant, 17th Symposium (International) on Combustion, The Combustion Institute, Pittsburgh, PA, 1979,... 

It is well known that the super-rate burning of nitropolymer propellants diminishes with increasing pressure in the region 5-100 MPa and that the pressure exponent of burning rate decreases. - ] This burning rate mode is called plateau burning. As for these nitropolymer propellants catalyzed with LiF and C, HMX propellants catalyzed with LiF and C also show plateau burning. 

The burning surface of an HMX propellant only becomes covered with carbonaceous materials when the propellant is catalyzed with both LiF and C. This surface structure is similar to the burning surface of an HMX propellant catalyzed with a lead compound and C. The results indicate that the combushon mode and the action of LiF are the same as those resulting from the use of lead compounds to produce super-rate and plateau burning of nitramine propellants. 

Like double-base propellants, CMDB propellants show super-rate and plateau burning when they are catalyzed with small amounts of lead compounds. Fig. 8.21 shows a typical plateau burning for a propellant composed of NC-NG and HMX.P I The chemical composition of the catalyzed propellant is shown in Table 8.1. 

Table 8.1 Chemical composition of super-rate and plateau burning propellant.

Fig. 8.22 The luminous flame front of the platonized propellant approaches the burning surface more rapidly than that of the non-catalyzed propellant when the pressure is increased in the plateau-burning pressure region.

Fig. 8. 23 Temperature gradient in the fizz zone increases in the super-rate burning region and then remains unchanged in the plateau-burning pressure region for the catalyzed propellant.

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