Super-rate region

If the catalyst acts in the fizz zone or in the dark zone, becomes smaller than r f n or respectively. As shown in Fig. 8.24, the behavior of qy corresponds to that of r y. Both catalyst activities have positive values in the super-rate region, decrease with increasing pressure in the plateau region, and finally both become negative above 3 MPa. This indicates that the catalyst acts as a positive catalyst in... 

The simplified burning-rate model given by Eq. (3.59) only represents the increased burning rate, i. e., super-rate burning, within the pressure region in which carbonaceous materials are formed on the burning surface. 

As the burning rate increases in the high-pressure region, the formation of carbonaceous materials diminishes and hence the super-rate burning also diminishes and becomes plateau burning. This negative catalytic effect of lead compounds is considered to produce mesa burning. 

Super-rate burning occurs when lithium fluoride (LiF) is incorporated into NC-NG or NC-TMETN double-base propellants. As shown in Fig. 6.27, the burning rate of a propellant catalyzed with 2.4% LiF and 0.1% C increases drastically in the pressure region between 0.3 MPa and 0.5 MPa. This super-rate burning effect diminishes gradually as the pressure is increased above 0.5 MPa. The non-cata-lyzed propellant is a conventional NC-NG double-base propellant composed of 55 % NC, 35% NG, and 10% DEP. The maximum burning rate increase is about 230% at 0.5 MPa. 

The dark zone length of liF-catalyzed propellants is increased by the addition of LiF in the region of super-rate burning, similar to the case of Pb-catalyzed propellants, as shown in Fig. 6.28. Table 6-11 shows the dark zone lengths and reaction times Xg in the dark zone producing the luminous flame at two different pressures,... 

Fig. 6.28 Flame stand-off distance is increased by the addition of LiF in the super-rate burning region.

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. 

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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