Combustion wave of a double-base propellant

The combustion wave of a double-base propellant consists of the following five successive zones, as shovm in Fig. 6.3 (I) heat conduction zone, (II) soHd-phase reaction zone, (III) fizz zone, (IV) dark zone, and (V) flame zone-l i -i -i ]... 

The thermal structure of the combustion wave of a double-base propellant is revealed by its temperature profile trace. In the solid-phase reaction zone, the temperature increases rapidly from the initial temperature in the heat conduction zone, Tq, to the onset temperature of the solid-phase reaction, T , which is just below the burning surface temperature, T. The temperature continues to increase rapidly from T to the temperature at the end of the fizz zone, T, which is equal to the temperature at the beginning of the dark zone. In the dark zone, the temperature increases relatively slowly and the thickness of the dark zone is much greater than that of the solid-phase reaction zone or the fizz zone. Between the dark zone and the flame zone, the temperature increases rapidly once more and reaches the maximum flame temperature in the flame zone, i. e., the adiabatic flame temperature, Tg. 

The temperature profile in the combustion wave of a double-base propellant is altered when the initial propellant temperature Tq is increased to Tq -i- ATq, as shown in Fig. 6.15. The burning surface temperature is increased to -i- AT, and the temperatures of the succeeding gas-phase zones are likewise increased, that of the dark zone from Tgto Tg-t- ATg, and the final flame temperature from 7 to Tf-t- ATf If the burning pressure is low, below about 1 MPa, no luminous flame is formed above the dark zone. The final flame temperature is Tg at low pressures. The burning rate is determined by the heat flux transferred back from the fizz zone to the burning surface and the heat flux produced at the burning surface. The analysis of the temperature sensihvity of double-base propellants described in Section 3.5.4 applies here. 

Fig. 6.3 Combustion wave stmcture of a double-base propellant.

Fig. 6.15 Combustion wave structure of a double-base propellant at different initial propellant temperatures and at high and low pressures.

Though the physicochemical properties of HTPE and HTPS are different, both are subject to a similar super-rate burning effect. However, the magnitude of the effect is dependent on the type of binder used. As in the case of double-base propellants, the combustion wave structures of the respective propellants are homogeneous, even though the propellant structures are heterogeneous and the luminous flames are produced above the burning surfaces. 

Thus, the combustion wave structure of double-base propellants appears to show a two-stage gas-phase reaction, taking place in the fizz zone and the dark zone. The thickness of the fizz zone is actually dependent on the chemical kinetics of the... 

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