Burning rate of HMX-CMDB propellant

Fig.8.9 Burning rates of HMX-CMDB propellants containing different mass fractions of HMX.

Figure 7-37. Burning rate of HMX-CMDB propellant as a function of (N02).

As in the case of double-base propellants, the burning rate of HMX-CMDB propellants is determined by the heat flux transferred back from the gas phase to the solid phase and the heat flux generated at the burning surface. The temperature gradient in the fizz zone of HMX-CMDB propellants, (f> = (dT/dx)js, is shown in... 

Important results are that the dark zone temperature (Tf) decreases even though the flame temperature (Tg) is increased by the increase of Sj(N02) at constant pressure as shown in Fig. 7-38. Furthermore, (f> decreases also as Sj(N02) increases, and thus the burning rate decreases as Sj(N02) increases, i.e., the burning rate of HMX-CMDB propellants decreases as Ij(HMX) increases at a constant pressure. The observed burning rate characteristics of HMX-CMDB propellants are understood without consideration of the diffusional process and the chemical reaction between the decomposed gases of the base-matrix and the HMX particles. This is a significant difference from the burning rate characteristics of AP-CMDB propellants. 

The temperature sensitivity of gas phase 4> defined in Eq. (3.79) and the temperature sensitivity of the condensed phase V defined in Eq. (3.80) are obtained from the data of the burning surface temperature Ts, the temperature in the fizz zone Tg, the activation energy in the fizz zone Eg, the heat of reaction at the burning surface Qj, the temperature gradient in the fizz zone (f>, and the burning rate r. Figure 7-43 shows the temperature sensitivity of the burning rate of HMX-CMDB propellants as... 

The effects of the catalyst on burning rate and flame reaction indicate that the super-rate burning phenomena observed in the combustion of HMX-CMDB propellants are fundamentally the same as the combustion phenomena of catalyzed double-base propellants. This implies that the lead catalysts act on the combustion of HMX to produce super-rate burning. 

Figure 7-40. Burning rate versus dark zone temperature of HMX-CMDB propellant at different pressures.

Since the energy contained within double-base propellants is limited because of the limited energies of nitrocellulose (NC) and nitroglycerin (NG), the addition of ammonium perchlorate or energetic nitramine particles such as HMX and RDX increases the combustion temperature and specific impulse. Extensive experimental studies have been carried out on the combustion characteristics of composite-modified double-base (CMDB) propellants containing AP, RDX or HMX parhclesli- l and several models have been proposed to describe the burning rates of these pro-... 

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. 

A study was conducted to find out the effect of addition of these nitroplasticizers on ballistic properties of AP and RDX/HMX filled CMDB propellants. The data generated clearly indicated that the incorporation of nitroplasticizer, that is, 1 1 mixture of BDNPF and BDNPA in place of diethyl phthalate (DEP) for AP and nitramine based CMDB propellants improved the burn rates as well as /sp and thermal decomposition behavior of these propellant formulations [193]. 

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