Combustion of CMDB Propellants

Kubota, N., and Masamoto, T., Flame Structures and Burning Rate Characteristics of CMDB Propellants, 16th Symposium (International) on Combustion, The Combustion Instimte, Pittsburgh, PA, 1976, pp. 1201-1209. 

Though the physical structures of CMDB propellants are heterogeneous, similar to those of composite propellants, the base matrix used as a binder burns by itself and the combustion mode of CMDB propellants appears to be different from that of composite propellants and double-base propellants. The burning rate of a CMDB propellant is dependent on the type of crystalline particles incorporated. 

The combustion temperatures are much higher in CMDB propellants than that of DB and composite propellants and therefore, inhibition systems for CMDB propellants should have better BS and ablative properties. As major ingredients of CMDB propellants are NC and NG similar to DB propellants, it is logical to use polyesters which have already proved their potential for DB propellants for inhibition of CMDB propellants. However, the unsaturated polyesters which function... 

When nitramine particles such as HMX or RDX particles are mixed with a doublebase propellant, nitramine composite-modified double-base propellants are formulated. Since HMX and RDX are stoichiometrically balanced materials, the use of these nitramine particles leads to a somewhat different mode of combustion as compared to AP-CMDB propellants. Since each nitramine particle can burn independently of the base matrix at the burning surface, a monopropellant flamelet is formed in the gas phase from each particle. The monopropellant flamelet diffuses into the reactive gas of the base matrix above the burning surface and a homogeneously mixed gas is formed. 

Triple-base propellants are made by the addition of crystalUne nitroguanidine (NQ) to double-base propellants, similar to the way in which nitramine is added to CMDB propellants as described in the preceding section. Since NQ has a relatively high mole fraction of hydrogen within its molecular structure, the molecular mass of the combustion products becomes low even though the flame temperature is reduced. Table 4.13 shows the chemical composition, adiabatic flame temperature, and thermodynamic energy,/ as defined in Eq. (1.84), of a triple-base propellant at 10 MPa (NC 12.6% N). 

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-... 

Fig. 8.6 Temperature profiles in the combustion wave structures of an RDX-CMDB propellant at different pressures.

Fig. 8.8 Mole fractions of the final combustion gases of HMX-CMDB propellants as a function of (N02)...

Aoki, I., and Kubota, N., Combustion Wave Structure of HMX-CMDB Propellants (Eds. Varma, M., and Chatterjee, A. K.), pp. 133-143, Tata McGraw-Hill Publishing Co., Ltd., India (2002). 

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. 

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