Metal Particles as Fuel Components

The molecular mass of the combustion products in the ramburner is increased by the formation of the oxidized metal particles. However, the temperature in the ramburner is also increased by the oxidation. The results of thermochemical calculations indicate that the specific impulse generated by the combustion in the ramburner is more dependent on the average combustion temperature than the average molecular mass of the products when metal particles are added. Table 15.4 shows the heats of combustion and the major oxidized products of the soHd particles used in ducted rockets. 

Al and Mg particles are favored metals in the formulation of pyrolants because of their high potential for ignitability and combustion. However, the combustion products of Al and Mg particles tend to agglomerate to form relatively large metal oxide particles. Since the densities and heats of combustion of Ti and Zr are higher than those of Al and Mg, Ti and Zr are more favorable for use as fuel metals in ducted rockets. 

Boron particles are incorporated into GAP pyrolants in order to increase their specific impulse.[8-i2] xhe adiabatic flame temperature and specific impulse of GAP pyrolants are shown as a function of air-to-fuel ratio in Fig. 15.10 and Fig. 15.11, respectively. In the performance calculation, a mixture of the combustion products of the pyrolant with air is assumed as the reactant. The enthalpy of the air varies according to the velocity of the vehicle (or the relative velocity of the air) and the flight altitude. The flight conditions are assumed to be a velocity of Mach 2.0 at sea level. An air enthalpy of 218.2 kj kg is then assumed. 

The combustion temperature in a gas generator is maximized at the stoichiometric mixture of 8 = 5. The specific impulse increases with increasing e (fuel-lean mixture). However, the thrust decreases as e is increased. The maximum thrust is obtained at the stoichiometric mixture ratio. It is evident that L increases with increasing b- The I p of a pyrolant containing 1b(0-2) is 1100 s and its T)-is about 1600 K at e = 20. 

Data for the combustion temperature in a gas generator are shown in Table 15.5. The GAP pyrolant without boron particles, b(0-0), burns incompletely. The 

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When metal particles are oxidized, a large amount of heat is generated. However, the oxidized products are agglomerated condensed-phase particles and very little gaseous productis formed. Therefore, the potential use of metal particles as fuel components of propellants and explosives is limited. When organic materials composed... 

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