GAP Pyrolants

As described in Sections 4.2.4.1 and 5.2.2, GAP is a unique energetic material that burns very rapidly without any oxidation reaction. When the azide bond is cleaved to produce nitrogen gas, a significant amount of heat is released by the thermal decomposition. Glycidyl azide prepolymer is polymerized with HMDI to form GAP copolymer, which is crosslinked with TMP. The physicochemical properties of the GAP pyrolants used in VFDR are shown in Table 15.3.PI The major fuel components are H2, GO, and G(g), which are combustible fragments when mixed with air in the ramburner. The remaining products consist mainly of Nj with minor amounts of GOj and HjO. 

Molecular mass Density Heat of formation Adiabatic flame temperature 1.98kgmo - 1.30x 105 kgm-5 957 k) kg- at 273 K 1465 K at 5 MPa  

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The highest flame temperature for a B-GAP pyrolant is obtained at b( 0.2), whereupon BN is produced, while that for an Al-GAP pyrolant is obtained at ai( 0.4), whereupon AIN is produced. Al reacts with N2 generated by the decom-... 

Table 11.3 Maximum flame temperatures of metal-GAP pyrolants.

The reaction between Ti and Nj occurs in the low-temperature region at below Ti(0-2) for Ti-GAP pyrolants. On the other hand, the reaction between Ti and C occurs in the high-temperature region at above Ti(0-2). The reactions of Ti with N2 and C are represented by ... 

The results of thermochemical experiments reveal that an exothermic reaction of GAP occurs at about 526 K and that no other thermal changes occur. When Mg or Ti parhcles are incorporated into GAP to formulate Mg-GAP or Ti-GAP pyrolants, two exothermic reactions are seen the first is the aforementioned exothermic decomposihon of GAP, and then a second reachon occurs at 916 K for the Mg-GAP pyrolant and at 945 K for the Ti-GAP pyrolant There is no reaction between either Mg or Ti and GAP at the temperature of the first exothermic reaction. Both Mg and Ti particles within GAP are ignited by the heat generated by the respechve second exothermic reactions. 

X-ray analysis results show the formation of MgN as a combustion product of Mg-GAP pyrolants. The reaction occurs with nitrogen gas formed by the decomposition of GAP according to ... 

However, no MgO is seen in the residue, indicating that this compound is not produced by reaction between Mg and CO. On the other hand, no TiN is seen in the residue of the Ti-GAP pyrolant, implying that there is no reaction between Ti and Nj to produce this compound. Ti particles react exothermically with carbon formed by the decomposition of GAP according to ... 

Thus, the combustion temperature of Ti-GAP pyrolants reaches the maximum value of 2000 K. 

Typical gas-generating pyrolants include (1) AP pyrolant composed of AP, ap(0.50), and HTPB, htpb(0-50), which is cured with isophorone diisocy-anate(lPDl) (2) NP pyrolant composed of NC, nc(0-70) and NG, ng(0-30), which is plasticized with diethyl phthalate (DEP) and (3) GAP pyrolant composed of gly-cidyl azide copolymer, qap(0-85), which is cured with hexamethylene diisocy-anate(HMDl) and cross-linked with trimethylolpropane (TMP). 

Fig. 15.6 shows the burning rate characteristics of A P, N P, and GAP pyrolants in a gas generator. The burning rate of the GAP pyrolant is seen to be much higher than... 

The specific impulse of each pyrolant is computed as a function of air-to-fuel ratio, as shown in Fig. 15.7. In the computations, the pressure in the ramburner is assumed to be 0.6 MPa at Mach number 2.0for a sea-level flight When GAP pyrolant is used as a gas-generating pyrolant, the specific impulse is approximately 800 s at e = 10. It is evident that AP pyrolant and NP pyrolant are not favorable for use as gas-generating pyrolants in VFDR. However, the specific impulse and burning rate characteristics of these pyrolants are further improved by the addition of energetic materials and burning rate modifiers. 

Fig. 15.8 shows a typical set of burning rate versus pressure plots for GAP pyrolants composed of GAP copolymer with and without burning-rate modifiers. The burning rate decreases as the mass fraction of the burning-rate modifier, denoted by (G), is increased. Graphite particles of diameter 0.03 pm are used as the burn-... 

Fig. 15.9 Specific impulse and combustion temperature of GAP pyrolants as a function of air-to-fuel ratio ramburner pressure 0.6 MPa and Mach number 2.0 at sea-level flight.

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. 

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... 

The temperature of the boron particles is raised by the heat generated by the decomposition of GAP. However, no combustion reaction occurs between the boron particles and the gaseous decomposition products of the GAP pyrolant. Thus, the temperature in the gas generator remains low enough to protect the attached nozzle from adverse heat... 

Fig. 15.15 shows the specific impulse of a GAP pyrolant as a function of e under variable flow conditions as obtained in a DCF test. The ramburner pressure ranges... 

Fig. 15.15 Theoretical and experimental specific impulses of a GAP pyrolant of a VFDR as a function of air-to-fuel ratio obtained by a DCF test.

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