Combustion of NC-NG Propellants

Combustion tests carried out for a rocket motor demonstrate a typical T combustion instability. Double-base propellants composed of NC-NG propellants with and without a catalyst (1 % nickel powder) were burned. Detailed chemical compositions of both propellants are given in Section 6.4.6 and the burning rate characteristics are shown in Fig. 6.29. The addition of nickel is seen to have no effect on burning rate and the pressure exponent is n = 0.70 for both propellants. 

Dibutylphthalate is used as a solv for aromatic nitrocompds, such as DNT Di-nitroethylbenzene. Silk (Ref 2) patented its use for the coating of NC NG propellants to serve as a deterrant, solvent, plasticizer 8e stabilizer. It is added during the mixing process of the propellant colloid and replaces a portion of the volatile solvent, thus reducing the possibility of the loss of vol solv. It functions in the burning of pro--pellants to cool the of combustion below... 

Table 4.10 shows a comparison of the theoretical combustion properties of NC-NG-DEP and NC-NG-GAP propellants at 10 MPa. Though the molecular mass of the combustion products. Mg, remains relatively unchanged by the replacement of DEP with GAP, the adiabatic flame temperature is increased from 2557 K to 2964 K when 12.5 % DEP is replaced with 12.5 % GAP. Thus, the specific impulse is increased from 237s to 253s. The density of a propellant, p, is also an important parameter in evaluating its thermodynamic performance. The density is increased from 1530 kg m to 1590 kg m" by the replacement of DEP with GAP. Since GAP is also compatible with DEP, double-base propellants composed of four major ingredients, NG, NG, DEP, and GAP, are also formulated. 

The combustion tests conducted for a rocket motor show that the combustion becomes unstable below 1.7 MPa and that the burning acquires a chuffing mode in the case of the uncatalyzed propellant. However, as expected, the combustion is stable even below 0.5 MPa for the nickel-catalyzed NC-NG propellant, as shown in Fig. 13.13. Propellants for which the flame temperature decreases with decreasing pressure tend to exhibit T combustion instability. 

V.V. Aleksandrov S.S. Khlevnoi, Surface Temperature During the Flameless Burning of Nitroglycerin Propellant , FizGoreniyaVzryva 6 (4), 438-43 (1970) (Russ) CA 75, 89714 (1971) [Prior exptn by these authors on a pro-pint consisting of NC, NG and DNT indicated that the surface temp, T, in nameless combustion does not depend on the initial temp. Other prior work to explore Tg involved measurement of the mean heat of vapn of NG and other propint volatiles at elevated temps and pressures. These measurements provided an estimate of... 

For comparison of NC-NG and NC-TMETN double-base propellants, both chemical compositions and thermochemical properties are listed in Table 4-13. Though the mass ratio of NC/NG (0.80) is much smaller than that of NC/TMETM (1.38), the combustion performance, such as Tf and Mg, appears to be equal, and is 109 kmolK/kg for both propellants. In the case of rocket motor operation, Isp and pp are also approximately equivalent for both propellants. 

The combustion wave of NC-NG-GAP propellant consists of successive two-stage reaction zones1161. The first gas phase reaction occurs at the burning surface and the temperature increases rapidly in the fizz zone. The second zone is the dark zone which separates the luminous flame zone from the burning surface. Thus, the luminous flame stands some distance above the burning surface. This structure is equivalent to that of the NC-NG double-base propellants described in this section. The temperature in the dark zone is increased from 1400 K to 1550 K at 3 MPa... 

Fig. 12.11 shows the structure of a rocket plume generated downstream of a rocket nozzle. The plume consists of a primary flame and a secondary flame.Fil The primary flame is generated by the exhaust combustion gas from the rocket motor without any effect of the ambient atmosphere. The primary flame is composed of oblique shock waves and expansion waves as a result of interaction with the ambient pressure. The structure is dependent on the expansion ratio of the nozzle, as described in Appendix C. Therefore, no diffusional mixing with ambient air occurs in the primary flame. The secondary flame is generated by mixing of the exhaust gas from the nozzle with the ambient air. The dimensions of the secondary flame are dependent not only on the combustion gas expelled from the exhaust nozzle, but also on the expansion ratio of the nozzle. A nitropolymer propellant composed of nc(0-466), ng(0-369), dep(0104), ec(0 029), and pbst(0.032) is used as a reference propellant to determine the effect of plume suppression. The burning rate characteristics of the propellants are shown in Fig. 6-31. Since the nitropolymer propellant is fuel-rich, the exhaust gas forms a combustible gaseous mixture with the ambient air. This gaseous mixture is ignited and afterburning occurs somewhat downstream of the nozzle exit. The major combustion products in the combustion chamber are CO, Hj, CO2, N2, and HjO. The fuel components are CO and H2, the mole fractions of which at the nozzle throat are co(0.47) and iH2(0.24).

C.E. Kirby, Flameless Combustion Mechanism of M-2 Double-Base Propellant , NASA Tech Note TND-6105 (1971) CA 74, 143953 (1971) [The author reports on the heat of reaction for the flameless combustion of M-2 double-base proplnt (NG 20, NC 77, and other ingredients 3%) detd at 2,07-1380kN/m2 by the use of differential scanning calorimetry and thermogravimetric analysis. The heat of reaction... 

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