Specific impulse theoretical

No upper limit is given. In Ref 5 is discussed its detonation by impact and in Refs 7 8 are briefly discussed its toxicity and fire expln hazard s. Hutchison (Ref 5a) gives its specific impulse (theoretical) as 197, viscosity 0.6c/stokes at 20° and temp of decompn 1600°. It will only propagate detonation in a pipe of diam greater than 1% inches... 

Aluminum-containing propellants deflver less than the calculated impulse because of two-phase flow losses in the nozzle caused by aluminum oxide particles. Combustion of the aluminum must occur in the residence time in the chamber to meet impulse expectations. As the residence time increases, the unbumed metal decreases, and the specific impulse increases. The soHd reaction products also show a velocity lag during nozzle expansion, and may fail to attain thermal equiUbrium with the gas exhaust. An overall efficiency loss of 5 to 8% from theoretical may result from these phenomena. However, these losses are more than offset by the increase in energy produced by metal oxidation (85—87). 

The influence of metal type on the specific impulse of propints has been described previously in this article (Table 16). The max theoretical specific impulse and density impulses (ISp x p ) for the oxidizers AN, AP and hydrazinium nitrate with 15 weight percent -fCH2)- binder have been calculated for various fuels (Ref 24). These data are in Tables 49-51. The ISp performance of nitronium perchlorate, lithium perchlorate and potassium perchlorate and metallized fuels with 4CH2>- binder are given in Table 52 (Ref 43)... 

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. 

When some portion of the AP particles contained within an AP composite propellant is replaced with nitramine particles, an AP-nitramine composite propellan-tis formulated. However, the specific impulse is reduced because there is an insufficient supply of oxidizer to the fuel components, i. e., the composition becomes fuel-rich. The adiabatic flame temperature is also reduced as the mass fraction of nitramine is increased. Fig. 7.49 shows the results of theoretical calculations of and Tf for AP-RDX composite propellants as a function of Irdx- Th propellants are composed of jjxpb(0-13) and the chamber pressure is 7.0 MPa with an optimum expansion to 0.1 MPa. Both I p and T)-decrease with increasing Irdx- The molecular mass of the combustion products also decreases with increasing Irdx due to the production of Hj by the decomposition of RDX. It is evident that no excess oxidizer fragments are available to oxidize this H2. 

When HNF or ADN particles are mixed with a GAP copolymer containing aluminum particles, HNF-GAP and ADN-GAP composite propellants are formed, respectively. A higher theoretical specific impulse is obtained as compared to those of aluminized AP-HTPB composite propellants.However, the ballistic properties of ADN, HNIW, and HNF composite propellants, such as pressure exponent, temperature sensitivity, combustion instability, and mechanical properties, still need to be improved if they are to be used as rocket propellants. 

Fig. 14.7 Theoretical and experimental specific impulse and Isp efficiency of aluminized AP-RDX-HTPB propellants as a function of (AI).

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.

In this equation F(th) is the theoretical thrust, R is the average rate of burning, /gp is a performance parameter related to the propellant called the specific impulse, D is the propellant density and Ap is the average area of the burning surface. 

In the simple two-component system of PVC binder and oxidizer, the important propellant properties of specific impulse, density, adiabatic flame temperature, and burning rate increase with an increase in solids loading. This is shown in Figure 8, where theoretical calculated values of specific impulse, adiabatic flame temperature, and density are given for a range of oxidizer content for PVC plastisol propellants comprised of only binder and oxidizer. [Calculated values of specific impulse reported throughout this paper are for adiabatic combustion at a rocket chamber pressure of 1000 p.s.i.a. followed by isentropic expansion to 1 atm. pressure with the assumptions that during the expansion process chemical compo-... 

The temperature coefficient of motor chamber pressure, irK, has been reported (17) to be about 0.09%/°F. in the static firing of small motors loaded with 2-in. diameter tubular grains (inside-outside burning). Measured specific impulse was reported to be 90% of theoretical. Higher percentages of theoretical specific impulse are obtained in larger motors. 

Figure 23. Theoretical specific impulse for an AP-A1-PBD propellant. Pc/Pe = 1000/14.7 p.s.i.a. optimum expansion 0° half-angle...

Theoretical Performance Requirements. Each propulsion system has a minimum performance level that must be achieved to conduct its required mission. After careful analysis of the mission profile, this required performance level is usually related in terms of required specific thrust or specific impulse (I8). This nomenclature defines the pound of thrust produced per pound per second of propellant flow ... 

Specific impulse, calculated by this technique, represents a 100% conversion of chemical energy to mechanical energy, and, therefore, is an upper limit to the performance available from a real rocket engine. However, regardless of the technique utilized, the theoretical Is of each of the systems are compared on a common basis (e.g.y at the same combustion chamber pressure, nozzle geometry, exit pressure, etc.) with the desired performance level dictated by the mission and engine system rquirements. 

Combustion efficiency is usually described in terms of specific impulse efficiency (percentage of theoretical specific impulse achievable). Specific impulse efficiencies depend greatly on both chemical composition of the propellant and the physical design of the injector, combustion chamber, and nozzle configuration. Efficiencies can thus vary from 90-98%. 

Table II. Theoretical Specific Impulse of Selected Propellant Systems...

Maximum theoretical specific impulse, lb.(f) sec./lb.(m)6 with liquid H2 391 422... 

Table VI. Maximum Theoretical Specific Impulse Values of Heterogeneous Fuels with Nitrogen Tetroxide...

The addition of aluminum powder to AP-nitramine composite propellants increases the specific impulse, as in the case of AP composite propellants. Fig. 7.50 shows the theoretical fp and 7 -values for AP-RDX composite propellants containing as a function of The propellants are composed of... 

Recently, the use of fluorine as an oxidant has been considered feasible. E.g. the reaction of fluorine with hydrazine gives a particularly large theoretical specific impulse (7S) amounting to 298 sec. 

A recent publication [71] suggests mixtures of oxygen difluoride as an oxidizer. This substance can give an 7S as high as ca. 400 sec when mixed with hydrogen. The mixture of oxygen difluoride and unsymmetrical dimethylhydrazine has a theoretical specific impulse of ca. 330 sec. 

Still higher magnitudes of specific impulse can be obtained theoretically by using non-chemical reactions, e.g. ions and electrons which arrive in an electric field at a speed close to that of light. Another method is based on the use of photon flux with the speed of light. 

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