Rocket propellant specific impulse

Solid rocket propellant Specific impulse /N s kg""1 Flame temperature/K... 

The prediction of rocket propellant specific impulse, as well as impulse under other conditions, may be reliably accomplished by calculation using as input the chemical composition, the heat of formation, and the density of the component propellant chemicals. Not only impulse but also the composition of exhaust species (and of species in the combustion chamber and the throat) may be calculated if the thermodynamic properties of the chemical species involved are known or can be estimated. The present standard computer code for such calculations is that described by Gordon and McBride.44 Theoretical performance predictions using such programs are widely used to guide propellant formulation efforts and to predict rocket propellant performance however, verification of actual performance is necessary. 

As for chemical thermal rockets, the performance of the rocket vehicle depends strongly upon propellant specific impulse which in turn is dependent upon the enthalpy change during the expansion process. 

The mass flow rate of the engine being rhS, and with m being the unit mass flow rate of propellant and S the cross-sectional surface area of the engine outlet, the thrust of the rocket is given by the momentum balance T = mS g, with the ejection velocity of the propellant in relation to the body of the rocket. The specific impulse is equal to the thrust provided per unit weight of propellant consumed (and therefore ejected) ... 

Elemental fluorine has been studied as a rocket propellant as it has an exceptionally high specific impulse value. 

Oxidizers. The characteristics of the oxidizer affect the baUistic and mechanical properties of a composite propellant as well as the processibihty. Oxidizers are selected to provide the best combination of available oxygen, high density, low heat of formation, and maximum gas volume in reaction with binders. Increases in oxidizer content increase the density, the adiabatic flame temperature, and the specific impulse of a propellant up to a maximum. The most commonly used inorganic oxidizer in both composite and nitroceUulose-based rocket propellant is ammonium perchlorate. The primary combustion products of an ammonium perchlorate propellant and a polymeric binder containing C, H, and O are CO2, H2, O2, and HCl. Ammonium nitrate has been used in slow burning propellants, and where a smokeless exhaust is requited. Nitramines such as RDX and HMX have also been used where maximum energy is essential. 

Propellants and Explosives. Hydrazine fuels include anhydrous hydrazine (AH), monomethyUiydrazine (MMH), and unsymmetrical dimethyUiydrazine (UDMH) for military and space programs. These compounds are used mainly as bipropeUant fuels, ie, with oxidizers, in rockets such as the Titan, MX missile, and the Ariane (UDA4H7X30. Using oxygen or fluorine as the oxidizer, hydrazine is exceeded only by hydrogen in specific impulse, ie, kilograms of thmst developed for each kilogram of fuel consumed per second (196). 

The ratio of rocket thrust to propellant mass flow, commonly called the specific impulse (/9p) of the propellant, represents a measure of the force developed per unit mass flow of propellant. From Eq. (2), it is apparent that high propellant-flame temperatures and low molecular-weight combustion products are required to produce high 7sp. 

It is rather interesting that the maximum specific impulse of a rocket propellant system occurs when (T2iMW2)1/2 is maximized, even though the rocket combustion process is not one of detonation [17],... 

Most composite propellants in wide use today use ammonium perchlorate as the oxidizer component. While such propellants benefit from high specific impulse and a lower vulnerability than double-base propellants based on nitroglycerine, they have a significant environmental impact, the exhaust fumes being rich in corrosive hydrogen chloride leading to acid rain after the launch of missiles/rockets. 

Though the oxidation potentials of potassium nitrate (KN KNO3) and sodium nitrate (SN NaN03) are high, both metal nitrates generate combustion products of high Mg, Thus, the specific impulse becomes low when KN or SN is used in a rocket propellant KN and SN are used as major ingredients of explosives and in pyrotechnics. KN is a weU-known material as a major component of black powder. 

Since rocket propellants are composed of oxidizers and fuels, the specific impulseis essenhally determined by the stoichiometry of these chemical ingredients. Ni-tramines such as RDX and HMX are high-energy materials and no oxidizers or fuels are required to gain further increased specific impulse. AP composite propellants composed of AP particles and a polymeric binder are formulated so as to make the mixture ratio as close as possible to their stoichiometric ratio. As shown in Fig. 4.14, the maximum is obtained at about p(0.89), with the remaining fraction being HTPB used as a fuel component. 

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. 

Since the combustion temperature of AN pyrolants is very low compared with other composite pyrolants, their specific impulse when used as rocket propellants is also low. However, they are used as gas generators for the control of various types of mechanics owing to the low temperature and low burning rate characteristics. 

The specific impulse of a rocket motor, I, as defined in Eq. (1.75), is dependent on both propellant combushon efficiency and nozzle performance. Since is also defined by Eq. (1.79), rocket motor performance can also be evaluated in terms of the characterishc velocity, c, defined in Eq. (1.74) and the thrust coefficient, Cp, defined in Eq. (1.70). Since c is dependent on the physicochemical parameters in the combustion chamber, the combushon performance can be evaluated in terms of c. On the other hand, Cp is dependent mainly on the nozzle expansion process, and so the nozzle performance can be evaluated in terms of Cp. Experimental values of and Cpgxp are obtained from measurements of chamber pressure, p, and thrust, F ... 

Nozzleless rockets are very simplified and low-cost rockets because no nozzles are used. Their specific impulse is lower than that of conventional rockets even when the same mass of propellant is used. Normally, a convergent-divergent nozzle is used to expand the chamber pressure to the atmospheric pressure through an isentropic change, which is the most effective process for converting pressure into propulsive thrust The flow process without a nozzle increases entropy and there is stagnahon pressure loss. 

Though the pyrolants used in gas-hybrid rockets burn in a similar manner as rocket propellants, their chemical compositions are fuel-rich. The pyrolants burn incompletely and the combustion temperature is below about 1000 K. When an atomized oxidizer is mixed with the fuel-rich gas in the secondary combustor, the mixture reacts to generate high-temperature combustion products. The combushon performance designated by specific impulse, is dependent on the combinahon of pyrolant and oxidizer. 

Though the specific impulse of a solid rocket is determined by the energetics of its propellant, the specific impulse of a ducted rocket is determined by the mixture ratio of the fuel flow rate from the gas generator and the airflow rate induced from the atmosphere. The ram pressure in the rambumer is raised by the shock wave formed at the air-intake. The combustion in the rambumer further increases the... 

The performance of rocket propellants is commonly studied by means of the specific impulse which can be expressed as the thrust delivered per unit weight of propellant consumed as shown by equation (3.9). 

For firework rockets the most important factors include the weight of the rocket, the weight of the propellant, the specific impulse of the propellant and the shape and size of the rocket. 

Combustion Kinetics, Importance in Rocket Propel fonts of. A brief review of the relations between the equations for specific impulse and the several equations used in explaining combustion reactions were given by A. vanTiggelen, ComptRendCongrlnternl-Chim 31e, Liege 1958 (Pub as IndChimBelge, Suppl) 1, Ind 25-8 (Pub 1959) (in French)... 

Hercopel a unique all-epoxide cure composite solid propellant with excellent mechanical and ballistic properties. Its outstanding performance in extended environments makes it well suited for tactical missiles Double-Base Solid Propellants a wide variety of physical and ballistic properties which can be tailored to meet specific performance requirements. Their high specific impulse and excellent reproducibility are two of the many reasons Hercules double-base propellants are found in many of our rocket motors and gas generators used for both military and space applications... 

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