Liquid propellant systems

To establish the relationship between current liquid propellant applications and the available propellant technology, this paper has been divided into three sections. A section on basic propellant considerations describes the normal parameters used to evaluate propellant candidates and their influence on the propulsion system. Although such considerations have been thoroughly discussed in many previous publications (e.g., Ref. 3), their importance in establishing the basic criteria for propellant system selection requires a limited review in this text as a background aid to the reader. Current liquid propellants and propellant candidates are discussed in a second section in terms of capabilities and limitations as well as potential application areas (the compositions of all propellants discussed are defined in the Nomenclature section at the end of this article). Finally, a section of propellant tailoring illustrates examples of propellant formulation and describes propellant problem-solving techniques. In conclusion, the results of these considerations are illustrated by the current liquid propellant systems. 

As a result of this constant evaluation and compromise between the demands of the vehicle and propulsion systems and the current propellant technology, various liquid propellant systems have been developed and are being applied in current vehicle systems (Table IV). In Table IV thrust level is used to demonstrate the size of the propulsion system. Some of the systems in this table have been phased out, while others are still in development. However, Table IV does represent the current status of operational liquid bipropellant systems. 

Mechanism for Deriving Energy. The mechanism by which propulsive energy is derived from propellant systems containing metals and their compounds is somewhat different from that of conventional liquid propellant systems. For hydrazine and nitrogen tetroxide, for example, their combustion leads to the formation of N2, H20, and H2 through a relatively simple series of intermediate species ... 

Much has been written on the drawbacks and benefits of various fuel/oxidizer systems. The purpose of this report is to discuss the efforts of chemist and engineer in developing a new liquid propellant system ready for use in a tactical mission. 

Figure IV. A. 1. immediately predicts that of elements with atomic numbers greater than 10 only Mg. Al. and Si and their hydrides would be worth considering from a specific impulse point of view. Mg, Al, and Si being metals, can be adopted in a liquid system, only as slurries. Some of their alkylates may be liquids however, no matter in what form they are introduced in liquid propellant systems their performance will not be higher than hydrogen. The reason is that these metals do not have a heat release appreciably greater than hydrogen and also form solid oxide products. Such products cannot be expanded through the nozzle and thus a specific impulse penalty is paid.

Applications. To date, the liquid propellant systems used in chemical propulsion range from a small trajectory control thruster with only 0.2 lbf (0.89 N) thrust for orbital station-keeping to large booster rocket engines with over l. 0 million lbf (4.44 MN) thrust. Bipropellant propulsion systems are the most extensively used type today for... 

It can be seen that future storable liquid propellant systems are in the 300-315 sec. range while future solid systems are around 290 sec. 

I T itrogen tetroxide is presently the work horse earth-storable oxidizer in liquid propellant systems. Present methods of analysis are wet chemical methods and are nonspecific. In order to fully understand the difficulties encountered in analyzing this compound, a brief review of its chemical and physical properties is presented. 

Liquid Propellant system based on two or more substances capable of spontaneous ignition on contact. 

On testing the shock sensitivity of materials for liquid-propellant systems, explosive reactions of graphite in OF2 were observed under shock loading at intensities corresponding to about 8200 atm [1]. 

---