Pyrolants as Igniters

Two types of igniters are used for ignition in solid rocket motors, those giving (i) high-volumetric and (ii) high-temperature combustion products. The combustion 

When a metallized energetic material is burned as a propellant igniter in a rocket chamber, a consequence of the aforementioned production of metal oxides as hot condensed particles is that there is very tittle associated pressure increase. However, the surface of the propellant grain in the chamber is ignited by the hot particles and a stable burning pressure is established. Typical metallized pyrolants used as igniters are shown in Table 11.1. 

Composition Mixture ratio by mass Metal oxides T K 

The most important process with regard to metal oxidation and combustion is the formation of metal oxides on the surface of the metal particles. Some metal particles become coated with an oxide layer that surrounds the unreacted metal, whereas in other cases finely divided metal oxides are formed that are expelled from the surface of the metal particle. When solid shells of metal oxides are formed, no additional supply of the oxidizer fragments (or molecules) to the metal particles is possible. The oxidation process is thus interrupted and incomplete combustion occurs. On the other hand, when the metal oxide is expelled from the surface, oxidizer fragments continue to be supplied to the underlying unreacted surface of the metal. 

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The smoke characteristics of three types of pyrolants, namely nitropolymer pyrolants composed of NC-NG with and without a nickel catalyst, and a B-KNO3 pyrolant, have been examined in relation to the use of these pyrolants as igniters of rocket motors. Though nitropolymer pyrolants are fundamentally smokeless in nature, a large amount of black smoke is formed when they burn at low pressures below about 4 MPa due to incomplete combustion. Metallic nickel or organonickel compounds are known to catalyze the gas-phase reaction of nitropolymer pyrolants. 

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