Parameters Influencing Regression Rate of Solid Rocket Fuels

This review paper provides a compilation of works from 1966 to 2018 pertaining to the study of altering the burn rate for solid fuel rockets. This paper serves to catalog the current state of research on burn rate altering additives and other common methods for tailoring the burn rate of solid rocket fuels for specific applications. Solid rocket motors (SRM) and hybrid rocket engines (HRE) both utilize solid fuels, while SRMs use a solid oxidizer mixed into the fuel and HREs use liquid or gas oxidizer separated from the fuel. There are many different methods for controlling the burn rate of these motors and engines, such as: fuel and oxidizer choice and concentration, additives, grain configuration, and combustion chamber pressure. The methods for controlling burn rate for each particular rocket type are discussed in their own sections, however most additives that mix with the solid fuel remain the same across the SRMs and HREs with the exception of those that behave as oxidizers. The main goal of this study of the modification, not just increasing, of the burn rate for these fuels is their use in long distance unmanned aerial vehicle (UAV) applications. HREs have many benefits that make them ideal for UAVs, including: low cost, added safety and ease of storage, and low burn rate. HRE have the added benefit of increased safety due to the physical separation of the fuel and oxidizer, and any additives that release oxygen during decomposition would not be ideal. Additives are a key element discussed in this paper, as the concentration can be varied to precisely tailor the burn rate of a mixture. The additives alter the burn rate by influencing the activation energy, heat of reaction, and efficiency of energy feedback.