Flame-spreading behavior in a fin-slot solid rocket motor grain (part ii)

To accurately predict the overall ignition transient for the reusable solid rocket motors of the space shuttle booster with head-end fin slots, it is necessary to have the knowledge of the flame-spreading rates in the fin-slot region. This paper is the second of a two part study and deals with the development of a flame-spreading correlation in the fin-slot region. A subscale (1:10) pie-shaped fin-slot motor was designed to perform diagnostic measurements for studying the flame-spreading behavior on the exposed propellant surface. Dynamic similarity was considered in the igniter designsothe impinging jet had a similar exit angle onto the propellant surfacein the fin-slot section. Flame-spreading measurements were gathered using a high-speed digital camera and nonintrusive optical measurement methods through an array of 36 near-infrared fast-response photodetectors installed perpendicular to representative regions of the propellant surface. Results showed that the flame-spreading phenomena was highly nonuniform, starting in the downstream portion of the fin-slot region before traveling back toward the igniter. A correlation was developed for the dimensionless flame-spreading time interval showing that it was inversely proportional to the pressurization rate to a power of 0.62, which depends strongly upon the flow parameters of the igniter induced flow and local propellant grain geometry.