Experimental Study of Erosive and Dynamic Burning in Polybutadiene-Based Composite Propellants

Erosive effects in polybutadiene-acrylonitrile- and hydroxyl-terminated-polybutadiene-based composite propellants are investigated using a planar geometry combustor. Head, mid, and aft-end motor pressure were measured as well as aft burning rate via the use of an ultrasonic transducer. The ultrasonic sensor performed very well, providing burning-rate histories that, when integrated, closely matched the measured web distance. The measurement revealed local unsteady behavior in some circumstances as well as a very high dynamic regression at ignition. From theoretical considerations, burning rate was shown to be a linear combination of base, erosive, and dynamic burning rate. The dynamic portion was removed, and erosive burning was studied using the classical Lenoir–Robillard model. Parameter estimates were made by fitting to an inferred burning rate based upon pressure measurements and confirmed by matching to ballistic reconstructions. The experiment covers mean chamber conditions ranging from 311 psi (2.14 MPa) to 641 psi (4.42 MPa) and port Mach numbers from 0.14 to 0.78. Data and reconstructions from five tests are included and indicate that the Lenoir–Robillard model is sufficient for estimating erosive burning. No significant differences were observed with regard to erosive burning for the polybutadiene acrylonitrile and hydroxyl-terminated polybutadiene propellants studied herein.