Measured particulate behavior in a subscale solid propellant rocket motor

Particle size distributions were measured in the combustion chamber, exhaust nozzle, and exhaust plume of a small, two-dimensional rocket motor that utilized aluminized propellants. Various nozzle contours and pressures to 4.36 MPa were utilized. For pressures less than approximately 2.4 MPa, D32 of the multimodal size distributions entering the nozzle decreased with increasing pressure. Above 2.4 MPa, the higher propellant burning rates significantly reduced particle agglomeration and increased C* efficiency. At higher pressures, D32 entering the nozzle was quite small (2-6 /u.) and monomodal, and did not vary appreciably with pressure. During tailoff, D32 was significantly larger than during the steady burn, indicating another possible source for plume signature variations. Exhaust particle D32 was 1.2-1.6 /* (with a <2, 8, 28 /* trimodal distribution), independent of pressure, nozzle inlet contour, exit Mach number, degree of underexpansion, or location aft of the exit plane. The existence of a small number of larger particles indicated that either particle collision and/or surface effects occurred in the nozzle convergence, or that the larger particles at the nozzle entrance were concentrated near the wall, out of the viewing volume in the center of the flow.