Radiographic Regression Rate Measurements in a Ramjet Combustor with Metallized Solid Fuels

Time-dependent measurements of web thickness and regression rate along the port of aluminum-loaded and boron carbide-loaded, hydroxyl-terminated polybutadiene (HTPB) fuel grains were obtained in a solid fuel ramjet combustor with X-ray radiography. The combustor was operated at three mass flux conditions, ranging from [Formula: see text], with consistent chamber pressures and inlet air total temperatures of 1300 kPa and 750 K, respectively. A cross-correlation-based edge detection scheme was used to extract the fuel grain edges within X-ray radiography images collected at 15 Hz. Cross-sectional photographs of the postcombustion fuel grain surfaces exhibited evidence of flow reattachment and large aft-end regression. Aluminized fuel grains exhibited average weight-based regression rates of [Formula: see text], and boron-carbide-loaded fuel grains yielded average regression rates of [Formula: see text]. X-ray measurements of change in port radius at the head end of the combustion chamber indicated flow reattachment. The absolute maximum of change in port radius, which ranged between approximately 8.6 and 10.3 mm for aluminized fuel grains and approximately [Formula: see text] for boron-carbide-containing fuel grains, did not always coincide with the flow reattachment location. Time-averaged regression rate profiles measured with X-ray radiography were relatively uniform along the port axis but smaller in magnitude compared to the weight-based measurements: approximately [Formula: see text] for the aluminum-loaded fuel grains and [Formula: see text] for the boron-carbide-loaded fuel grains. Pre-ignition fuel regression, with a rate of [Formula: see text], was determined to be the cause of the overprediction of regression rate by weight-based measurements compared to X-ray measurements.