Solid-Fuel Ramjet Regression Rate Measurements Using X-Ray Radiography and Ultrasonic Transducers

The instantaneous fuel regression rate within a solid-fuel ramjet combustor was characterized using X-ray radiography and ultrasonic transducer measurements. Experiments were performed with cylindrical center-perforated hydroxyl-terminated polybutadiene fuel grains at three mass fluxes ([Formula: see text]) with consistent inlet total temperatures and chamber pressures. Ultrasonic transducer measurements demonstrated changes of web thickness ranging from 7.50 to 9.85 mm and regression rate measurements ranging from 1.35 to [Formula: see text]. The local maxima of change in the web thickness due to flow reattachment and erosive burning were consistently measured with the ultrasonic transducers. Changes in the port radius on the order of 8–9 mm and regression rates of approximately [Formula: see text] were deduced from the X-ray radiography images. The structure of the flow reattachment region was evident in measurements from the X-ray radiography images captured near the combustor entrance, whereas images captured at the midlength of the combustor exhibited more uniform fuel regression profiles. Ultrasonic measurements of change in the web thickness were consistently greater in magnitude relative to X-ray radiography measurements. X-ray radiography imaging allowed for the more accurate measurement of fuel regression with the greatest axial spatial resolution, whereas ultrasonic transducer measurements yielded the greatest radial spatial resolution. The change in web thickness calculated with weight-based techniques yielded smaller-magnitude measurements of change in the web thickness relative to X-ray radiography. The regression rate was largely invariant with the mass flux within the investigated operating regime.