The internal flow structures of detonation wave were experimentally investigated in an optically accessible hollow rotating detonation combustor with multiple chamber lengths. The cylindrical RDC has a glass chamber wall, 20 mm in diameter, which allowed the capture of the combustion self-luminescence. A chamber 70 mm in length was first tested using C2H4–O2H and H2H–O2H as propellants. Images with a strong self-luminescence region near the bottom were obtained, confirming the small extent of the region where most of the heat release occurred as found in previous research. Based on the visualization experiments, RDC with shorter chamber walls of 40 and 20 mm were tested. The detonation wave was also observed in the shorter chambers, and its velocity was unaffected by the difference in chamber length. Thrust performance was also maintained compared to the longer chamber, and the short cylindrical RDC had the same specific impulse tendency as the cylindrical (hollow) or annular 70-mm chamber RDC. Calculation of the pressure distributions of various chamber lengths revealed that they were consistent with the measured pressure at the bottom and exit. The short-chamber cylindrical RDC with equal length and diameter maintained thrust performance similar to the longer annular RDC, further expanding the potential of compact RDC.
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