Rotating Detonation Engine Combustion Chamber Linear Acoustic Analysis

Rotating detonation engines (RDEs) have been shown to produce detonation waves that travel at velocities between the hot-gas speed of sound and the Chapman-Jouguet (CJ) velocity. The reason why the wave velocities of rotating detonation engines are typically less than those of ideal CJ detonations has yet to be explained, although this deficit is commonly attributed to incomplete combustion. To understand this phenomenon, a literature survey of experimental detonation wave velocities reported in different RDEs has been conducted. Linear acoustic theory was then applied to the corresponding combustion chamber geometries. The RDE combustion chambers were simulated as closed-closed thin-gap constant area annular acoustic cavities. The bulk speed of sound of the cavities was assumed to be the burned gas acoustic velocity with properties determined using NASA Chemical Equilibrium with Applications (CEA) solver. The reported engine fundamental frequencies are in good agreement with the natural acoustic frequencies of the combustion chamber geometries. The reported engine fundamental frequencies were found to couple with the pure tangential or tangential-longitudinal mixed modes of the combustion chambers.