LAUSR

Abstract In the present work, different combustion modes and the transition mechanism were experimentally investigated in a confined combustion chamber. A H2–O2–N2 mixture with variable oxygen concentration was used as test fuel. Different numbers of perforated plates with varying porosities were employed to change the flame propagation velocity. Depending on the initial thermodynamic conditions, four types of combustion modes were observed: normal combustion (mode 1), end-gas autoignition without detonation (mode 2), end-wall detonation (mode 3), and side-wall detonation (mode 4). It was found that with the transition of the combustion mode from mode 1 to mode 4, the overall level of pressure and pressure oscillation increased due to autoignition and detonation. Moreover, the effects of ignition delay time and flame propagation velocity on the combustion mode transition were studied. With increasing oxygen concentration, the ignition delay time was shortened, and the flame propagation was accelerated, which consequently caused the combustion mode to evolve from mode 1 to mode 4. In addition, different perforated plate configurations were employed to separately investigate the effects of the flame propagation velocity on the combustion mode transition. In summary, the combustion mode was jointly affected by the ignition delay time and flame propagation velocity. Both a shorter ignition delay time and a higher flame propagation velocity were favorable for the occurrence of autoignition and detonation.