Experimental investigation of combustion modes and transition mechanism in confined combustion chamber

摘要

In the present work, different combustion modes and the transition mechanism were experimentally investigatedin a confined combustion chamber. A H_2 –O_2 –N_2 mixture with variable oxygen concentrationwas used as test fuel. Different numbers of perforated plates with varying porosities were employed tochange the flame propagation velocity. Depending on the initial thermodynamic conditions, four types ofcombustion 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 withthe transition of the combustion mode from mode 1 to mode 4, the overall level of pressure and pressureoscillation increased due to autoignition and detonation. Moreover, the effects of ignition delay timeand flame propagation velocity on the combustion mode transition were studied. With increasing oxygenconcentration, the ignition delay time was shortened, and the flame propagation was accelerated, whichconsequently caused the combustion mode to evolve from mode 1 to mode 4. In addition, different perforatedplate configurations were employed to separately investigate the effects of the flame propagationvelocity on the combustion mode transition. In summary, the combustion mode was jointly affected bythe ignition delay time and flame propagation velocity. Both a shorter ignition delay time and a higherflame propagation velocity were favorable for the occurrence of autoignition and detonation.