湍流预混钝体火焰引燃几率的模拟和实验研究
The ignition characteristics of a premixed bluff-body burner under lean conditions wereinvestigated experimentally and numerically with a physical model focusing on ignitionprobability. Visualisation of the flame with a 5 kHz OH* chemiluminescence cameraconfirmed that successful ignitions were those associated with the movement of thekernel upstream, consistent with previous work on non-premixed systems. Performingmany separate ignition trials at the same spark position and flow conditions resultedin a quantification of the ignition probability Pign, which was found to decrease withincreasing distance downstream of the bluff body and a decrease in equivalence ratio.Flows corresponding to flames close to the blow-off limit could not be ignited, althoughsuch flames were stable if reached from a richer already ignited condition. A detailedcomparison with the local Karlovitz number and the mean velocity showed that regionsof high Pign are associated with low Ka and negative bulk velocity (i.e. towards thebluff body), although a direct correlation was not possible. A modelling effort thattakes convection and localised flame quenching into account by tracking stochasticvirtual flame particles, previously validated for non-premixed and spray ignition, wasused to estimate the ignition probability. The applicability of this approach to premixedflows was first evaluated by investigating the model’s flame propagation mechanismin a uniform turbulence field, which showed that the model reproduces the bendingbehaviour of the ST-versus-u curve. Then ignition simulations of the bluff-body burnerwere carried out. The ignition probability map was computed and it was found that themodel reproduces all main trends found in the experimental study.