An experimental study of transient effects in a pulsed, piloted, non-premixed turbulent jet flame

This paper reports an experimental investigation of the effects of pulsing a pilot-stabilised turbulent non-premixed turbulent. The pulse consists of a burst of fuel that induces a sudden increase in the otherwise steady velocity from a value where the flame is fully burning to a level higher than the blow-off velocity. The duration of the pulse is 10ms. The transient velocity field is measured along with the high-speed imaging of LIF-OH as well as OH-chemiluminescence (OH*) at various axial locations in the jet. It is found that, with downstream distance, the pulse width is slightly shorter and the peak velocity of the pulse decays at a faster rate than the normal velocity decay of the fluid. The disturbance travels along the jet at the convective velocity. Image sequences of LIF-OH show that, in the region extending from about x/D∼15-35, the flame extinguishes totally for a duration similar to the pulse width. These findings support and extend findings reported earlier by the same group [1].