A new experimental technique for the study of turbulent premixed flames

In this paper, a new experimental technique is described that has been developed to study turbulent premixed flame kernels in the early stages of propagation. The turbulent flow field was generated in a shock tube, using a shock wave to produce a flow over a round bar grid. The shock wave was then reflected back into this grid flow to amplify the turbulent fluctuations and reduce the mean velocity to zero. The gas was ignited after the passage of the reflected shock, and the flame kernels observed for periods of up to 12 ms before the arrival of the reflected expansion fan. Measurements of the turbulent burning velocity were made from schlieren photographs of the propagating flame, with values of the rms fluctuating velocity being obtained in a nonreacting flow using an LDA system. Turbulent methane/air flames were studied using this technique, with rms velocities up to 7.5 ms(-1) being obtained in the region behind the reflected shock. Turbulent Reynolds numbers in the range 3400-5800 were achieved, with Damkohler numbers in the range 0.8-6.5. The results obtained were compared with the previous correlations and were shown to lie in the broken flamelet and corrugated flame regimes.