Flame front/turbulence interaction for syngas fuels in the thin reaction zones regime: turbulent and stretched laminar flame speeds at elevated pressures and temperatures

Experiments were performed in dump-stabilized axisymmetric flames to assess turbulent flame speeds (S-T) and mean flamelets speeds (stretched laminar flame speeds, S-L,S-k). Fuels with significantly different thermodiffusive properties have been investigated, ranging from pure methane to syngas (H-2-CO blends) and pure hydrogen, while the pressure was varied from 0.1 to 1.25 MPa. Flame front corrugation was measured with planar laser-induced fluorescence (PLIF) of the OH radical, while turbulence quantities were determined with particle image velocimetry (PIV). Two different analyses based on mass balance were performed on the acquired flame images. The first method assessed absolute values of turbulent flame speeds and the second method, by means of an improved fractal methodology, provided normalized turbulent flame speeds (S-T/S-L,S-k). Deduced average Markstein numbers exhibited a strong dependence on pressure and hydrogen content of the reactive mixture. It was shown that preferential-diffusive-thermal (PDT) effects acted primarily on enhancing the stretched laminar flame speeds rather than on increasing the flame front corrugations. Interaction between flame front and turbulent eddies measured by the fractal dimension was shown to correlate with the eddy temporal activity.