Correlation of turbulent burning velocity for syngas/air mixtures at high pressure up to 1.0MPa

Instantaneous flame front structures of the turbulent premixed flames of syngas/air and CH₄/air mixtures were investigated using OH-PLIF technique at high pressure up to 1.0MPa, through which the turbulent burning velocities were derived and correlated with the turbulence intensity. Results show that both syngas/air and CH₄/air mixtures, S_T/S_L increases remarkably with the increase of u'/S_L particularly in the weak turbulence region. For the syngas/air mixture, the intensity of flame front wrinkle is promoted with the increase of hydrogen fraction in the syngas due to the increased preferential diffusive-thermal instability. Compared to CH₄/air mixture, the syngas flames possess much wrinkled flame front with much smaller fine cusps structure, and with increasing u'/S_L, the rate of the increase of S_T/S_L for the syngas/air mixtures is more significant than that of CH₄/air mixtures. This demonstrates that the increase of flame front area due to turbulence wrinkling is promoted by flame intrinsic instability for syngas/air mixtures. The values of S_T/S_L for all mixtures increase with the increase of pressure because of the decrease of flame thickness which promotes the hydrodynamic instability. A general correlation of turbulent burning velocity for the syngas/air and CH₄/air mixtures was obtained in the form of S_T/S_L∝a[(P/P₀)(u'/S_L)]ⁿ.