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

• OH-PLIF measurement was conducted for syngas turbulent premixed flames at 1.0 MPa.
• Flame front structure was compared for various syngas composition.
• Combined effect of pressure and syngas composition was examined.
• Different turbulence–flame interaction between syngas and CH4 was studied.
• Correlation of turbulent burning velocities was obtained at high pressure.

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 1.0 MPa, through which the turbulent burning velocities were derived and correlated with the turbulence intensity. Results show that both syngas/air and CH4/air mixtures, ST/SL increases remarkably with the increase of u′/SL 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′/SL, the rate of the increase of ST/SL 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 ST/SL 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 ST/SL ∝ a[(P/P0)(u′/SL)]n.