Flame front structure of turbulent premixed flames of syngas oxyfuel mixtures

• OH-PLIF measurement was conducted for turbulent premixed syngas oxyfuel flames.
• Instantaneous flame front structures were derived in quantitative.
• Flame surface density and curvature radius of syngas oxyfuel turbulent flames were obtained.
• Turbulent flame front structure of syngas oxyfuel/air mixtures were compared with CH4/air.

In order to investigate oxyfuel combustion characteristics of typical composition of coal gasification syngas connected to CCS systems. Instantaneous flame front structure of turbulent premixed flames of CO/H2/O2/CO2 mixtures which represent syngas oxyfuel combustion was quantitatively studied comparing with CH4/air and syngas/air flames by using a nozzle-type Bunsen burner. Hot-wire anemometer and OH-PLIF were used to measure the turbulent flow and detect the instantaneous flame front structure, respectively. Image processing and statistical analyzing were performed using the Matlab Software. Flame surface density, mean progress variable, local curvature radius, mean flame volume, and flame thickness, were obtained. Results show that turbulent premixed flames of syngas possess wrinkled flame front structure which is a general feature of turbulent premixed flames. Flame surface density for the CO/H2/O2/CO2 flame is much larger than that of CO/H2/O2/air and CH4/air flames. This is mainly caused by the smaller flame intrinsic instability scale, which would lead to smaller scales and less flame passivity response to turbulence presented by Markstain length, which reduce the local flame stretch against turbulence vortex. Peak value of Possibility Density Function (PDF) distribution of local curvature radius, R, for CO/H2/O2/CO2 flames is larger than those of CO/H2/O2/air and CH4/air flames at both positive and negative side and the corresponding R of absolute peak PDF is the smallest. This demonstrates that the most frequent scale is the smallest for CO/H2/O2/CO2 flames. Mean flame volume of CO/H2/O2/CO2 flame is smaller than that of CH4/air flame even smaller than that of CO/H2/O2/air flame. This would be due to the lower flame height and smaller flame wrinkles.