Effects of inert dilution on the propagation and extinction of lean premixed syngas/air flames

The dilution effects of inert components N2 and CO2 on the propagation and extinction of lean premixed H2/CO/air syngas flames were experimentally and numerically investigated. Extinction stretch rates were measured using the counterflow technique while laminar flame speed data were obtained from literatures. Numerical simulations were conducted at 1-D freely propagating configuration and opposed-jet configuration with detailed chemistry and molecular transport description. The numerical results well predicted the experimental measurements. Both results revealed that CO2 dilution had more profound effect on flame propagation and extinction than N2 dilution. In addition, numerical simulation assessed the preferential importance in a rather quantitative manner among the three effects, i.e., the thermal effect, the diffusivity change effect and the chemical effect with artificial manipulation of mass diffusivities and chemical reactions of CO2 and N2. The results showed that the thermal effect dominated the reduction of laminar flame speed and extinction strain rate. The chemical effect caused by CO2 dilution was slightly stronger to the reduction of extinction limit than to that of laminar flame speed. The diffusivity change effect is negligible for both CO2 and N2 dilutions. N2 only acts as a thermal inert in the propagation and extinction of the H2/CO/air flames.