| Abstract
| - Many combustion systems use the technique called exhaust gas recirculation. Thus, the effects of N 2/CO 2 dilution on the combustion characteristics have been of interest. In this study, the dilution effects on the flame propagation velocity (FPV) of an oxy-methane premixed mixture were investigated using a state-of-the-art annular stepwise diverging tube. The relationship between FPV and the length scale was measured for various equivalence ratios in the dilution ratio range 65-75% N 2 and 50-65% CO 2. The characteristic variations of FPV in each dilution case could be described as a surface in a concentration-length-velocity diagram, and this provides a bird’s eye view of the dilution effects on flame propagation. Two distinctive scalar values of the quenching distance and the critical FPV were investigated. At the same dilution ratio, CO 2 dilution caused more significant variation than N 2 dilution did regarding FPV, quenching distance, and flammable limits. In particular, the critical FPV was compared with the laminar burning velocity (LBV) calculated using a PREMIX code employing GRI-3.0. In addition, fictitious species (F-N 2/F-CO 2) were used in the reaction mechanism to distinguish chemical effects. Conclusively, results showed that CO 2 dilution reduced LBV significantly not only by its larger thermal capacity but also by its active involvement in the chemical reaction.
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