Effect of Carbon Dioxide on the Laminar Burning Speed of Propane–Air Mixtures

This experimental research examined the effect of CO₂ as a diluent on the laminar burning speed of propane–air mixtures. Combustion took place at various CO₂ concentrations (0–80%), different equivalence ratios (0.7$<ϕ<$1.2) and over a range of temperatures (298–420 K) and pressures (0.5–6.2 atm). The experiments were performed in a cylindrical constant volume chamber with a Z-shaped Schlieren system, coupled with a high-speed CMOS camera to capture the propagation of the flames at speeds up to 4000 frames per second. The flame stability of these mixtures at different pressures, equivalence ratios, and CO₂ concentrations was also studied. Only laminar, spherical, and smooth flames were considered in measuring laminar burning speed. Pressure rise data as a function of time during the flame propagation were the primary input of the multishell thermodynamic model for measuring the laminar burning speed of propane-CO₂-air mixtures. The laminar burning speed of such blends was observed to decrease with the addition of CO₂ and to increase with the gas temperature. It was also noted that the laminar burning speed decreases with increasing pressure. The collected experimental data were compared with simulation data obtained via a steady one-dimensional (1D) laminar premixed flame code from Cantera, using a detailed H₂/CO/C₁–C₄ kinetics model encompassing 111 species and 784 reactions.