Investigation of the Flame Stability and Laminar Burning Speed of Propylene/Air/Carbon Dioxide Mixtures Under Conditions of Elevated Temperatures and Pressures

Abstract Propylene is a chemical compound with the molecular formula C3H6. It is considered a natural refrigerant and has gained attention in recent years due to its low environmental impact. However, it is highly flammable. To reduce its flammability, it is proposed to mix propylene with carbon dioxide. In this study, the laminar burning speed of mixtures of propylene, carbon dioxide, and air has been measured at high temperatures and pressures. Pictures of flame propagation are captured by a Z-shaped Schlieren system with a high-speed complementary metal-oxide-semiconductor (CMOS) camera. These pictures have been used to determine if the flame is smooth or it is cellular and unstable. The measurement was performed in a constant volume cylindrical chamber. Laminar burning speed was obtained only for those flames that were smooth and spherical. Also, burning speed was only measured for flame radii larger than 4 cm. The burning speed was calculated by a thermodynamic model with the pressure rise data as an input. Propylene/air/carbon dioxide mixtures were burned at different initial temperatures, pressures, and fuel/air equivalence ratios (ϕ) and diluted with concentrations of carbon dioxide (D). The experimental measured values of the burning speed were fitted to power-law correlation. The laminar burning speed was calculated at the temperature range of 298 K–500 K, pressure range of 0.5 atm–4.2 atm, equivalence ratio range of 0.8–1.2, and concentrations of CO2 range of 0–60% in the unburned mixture. These data have increased the range of data from the previously reported values drastically.