Experimental and Numerical Study of Flame Kernel Formation Processes of Propane-Air Mixture in a Pressurized Combustion Vessel

Fuel lean combustion and exhaust gas dilution are known to increase the thermal efficiency and reduce NOx emissions. In this study, experiments are performed to understand the effect of equivalence ratio on flame kernel formation and flame propagation around the spark plug for different low turbulent velocities. A series of experiments are carried out for propane-air mixtures to simulate engine-like conditions. For these experiments, equivalence ratios of 0.7 and 0.9 are tested with 20 percent mass-based exhaust gas recirculation (EGR). Turbulence is generated by a shrouded fan design in the vicinity of J-spark plug. A closed loop feedback control system is used for the fan to generate a consistent flow field. The flow profile is characterized by using Particle Image Velocimetry (PIV) technique. High-speed Schlieren visualization is used for the spark formation and flame propagation. To support the experimental activity and to better understand the effects of local flow and turbulence on the combustion process, CFD simulations were carried out at both reacting and non-reacting conditions using the OpenFOAM code with suitable libraries (Lib-ICE) developed for combustion modeling. The full vessel geometry was considered and the rotation of the fan, used to generate turbulence and velocity fields, was modeled. In this way it was possible to identify the expected combustion regimes and to clarify the effects of the spark-plug geometry on the flame propagation process.