Instantaneous Flow Field Effects on the Flame Kernel in S.I.Engine by Simultaneous Optical Diagnostics

Many studies were done about the link between the flame kernel behavior and the global combustion stability. It was shown that aerodynamics and mixture preparation are predominant for flame propagation. Multidimensional optical diagnostic techniques have become an important tool to study combustion inside engines. One-point measurements of flow field have been done in order to look at the impact on global combustion analysis. But the effect of the instantaneous flow field at the vicinity of the spark plug and at the spark timing on the flame kernel was not well explored. It is the objective of this paper: to quantify as well as possible, the effects of the instantaneous local velocity field at the vicinity of the spark plug and just prior spark, on the flame kernel propagation. For that, in a classical transparent 4-valve Spark Ignition engine, fuelled with methane to provide homogeneous mixture, we firstly characterized mean flow fields, by Particle Imaging Velocimetry, for different conditions. Secondly, we get instantaneous flow field prior ignition and quasi-simultaneously, recorded chemiluminescence images. It was found that the flame kernel development is strongly related with the local aerodynamics flow-field.