Velocity, Vorticity, and Strain-Rate Ahead of a Flame Measured in an Engine Using Particle Image Velocimetry

Particle Image Velocimetry (PIV) was used to make instantaneous velocity measurements over a 24 mm by 32 mm area in a fired two-stroke cycle engine. The unburned-gas regions of the photographs were successfully interrogated adjacent to the flames and with sufficient resolution to resolve the velocity integral-length scales. A highpass filtering algorithm, different from that used in a previous motored-engine study, was implemented to allow for the arbitrary flame boundary. The large-scale vorticity in this study was considerably higher than in a previous study where a different engine was used. The large-scale normal and shear strain-rates distributions revealed only a small increase over those in the previous study, and the magnitude of the vorticity and shearstrain-rate appeared to be larger near the flame. However, the data are too limited to offer general conclusions about the flow.