Single Pulse Planar Laser Induced Fluorescence Imaging of Hydroxyl Radicals in a Spark Ignition Engine 932701

Planar laser induced fluorescence (PLIF) imaging of hydroxyl (OH) radicals is applied to a single cylinder spark ignited internal combustion engine (ICE) to study the development of turbulent flames. A single laser pulse from an excimer laser is formed into a two-dimensional (2-D) light sheet which intersects the flame in the combustion chamber at different delay times after the spark ignition, and 1 mm below the spark plug. The PLIF images are then captured with an intensified charge coupled device (CCD) camera, which is time gated with the laser pulse. The single-laser pulse PLIF images are then stored with a video cassette recorder (VCR) for further analysis. Real-time PLIF images were observed at different delay times after the spark ignition from consecutive engine cycles and at different engine speeds running on propane. Cycle-to-cycle variations were observed. Additionally, the turbulence interaction with the flame front increased as a function of the delay after the spark and the engine speed. The transition from a smooth flame front to a highly wrinkled turbulent flame front is observed. The flame development time decreased as a function of the engine speed. Simultaneous PLIF and elastic (Mie + Rayleigh) scattering images obtained yielded the reaction zone thickness, when liquid iso-octane fuel was used.