Speaker: Prof. Volker Sick

Department of Mechanical Engineering

University of Michigan

Abstract:

The turbulent nature of many technologically important processes requires that we study them with techniques that provide adequate spatial and temporal resolution. Furthermore, having the ability to measure non-phase-averaged image sequences is an important goal for advanced experimental investigations.

Meeting all three requirements as listed above is difficult and often, measurement techniques only address two out of the three. Popular examples are traditional planar laser induced fluorescence (PLIF) and particle image velocimetry (PIV) imaging techniques.

In this talk, PLIF and PIV techniques that acquire images at rates of 12 kHz and more for tens of thousands of subsequent frames are described.

The application of those techniques is demonstrated for studies of spray-guided gasoline direct injection engines. These rely on accurate and consistent preparation of an ignitable fuel/air mixture around the spark plug. Ignition occurs in the trailing part of the spray plume and one can expect to find large spatial and temporal gradients in fuel/air ratio that extent far above and below the ignition limits. Indeed, this is confirmed by following the spatial and temporal evolution of the equivalence ratio around the spark plug with crank angle resolution using PLIF of biacetyl or toluene that was added to isooctane fuel as a fluorescence tracer. The flow around the spark plug, investigated with PIV, is strongly affected by the spray and the spark discharge. Once combustion starts, it can be conveniently followed by monitoring hydroxyl chemiluminescence or thermal radiation from soot. Observed flame propagation reflects the development of the fuel/air mixing process throughout the engine cycle under study.