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We report the development of optimized fluorescent dye-doped tracer particles for gas-phase particle image velocimetry (PIV) and their use to eliminate ‘flare’ from the images obtained. In such applications, micron-sized tracer particles are normally required to accurately follow the flow. However, as the tracer size is reduced the amount of light incident on the particle diminishes and consequently the intensity of emitted light (fluorescence). Hence, there is a requirement to identify dyes with high quantum yield that can be dissolved in conventional tracer media at high concentrations. We describe the selection and characterization of a highly fluorescent blue-emitting dye, Bis-MSB, using a novel method, employing stabilized micro-emulsions, to emulate the fluorescence properties of tracer particles. We present the results of PIV experiments, using 1 µm tracer particles of o-xylene doped with Bis-MSB, in which elastically scattered ‘flare’ has been successfully removed from the images using an appropriate optical filter.

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Two-and three-component multi-phase air/fuel measurements have been performed on a GDI injector. UV-excitable fluorescent tracers have been used to seed the gas phase, and the naturally occurring droplets in the fuel are the other phase. A high-pressure multi-hole GDI injector was mounted in a rig with a glass barrel to simulate the engine cylinder and provide optical access. Images were obtained under controlled conditions of fuel pressure and injection duration. Flow phase and pulse order have been determined from a single 3CCD colour camera. Suitable corrective processes have been adapted and implemented to account for crosstalk and chromatic aberrations so that the uncertainty of the velocity vectors produced is comparable to that of conventional PIV using 532 nm illumination. Multi-phase air/fuel vector maps have been produced. A second colour camera has been added to obtain stereo velocity measurements providing previously unavailable simultaneous information on the multi-phase (fuel/air) interaction with three velocity components.

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