Hollow-core waveguides for particle image velocimetry

The use of a hollow-core fibre waveguide to deliver a light sheet for particle image velocimetry (PIV) inside an optically accessed internal combustion engine is presented. Fibre delivery applied to such small scale, high-speed fluid flow applications gives the potential to minimize the optical access required to an enclosed measurement volume. A 0.54 mm internal diameter hollow fibre was used to deliver 13 mJ, 8 ns pulses from a frequency-doubled (532 nm) Nd:YAG laser. The output from the fibre was focused into a thin light sheet and used to take PIV measurements as the test engine was cycled. Comparative measurements were also taken using a conventionally (bulk optic) delivered light sheet with closely similar properties. The PIV data taken using the two techniques are compared to demonstrate that the use of a hollow-core fibre generates similar data quality to conventional measurement techniques and is a viable alternative when complex access is required.