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17 Jun 2002
A laser-induced fluorescence system reveals diesel spray concentrations and is set to aid engine design.
From Opto & Laser Europe
Researchers in Spain have used laser-induced fluorescence to measure diesel concentrations in isothermal sprays for the first time. The team says that the technique, which uses laser sheets to excite natural fluorescence and employs a new Mie scattering correction method, is promising for applications such as studying diesel spray formations and assisting engine design (Optics Express 10 309).
Cylindrical lenses manipulate the laser output into a sheet in an effect known as planar laser-induced fluorescence (PLIF). This illuminates the spray along one dimension, enabling the acquisition of tomographic data.
A pulsed Nd:YAG laser operating at 355 nm excites the diesel's natural fluorescence, so no additive compounds are required. José Pastor and colleagues from the Universidad Politécnica de Valencia used pulses with a maximum energy of 102 mJ and a pulse duration of 7 ns.
According to Pastor, commercial diesel fluoresces from 380 nm to about 500 nm, with a maximum seen at 396 nm. He used a cooled, intensified CCD camera fitted with a 10 nm wide interference filter centred on 400 nm to gather the fluorescent signal and form the PLIF image.
An interference filter 2 nm wide and centred at 532 nm was fitted to the camera to capture the scattered incident light. "Spurious 532 nm laser radiation allows isolation of the Mie scattering information, since the absorption coefficient of the fuel at 532 nm is negligible," said Pastor. This means that Mie scattering losses can be captured, and allows correction of the PLIF-calculated diesel concentration.
Pastor says that the main application of the EC-funded work will be to study the internal structure of diesel sprays, aiding the design of fuel-injection systems. "The objective is to reduce pollutant emissions and improve performance of diesel engines," he said.
Author
Jacqueline Hewett is news reporter on Optics.org and Opto & Laser Europe magazine.
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