A thickness measurement technique based on low-coherence interferometry applied to a liquid film with thermal gradient

Nicolas Borgetto (1) , Cédric Galizzi (1) , Frédéric André (1) , Dany Escudié (1)

1 CETHIL - Centre de Thermique de Lyon

Certain combustion engine technologies can imply the formation of a liquid film on the walls of the combustion chamber, which produces significant pollutant emission. In this context, experimental study of the flame/film interaction is necessary, which in turn necessitates the measurement of the liquid film thickness. For this purpose, a low-coherence interferometry technique has been used in a specific configuration involving reactive flow and, consequently, temperature gradients, which contribute to measurement errors because of the thermo-optic coefficient. In the present work, in order to estimate these errors, the group refractive indexes of hexane, heptane and octane were measured by low-coherence interferometry according to the temperature at a wavelength of 1310 nm. The comparison of the thermo-optic coefficients indicated a good concordance between experimental data and the application of models derived from electromagnetic theory. The knowledge of these coefficients permits the estimation of a fairly reasonable film thickness uncertainty.

Mots clés: Low-coherence interferometry Liquid film Thickness measurement Group refractive index Temperature gradient Alkanes

Domaines: Thermique [physics.class-ph]; Thermique [physics.class-ph]

Nicolas Borgetto, Cédric Galizzi, Frédéric André, Dany Escudié. A thickness measurement technique based on low-coherence interferometry applied to a liquid film with thermal gradient. Experimental Thermal and Fluid Science, 2010, 34 (8), pp.1242-1246. ⟨10.1016/j.expthermflusci.2010.05.004⟩. ⟨hal-00541810⟩