Goniometric characteristics of optical fibres for temperature measurement in diesel engine exhaust filters

Abstract

The accurate in situ, non-contact measurement of the temperature distribution within diesel after-treatment filters requires the employment of optical fibres with special tip geometry. The goniometric characteristics of optical fibres with flat, 45° angled and bent and polished tips are studied such that the specific radiation acceptance region can be determined. One 2 mm diameter fused silica and two 0.425 mm diameter sapphire optical fibres are examined. Detailed discussion of the relative intensity profiles observed for these fibres is presented. Of the three fibres evaluated, the 45° angled tip geometry provides the most precise response for measuring radiation emitted from the internal filter walls. Exploiting the characteristics of total internal reflection, the 45° angled tip fibre accepts the maximum quantity of incident radiation at an angle perpendicular to the optical axis.