A study on optical characteristics and quality monitoring of diesel exhaust fluid

In an effort to reduce environmental pollution, the urea-Selective Catalytic Reduction (SCR) system is used to reduce NOx emissions from diesel engines with diesel exhaust fluid (DEF) as a reductant. ISO 22241-1:2006 specifies the quality characteristics of the DEF in order to maintain efficiency of the SCR system and hence it is essential that the concentration of urea in DEF is accurately monitored. In this paper an optical based measurement system is proposed for measuring the variation in urea concentration in DEF. The prototype of the measurement system is fabricated with all associated electronics and tested for 1% change in urea concentration with ultraviolet (UV), visible and near-infrared (N-IR) optical source. The measurement system is found to be highly repeatable with a sensitivity of 0.0734 V/% of urea in UV range, 0.0706 V/% of urea in visible range and 0.0595 V/% of urea in IR range. The other contribution of this work includes calculation of molar absorptivity constant and absorbance spectrum of the urea solution at various concentrations using standard UV-visible-NIR spectrophotometer.