Quality monitoring of diesel exhaust fluid in vehicles using diffractive interference sensors

In this paper, we describe a simple design for an optical sensing device based on differential interferometry that can be deployed as an in-line sensor for monitoring the quality of diesel exhaust fluid inside engines of diesel vehicles. This sensor can precisely determine (to within ±1% and lower) the percentage of urea in diesel exhaust fluid (DEF), which is a critical reactant in the selective catalytic reduction (SCR) process for reducing harmful nitrous oxide emissions from diesel vehicles into the environment. The operating principle is based on diffraction of laser light from a regularly spaced microarray. Preliminary performance results indicate that our sensor can precisely determine the concentration of urea in the DEF to within ±0.0045%.