Electrical Conductivity Based Quality Measurement of Diesel Exhaust Fluid

Abstract

In an effort to reduce environmental pollution, the urea-selective catalytic reduction system is used to reduce NO_x emissions with urea additive diesel exhaust fluid (DEF) as reductant in the exhaust of diesel engines. ISO 22241-1:2006 specifies the quality characteristics of the DEF in order to maintain efficiency, and hence it is essential that the concentration of urea in DEF is accurately monitored. In this paper an online, four-electrode, temperature compensated, electrical conductivity measurement system based on Van der Pauw theory is proposed for measuring the variation in urea concentration in DEF. The equivalent circuit model of the measurement system is developed using the Randles circuit and the equivalent circuit parameters are determined from impedance analyses of system. The prototype of the measurement cell is fabricated with all associated electronics and tested for 0.25% change in urea concentration. The experimental results are compared with results obtained from the Randles equivalent circuit model of the measurement system. The temperature effect on the measurement system is abridged from 28.75 to 2.575 mV/grad with the design of simple electronic circuit.