The Global trend to reduce toxic emissions associated with the expansion of Diesel engines usage led to the implementation of new regulations aimed at the reduction of diesel engine emissions. Since 2012, the PRONCONVE P7, which mandates a reduction in NOx emissions, has been in place in Brazil. Therefore, heavy duty vehicle manufacturers had to implement an after treatment system in new vehicles, where an aqueous urea solution (ARLA 32 in Brazil or AdBlue in some other countries) is injected into a Selective Catalytic Reduction (SCR) system to convert NOx gases into N2 and water. The Arla 32 is stored in a tank which needs to be periodically refilled at gas stations. As the ARLA 32 is an aqueous solution with no characteristic odor or color, it can be easily adulterated without any visible sign. A diluted or contaminated ARLA 32 will affect the system performance and cause significant problems for the truck owner, such as loss of engine power, greater maintenance cost and potentially damage the SCR system.
In this work, we will describe the results of a feasibility study that shows that near-infrared spectroscopy can be used to detect adulterated ARLA 32. Near-infrared spectroscopy is an attractive technique because of its selectivity and low temperature sensitivity, unlike the traditional sensor technologies used in the automotive industry such as capacitive, inductive or impedance sensors. Additionally, we will also discuss the design of a low cost prototype sensor based on nearinfrared absorption that can be used to test ARLA 32 at the point of sale and discuss its limitations.