Impact of AdBlue Composition and Water Purity on Particle Number Increase

Previous studies have shown that dosing AdBlue into the exhaust system of diesel engines to reduce nitrogen oxides can lead to an increase in the number of particles (PN). In addition to the influencing factors of exhaust gas temperature, exhaust gas mass flow and dosing quantity, the dosed medium itself (AdBlue) is not considered as a possible influence due to its regulation in ISO standard 22241. However, as the standard specifies limit value ranges for the individual regulated properties and components for newly sold AdBlue, in reality there is still some margin in the composition. This paper investigates the particle number increase due to AdBlue dosing using several CPCs. The increase in PN is determined by measuring the number of particles after DPF and thus directly before dosing as well as tailpipe. Several AdBlue products from different sources and countries are measured and their composition is also analyzed with regard to the limit values regulated in the standard. This shows that differences in the PN increase can be determined for the various products. In addition, two measurements are carried out with pure water as a main component of AdBlue in the form of single and double distilled water. Interestingly, the dosing of pure water also shows an increase in PN depending on the purity of the water. Furthermore, two AdBlue products are artificially aged in order to violate the standardized limit values, which is a feasible use case with regard to ISC tests, and subsequently measured. Since these impurities cannot be influenced but have a noticeable effect on the measured PN, it is important to quantify this and, if necessary, to take it into account in legislation.