Evaluation of Measurement Procedures for Solid Particle Number (SPN) Measurements during the Periodic Technical Inspection (PTI) of Vehicles.

Periodic technical inspection (PTI) of vehicles guarantees safety and environmental compliance during their lifetime. Particulate matter emissions of diesel vehicles are controlled with opacity measurements. After the introduction of diesel particulate filters (DPFs), particulate matter emissions have drastically decreased and the sensitivity of the opacity method is questioned. Several countries have already or are planning to introduce a solid particle number (SPN) method at their PTI that will either substitute or complement opacity measurements. However, there are differences in the measurement procedures and the limit values. In this study, we compared the different approaches and investigated topics which are still not well defined, such as the uncertainty of the SPN-PTI instruments, repeatability of the procedures, impact of the DPF fill state, and the correlation between type-approval SPN emissions and SPN concentrations during PTI tests. Finally, we compared the SPN-PTI instruments with the opacity meters. Our results showed that SPN-PTI measurements can detect tampered and defective DPFs. We also made suggestions on the measurement procedures and the concentration limit.