Measuring NOx during periodic technical inspection of diesel vehicles

Background

All light-duty (LD) and heavy-duty (HD) vehicles circulating in the European Union undergo regular checks during mandatory periodic technical inspections (PTI). These inspections promote road safety and environmental protection. Vehicles with defective deNOx aftertreatment systems can result in high emissions of NOx, which is an important air pollutant. The ongoing revision of the “so-called” Roadworthiness Package by the European Commission propose including a new method for measuring NOx from vehicles’ exhaust during PTI (NOx-PTI).

Results

The results obtained showed an increase in NOx emissions, 8 to 28 times, when the selective catalytic reduction (SCR) unit was not working. The applicability of the NOx-PTI idling test procedure to Euro VI HD vehicles was also investigated satisfactorily. Furthermore, methods to warm-up the vehicle’s aftertreatment prior to the NOx-PTI idling test, including standing still free accelerations and urban speed drives, as well as systems conditions before the test, were studied. Five different NOx analysers were assessed against reference equipment to ensure the accuracy of NOx measurements to assess their suitability for PTI purposes. The findings indicate that an urban speed drive is suitable for warming up both LD and HD vehicles. The tested analysers appeared to be suitable for use in PTI.

Conclusions

The high NOx emissions recorded when the SCR unit was not working, and their potential environmental impact, highlight the importance of a PTI test capable of detecting malfunctioning vehicles. The study demonstrated that the idle test procedure, testing conditions, and NOx analysers used were effective in performing a NOx-PTI check on both light- and heavy-duty Diesel vehicles, successfully discriminating between functioning and malfunctioning SCR systems.