Particulate emissions of heavy duty diesel engines measured from the tailpipe and the dilution tunnel

In China particulate matter (PM) is the leading environmental risk factor to morbidity and mortality, with transport being the main source of PM pollution in cities. China VI emission limit standards, which are one of the most stringent worldwide, have only recently been introduced and there is lack of studies assessing the PM emissions of new engines. In Europe, there are discussions ongoing to permit sampling directly from the tailpipe with fixed dilution for determining the solid particle number (SPN) emissions during type approval of heavy duty engines; something that is practically allowed for on-road testing. In this study the particulate emissions of seven engines were measured. Three of them were fulfilling the China VI limits, two China V, while two of them were China III engines retrofitted with diesel particulate filters (DPFs). One system with evaporation tube was installed at the full dilution tunnel, as prescribed in the regulation, and another one with catalytic stripper was sampling from the tailpipe, both measuring >23 nm and >10 nm particles. The results showed a wide range of particulate emission levels depending on the engine, the existence of a DPF, the connection point of the crankcase ventilation, and the occurrence of active or passive regeneration. The system at the tailpipe measured on average 20% lower than the system at the dilution tunnel. The system at the dilution tunnel measured much higher during one regeneration due to re-nucleation of volatiles downstream of the evaporation tube. For one engine, the emissions of the evaporation tube system were more than double when the crankcase ventilation was connected downstream of the aftertreatment devices. The main message from this study is that a catalytic stripper is necessary for sub-23 nm measurements and tailpipe sampling with fixed dilution is a plausible option.