Abstract
The solid (or nonvolatile) particle number (SPN) emissions of light-duty and heavy-duty vehicles and engines are regulated in the European Union. The measurements are conducted from the tailpipe during on-road tests, but from the dilution tunnel in the laboratory under controlled conditions. Recently, dedicated laboratory studies for the evaluation of the measurement uncertainty at the two sampling locations found differences due to the formation of nonvolatile particles, i.e., particles that do not evaporate in the thermal pre-treatment part of the particle number systems. In order to investigate the origin of these particles, measurements at the tailpipe, the transfer tube, and the dilution tunnel were conducted with cold and hot dilution and instruments with different lower detection limits (4 nm, 10 nm, and 23 nm). The results showed that sub-23 nm nonvolatile particles could be detected in the dilution tunnel, but not at the tailpipe, due to growth of low volatility compounds in the transfer tube and the finite residence time in the thermal pretreatment part of the particle number systems. When measuring below 23 nm, diluting at the tailpipe or reducing the residence time in the transfer tube to the dilution tunnel is important in order to minimize such differences.
Highlights
In the European Union (EU) the solid particle number (SPN) emissions are regulated since 2011 for compression ignition light-duty vehicles, since 2013 for heavy-duty diesel engines, since 2014 for positive ignition heavy-duty engines and gasoline direct injection vehicles, and since 2017 for non-road engines (19–560 kW), inland waterway vessels (>300 kW), and rail traction engines [1,2]
While the solid (or nonvolatile) particle number (SPN) sampling on the road is done directly from the tailpipe of the vehicle, the sampling in the laboratory is done after dilution of the whole exhaust in a dilution tunnel with constant volume sampling (CVS)
This study focused on a moped, formation of sub-23 nm particles was reported with motorcycles [25], a compressed natural gas (CNG) vehicle, and a diesel one during regeneration of the DPF [11]
Summary
In the European Union (EU) the solid (or nonvolatile) particle number (SPN) emissions are regulated since 2011 for compression ignition (diesel) light-duty vehicles, since 2013 for heavy-duty diesel engines, since 2014 for positive ignition heavy-duty engines and gasoline direct injection vehicles, and since 2017 for non-road engines (19–560 kW), inland waterway vessels (>300 kW), and rail traction engines [1,2]. For light-duty vehicles the tests are complemented by on-road real driving emissions (RDE) tests since 2017 (Regulation (EU) 2017/1151). For the on-road tests, the portable emissions measurement systems (PEMS) have simpler specifications: they must contain an evaporation tube with wall temperature >300 ◦ C. The comparison of the PEMS and the PMP systems in the laboratory, the so-called validation test, gives differences up
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