Abstract
Onboard measurement of non-volatile particle number (PN) emissions with portable emissions measurement systems (PEMS) was introduced for the type-approval of passenger cars in Europe since 2017 and is foreseen for heavy-duty (HD) vehicles in 2021. First studies on the performance of PN-PEMS with HD engine exhaust revealed larger differences between established PN-PEMS techniques than what was observed for passenger cars. Particles forming in selective catalytic reduction (SCR) systems for NOx of late technology HD engines have recently been identified as a potential reason for the observed differences. The formed particles have a size distribution peaking below the regulatory limit of 23 nm and most importantly acquire high (more than one) positive charges at the elevated exhaust temperatures. Precise measurement of such highly charged nanosized particles with PN-PEMS instrumentation utilizing diffusion charger (DC) based counters requires proper conditioning of these charges. Two approaches were investigated in this study: (a) an electrofilter (EF) to completely remove charged particles below the regulated size and (b) a tandem negative-positive corona (TC) charger to directly condition pre-charged particles. The two technical solutions were tested alongside the unmodified DC-based PN-PEMS, a PN-PEMS utilizing a condensation particle counter (CPC) and a reference stationary PN system using exhaust of two SCR-equipped HD engines. The results confirmed that the particles forming in such SCR systems are responsible for the observed inconsistencies and that both technical solutions efficiently address the interferences of these pre-charged nanoparticles.
Highlights
Air pollution is recognized as an important global environmental and health risk factor
The results confirmed that the particles forming in such selective catalytic reduction (SCR) systems are responsible for the observed inconsistencies and that both technical solutions efficiently address the interferences of these pre-charged nanoparticles
The results of the present study proved that the previously reported overestimations of diffusion charger (DC)-based
Summary
Air pollution is recognized as an important global environmental and health risk factor. In Europe, the most serious pollutants in terms of harm to human health are particulate matter (PM), nitrogen dioxide (NO2 ) and ground-level ozone (O3 ) [1]. PM causes damage to ecosystems and cultural sites, Appl. Sci. 2019, 9, 1051 and reduced visibility and is recognized as an important global risk factor for disease [2]. Vehicle (USA) and the introduction of the non-volatile particle number (PN) method in the European Union (EU). This method counts non-volatile (sometimes called solid) particles, defined as those surviving a thermal pre-treatment stage at 350 ◦ C, with a diameter greater than 23 nm [3]. The limit value is 6 × 1011 particles per km (#/km) for passenger cars or per kWh (#/kWh) for heavy duty (HD) engines
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