Aerosol-dynamics experiments and simulations of vehicle exhaust emissions

The type-approval regulatory framework of light- and heavy-duty vehicles in many countries includes a solid particle number (SPN) limit. Particle number measurements in the laboratory are typically conducted at a dilution tunnel using constant volume sampling (CVS). Particle losses that may occur at the transfer lines from the tailpipe to the dilution tunnel are not taken into account and can result in differences in measurements at different locations or in comparisons with direct tailpipe measurements, e.g., with portable emission measurement systems (PEMS). This study presents a model that calculates particle losses in standard laboratory setup transfer lines under steady and transient speed conditions of modern vehicles. The model was initially validated with experimental results. A parametric analysis showed that thermophoresis is the primary mechanism contributing to particle losses, with values exceeding 10% during diesel particulate filter (DPF) regeneration or highway trips of gasoline vehicles. Diffusional losses occur only at low exhaust flow rates, such as idling, but remain below 5% down to 10 nm particle sizes. Particle agglomeration in the exhaust flow of modern vehicles equipped with particulate filters can occur during DPF regeneration or for plug-in hybrids at high-load engine cold start, but result in less than 2% of losses when the whole test cycle is considered.Copyright (c) 2025 American Association for Aerosol Research