Sub-23 nm Particle Emissions from Gasoline Direct Injection Vehicles and Engines: Sampling and Measure

Nowadays, the regulation regards only the particles larger than 23 nm. The attention is shifting towards the sub-23 nm particles because of their large presence at the exhaust of the modern engines and their negative impact on human health. The main challenge of the regulation of these particles is the definition of a proper procedure for their measure. The nature of the sub-23 nm particles is not well understood, and their measure is strongly affected by the sampling conditions leading to not reliable measure. The aim of this paper is to provide information on the emissions of sub-23 nm particles from GDI vehicles/engines. At the same time, the presence of volatiles, which mainly contribute to the formation of sub-23 nm particles, was evaluated and the effect of sampling conditions was investigated. The analysis was performed on a 1.8L GDI powered vehicle, widely used both in North America and Europe, and a 4-cylinder GDI engine, whose features are similar to those of the vehicle. For both the facilities, vehicle and engine, the Worldwide harmonized Light vehicles Test Cycle (WLTC) was performed. Particle emissions were characterized in terms of number and size by using both commercial systems and prototype systems developed within the European Project SUREAL23. For the vehicle analysis a MEXA 2000 SPCS, for particles larger than 23 nm, and the Induced Current Aerosol Detector (ICAD), developed with in the SUREAL23 European Project, for particles larger than 11 nm, were used. A commercial Engine Exhaust Particle Sizer (EEPS), working in the size range 5.6-560 nm, was used for the sizing and counting of the particles emitted from the GDI engine. For the characterization of the sampling conditions on the measurements were performed on the GDI engine. In this case the sampling was performed by a Particle Measurement Programme (PMP) compliant system, which permits to change the main sampling parameters, i.e. the temperature of the dilution air and of the evaporation chamber, to enhance the nucleation and/or condensation of volatiles. At the decrease of the sampling temperatures, a large concentration of sub-23 nm particles were measured suggesting the presence of large volatile material especially in the first phase of the Cold-start WLTC.