Assessment of particulate matter emission from Diesel vehicles equipped with DPF and fromgasoline direct injection (GDI)vehicles using sampling by TEM grid filtration
Résumé
Epidemiological studies have linked exposure to particles matter less than 2.5 microns in diameter (PM2.5) with adverse health effects as cardiovascular or pulmonary diseases that cause premature death. The contribution of the transportation sector to the average total emission of PM2.5 in the ambient air is 1 2% [1]. This latter value is likely higher in areas near emission sources (i.e. urban area). Since 2011, all Diesel cars are equipped with a Diesel Particulate Filter (DPF) and respect European standards (Euro 6) for particulate matter emissions which combine a limit number (PN: 6.0×10^11 particulates/km) with a limit mass (PM: 4.5 mg/km). For gasoline direct injection (GDI) light vehicles, there is a limit number of 6.0×10^12part/km (Euro 6b) until 2017. Beyond, PN will be limited to 6×10^11 part/km (Euro6c) as Diesel vehicles with the introduction of the WLTC cycle, designed to be as close as possible to the real driving conditions. In this study, which is part of CAPPNOR project (supported by ADEME), we used a new particle collection technique, a MSP (Mini - Particles Sampler) [2], based on filtration through one class of TEM dedicated supports, namely TEM porous grids,to directly collect and characterize particles emitted from Euro5 vehicles: two Diesel vehicles equipped with two DPF technologies (a DPF regenerated with a Fuel Borne Catalyst (FBC) and a Catalytic Diesel Particulate Filter (CDPF)) and one Gasoline Direct Injection (GDI) vehicle. Collections were carried out during various engine operations and three driving cycles (NEDC, WLTP and ARTEMIS). Characterizations were performed with TEM coupled with EDX analysis and were focused on the physical size distribution, the morphology, the mass and the chemical compositions of particles emitted during cold and hot start and also during DPF regenerations for Diesel vehicles. Diesel engines equipped with DPF mainly emit particles during cold start and DPF regenerations. During cold start particles emitted are mainly carbon soot. During the DPF regenerations, PM size distributions are classified as bimodal, mainly consisting of the nucleation and accumulation modes. Typically, these particles are composed of a complex mixture of soot and droplet like particles. The increase of engine speeds during cycles resulted in increase of fractions of metal contents (Ni, Fe, Cr, Mn...) in particulate matters. GDI engines can emit significantly high PN concentration, mainly carbon soot, depending on the engine operating conditions. GDI will need additional improvements to reach the threshold of Euro 6c, whether by engine calibration and/or by implementing a particulate filter.