Physical Characterization of Exhaust Particle Emissions from Late Technology Gasoline Vehicles

The study assesses the feasibility of introducing the regulated particle number measurement procedure for the regulation of gasoline vehicles, focusing on the established cut-off size of 23 nm. A range of late technology gasoline vehicles were tested under regulated and unregulated test conditions. The results indicated a distinct emission behavior of Direct Injection Gasolines (G-DI), Port Fuel Injection gasolines (PFI) and Diesels equipped with Particulate Filters (DPF), that differed both in terms of the absolute levels but also with respect to the fraction of undetected nano-sized non-volatile particles. The latter was found to be around 20% (based on comparisons with a Condensation Particle Counter (CPC) having a 50% cut-off size at 4.5 nm) for three G-DI vehicles tested, but ranged between 40 and 70% for the two PFIs measured. Interestingly, a relatively large fraction of undetected nanosized was also observed for two late technology DPFs, ranging between 30 and 50%. To a large extent these differences originate from differences in the size distributions and the relatively blunt shape of the counting efficiency curve of PMP compliant CPCs. Under conditions favouring nucleation mode formation in the dilution tunnel, excessive particle concentrations were detected by the low cut-off size CPCs, and especially the one with a d50 at 4.5 nm, that could exceed those of the PMP compliant CPC by up to one order of magnitude. However, the concentration of these nano-sized particles was found to decrease with increasing the dilution ratio in the first stage of the Volatile Particle Remover (VPR), indicating that this is rather a volatile artifact possibly originating from re-nucleation of evaporated material downstream of the VPR. The study also investigated the potential offered by a range of available approaches to effectively control particle emissions from G-DIs. These included the use of a Gasoline Particulate Filter (GPF), the introduction of ethanol in the fuel but also an advanced engine concept combining port and direct fuel injection. The GPF system was found to very efficient in controlling particle number emissions under all driving conditions, having no visible impact on carbon dioxide emissions. The use of fuel with hi-ethanol content (75-85%) was also found to be beneficial especially at high engine loads (up to 97% reduction of non-volatile particle numbers ) and during cold start operation (up to 70% reduction). The tests with the “hybrid” G-DI-PFI vehicle indicated that there exists the potential for significant reduction of PM formation through engine measures. The non-volatile particle number emissions of this vehicle remained below the diesel limit over all hot start tests.JRC.F.8-Sustainable Transpor