Traditional port-fuel injection vehicles are quickly being replaced by the GDI technology in many markets. It is expected that GDI vehicles will represent around 50% of the vehicle fleet in 2020. These vehicles have been introduced promising enhanced engine power and fuel efficiency and hence lower CO₂ emissions in comparison with PFI vehicles. However, an important drawback of the GDI technology is the release of nanoparticles of unknown toxicity.

GDI vehicles can release up to 10¹² particles/km, exceeding those of current diesel vehicles, which are now equipped with filters, by orders of magnitude. In other words, most GDI vehicles cannot fulfill the Euro-5 particle number limit of 6 × 10¹¹ particles/km applied to diesel vehicles, which is valid for all new type approvals since September 2011 and for all new cars since January 2013.

GDI particles resemble those of diesel vehicles without aftertreatment. They are agglomerates of soot-like nanoparticles formed in the engine under high pressure. In 2012, the WHO classified untreated diesel exhaust as a group 1 carcinogen inducing lung cancer in humans. Due to the striking similarities, concerns on GDI exhausts are on the rise because these exhausts might also be carcinogenic to humans. Therefore, detailed studies on the genotoxic potential of GDI vehicle exhausts are urgently needed to assess these new risks.

—Muñoz et al.

In the study, the team compared emissions of a flex-fuel Euro-5 GDI vehicle operated with gasoline (E0) and two ethanol/gasoline blends (E10 and E85) and reported effects on particle, polycyclic aromatic hydrocarbon (PAH), and alkyl- and nitro-PAH emissions and assessed their genotoxic potential.

They applied two driving cycles simulating transient and steady driving. They used the worldwide harmonized light-duty vehicle test cycle (WLTC), which includes urban, extra-urban, highway, and motorway driving. The cycle was investigated under cold- (cWLTC) and hot-start conditions (hWLTC). They also applied a steady-state cycle (SSC) representing mean velocities of the WLTC and idle.

The researchers established a relationship between particle number (PN) and PAH emissions under transient and steady driving under hot- and cold-start conditions. The findings indicated that the release of particles and PAHs, including the genotoxic ones, are well-correlated and that blending with ethanol reduces particle and PAH formation in the engine.

Ethanol blending improves the combustion efficiency and suppresses particle, PAH, and nitro-PAH formation in the engine, thereby lowering the genotoxic potential of GDI vehicle exhausts.

Percentage PAH reduction and genotoxic potential. Upper diagrams compare PAH reductions (%) from E10 (left) and E85 (right) blends relative to gasoline (E0). The influence of ring number in hot- (red) and cold-started (blue) WLTC (first row) and boiling point (°C) of individual PAHs (second row) in the hot WLTC is given. Cumulated genotoxic potentials (ng TEQ/km) of genotoxic PAHs and respective patterns are shown in lower diagrams. Name, color code, toxicity equivalence factor of genotoxic PAHs, and fold-reduction relative to E0 data in the cWLTC are also included. Muñoz et al. Click to enlarge.

Resources

• Maria Muñoz, Norbert V. Heeb, Regula Haag, Peter Honegger, Kerstin Zeyer, Joachim Mohn, Pierre Comte, and Jan Czerwinski (2016) “Bioethanol Blending Reduces Nanoparticle, PAH, and Alkyl- and Nitro-PAH Emissions and the Genotoxic Potential of Exhaust from a Gasoline Direct Injection Flex-Fuel Vehicle” Environmental Science & Technology doi: 10.1021/acs.est.6b02606