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Passive Hydrocarbon Trap to Enable SULEV-30 Tailpipe Emissions from a Flex-Fuel Vehicle on E85 Fuel
ISSN: 1946-3952, e-ISSN: 1946-3960
Published April 03, 2018 by SAE International in United States
Citation: Lupescu, J., Xu, L., Nunan, J., and Alltizer, C., "Passive Hydrocarbon Trap to Enable SULEV-30 Tailpipe Emissions from a Flex-Fuel Vehicle on E85 Fuel," SAE Int. J. Fuels Lubr. 11(4):427-441, 2018, https://doi.org/10.4271/2018-01-0944.
Future LEV-III tailpipe (TP) emission regulations pose an enormous challenge forcing the fleet average of light-duty vehicles produced in the 2025 model year to perform at the super ultralow emission vehicle (SULEV-30) certification levels (versus less than 20% produced today). To achieve SULEV-30, regulated TP emissions of non-methane organic gas (NMOG) hydrocarbons (HCs) and oxygenates plus oxides of nitrogen (NOx) must be below a combined 30 mg/mi (18.6 mg/km) standard as measured on the federal emissions certification cycle (FTP-75). However, when flex-fuel vehicles use E85 fuel instead of gasoline, NMOG emissions at cold start are nearly doubled, before the catalytic converter is active. Passive HC traps (HCTs) are a potential solution to reduce TP NMOG emissions. The conventional HCT design was modified by changing the zeolite chemistry so as to improve HC retention coupled with more efficient combustion during the desorption phase. Increased trapping efficiently was achieved by (a) modifying the acidic properties of the zeolite, (b) inclusion of Pd in order to more efficiently trap alkenes and NOx, and (c) the introduction of a new redox function that promoted HC combustion prior to the full desorption phase of the trap. A 2.0 L direct-injection Ford Focus with E85 fuel, utilizing the newly designed HCT developed by Ford and Umicore and having a significantly reduced platinum group metal (PGM) loading of only 0.53 g/L, was able to lower NMOG emissions by about 60% compared to the baseline underbody three-way catalyst (TWC). This in turn achieved combined NMOG + NOx emissions at an average of 19 mg/mi (11.8 mg/km), just below the SULEV-20 limit. The new trap formulation not only improved HC storage and conversion efficiency but substantially decreased the PGM content in line with current LEV-II partial zero-emission vehicle (PZEV) underbody loadings and will ensure continued sales of future flex-fuel vehicles.