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NREL study probes emissions impact of butanol-gasoline blends in light-duty vehicles

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Summary of significant emissions results from the fuel testing. Credit: ACS, Ratcliff et al. Click to enlarge.

Results of a study led by a team from the National Renewable Energy Laboratory on the impact of butanol-gasoline blends on light-duty vehicle emissions suggest that widespread deployment of n-butanol or i-butanol in the gasoline pool could result in changes to the estimated emissions of alcohols and carbonyls in the emissions inventory. Given equivalent deployment of butanols and ethanol, the results suggest emissions of unburned alcohols would decrease, but carbonyl emissions would increase; some of these compounds have poorly understood health effects, they note.

The carbonyls acetaldehyde and formaldehyde are classified as carcinogens or probable carcinogens by the National Institute for Occupational Safety and Health (NIOSH), International Agency for Research on Cancer, and the EPA. NIOSH considers butyraldehyde to have similar reactivity and mutagenicity to acetaldehyde.

This study points to the need for more extensive emissions measurements for these new fuels as well as research to gain a better understanding of the biological effects of the NMOG components that they produce, the team concludes.

In the study, published in the ACS journal Environmental Science & Technology, they splash-blended certification gasoline with alcohols to produce four blends: ethanol (16 vol%); n-butanol (17 vol%); i-butanol (21 vol%); and an i-butanol (12 vol%)/ethanol (7 vol%) mixture.

They tested these fuels in a 2009 Honda Odyssey (a Tier 2 Bin 5 vehicle) over triplicate LA92 cycles, and determined emissions of oxides of nitrogen, carbon monoxide, non-methane organic gases (NMOG), unburned alcohols, carbonyls, and C1−C8 hydrocarbons (particularly 1,3-butadiene and benzene).

Among the large, statistically significant fuel effects on regulated emissions:

  • i-butanol delivered a 29% reduction in CO from E16 and a 60% increase in formaldehyde emissions, compared to certification gasoline.

  • Ethanol produced the highest unburned alcohol emissions of 1.38 mg/mile ethanol, while butanols produced much lower unburned alcohol emissions (0.17 mg/mile n-butanol, and 0.30 mg/mile i-butanol); these reductions were offset by higher emissions of carbonyls.

  • Formaldehyde, acetaldehyde, and butyraldehyde were the most significant carbonyls from the n-butanol blend, while formaldehyde, acetone, and 2-methylpropanal were the most significant from the i-butanol blend.

  • The 12% i-butanol/7% ethanol blend was designed to produce no increase in gasoline vapor pressure. This fuel’s exhaust emissions contained the lowest total oxygenates among the alcohol blends and the lowest NMOG of all fuels tested.

Resources

  • Matthew A. Ratcliff, Jon Luecke, Aaron Williams, Earl Christensen, Janet Yanowitz, Aaron Reek, and Robert L. McCormick (2013) “Impact of Higher Alcohols Blended in Gasoline on Light-Duty Vehicle Exhaust Emissions,” Environmental Science & Technology doi: 10.1021/es402793p

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