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UW Madison team finds methylbutenol a potentially promising biofuel for blending with gasoline

A team at the University of Madison-Wisconsin studied critical sooting equivalence ratios and subsequent particulate formation during spark-ignition combustion for blends of ethanol, isobutanol (2-methyl-1-propanol), and methylbutenol (2-methyl-3-buten-2-ol) with gasoline using premixed prevaporized (PMPV) fueling.

Broadly, they found that increases in alcohol content consistently decreased the chemical sooting tendency and particulate emissions for all alcohol–gasoline blends tested.

The level of decrease in particulate on a volume basis was ordered isobutanol < methylbutenol < ethanol. On an oxygen weight percent basis, the order is ethanol < isobutanol < methylbutenol.

The researchers said that the results demonstrate that methylbutenol has a lower chemical sooting tendency than isobutanol, and, given its other properties, is a potentially promising biofuel for blending with gasoline. An open-access paper on the study appears in the journal Fuel.

Methylbutenol (2-methyl-3-buten-2-ol, MBO) is higher carbon-number alcohol terpenoid and naturally occurring volatile organic compound (VOC) emitted by certain species of pine trees in North America. Methylbutenol has also been identified as being able to be produced from lignocellulosic biomass by engineered E. coli which indicates the possibility for large scale production.

At this time, there is little information in literature referring to the use of methylbutenol as a fuel or fuel additive; however, an initial look at some of its properties shows promise. Its energy density is closer to gasoline than isobutanol at only 8% less on a volumetric basis. Its boiling point is in the middle of the range for gasoline and its HOV is the closest to gasoline out of the three alcohols. One of the reasons ethanol (and isobutanol) is favored as gasoline fuel additive is its high octane number, a characteristic which methylbutenol also shares.

Given its properties, it is possible that methylbutenol could be an attractive alternative to ethanol or isobutanol as a gasoline additive.

—Sakai and Rothamer (2022)

In the experiments, the different air–fuel mixtures were supplied to the engine in a well-mixed gaseous state allowing the chemical sooting tendency of the fuels, as measured by the critical sooting equivalence ratio, to be quantified.

The engine was operated at a fixed load and phasing with varying equivalence ratio to determine the critical sooting equivalence ratio and evolution of the particle size distribution (PSD) for each fuel.

Each alcohol was splash-blended with a gasoline blendstock for oxygenate blending (BOB) at three different blend levels. Ethanol was blended at 10, 20, and 30% by volume (E10, E20, and E30). Isobutanol and methylbutenol blends were matched to ethanol on an oxygen weight percent basis resulting in blends of 16, 32, and 49% and 18, 37, and 56% by volume for isobutanol and methylbutenol, respectively.

The results shown here indicate that methylbutenol performs similar to, and can exceed, isobutanol and ethanol in terms of particulate reduction in premixed SI combustion. Future work should include studies of methylbutenol–gasoline blends under direct-injection operation to examine its combustion and sooting performance when physical effects of the fuel are introduced.

—Sakai and Rothamer (2022)

Resources

  • Stephen Sakai, David Rothamer (2022) “Relative particle emission tendencies of 2-methyl-3-buten-2-ol–gasoline, isobutanol–gasoline, and ethanol–gasoline blends from premixed combustion in a spark-ignition engine,” Fuel, Volume 324, Part C, doi: 10.1016/j.fuel.2022.124638

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