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DOE Co-Optima report identifies top ten bio-blendstocks for efficiency in boosted SI engines

A new Co-Optimization of Fuels & Engines (Co-Optima) report describes the top ten biofuel-derived blendstock candidates. These top candidates, when blended with petroleum and used in a boosted spark ignition (BSI) engine, will offer environmental benefits and boost energy efficiency all while being available at a competitive price.

One of the first of its kind, this comprehensive systematic assessment includes a broad range of biomass-derived molecules and mixtures across many chemical families—more than 400 bio-derived molecules. This work will help the research community better understand the efficiencies that biofuels bring to the table, and identifies the biofuels that enable more efficient engine design and operation.

These blendstocks are best-suited for light-duty (LD) gasoline BSI engines. The blendstocks were identified using a fuel property basis using the BSI merit function. The merit function determines potential improvements in engine efficiency, was used to evaluate the performance of candidate bio-blendstocks in blends up to 30%. Those that exceeded the efficiency of an E10 premium were included in this list.

The top 10 blendstocks identified with the potential to increase engine efficiency by 10% using the efficiency merit function were:

  • i-Butanol
  • Cyclopentanone
  • Di-isobutylene
  • Ethanol
  • Furan mixture
  • Fusel alcohol mixture
  • Methanol
  • Prenol
  • i-Propanol
  • n-Propanol


The blendstocks all have the potential to reduce life-cycle greenhouse gas emissions by at least 60 percent.

All the top-performing blendstocks showed potential to be produced at a competitive cost. Six of these blendstocks had the fewest significant practical barriers to adoption and use: di-isobutylene; ethanol; isobutanol; n-propanol; isopropanol; and a fusel alcohol blend.

However, the team identified a number of outstanding challenges for the most promising blendstocks.

First and foremost, only three (ethanol, isobutanol and di-isobutylene) are currently allowed in market fuels. Any new blendstocks would have to go through the normal fuel certification process. Second, the production cost of all of blendstocks identified is significantly higher than fuels on the market today; finding ways to value the enhanced fuel properties could help, along with process improvements. Third, fuel system and infrastructure compatibility, emissions impacts, and health and safety impacts would have to be determined to be acceptable prior to the fuel certification process. Finally, the efficiency and environmental impacts must be confirmed in engine tests and more detailed analyses, along with opportunities for refinery integration.

—Top 10 Bio-Blendstocks

The Co-Optimization of Fuels & Engines (Co-Optima) team includes experts from nine national laboratories: Argonne, Idaho, Lawrence Berkeley, Lawrence Livermore, Los Alamos, Oak Ridge, Pacific Northwest, and Sandia National Laboratories and the National Renewable Energy Laboratory. The team’s expertise includes biofuel development, fuel property testing and characterization, combustion fundamentals, modeling and simulation from atomic scale to engine scale, and analysis.


  • Gaspar, Daniel J., West, Brian H., Ruddy, Danial, Wilke, Trenton J., Polikarpov, Evgueni, Alleman, Teresa L., George, Anthe, Monroe, Eric, Davis, Ryan W., Vardon, Derek, Sutton, Andrew D., Moore, Cameron M., Benavides, Pahola T., Dunn, Jennifer, Biddy, Mary J., Jones, Susanne B., Kass, Michael D., Pihl, Josh A., Pihl, Josh A., Debusk, Melanie M., Sjoberg, Magnus, Szybist, Jim, Sluder, C S., Fioroni, Gina, and Pitz, William J. (2019) “Top Ten Blendstocks Derived From Biomass For Turbocharged Spark Ignition Engines: Bio-blendstocks With Potential for Highest Engine Efficiency.” United States: N. p. Web. doi: 10.2172/1567705.



What is a boosted spark ignition (BSI) engine?
Is it turbocharged or supercharged, or something different?

Account Deleted

Boosted spark ignition engines can have a turbocharger and/or supercharger (some have both since turbos have a delay to spool up rpm at low speeds). This also includes electric turbochargers which act like a supercharger at low rpm.
Fuel octane requirements for gasoline engines ("spark ignition") vary with the compression ratio of the engine; diesel or compression ignition engines have cetane requirements that vary with the compression ratio. Engines with higher compression ratios, i.e. "boosted", usually require higher octane fuels. Higher the octane rating on fuel the less volatile (anti-knock on spark ignition engines) and the slower the fuel burns.

The Lurking Jerk

@gryf: That's what alcohol is really good at- significantly higher compression ratios than that of gasoline. So the engine can wring more work out of the fuel even though alcohol has less energy per gallon than gasoline.

Account Deleted

That's right Ethanol has an octane rating of 113, over a decade ago Ethanol Boosting Systems LLC showed that direct injection and turbocharging would increase the efficiency of spark ignition engines. Rolf Reitz who has a recent post in GCC (see raised the efficiency of an Ethanol fueled Reactivity Controlled Compression Ignition (RCCI) engine to efficiencies as high as 59% (achieved with E85/diesel).

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