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Co-Optima Leads High-Speed Chase for Co-Optimization of Fuels and Turbocharged Spark-Ignition Engines

Mar. 30, 2020

For the past four years, researchers from the National Renewable Energy Laboratory (NREL) have collaborated with other top U.S. scientists, engineers, and analysts on the Co-Optimization of Fuels & Engines (Co-Optima) initiative. A new report summarizes findings from this first phase of the initiative, which has focused primarily on turbocharged (or “boosted”) spark-ignition (SI) engines for light-duty vehicles, identifying the fuel properties and engine parameters that mitigate knock and emissions, while maximizing efficiency and performance.

Pipettes over fuel samples marked with a blue grid.

NREL Vehicle Technologies Program Manager and former Co-Optima Project Leader John Farrell is lead author of the report, which highlights researchers’ answers to three vital questions:

  • What fuels do engines want?
  • What fuels should we make?
  • What will work in the real world?

“This Co-Optima work has had a profound impact on biofuels research here at NREL and around the world,” said NREL Senior Research Fellow, Advanced Fuels and Combustion Platform Leader, and Co-Optima Leadership Team Member Robert McCormick. “We are focusing more intently than ever on fuel options with properties that are demonstrably capable of delivering needed efficiency, performance, and environmental attributes.”

Much of the Co-Optima research is concentrated on components known as blendstocks, which can be produced from a wide spectrum of domestic resources including renewable, non-food, domestic biomass such as forestry and agricultural waste, as well as petroleum or natural gas. In addition to leading the national laboratory activities during this first phase, NREL researchers played a central role in the Co-Optima team’s:

  • Developing screening criteria, experiments, and simulations to identify six candidate blendstocks with the desired properties and the fewest significant practical barriers to adoption
  • Compiling the Fuel Properties Database for use by the wider research community
  • Establishing experimental and analytical methods to accurately predict how heat of vaporization impacts particulate matter formation and knock in SI engines with oxygenate-based fuels, revealing underlying engine conditions and causes of failure
  • Performing engine combustion experiments and emissions measurements to validate fuel property hypotheses, as well as data analyses and machine learning studies focused on creating new metrics to predict boosted SI engine soot emissions.

The Co-Optima team discovered that three fuel properties—research octane number, octane sensitivity, and heat of vaporization—have the greatest impact on boosted SI engine efficiency. Further assessment revealed that all six of the top-performing blendstocks (di-isobutylene, ethanol, a fusel alcohol blend, isobutanol, n-propanol, and isopropanol) have the potential for wide-scale commercialization, with the ability to reduce lifecycle greenhouse gas emissions and boost refinery profitability.

The first-of-its-kind Co-Optima effort is designed to provide American industry with the scientific underpinnings needed to maximize vehicle performance and efficiency, leverage domestic fuel resources, and reduce lifecycle emissions. Sponsored by the U.S. Department of Energy’s Office of Energy Efficiency and Renewable Energy’s Vehicle Technologies Office and Bioenergy Technologies Office, Co-Optima partners include NREL as well as Argonne, Idaho, Lawrence Berkeley, Lawrence Livermore, Los Alamos, Oak Ridge, Pacific Northwest, and Sandia National Laboratories, as well as more than 20 university and industry partners.

Read the full report, get more information on Co-Optima activities, and learn about NREL's fuels and combustion research.