NREL releases first findings from Co-Optimization of Fuels & Engines initiative

In Colorado, 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.

The report highlights researchers’ answers to three vital questions:

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

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 feedstocks 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.