Three years after embarking upon rigorous evaluation of a pool of more than 400 candidates (earlier post), researchers with the US Department of Energy (DOE) Co-Optimization of Fuels & Engines (Co-Optima) initiative have identified the six blendstocks—di-isobutylene, ethanol, fusel alcohol blend, isobutanol, isopropanol, and n-propanol—that exhibit the greatest potential to increase efficiency significantly when combined with petroleum-based fuels in boosted (or turbocharged) spark-ignition engines for light-duty vehicles.

Ten blendstocks from four chemical familes with the greatest potential to increase boosted SI engine efficiency (as determined by merit function scores). The assessment found the six blendstocks in white had the fewest significant barriers to adoption. Source: DOE.

Co-Optima research is also addressing challenges specific to medium-duty and heavy-duty trucks, exploring strategies for mixing-controlled compression ignition and advanced compression ignition engines.

While fuel economy ratings of today’s cars significantly outstrip those of just a decade ago, cost-effective efficiency improvements remain limited by existing engine designs and fuel formulas. A newly released DOE report—FY18 Year in Review—outlines how Co-Optima’s examination of fuels as dynamic design variables that can work with modern engines is providing industry with the scientific underpinnings needed to accelerate introduction of high-performance fuels and engines that reduce energy consumption, improve air quality, and lower drivers’ costs.

The report spotlights significant FY18 Co-Optima accomplishments including:

• Characterization of fuel properties and engine parameters capable of delivering a 10% increase in fuel economy for LD vehicles with boosted SI engines.

  Co-Optima research and analysis identified the fuel properties needed for optimal operation of boosted SI LD engines through development of a merit function. Because the merit function predicts the percent change in engine efficiency based on changes to fuel properties, it is a much better gauge to assess impacts of fuel changes than common metrics such as anti-knock index which do not relate directly to engine efficiency. The merit function quantifies the impact of six fuel properties—research octane number (RON), octane sensitivity (S), heat of vaporization (HOV), flame speed, particulate matter index (PMI), and catalyst light-off-temperature—on boosted SI efficiency.

  It represents the most detailed correlation to date of fuel properties and engine efficiency. The distinct algebraic form of the merit function has the unique attribute of being able to assess the tradeoffs between the impact of different fuel properties, revealing how to meet the same efficiency target through different combinations of fuel properties. For example, a decrease in RON can be offset by increasing S.

  —FY18 Year in Review

• Identification of 10 blendstocks from four chemical families with the greatest potential to increase boosted SI efficiency and break down technical, economic, and environmental barriers to their near-term commercialization, including the six blendstocks with the fewest barriers.

• Correlation of molecular structure with key fuel properties and metrics.

• Creation of new computational tools to more rapidly identify new blendstocks and interpret data.

• Establishment of modeling and analysis methods to characterize economic value and environmental performance across the supply chain.

• Demonstration that autoignition performance of a broad range of fuels under ACI conditions correlates poorly with octane index, highlighting the need for new metrics.

This objective scientific research is giving industry the knowledge and tools to more rapidly improve today’s combustion engines and petroleum-based fuels, while also blazing a trail for more revolutionary long-term changes in component design and fuel formulas.

—NREL Vehicle Technologies Program Manager John Farrell

Farrell served as Co-Optima project leader from its early planning stages and 2015 launch through December 2018. Fellow leadership team member Robert Wagner of Oak Ridge National Laboratory recently assumed management responsibilities for the project.

At this June’s Vehicle Technologies Office Annual Merit Review Meeting, DOE honored the Co-Optima research team for its achievements. The award recognizes the team’s groundbreaking work to improve fuels and engines synergistically—described in detail in the recently published report.

Much of the Co-Optima research is focused on 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. They have the potential to deliver deep cuts in polluting emissions from transportation, create much-needed new jobs in rural areas, leverage a billion-ton annual biofeedstock resource, and keep energy dollars in the United States, DOE says.

Sponsored by DOE’s Vehicle Technologies Office and Bioenergy Technologies Office, Co-Optima partners include NREL, Argonne, Idaho, Lawrence Berkeley, Lawrence Livermore, Los Alamos, Oak Ridge, Pacific Northwest, and Sandia National Laboratories.