Analytical Examination of the Relationship Between Fuel Properties, Engine Efficiency, and R Factor Values 2019-01-0309
Efforts are underway globally to reduce the energy use and greenhouse gas footprint of transportation. In the United States, corporate average fuel economy, or CAFE, standards describe the minimum fuel economy that must be attained by each vehicle manufacturer each year based on vehicle sales. These standards will require substantial improvements in fuel economy in the coming decade. Within this context, there is renewed interested in the potential benefits that may be realized through improving the anti-knock performance of gasoline blends in the marketplace. Engine studies were performed at Oak Ridge National Laboratory (ORNL) using a model year 2013 Ford EcoBoost 1.6-liter, 4-cylinder engine. A matrix of fuels was studied to assess the octane improvement needed to enable compression ratio increase. ON/CR values of 5.6, 3.7, and 3.0 were used in combination with the measured RON values for the fuels in both the AVFL-20 Phase 3 and the FWG matrices to project the efficiency benefit of CR increase expected to be enabled by each fuel. These benefits were applied to baseline energy consumption values for a small SUV as projected by Autonomie and a surrogate for the EPA 5-cycle fuel economy developed to express the fuel economy improvements offered by each fuel as a single value. All of the fuels provided a decrease in total energy consumption, ranging from 1.5 – 6.0%. Impacts to volumetric fuel economy ranged from 6.6% poorer to 10.7% better. The difference in efficiency improvements projected for 3.0 ON/CR compared to 5.6 ON/CR ranged from 1.4 – 1.8% depending upon the fuel.