Effects of Fuel Octane Rating and Ethanol Content on Knock, Fuel Economy, and CO2 for a Turbocharged DI Engine

Engine dynamometer testing was performed comparing fuels having different octane ratings and ethanol content in a Ford 3.5L direct injection turbocharged (EcoBoost) engine at three compression ratios (CRs). The fuels included midlevel ethanol splash blend and octane-matched blend fuels, E10-98RON (U.S. premium), and E85-108RON. For the splash blends, denatured ethanol was added to E10-91RON, which resulted in E20-96RON and E30-101 RON. For the octane-matched blends, gasoline blendstocks were formulated to maintain constant RON and MON for E10, E20, and E30. The match blend E20-91RON and E30-91RON showed no knock benefit compared to the baseline E10-91RON fuel. However, the splash blend E20-96RON and E10-98RON enabled 11.9:1 CR with similar knock performance to E10-91RON at 10:1 CR. The splash blend E30-101RON enabled 13:1 CR with better knock performance than E10-91RON at 10:1 CR. As expected, E85-108RON exhibited dramatically better knock performance than E30-101RON. The data were used in a vehicle simulation of a 3.5L EcoBoost F150, which showed that E20-96 RON at 11.9:1 CR offers 5% improvement in tailpipe CO2 emissions and 1% improvement in miles per gallon (MPG) fuel economy relative to E10-91RON at 10:1 CR. E30-101 RON at 13:1 CR in this vehicle yielded 6-9% improvement in CO2 emissions and 2% worse to 1% better MPG fuel economy, depending on the drive cycle. The match blend fuels resulted in no opportunity for improved efficiency, and degradation of MPG fuel economy due to reduced heating value per volume.