Effect of High RON Fuels on Engine Thermal Efficiency and Greenhouse Gas Emissions 2019-01-0629

Increasing fuel octane is a well-known enabler for increasing spark-ignited engine efficiency. This research explores the impact of such a strategy on ‘well-to-wheel’ greenhouse gas emissions by considering 1) increases in emissions from producing higher octane fuels in the refinery, and 2) reductions in vehicle emissions through use of fuel-efficient engines optimized for such higher octane fuels. It also examines the impact of increases in fuel cost when refineries shift fuel production to higher octane. Three refinery configurations with different capacities to produce higher octane fuels were studied by simulating operations at three levels of high-octane gasoline production, as a function of the octane value for the high-octane grade. Two spark-ignited engine designs were considered, with different potential to take advantage of higher octane fuel to increase efficiency. ‘Well-to-tank’ GHG emissions increased modestly with higher octane production, while fuel costs increased strongly at high octane production levels. The net impact on WTW GHG emissions (gCO2/mile) and fuel cost ($/mile) both depended on how effectively the engine could take advantage of higher octane fuel. The more octane-sensitive engine design allowed for reduced WTW GHG emissions as octane increased. This engine also enabled lower cost-per-mile for modest fuel cost increases, but not at high octane production levels. The engine optimized for current U.S. regular fuel showed little WTW GHG response to increased octane, and cost-per-mile increased with high octane production.