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Diminishing Benefits of Federal Reformulated Gasoline (RFG) Compared to Conventional Gasoline (CG)
ISSN: 1946-3952, e-ISSN: 1946-3960
Published December 20, 2018 by SAE International in United States
Citation: Hoekman, S., Leland, A., and Bishop, G., "Diminishing Benefits of Federal Reformulated Gasoline (RFG) Compared to Conventional Gasoline (CG)," SAE Int. J. Fuels Lubr. 12(1):5-28, 2019, https://doi.org/10.4271/04-12-01-0001.
The Federal reformulated gasoline (RFG) program originated with the 1990 Clean Air Act Amendments to address high ozone and air toxics levels in major urban areas. These areas include portions of 17 states and represent approximately 30% of the total U.S. gasoline volume. Initially, formulation changes were limited to addition of oxygen and reductions in benzene and fuel Reid vapor pressure (RVP) levels. These reformulations were intended to meet minimum emissions reduction targets for volatile organic compounds (VOCs), air toxics, and oxides of nitrogen (NOx) when compared to a 1990 baseline gasoline in a “1990 technology” vehicle fleet. The United States Environmental Protection Agency (U.S. EPA) developed two computational models, the Simple Model in 1995 and the Complex Model in 1998, for use in demonstrating compliance with the regulations.
This article reviews the derivation and evolution of the RFG program. Initially, RFG’s emissions reduction benefits compared to conventional gasoline (CG) resulted primarily from differences in fuel sulfur levels, benzene content, and RVP. However, due to other regulatory changes over the past two decades, the compositions of CG and RFG have nearly converged. Inserting annual average gasoline properties into the Complex Model shows that RFG’s predicted NOx and toxics reduction benefits have largely disappeared, while a VOC reduction benefit persists. This benefit results from CG’s higher summertime vapor pressure, due to the 1 psi RVP increase that is allowed for CG containing 10 vol.% ethanol.
Due to fleet turnover and introduction of low-emitting, advanced technology vehicles, fleet-wide vehicle emissions have decreased dramatically over the past 20 years. Considering this, along with the general erosion of RFG’s emissions reduction benefits, it is unlikely that RFG provides any demonstrable air quality benefit compared to CG today. RFG’s residual VOC benefit likely could be maintained by application of simpler RVP controls, rather than by continuation of the outdated RFG program.