Engine Materials Compatibility with Alternate Fuels

Abstract

The compatibility of aluminum and aluminum alloys with synthetic fuel blends comprised of ethanol and reference fuel C (a 50/50 mix of toluene and iso-octane) was examined as a function of water content and temperature. Commercially pure wrought aluminum and several cast aluminum alloys were observed to be similarly susceptible to substantial corrosion in dry (< 50 ppm water) ethanol. Corrosion rates of all the aluminum materials examined were accelerated by increased temperature and ethanol content in the fuel mixture, but inhibited by increased water content. Pretreatments designed to stabilize passive films on aluminum increased the incubation time for onset of corrosion, suggesting film stability is a significant factor in the mechanism of corrosion. STATEMENT OF OBJECTIVES• Conduct a systematic assessment of aluminum corrosion in ethanol fuel • Develop a mechanistic understanding of aluminum corrosion associated with increased ethanol content • Identify cause(s) of potential galvanic corrosion associated with aluminum engine components • Consistent with the corrosion mechanism, identify potential mitigation techniques • Develop rapid test protocols to enable anticipation of potential problems in design stage BENEFITS TO THE FUNDING DOE OFFICE'S MISSIONThe ever increasing rate of fossil fuel consumption coupled with the desire for energy independence has influenced the United States to enact legislation to integrate renewable biofuels such as ethanol into the nation's fuel supply [1]. The U.S. Department of Energy (DOE) Office of Vehicle Technologies aims to facilitate this transition by removing technical hurdles and reducing cost barriers for emerging vehicle technologies. In alignment with this goal, the purpose of this investigation was to systematically examine the potential impact of changing fuel compositions on fuel compatibility with materials of interest for lightweight engine materials. The focus of the effort has been on aluminum and its alloys, primarily because of its low density and extensive use in automotive engines as a piston and head material for fuelefficient vehicles.The addition of ethanol to gasoline is expected to be a source of concern for increased corrosion in two primary ways. Firstly, compared to gasoline, ethanol has significant affinity for water. Thus, additions of ethanol to transportation fuel invite the possibility of aqueous corrosion of all materials in contact with the fuel, including vehicle fuel systems and engines as well as the infrastructure for distributing and dispensing the fuel. Due to the hygroscopic nature of ethanol, absorbed water can separate from the 2 organic fuel phase leading to a number of potential issues with fuel and containment corrosion [2]. Secondly, ethanol is orders of magnitude more electrically conductive than gasoline [3], so even modest additions of ethanol can contribute to corrosion possibilities in ethanol fuel blends, such as galvanic attack, that are not observed in ethanol-free gasoline. There are mixed reports suggesting var...