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In the past decade, a significant market has emerged for automotive fuels produced from renewable sources. Blends containing low concentrations of ethanol have been the readily-available choice for providing renewable content in gasoline fuels. The simple addition of ethanol to gasoline significantly increases the mixture's vapor pressure, which can promote higher vehicle evaporative emissions. Gasoline specifications and blending practices have been updated to help offset the increase to vapor pressure and evaporative emissions. However, recent studies have shown that even at reduced vapor pressure, ethanol can increase gasoline evaporative emissions by enhancing the permeation of hydrocarbons through the elastomeric materials found in vehicle fuel systems. Technology is currently in development that will allow for the production of isobutanol from renewable sources.

Findings from an intermediate ambient temperature vehicle driveability study for isobutanol gasoline blends are reported. The pattern for the study was Coordinating Research Council Project CM-138-02, which investigated the effects of ethanol on cold-start/warm-up performance and Driveability Index. Objectives of the present study were: (a) to evaluate the efficacy of the current ASTM Driveability Index (DI) in predicting cold-start and warm-up driveability performance for isobutanol gasolines and (b) if required, identify modifications to the DI definition and specification limits for isobutanol blends. The test fuel matrix included fifteen fuels with nominal vapor pressures of 55 kPa (8 psi) at DI levels of 1150, 1200, 1250, and 1300 and isobutanol concentrations of 0, 16, and 24 volume percent. Twelve port- and direct-fuel-injected vehicles, which included US Tier 2 passenger cars and light-duty trucks from model years 2005 through 2008, were used to evaluate the test fuels.

The compatibility of plastic materials used in gasoline storage and dispensing applications was determined for test fuels representing neat gasoline (Fuel C), and blends containing 25% ethanol (CE25a), 16% isobutanol (CiBu16a), and 24% isobutanol (CiBu24a). A solubility analysis was also performed and compared to the volume swell results obtained from the test fuel exposures. The plastic specimens were exposed to each test fuel for16 weeks at 60°C. After measuring the wetted volume and hardness, the specimens were dried for 65 hours at 60°C and then remeasured for volume and hardness. Dynamic mechanical analysis (DMA), which measures the storage modulus as a function of temperature, was also performed on the dried specimens to determine the temperature associated with the onset of the glass-to-rubber transition (Tg). For many of the plastic materials, the solubility analysis was able to predict the relative volume swell for each test fuel.

The compatibility of plastic materials used in fuel storage and dispensing applications was determined for a test fuel representing gasoline blended with 10% ethanol. Prior investigations were performed on gasoline fuels containing 25, 50 and 85% ethanol, but the knowledge gap existing from 0 to 25% ethanol precluded accurate compatibility assessment of low level blends, especially for the current E10 fuel (gasoline containing 10% ethanol) used in most filling stations, and the recently accepted E15 fuel blend (gasoline blended with up to15% ethanol). For the majority of the plastic materials evaluated in this study, the wet volume swell (which is the parameter most commonly used to assess compatibility) was higher for fuels containing 25% ethanol, while the volume swell accompanying E10 was much lower.

The compatibility of elastomeric materials used in fuel storage and dispensing applications was determined for test fuels representing neat gasoline and gasoline blends containing 10 and 17 vol.% ethanol, and 16 and 24 vol.% isobutanol. The actual test fuel chemistries were based on the aggressive formulations described in SAE J1681 for oxygenated gasoline. Elastomer specimens of fluorocarbon, fluorosilicone, acrylonitrile rubber (NBR), polyurethane, neoprene, styrene butadiene rubber (SBR) and silicone were exposed to the test fuels for 4 weeks at 60°C. After measuring the wetted volume and hardness, the specimens were dried for 20 hours at 60°C and then remeasured for volume and hardness. Dynamic mechanical analysis (DMA) was also performed to determine the glass transition temperature (Tg). Comparison to the original values showed that all elastomer materials experienced volume expansion and softening when wetted by the test fuels.