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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.

A multi-year technology validation program was completed in 2001 to evaluate ultra-low sulfur diesel fuels and passive diesel particle filters (DPF) in several different diesel fleets operating in Southern California. The fuels used throughout the validation program were diesel fuels with less than 15-ppm sulfur content. Trucks and buses were retrofitted with two types of passive DPFs. Two rounds of emissions testing were performed to determine if there was any degradation in the emissions reduction. The results demonstrated robust emissions performance for each of the DPF technologies over a one-year period. Detailed descriptions of the overall program and results have been described in previous SAE publications [2, 3, 4, 5]. In 2002, a third round of emission testing was performed by NREL on a small subset of vehicles in the Ralphs Grocery Truck fleet that demonstrated continued robust emissions performance after two years of operation and over 220,000 miles.