Effects of 7, 9, and 10 psi Vapor Pressure Fuels on Multi-Day Diurnal Evaporative Emissions of Tier 2 and LEV II Vehicles

In order to meet more stringent evaporative emissions requirements, multiple advancements in vehicle fuel system and carbon canister technologies have been made. Regardless of technological advancements, the vapor pressure of the fuel remains a vital property in controlling evaporative emissions. A series of tests were performed to explore the effects of vapor pressure on multiday diurnal evaporative emissions for 9 and 10 psi Reid Vapor Pressure (RVP) 10% ethanol (E10) gasoline-blend fuels, followed by tests with 7 psi RVP E10 gasoline on a subset of the same vehicles. A test procedure was developed to monitor evaporative emissions, canister loading profiles and breakthrough emissions for each of the fuels. A total of five vehicles were tested on all 3 fuels, blended to represent 7, 9, and 10 psi at sea level. Tests were run over 14 days using the United States (U.S.) Federal Diurnal Cycle (72°F to 96°F) in a Sealed Housing for Evaporative Determination (SHED) at a test facility in Colorado. Two of the five vehicles had evaporative emissions systems that met the California Air Resources Board (CARB) requirements for a Partial Zero Emission Vehicle (PZEV), while the other three vehicles were certified to U.S. Tier 2 evaporative emissions standards. The data collected throughout the testing provide a correlation between the hydrocarbon slip from the vehicle canister and the fuel vapor pressure. The data indicate that achieving lower evaporative emissions can be accomplished through the use of decreased vapor pressure fuels.