Effects of Gasoline Properties on Emissions of Current and Future Vehicles - T50, T90, and Sulfur Effects - Auto/Oil Air Quality Improvement Research Program

Exhaust emissions were measured using a matrix of fuels designed to expand on prior AQIRP work by investigating potential interactive effects of fuel distillation parameters T₅₀ and T₉₀, and of T₉₀ and fuel sulfur content. (T₅₀ and T₉₀ represent the temperature at which 50 or 90% of the fuel distills in a standard test.) This fuel matrix was used also to investigate whether fuel effects found in prior work with then-current vehicle technology can be expected to continue in future lower emission vehicles. An additional pair of fuels was included to extend the range of T₅₀. The vehicles were half of the AQIRP Current fleet (ten vehicles) used in prior studies, and two new fleets of six vehicles each. One of the new fleets was designed to 1994 Federal Tier 1 standards, and the other was Advanced Technology prototypes targeted for lower emission levels of 1995 and later.

A set of six fuels was tested in all three fleets. In these six fuels, T₅₀ and T₉₀ were designed to vary independently at a fixed low sulfur level. Two additional fuels with a higher sulfur content were tested in the Current and Federal Tier 1 fleets. Along with two fuels from the matrix of six T₅₀/T₉₀ fuels, these higher sulfur fuels made up a four-fuel matrix in which T⁹⁰ and sulfur varied independently. Two fuels intended to extend the range of T₅₀ beyond the main experiment were tested in the Current and Federal Tier 1 fleets.

Overall, the observed fuel effects appear sufficiently consistent among the test fleets that fuel effect predictions based on Current fleet data should continue to be generally valid for vehicles equipped with newer emission control technology. This tentative conclusion remains to be validated by detailed ozone modeling planned later in the AQIRP program.