Emissions from Low- and Mid-level Blends of Anhydrous Ethanol in Gasoline 2019-01-0997

Typically ethanol is present in gasoline as a 10% blend (E10), although E15, E85 (51 to 83%), and E0 are also consumed. Numerous studies of tailpipe regulated emissions have been conducted to compare emissions from E10 and E0 and there is a growing body of literature addressing blends from E15 to E40. Isolating the effect of ethanol in a study is philosophically difficult, because the ethanol naturally displaces some hydrocarbons, because the ethanol interacts with the remaining gasoline, and because properties of mixing are often nonlinear. Some studies have used splash blending, simply mixing the ethanol with a reference gasoline to produce a blend for comparison to the reference. Others have used match blending, where the objective is to match selected properties of the blend to properties of a reference gasoline. Recent studies have examined both port injected and direct injected engines, the latter being both naturally aspirated and turbocharged, and differing test cycles have been used. In consequence, the conclusions of the studies are not uniform. We have examined the available data and statistical analyses to determine the effects of blending approach, engine technology and test cycle on the comparative emissions. Of central interest are the parameters selected to be constant in match blending to prepare fuels at different ethanol levels. Distillation matching must acknowledge the effect of ethanol on the curve, demanding correction by selective addition of hydrocarbons. Some studies have employed aromatic content and the particle mass index for additional matching. With splash blending studies, the parameters vary by inherent nature of the mix, and octane rating rises with ethanol content. We explain the statistics and causes behind variability of results, and compare the match blends employed in studies to common refinery practice in producing gasoline.