Oxygenates screening for AdvancedPetroleum-Based Diesel Fuels: Part 2. The Effect of Oxygenate Blending Compounds on Exhaust Emissions

Adding oxygenates to diesel fuel has shown the potential for reducing particulate (PM) emissions in the exhaust. The objective of this study was to select the most promising oxygenate compounds as blending components in diesel fuel for advanced engine testing. A fuel matrix was designed to consider the effect of molecular structure and boiling point on the ability of oxygenates to reduce engine-out exhaust emissions from a modern diesel engine. Nine test fuels including a low-sulfur (∼1 ppm), low-aromatic hydrocracked base fuel and 8 oxygenate-base fuel blends were utilized. All oxygenated fuels were formulated to contain 7% wt. of oxygen. A DaimlerChrysler OM611 CIDI engine for light-duty vehicles was controlled with a SwRI Rapid Prototyping Electronic Control System. The base fuel was evaluated in four speed-load modes and oxygenated blends only in one mode. Each operating mode and fuel combination was run in triplicate. The Bosch smoke number, total PM, total volatile fraction (TVF), NOx, CO, THC, CO₂, and O₂ were measured. Dry PM, which is assumed to form during the combustion process, was calculated by subtracting the TVF from the total PM. PM emissions reductions were proportional to the oxygen content of the fuel, averaging 26.1 percent below that of base fuel. Spread in the dry PM emissions indicated that fuel properties other than oxygen content play a role in the soot formation mechanism. In some cases, NOx emissions can increase significantly. Based on Total PM emissions and other considerations, Tripropylene Glycol Mono-Methyl Ether and Di Butyl Maleate were identified as the most promising candidate oxygenate compounds for future engine testing.