The blending of oxygenated compounds with gasoline is projected to increase because oxygenate fuels can be produced renewably, and because their high octane rating allows them to be used in substitution of the aromatic fraction in gasoline. Blending oxygenates with gasoline changes the fuels' properties and can have a profound affect on the distillation curve, both of which are known to affect engine-out emissions.
In this work, the effect of blending methanol and ethanol with gasoline on unburned hydrocarbon and particulate emissions is experimentally determined in a spray guided direct injection engine. Particulate number concentration and size distribution were measured using a Cambustion DMS500. These data are presented for different air fuel ratios, loads, ignition timings and injection timings. In addition, the ASTM D86 distillation curve was modeled using the binary activity coefficients method for the fuel blends used in the experiments.
In general, unburned hydrocarbon emissions were reduced at low load but increased at high load for the alcohol blends. The effect on particulate emissions was dependent on the operating point: for rich mixtures the accumulation mode number concentration and count median diameter were reduced with the oxygenate blends. However, blending gasoline with oxygenates also caused the nucleation mode number concentration to increase, particularly for M85. The distillation curve modeling showed that blending oxygenates affects the distillation curve much more than would be expected from a linear blending relationship: the front end volatility is reduced a little, whilst the mid range volatility is increased significantly, particularly for methanol blends.