A Parametric Study of the Flammability of Dieseline Blends with and without Ethanol 2019-01-0020
Low Temperature Combustion using compression ignition may provide high efficiency combined with low emissions of oxides of nitrogen and soot. This process is facilitated by fuels with lower cetane number than standard diesel fuel. Mixtures of gasoline and diesel (“dieseline”) may be one way of achieving this; however, a gasoline/diesel mixture in a fuel tank can result in a flammable headspace, particularly at very cold ambient temperatures. A mathematical model to predict the flammability of dieseline blends, including those containing ethanol, was previously validated. In this paper, that model is used to study the flammability of dieseline blends parametrically. Gasolines used in the simulations had Dry Vapour Pressure Equivalent (DVPE) values of 45, 60, 75, 90 and 110 kPa. Simulations were carried out for dieseline blends containing ethanol with two types of specifications - a fixed ethanol volume percent in the dieseline blend (0-50% ethanol), or blends containing specified EXX gasolines (E10, E20, E30, E40, E60 and E85) added to diesel fuel. Predicted Upper Flammability Limit (UFL) temperatures and blend DVPEs are presented for all blends studied, as a function of diesel volume percent in the blend. It was concluded that the UFL temperatures of all alcohol-free dieseline blends studied were well correlated with blend DVPE, regardless of which base gasoline was used in the blend. When correlated using DVPE, the molecular weight of the diesel fuel or gasoline had no effect on the predicted UFL temperature. For any particular dieseline blend containing a given amount of ethanol or EXX gasoline, the UFL temperatures could be correlated fairly well using DVPE, albeit not as closely as in the case of pure hydrocarbon blends. Ethanol usually raised the UFL temperature compared to hydrocarbon-only dieseline, particularly at lower values of DVPE, but some high DVPE blends had similar UFL temperatures with or without ethanol. The data presented allow UFL temperatures to be estimated for a wide variety of dieseline blends.