Blends of gasoline, diesel fuel and ethanol (“dieseline”) have shown promise in
engine studies examining low temperature combustion using compression ignition.
They offer the possibility of high efficiency combined with low emissions of
oxides of nitrogen and soot. However, unlike gasoline or diesel fuel alone, such
mixtures can be flammable in the headspace above the liquid in a vehicle fuel
tank at common ambient temperatures. Quantifying their flammability
characteristics is important if these fuels are to see commercial service. The
parameter of most interest is the Upper Flammable Limit (UFL) temperature, below
which the headspace vapour is flammable. In earlier work a mathematical model to
predict the flammability of dieseline blends, including those containing
ethanol, was developed and validated experimentally. It was then used to study
the flammability of a wide variety of dieseline blends parametrically. Gasolines
used in the simulations had DVPEs (Dry Vapor Pressure Equivalent) varying from
45 to 110 kPa. The parametric study revealed that the UFL temperatures of all
alcohol-free dieseline blends were well correlated by blend DVPE, and the same
correlation was found regardless of which gasoline or diesel fuels were used in
the blends. For dieselines containing ethanol, the UFL temperatures could also
be correlated using blend DVPE, but the UFL temperatures with ethanol present
were different than for the alcohol-free blends at any given DVPE and varied
with ethanol content. The results were presented graphically, from which UFL
temperature could be estimated for any specific dieseline of interest. However,
using the graphical data for broader analyses would be extremely time consuming.
In the work reported here, explicit correlation equations have been derived that
allow UFL temperature to be determined directly for dieseline blends with or
without ethanol. The results have been shown to agree with the predictions of
the full mathematical model on which they are based with an RMS error of less
than 1°C. The equations can be used to quickly compare the UFL temperatures of a
wide variety of dieseline formulations and to evaluate the impact of practical
issues arising in-service, such as blending errors or regional variations.