Effect of Gasoline Fuel Additives on Combustion and Engine Performance

minimum transmission 
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SM
D
, µ
m
Pressure, bar
Dodecane
25% Hexene/75% Dodecane
50% Hexene/50% Dodecane
75% Hexene/25% Dodecane
Hexene

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5.2 Droplet Sizing with Alternative Fuels 
128 
Figure 5.13: Pressure dependence of hexene and dodecane in pure and blended forms at 
50% transmission 
Due to the SMD values’ tendency to incline towards pure dodecane values at 
minimum transmission, also 50 % transmission results were analysed. This can be 
seen in Figure 5.13. At 50% transmission, separation of SMD was similarly 
experienced at higher pressures. However, no trend for fuel blends to tend towards 
either of the pure fuel forms under any injection pressure could be noted, although the 
SMD values did seem to converge at lower pressures. This could be explained by 
different evaporation rates for hexene and dodecane. Fuel vaporisation rates are 
dependent on total spray surface area which is higher at increased injection pressures 
as a result of improved atomisation characteristics. Both, the flash and boiling points 
for hexene are lower than for dodecane, meaning superior evaporation rates at ambient 
conditions. It is possible that as a result of improved atomisation quality, the effect of 
evaporation rate differences was amplified and divergence in SMD values is seen at 
higher injection pressures. The results at 50 % transmission suggest that previously 
mentioned experimental repeatability limits could be used to explain pure hexene 
SMD values at minimum transmission.
Furthermore, it is known that the main properties to affect droplet size, besides 
injection pressure, are the fuel surface tension, viscosity and density. Alptekin and 
Canacki [243] and Tat and Van Gerpen [244] measured surface tension, viscosity and 
density of different binary fuel blends and found that all the aforementioned properties 
change proportionately and linearly to their constituent components. Although this 
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