Effect of Gasoline Fuel Additives on Combustion and Engine Performance

SM
D,
 µm
Pressure, bar
16 Degrees
20 Degrees
25 Degrees

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5.2 Droplet Sizing with Alternative Fuels 
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injection would only have increased to 20 °C and 25 °C, respectively. However, it is 
clear that droplet size decreases with increased temperature. Higher temperatures 
resulted in lowered viscosity, which in turn increased the quantity of fuel being 
injected for a given pressure condition. The increased fuel quantity meant that in some 
cases, the transmission of light from the laser dropped below 2 %. Since this is outside 
the measurement range for the laser system, these data points were ignored. 
These results are in good agreement with theory in Section 2.3.2. Increased 
temperature has an effect on SMD, through what is thought to be a viscosity modifying 
effect. This is because of changes in laser power levels that decreased significantly for 
given pressure conditions as a result of improved flow conditions within the injector 
nozzle. The transmissions at different injection pressures can be seen in Figure 5.10.  
Figure 5.10: Minimum laser transmission levels at different temperature and injection 
pressure conditions 
It is evident that fuel quantities are higher for higher temperature conditions at 
the measured location. It can also be noted that at higher temperatures much reduced 
decrease in transmission levels is experienced. This could be a result of injector 
internal flow characteristics whereby a throttling effect occurs. Reduction in viscosity 
enabled increased flow rates up to a certain value, after which increases in fuel 
injection pressure were not followed by increases in fuel quantity to the same degree. 
Interestingly, droplet size did not appear to be affected by this phenomenon and 
reductions in SMD of similar magnitude continue to occur even past the point where 
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