Effect of Gasoline Fuel Additives on Combustion and Engine Performance

Figure 4.8: Change in minimum transmission levels with increasing injection pressure 
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4.1 Spray Features 
101 
Figure 4.9: Droplet size shot-to-shot variation at 50 bar and minimum transmission 
Figure 4.9 displays the analysis of shot-to-shot variation for 50bar injection 
pressure at minimum transmission. This helped set a suitable number of spray events 
to obtain a reliable and representative droplet size figure per given condition as well 
as quantify experimental repeatability. This analysis was only carried out at the 
extremes of 50 bar and 110 bar only. An overall standard deviation for 50 injections 
at 50 bar injection pressure was found to be 0.74 µm (SMD = 12.36 µm) and 0.69 µm 
(SMD = 7.01 µm) at 110 bar. A cumulative average was calculated along with % 
change for each subsequent point for 50 sprays. For both pressures % change after 30 
injections was below 0.3 %. Because of some earlier results that showed a possibility 
of an outlier result occurring that could affect the overall average SMD, the total 
number of repeats per condition was increased to 50 sprays. 
4.1.3
 
Base Gasoline Fuel Characteristics 
Figures 4.10 and 4.11 display the SMD averages for base fuel at minimum and 
50 % transmission, respectively. At both transmission levels the droplet sizes were 
found to behave in a very similar manner.
It was found that increasing injection pressure from 50-110 bar at minimum 
transmission reduced the droplet size by 39.1 % and 37.3 % at 50 % transmission. The 
experimental repeatability had largest standard deviation at 50 bar and 50 % 
transmission case of 0.64 µm. Smallest occurred at 110 bar and minimum transmission 
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