Effect of Gasoline Fuel Additives on Combustion and Engine Performance

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4.1 Spray Features 
104 
Figure 4.14: Droplet size difference between minimum and 50 % transmission levels
transmission. This could be explained by the more transient events occurring at much 
higher droplet velocities during the earlier stages of a spray event where aerodynamic 
forces are higher and the resulting droplet primary and secondary break up processes 
take place. 50 % transmission was reached up to 8 ms after SOI for 50 bar injection 
pressure and the measurements were taken on the trailing edge of the spray. It is worth 
mentioning, however, that this cyclic variation was, based on standard deviations for 
all pressure conditions, within or very close to the experimental repeatability limits 
and as such no additional benefit was thought to result from adjusting laser system 
timing to sprays any further. Furthermore, for future presentation of results, it was 
decided that unless specifically stated, SMD at 50 % transmission was not further 
considered and SMD only at the minimum transmission level was analysed. 
Comparison of the base fuel characteristics against empirically established 
relationships discussed in Section 2.3 is presented in Figure 4.15. Since all empirical 
relationships are profoundly dependent upon experimental set up, data is normalised 
against the maximum droplet size value in each set to enable direct comparison of 
pressure effect on droplet size. 
Very good agreement is seen between the results that of Knight and Elkotb 
[142] and the current study while Hiroyasu and Kodota [143] found pressure 
dependence to be of lesser effect. It is worth mentioning that when comparing the 
actual calculated values, Hiroyasu and Kodota’s [143] were in fact the closest to 
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