Effect of Gasoline Fuel Additives on Combustion and Engine Performance

Figure 5.17: Surface tension and viscosity of hexene and dodecane binary mixtures 
Furthermore, as described in Section 5.2.2.1, a linear relationship between different 
fuel blend viscosities, surface tensions and densities has been measured by several 
researchers. It was, therefore, expected that a linear relationship between the mixtures 
and pure components would also be detected in the surface tension and viscosity 
measurements. Figure 5.17 displays this relationship for the hexene and dodecane pure 
forms and binary mixtures. It can be seen that surface tension measurements displayed 
a strong linear relationship. 
Viscosity measurements of additive carrying gasoline with the drag reducing 
agents DRA and DRB provided some noteworthy results. As expected from literature 
survey, the additives increase the viscosity of the base fuel. In case of both the 
additives, the base fuel viscosity nearly tripled to 2.25 cP for DRA and 2.20 cP for 
DRB. Since the SMD investigations with these additives demonstrated no 
distinguishable change Section 5.1.3, further analysis on post injection fuels was 
carried out. For both additives, a fuel sample consisting of 200 injections at 110 bar 
injection pressure was analysed. The measurements showed a large drop in viscosity 
to 1.18 cP and 1.20 cP for DRA and DRB additives, respectively. This reduction was 
thought to originate from additive break-up/degradation during the highly turbulent 
0.2
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20
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Vi
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 c
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Su
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 Ten
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/d
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Surface Tension
Viscosity

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5.4 Conclusion 
136 
flow through the injector nozzle at high pressures during injection events. Reader is 
advised to refer to Appendix B for estimated turbulence level calculations. Although 
viscosity remained nearly 50% higher than the base fuel, it was assumed that at such 
low fuel viscosities the change in droplet size is unidentifiable with the measured SMD 
repeatability levels experienced in current study.
It is likely that the fuel volatility also played an important part. Although fuel 
atomisation study was carried out at ambient temperature, as seen from Table 5.2, it is 
significantly higher than the flash point of gasoline. Since the SMD measurements 
were taken at large distances from the injector nozzle, any additive effects might have 
been overpowered by the fuel evaporation rates.