Effect of Gasoline Fuel Additives on Combustion and Engine Performance

2.3.4
 
Fuel Additive Effects on Atomisation Characteristics 
Research into the effects of fuel additives on fuel spray characteristics is 
limited. This is partly due to the quantities of additives involved compared to that of 
the base fuels but also due to the proprietary nature of the chemicals in use. Higgins 
et al. [10, 9] investigated the effect of ignition promoter 2-EHN on liquid length and 
the cone angle of non-combusting hot diesel sprays. At treat rates of 4,000 ppm of 
additive in fuel, the conclusion drawn was that the additive does not alter the fuel spray 
beyond the experimental repeatability. Any effect that was seen was a resultant of 
ignition promoting radicals that 2-EHN provides and not of physical nature. Felton et 
al. [8] studied the effects of two detergent additives on droplet size and evaporation 
mixed into two diesel-type fuels. They found that at high treat rates the additives had 
the capability to hinder evaporation of fuel and increase droplet size but that it was 
also highly dependent on base fuel characteristics and only applied to the fuel with 

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2.4 Combustion Analysis 
61 
high aromatics content. The diesel fuel with more common characteristics to modern 
automotive fuels did not exhibit any noticeable change in evaporation or atomisation 
characteristics.
The effect of additives on fuel atomisation is not fully understood. Although 
the quantities involved are small, properties such as viscosity and surface tension 
could be altered significantly and a study into the effect of additives from a variety of 
functional groups on fuel atomisation would provide valuable insight into the 
mechanisms at work.
2.4
 
Combustion Analysis 
Combustion characteristics are dependent on a number of factors including 
physical and chemical properties of fuels. Physical processes inherently affect 
combustion characteristics through effects on fuel spray atomisation and subsequent 
air-fuel mixing. Additional contributions to variations in combustion quality arise 
from changes in fuel chemistry. Such changes affect the way a fuel behaves and what 
chemical reaction paths are promoted or suppressed during oxidation processes. In this 
section methods of analysing combustion characteristics and efficiency are introduced, 
including techniques that are used involving optical and non-optical methods.