Effect of Gasoline Fuel Additives on Combustion and Engine Performance

 

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Abstract 
Ever increasing emissions regulations and demand for fuel economy have 
brought about great advances in fuel and engine technologies. Improving engine 
efficiency through the use of fuel additives has been practiced for nearly a century but 
advances to direct injection gasoline engines have presented new obstacles that need 
to be overcome. With direct injection systems often suffering from reduced timescales 
allowed for combustion processes, atomisation and vaporisation characteristics have 
become of paramount significance. 
Present study aimed at adding to the field of knowledge by experimentally 
investigating commercial fuel additives of different functionalities against their effects 
on fuel atomisation and combustion characteristics. Fuel atomisation was evaluated 
through the use of a laser diffraction system and measurement of fuel viscosity and 
surface tension. Additives from six functional groups were investigated. Additionally, 
effects of anti-knock and ignition promoting additives on gasoline combustion 
behaviour were studied in a constant volume combustion vessel and a single cylinder 
research engine. Flame speed, heat release rate and emissions output were compared 
for three commercially available combustion improvers. 
Investigation into the effect of fuel additives on the physical properties and 
therefore on fuel atomisation and sprays revealed that in commercially employed 
quantities, no significant change in recorded Sauter Mean Diameter could be observed. 
Combustion investigations in a combustion vessel demonstrated that the low 
temperature reactions initiated by ignition promoting additive reduced CO emissions 
up to 37.7 % which could be attributed to possible reduced flame quenching near 
combustion chamber walls. However, in high quantities this reduction in CO levels 
was not experienced. Addition of anti-knock additives resulted in increased NO
x
emissions, which was thought to result from increased combustion durations. Present 
work has clarified fuel additive function and interactions with combustion processes 
and has demonstrated that gasoline fuel additives do not interfere with combustion 
processes outside their intended functionality.

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