Effect of Gasoline Fuel Additives on Combustion and Engine Performance

2.4.4.4
 
Particulate Emissions 
According to Myung et al. [215], particulate matter (PM) and particulate 
number (PN) formation in gasoline engines is related to DI engines. Namely, the 
emissions are related to non-uniform fuel air mixture and wetting of combustion 
chamber walls that can inherently occur under cold start and transient high fuel 
injection rate conditions. Cold conditions inhibit evaporation of fuel which hinders 
air-fuel mixing and results in fuel rich areas where insufficient oxygen levels cause 
pyrolysis of fuel to occur. Their experiments with liquefied petroleum gas addition 
showed significant promise of the fuel to reduce PN concentrations by up to 99 %. 
Further improvements can be achieved by improved injector design. Using multi-hole 
DI injectors and spray-guided (as opposed to wall guided) injection systems where 
fuel is injected towards the ignition source can significantly reduce wetting of cylinder 
walls. 

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2.5 Summary 
71 
2.4.5
 
Fuel Additive Effects on Combustion 
Additives are directly or indirectly aimed at improving the efficiency of an 
internal combustion engine. However, direct effects on the combustion characteristics 
are only assumed to come from the combustion improvers, be it through improving 
the fuel’s cetane or octane number. Ickes et al. [50] and Higgins et al. [10, 9] have 
shown that 2-EHN cetane improver can significantly improve diesel fuel’s ignition 
characteristics but also contribute towards NO
x
emissions. However, the additive 
derived emissions are often offset by improvements in overall emissions resulting 
from enhanced combustion characteristics. Colucci et al. [11] used a cetane improver 
in gasoline in small quantities and completely eliminated misfires under cold start 
conditions, thus significantly improving unburned hydrocarbon emissions. They 
argued that the fuel anti-knock properties under low treat rates are not affected but 
provided no quantitative information regarding a possible change in octane rating.
Fuel consumption, emissions and efficiency of internal combustion engines is 
also indirectly affected by additives other than CI. As previous review has revealed, 
significant increase in ORI can result from CCD build up, meaning DCA are required 
for smooth running engines. Rang and Kann [14] bring to attention the catalytic effect 
some organometallic DCA can exhibit meaning additives could affect engine running 
outside their functionality. Similar analogies could occur in ashless additives that use 
nitrogen in their composition. Since many CI chemistries include nitrogen compounds, 
improvements in combustion characteristics could result from additives of different 
primary functionality that contain similar molar groups.