Effect of Gasoline Fuel Additives on Combustion and Engine Performance

2.4.4
 
Emissions 
Vehicle emission levels have increasingly been one of the driving forces in 
engine and fuel technology research. All countries within the EU follow the same 
regulations for new cars. The regulated emissions include carbon monoxide, unburned 
hydrocarbon, nitric oxide, nitrogen dioxide and particulate emissions. Additionally 
from the start of EURO 6 standard, the total number of particulates (in addition to 
weight) will also be measured. As briefly mentioned in Section 2.1, fuel additives can 
be successfully utilised to reduce regulated emission levels.
2.4.4.1
 
Carbon Monoxide 
Carbon monoxide (CO) primarily results from incomplete combustion that is 
caused by oxygen starvation during combustion that would allow for complete 
oxidation of the fuel. However, slow burning rates could also result in an increase in 
emissions. Incomplete combustion is mostly reached during cold start periods as well 
as transient events during full load situations where fuel rich mixtures are employed. 
Better burning rates and lean mixtures enable lower CO levels. Ji and Wang [194] 
experimented with hydrogen addition to fuels to improve the lean burn limits of 
gasoline. They found reductions of CO emissions by more than 75 % were possible 
with 4.5 % hydrogen in gasoline. Furthermore, reduction in cold start emissions was 
reported by Chen et al. [195] with gasoline-ethanol blends, where ethanol 

---

2.4 Combustion Analysis 
68 
concentration was between 20-30 % in fuel. Similar results were reported by Al-Hasan 
[196] where 20 % ethanol blend gave lowest CO emission levels. Emissions are of 
great interest and even diesel-gasoline fuel blends have been studied for effects on 
cold start CO release rate [197].