Effect of Gasoline Fuel Additives on Combustion and Engine Performance

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urnin
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 Velo
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Spark Energy, mJ
CI-A 1X
CI-A 10X
CI-I Base
CI-I 1X
CI-I 10X
CI-Additional Base
CI-Additional 1X

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6.2 Gasoline Vapour Combustion 
145 
energy input. These result compare favourably to several researchers [221, 259], who 
found the benefit of increased ignition energy to manifest in better lean burning 
capabilities due to assistance in flame kernel development rather than improvements 
in the following reaction rates.
Figure 6.8: Time taken to peak heat release rate for applied spark energies 
Figure 6.9: Time taken to peak pressure for applied spark energies 
The smallest spark energy measured during the experiments was 8.7 mJ for CI-I 10X 
while minimum ignition energy required to ignite gasoline-air mixtures has been 
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 m
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Spark Energy, mJ
CI-A 1X
CI-A 10X
CI-I Base
CI-I 1X
CI-I 10X
CI-Additional Base
CI-Additional 1X
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Spark Energy, mJ
CI-A 1X
CI-A 10X
CI-I Base
CI-I 1X
CI-I 10X
CI-Additional Base
CI-Additional 1X

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6.3 Engine Testing 
146 
reported to be 0.8 mJ [260]. Therefore, it can be concluded that irrespective of 
available spark energy, combustion characteristics for a homogeneous air-fuel mixture 
in gaseous form remain unaffected as long as the minimum ignition energy is 
achieved. 
6.3
 
Engine Testing 
Following the investigations in the combustion vessel, it was evident that no 
definite conclusions on additive effectiveness on chemical reactions during 
combustion could be made. Therefore, the same additives were tested further under 
engine conditions in a single cylinder research engine. Due to difficulties with the 
stability of the employed lambda sensor readings, the equivalence ratio could only be 
kept constant for a set of tests, thus, results are presented for each additive and the 
corresponding base fuel test separately from other additives. All fuels were tested at a 
range of different spark advance angles and followed methods described in Chapter 4. 
The findings of the engine investigations are presented in Figures 6.10 – 6.27. 
Figures 6.10 – 6.12 display the knock intensities (KI) for the test fuels. It can 
be observed that, as expected, the CI-A additive promotes auto ignition in gasoline 
fuel. For the tested range of spark timings, the base fuel and CI-A 1X behaved 
similarly up to spark advance angle of 50 CAD after which about a 39.4 % increase in 
KI could be seen. CI-A 10X demonstrated similar combustion characteristics only at 
very late spark advance angles. Advancing spark earlier than 35 CAD caused a sudden 
increase in the KI that peaked at 45 CAD. At that point a 185.2 % increase in knock 
intensity was experienced.
KI measurements for CI-I are displayed in Figure 6.11. Up to spark timing of 
45 CAD all fuels exhibited similar characteristics. However, advancing the spark 
further caused an increase in KI for both the base and 1X concentration fuels. Very 
similar characteristics were seen throughout the measured range for the two fuels 
except for very early spark timing where a 28.6% decrease in KI was seen. At 10X 
concentration, CI-I displayed strong anti-knocking properties with no spark advance 
points in the measured range where sudden increase in KI could be seen. Largest 
decrease in the KI level of 73.3% compared to the base fuel was experienced at the 
ignition advance of 65 CAD.

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6.3 Engine Testing 
147