Effect of Gasoline Fuel Additives on Combustion and Engine Performance

H
RR,
 k
J
/s
Peak Pressure, bar
CI-A Base
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 
141 
Figure 6.3: Relationship between NO
x
 emissions and recorded peak pressure 
In Figure 6.4, the dependence of peak pressure on initial pressure is displayed. 
It can be seen that initial conditions were within a small range and seemed not to affect 
the final pressures within the combustion vessel. Furthermore, similar correlations 
Figure 6.4: Peak pressure dependence on initial pressure conditions 
were seen between the vessel wall/ initial air temperature and the final pressure, heat 
release rate and flame speed. Since pre-ignition gas mixture preparation protocol was 
1,200
1,600
2,000
2,400
2,800
3,200
7.10
7.30
7.50
7.70
7.90
8.10
NO
x
, 
pp
m
Peak Pressure, bar
CI-A Base
CI-A 1X
CI-A 10X
CI-I Base
CI-I 1X
CI-I 10X
CI-Additional Base
CI-Additional 1X
7.2
7.3
7.4
7.5
7.6
7.7
7.8
7.9
8.0
8.1
8.2
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
P
ea
k
 P
re
ss
ure,
 ba
r
Intial Pressure, bar
CI-A Base
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 
142 
the same for all fuels, it was expected that any changes in combustion characteristics 
would be a resultant of an additive action.
Overall, the experimental investigation of additives produced inconclusive 
results. Although changes were seen between base fuels and the following additive 
tests, comparison of the three base fuel tests that were carried out, revealed the changes 
could have instead been caused by low experimental repeatability. The CI-A, CI-I and 
CI-Additional base fuel results extended over much of the recorded range for all fuels. 
The largest effect from an additive on combustion characteristics was seen for CI-A 
at 1X concentration. Figure 6.5 displays the relationship between the CO emissions 
and burning velocity for all fuels. Compared to the next best recorded result, fuel 
bound CI-A at 1X concentration reduced the CO emissions by 37.7% and increased 
burning velocity by 5.4%. It was thought that the reduction in the CO emissions could 
have originated from reduced flame quenching at the inner surfaces of the combustion 
vessel. The low temperature of the walls compared to the flame front temperature 
could have resulted in flame being extinguished due to insufficient energy levels 
available for subsequent reactions. As described in Section 2.1.2, CI-A additive 
provides ignition promoting radicals at low temperatures, thus, making it possible that 
in the current set of experiments the flame quenching took place closer to the wall 
surfaces and a more complete oxidation occurred as a result.