Effect of Gasoline Fuel Additives on Combustion and Engine Performance

CO
 Co
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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 
144 
have been also noted by other researchers when metallic antiknock additives have been 
used. TEL containing n-heptane flame speeds were investigated in an engine by Curry 
[256] and flame propagation speed reductions of up to 50 % were witnessed. An 
extensive review carried out by Linteris et al. [257] reveals that the main processes 
responsible for reductions in flame speeds are gas-phase catalytic cycles which 
involve oxides and hydroxides. The concentration of chain-carrying radicals is 
reduced by reactions with inhibitors provided by the metallic additives in the flame 
reaction zone. Furthermore, it has been found that the existence of the inhibitors and 
subsequent reactions produces additional scavenging species, thus, creating an 
amplifying effect [258]. 
An additional factor that could have had an effect on combustion was thought 
to originate from the spark energy input at the beginning of the combustion event. The 
applied spark discharge energy was measured for all events except for CI-A Base. 
Although a small change was experienced in fuel burning velocity for CI-A 1X, Figure 
6.7 shows that throughout all tests no correlation between applied spark energy and 
burning velocity could be seen. Furthermore, since higher spark energy could improve 
early flame development, it was thought that the time needed to reach peak heat release 
rate and pressure could have been reduced. 
Figure 6.7: Burning velocities for different applied spark energies 
Figures 6.8 and 6.9 display, however, that the time taken from spark discharge 
to maximum heat release rate and pressure, respectively, was not affected by the 
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