Effect of Gasoline Fuel Additives on Combustion and Engine Performance

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4.2 Combustion Investigations 
112 
vacuum pressures were generated by the analyser which affected the readings. 
Furthermore, allowing for extra air to be pulled into the vessel (to avoid vacuum 
pressures) diluted the exhaust gases quickly, and no stable readings could be recorded. 
Therefore, initial pressure was raised to 0.7 bar which was found to be 
sufficient to allow for up to a 60 second period during which stable readings could be 
logged. Characteristic emissions recordings for raised initial pressure conditions can 
be seen in Figure 4.23. 
Figure 4.23: Emissions readings from combustion vessel. At t
1
 data logging commences, at t
2
 
the gas analyser sampling is activated and vacuum pressure is generated in gas supply line, 
at t
3
 the exhaust gases are released from the vessel and at t
4
 air inlet to the combustion 
vessel is opened to avoid vacuum pressures occurring. Typical area used for averaging is 
displayed by the shaded area 
Figure 4.24 displays the peak pressures for different equivalence ratios at 
atmospheric and raised initial pressure conditions. For both cases, the ignitability 
limits were found to be from around φ = 0.8 to φ = 1.8 and peak pressure occurred at 
around φ = 1.5 after which a sharp decrease in the pressure was observed. Due to soot 
production at higher than stoichiometric equivalence ratios, additive comparison tests 
were carried out under lean conditions. Any soot produced would give rise to errors 
in emissions analysis of subsequent combustion events, where burning of soot from 
the vessel walls could increase CO and CO
2
readings. Moreover, this could affect
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