Effect of Gasoline Fuel Additives on Combustion and Engine Performance

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4.2 Combustion Investigations 
114 
 
Figure 4.25: Sample pressure and heat release traces, averaged over 300 cycles at spark 
timing of 40° BTDC 
 
Figure 4.26: Peak pressure, knock intensity peak heat release rate and IMEP characteristics 
for base fuel with different spark timing 
pressures were reached while the peak heat release rate decreased. This was due to the 
time instant when the combustion event occurred. As spark was advanced, more of the 
combustion occurred in the compression stroke. This meant that higher pressures were 
reached within the cylinder. Similarly, the heat release rate decreased with advancing 
the spark timing. Heat release rate is dependent upon the conditions within the cylinder 
and by advancing the timing of spark lower pressures and subsequently lower 
temperatures were experienced at the time of spark [29, 194]. IMEP could be seen to 
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