The effect of various ignition timing on spark ignition (SI) engines with bioethanol-isooctane
mixtures has been widely studied. In the present studies, we used three different ignition angle
positions, namely 9◦, 12◦, and 15◦ BTDC to increase the combustion pressure in the combustion
chamber. In addition to macroscopic observations through engine performance, observations are
also carried out from a molecular perspective, i.e.; atomic, bond, and bond angle properties of
bioethanol-isooctane fuel. The result shows that more atoms of the isooctane carbon chain are
non-rotatable (23 atomic bonds) than the 8 bonds of the bioethanol carbon chain. Furthermore,
isooctane also has a wider bond angle (around 121.1745◦) than the bond angle of ethanol (around
110.0476◦). The unique properties of the atoms in the carbon chains of these two fuels have a
direct impact on engine performance. The results show that the viscosity of bioethanol is lower
when compared to isooctane, which indicates that the bioethanol molecules are more reactive
and flammable. The result also found that at an ignition angle of 12◦ the BE50 engine has the best
performance. Moreover, the test results also show that bioethanol produces clean combustion as
evidenced by the lowest CO and HC gas emissions.