While the emission values of UHC, CO and NOx decreased by using pure ethanol and methanol instead of unleaded gasoline fuel at all CRs, the CO2 emission values decreased at the CR of 9.0:1 and then it began to peak up again. The obtained exhaust emission results from unleaded gasoline at the original CR, it was a reduction of the minimum values of the UHC emissions that were obtained from pure ethanol and methanol. They were about 29.01% and 40.12%, respectively, at a CR of 8.5:1. At the same time, the CO emission was about 34.65% and 44.88% for pure ethanol and methanol, but the CO2 emission had increased to about 1.46% with ethanol and to about 2.19% with methanol at the CR of 9.0:1. Meanwhile, the maximum values of NOx emissions had decreased to about 18.1% with ethanol and to about 22.97% with methanol.