The alcohol/air mixtures are successful in the practical use as gasoline and diesel fuel additives and this has motivated the full investigation of their combustion chemistry. The AIT for alcohol/air mixtures shows the large inconsistency due to various physical-chemical factors which effect its values as the chemical composition, concentration, volume and shape of the flask. The novelty of the article is the investigation of the effect of alcohol’s isomeric structure on its combustion properties with no change in the fuel’s physical-chemical properties. This paper describes a series of experiments performed to study the autoignition characteristics of propanol isomer (1-propanol and 2-propanol)–air binary mixtures. The experiments were conducted in two different experimental arrangements—a 500 ml spherical vessel and a 250 ml conical vessel—for different liquid equivalence ratios between 50 (l and 300 (l, and initial temperatures between 25 and 700 °C. We explored isomeric effect, and effects of the flask shape and volume on the measured AIT by using both the EN 14522:2005 and ASTM E659-78:2005 methods.