Recognizing that low-temperature ignition of alkanes is usually associated with one heat release peak, we report herein that, for iso-octane under certain ranges of initial temperatures and pressures, two separate heat release peaks were observed through computational simulations using several kinetic mechanisms. The inherent chemical reason for this phenomenon is discussed using reaction channel analysis and is identified to result from the competition between R + O-2 -> RO2 and the beta scission reactions. By further utilizing sensitivity and path flux analyses, an isomeric effect is identified in that the different isomeric structures produced through the H-abstraction reactions can lead to differences in the subsequent low-temperature reaction pathways.