Controlled auto ignition (CAI) or, also known homogenous compressed ignition, is an advanced combustion technology allowing a lower NOx emission and fuel consumption that can relieve the energy demand based on petroleum. The objective of this study is to determine the effects of spark ignition (SI), spark assist controlled auto ignition (SI-CAI) and pure CAI combustion modes on the performance and emissions in a modified IC engine. For this purpose, the emissions, performance, and heat release analyses for these combustion modes were obtained at two different engine speeds (1500-2000 rpm) and various excess air ratio (EAR) in the range of 1.0-13 with 0.1 increments for both wide open throttle (WOT) and 50% opening throttle positions. The results showed that CAI combustion mode produced lower NOx emissions, although it resulted in higher CO and HC emission than those under SI and SI-CAI combustion modes. In addition, brake mean effective pressures (BMEP) were obtained as higher values under SI-CAI combustion mode. Therefore, SI-CAI combustion mode provided a wider operational range than that of the CAI combustion mode. However, the SI-CAI combustion modes resulted in high NOx emissions, but relatively lower values than those under SI combustion mode. (C) 2016 Elsevier Ltd. All rights reserved.