This study presents experimental results of engine performance, combustion analyzes and emissions values in an SI engine fueled by gasoline-acetylene blends. The experiments were carried out at 1500 rpm engine speed, different loads (25% and 50%) and optimum spark timing under different mixture conditions. Engine was operated up to 1.70 and 2.12 excess air ratios for 500 gill and 1000 gill acetylene flow rate at 25% load, respectively. For 50% load, engine was operated up to 1.82 excess air ratios for 1000 g/h acetylene flow rate. Engine parameters such as brake thermal efficiency, cylinder pressure, mass fraction and emission values (CO, UHC and NOx) were analyzed for each fuel blends. Results were shown that due to decreased ignition timing to prevent knocking, the addition of acetylene to gasoline decreased brake thermal efficiency at rich and stoichiometric conditions and increased the CO emissions. Acetylene adding at lean mixtures caused an increase in brake thermal efficiency and a decrease in CO emissions, because of proper ignition advance. Furthermore, adding of acetylene increased combustion limits, significantly reduced UHC emissions but increased NOx emissions. Moreover, NOx emissions obtained from mixture with acetylene were measured quite low at high excess air ratios. (C) 2019 Elsevier Ltd. All rights reserved.