In this study, effects of synthetic gas constituents on combustion and emission behavior of premixed H-2/CO/CO2/CNG blending synthetic gas flames were experimentally investigated in a swirl stabilized laboratory scale combustor. Effects of these constituents on flashback and blowout equivalence ratios of respective mixtures were also determined. Firstly, mixtures of CNG/H-2/CO with varying H-2/CO ratios were tested and then each mixture was diluted with the same amount of CO2 (20% by volume) to better represent synthetic gas. H-2/CO ratios of tested gas mixtures were so adjusted that heating value of each gas mixture was low, moderate or high. Combustion behavior of such mixtures was evaluated with respect to measured axial and radial temperature values. Moreover, emission behavior was analyzed by means of emitted CO, CO2 and NOx levels. Flame temperature measurements were conducted with B and K type thermocouples. Emission measurements were performed with a flue gas analyzer, which was equipped with a ceramic coated probe, as well. Results of this study revealed the great impact of gas composition on combustion and emission behavior of studied flames. Two main findings are: H-2/CO ratio slightly alters temperature distribution throughout combustor, while hydrogen reaction kinetics play the most significant role in synthetic gas combustion (1), CO2 addition tremendously increases emissions of CO (2). (C) 2018 Energy Institute. Published by Elsevier Ltd. All rights reserved.