Demand for the clean and sustainable energy encourages the research and development in the efficient production and utilisation of syngas for low-carbon power and heating/cooling applications. However, diversity in the chemical composition of syngas, resulting due to its flexible production process and feedstock, often poses a significant challenge for the design and operation of an effective combustion system. To address this, the research presented in this paper is particularly focused on an in-depth understanding of the heat generation and emission formation of syngas/producer gas flames with an effect of the fuel compositions. The heat generated by flame not only depends on the flame temperature but also on the chemistry heat release of fuel and flame dimension. The study reports that the syngas/producer gas with a low H2:`1CO maximises the heat generation, nevertheless the higher emission rate of CO2 is inevitable. The generated heat flux at H2:CO = 3:1, 1:1, and 1:3 is found to be 222, 432 and 538 W m(-2) respectively. At the same amount of heat generated, H-2 concentration in fuel dominates the emission of NOx. The addition of CH4 into the syngas/producer gas with H2:CO = 1:1 also increases the heat generation significantly (e.g. 614 W m(-2) at 20%) while decreases the emission formation. In contrast, adding 20% CO2 and N-2 to the syngas/producer gas composition reduces the heat generation from 432 W m(-2) to 364 and 290 W m(-2), respectively. The role of CO2 on this aspect, which is weaker than N-2, thus suggests CO2 is preferable than N-2. Along with the study, the significant role of CO2 on the radiation of heat and the reduction of emission are examined. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.