Distributed combustion has demonstrated significant performance gains, especially on combustion efficiency and near zero pollutants emission. Controlled mixture preparation between air, fuel and internal hot reactive gases prior to mixture ignition is a critical requirement to achieve distributed combustion condition. Though distributed combustion have been extensively studied using a variety of geometries, heat loads and intensities, and fuels, limited information is available on the role of hot reactive gas entrainment and the resultant thermal field uniformity. In this paper, the impact of internal entrainment of hot reactive gases on thermal field uniformity and pollutants emission is investigated. A mixture of nitrogen and carbon dioxide was introduced to the fresh air stream prior to mixing with the fuel and its subsequent combustion to simulate the product gases from within the combustor. Increase in the amounts of nitrogen and carbon dioxide (simulating increased entrainment) significantly reduced pollutants emission, enhanced thermal field uniformity, and increased the reaction volume to occupy larger portion of the combustor. This was evident through spatial temperature measurements in the combustor along with the enhanced distribution of the flame visible signature and OH* chemiluminescence signal. The temperature data demonstrated that lowering oxygen concentration from 21% to 15%, through increased entrainment, promoted distributed combustion conditions with lower overall temperature rise throughout the combustor. In addition, the peak temperature regions associated with swirl burners disappeared, eliminating most of the hot spots in the combustor. The enhanced thermal field uniformity and reduced temperature variation provided ultra-low emissions, demonstrating the impact of enhanced thermal flowfield uniformity on emissions. Experiments performed at different equivalence ratios and entrained gas temperatures demonstrated similar behavior of thermal field uniformity and ultra-low emissions. (C) 2015 Elsevier Ltd. All rights reserved.