Colorless Distributed Combustion (CDC) has been demonstrated to provide ultra-high combustion intensity, increased performance in terms of ultra-low emissions, uniform thermal field, combustion stability and enhanced efficiency. CDC has been examined under both swirling and non-swirling configurations using different injection velocities to seek improved distributed combustion. CDC performance has also been evaluated at different operational temperatures and equivalence ratios. The results are analyzed to determine the key factors that affect distributed combustion regime. Data showed key parameters for distributed combustion include recirculation ratio (defined as the ratio of the recirculated mass in the combustor to the mass of the fresh mixture), flow injection velocity, fuel injection scheme, and geometrical configuration for the operating condition. The results showed that increase in recirculation ratio and air injection velocity foster distributed reaction conditions. Fuel injection location and separation distance between air and fuel injection points played a critical role on fuel mixing and the resulting emissions. Impact of temperature and pressure varied with the operating equivalence ratio. A hybrid combination of the above parameters provides distribution index (DI) that reveals how well the chemical reaction zone is distributed within the combustion regime. (C) 2014 Elsevier Ltd. All rights reserved.