Non-premixed and premixed modes of Colorless Distributed Combustion (CDC) are investigated for application to gas turbine combustors. The CDC provides significant improvement in pattern factor, reduced NOx emission uniform thermal field in the entire combustion zone for it to be called as a isothermal reactor, and lower sound levels. Basic requirement for CDC is mixture preparation through good mixing between the combustion air and product gases so that the reactants are at much higher temperature to result in hot and diluted oxidant stream at temperatures that are high enough to auto-ignite the fuel and oxidant mixture. With desirable conditions one can achieve spontaneous ignition of the fuel with distributed combustion reactions. Distributed reactions can also be achieved in premixed mode of operation with sufficient entrainment of burned gases and faster turbulent mixing between the reactants. In the present investigation two non-premixed combustion modes and one premixed combustion mode that provide potential for CDC is examined. In all the configurations the air injection port is positioned at the opposite end of the combustor exit, whereas the location of fuel injection ports is changed to give different configurations. The results are compared for global flame signatures, exhaust emissions, acoustic signatures, and radical emissions using experiments and flow field, gas recirculation and mixing using numerical simulations. Ultra low NOx emissions are observed for both the premixed and non-premixed combustion modes, and almost colorless flames (no visible flame color) have been observed for the premixed combustion mode. The non-premixed mode was also provided near colorless distributed combustion. The reaction zone is observed to be significantly different in the two non-premixed modes.
