Investigation of Distributed Combustion for Gas Turbine Application: Forward Flow Configuration

Colorless Distributed Combustion (CDC) has been investigated here for high efficiency and ultra low pollution gas turbine combustors applications. In this paper forward flow configurations have been examined. Basic requirement for CDC is carefully tailored mixture preparation prior to ignition through a combination of product gas recirculation, controlled mixing between the fresh combustion air and recirculated gases to form hot and diluted oxidizer. Rapid mixing between the injected fuel and hot oxidizer is desirable prior to spontaneous ignition of the mixture in the entire combustion zone to achieve 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 forward flow modes are considered in which three non-premixed and one premixed combustion mode have been examined that showed favorable CDC combustion conditions. In the forward flow configurations the air injection port is positioned at a location opposite to the combustor exit. The location of fuel injection ports is changed to give different configurations. The thermal intensity for the present investigation is 28MW/m³-atm simulating gas turbine conditions. Increase in thermal intensity (lower combustion volume) presents many challenges, such as, lower residence time, lower recirculation of gases and confinement effects on the jet characteristics. The results are presented on the global flame signatures, exhaust emissions, and emission of radical species using experiments and flowfield dynamics using numerical simulations. Ultra low NOx emissions are found for both the premixed and non-premixed combustion modes investigated here. The reaction zone is observed to be significantly different in different combustion modes.