FLAMELESS OXIDATION COMBUSTOR DEVELOPMENT FOR A SEQUENTIAL COMBUSTION HYBRID TURBOFAN ENGINE

A promising method of reducing NOx emissions in combustion systems is the Flameless oxidation (FO), which is based on significant dilution of the oxygen concentration in the reactant stream and elevating its temperature to above auto ignition level. The present work is aimed at developing an FO based combustor for a sequential combustion turbofan engine, where the primary combustor is fuelled with H-2 and the secondary combustor with hydrocarbon (jet or bio-jet) fuel. The work was performed within the framework of the European project AHEAD (www.ahead-euproject.eu). Being situated between the high pressure and the low pressure turbines, the inlet conditions to the FO combustor are non-conventional. CHEMKIN simulations revealed the theoretical feasibility of a combustion system to operate in the FO mode of combustion under the specific Take off and Cruise operating conditions. Several design iterations were conducted to find an appropriate geometrical configuration that would allow for such a system to operate in a stable manner. The design iterations were followed by intensive CFD simulations (FLUENT) and a final design was a achieved where the predictions indicated nearly uniform internal temperature distribution with low mass fraction of CO (14.4ppm) and NOx (0.5 ppm) at the exhaust. A separate experimental verification study was performed and confirmed the ability of the CFD model to predict the behaviour of such a combustion configuration within the hybrid turbofan engine and its results will be published elsewhere.