Since its discovery, the flameless combustion (FC) regime has been a promising alternative to reduce pollutant emissions of gas turbine engines. This combustion mode is characterized by well-distributed reaction zones, which potentially decreases temperature gradients, acoustic oscillations, and NO_x emissions. Its attainment within gas turbine engines has proved to be challenging because previous design attempts faced limitations related to operational range and combustion efficiency. Along with an aircraft conceptual design, the AHEAD project proposed a novel hybrid engine. One of the key features of the proposed hybrid engine is the use of two combustion chambers, with the second combustor operating in the FC mode. This novel configuration would allow the facilitation of the attainment of the FC regime. The conceptual design was adapted to a laboratory scale combustor that was tested at elevated temperature and atmospheric pressure. In the current work, the emission behavior of this scaled combustor is analyzed using computational fluid dynamics (CFD) and chemical reactor network (CRN). The CFD was able to provide information with the flow field in the combustor, while the CRN was used to model and predict emissions. The CRN approach allowed the analysis of the NO_x formation pathways, indicating that the prompt NO_x was the dominant pathway in the combustor. The combustor design can be improved by modifying the mixing between fuel and oxidizer as well as the split between combustion and dilution air.

The Flameless Combustion (FC) regime is promising to the attainment of lower emissions in gas turbine engines. The well-distributed reactions, with low peak temperatures present in the regime result in lower emissions and acoustic oscillations. However, the attainment of the FC regime on gas turbine engines has not been successful, as most of the previous design attempts failed with respect to combustion efficiency, operational range, or difficulty to integrate in an engine. Along with a novel aircraft concept, a conceptual design of a gas turbine engine with two sequential combustion chambers was presented.1 As the aircraft would allow the use of cryogenic fuels, the first (and main) combustion chamber envisages the use of hydrogen or natural gas. The inter-turbine burner (ITB) is the subsequent chamber, and would operate under the FC regime with conventional fuels.