Emission Modeling of an Interturbine Burner Based on Flameless Combustion

Abstract

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 NOx 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 NOx formation pathways, indicating that the prompt NOx 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.

Modeling Pollutant Emissions of Flameless Combustion With a Joint CFD and Chemical Reactor Network Approach

“…When temperature, velocity direction, Y CH4 and Y H2O are employed as clustering criteria, the NO x trend obtained with GRI 2.11 reaction mechanism is monotonic and its slope is the opposite of the experimental data: condition a had the highest NO x value. For GRI 3.0, overall values are higher than those of GRI 2.11 (a behavior previously reported by Perpignan et al, 2018b), but condition a has a lower value than condition b, making the overall trend non-monotonic. The values, however, are not in good agreement with experiments for both chemical reaction mechanism.…”

“…The adoption of EGR might cause the required conditions for FC to occur, as O 2 concentrations drop and initial temperatures rise. Studying FC, the work of Perpignan et al (2018b) showed the results of a CRN manually built based on CFD made with the Flamelet Generated Manifolds (FGM) approach, which is also employed in the present work. The authors achieved better agreement with CO and NO x experimental data using the CRN than with the reacting CFD.…”

“…This resulted in different numbers of reactors for each test condition and imposed clustering criteria. Simulations were performed with both GRI 3.0 and GRI 2.11 mechanisms, to investigate the effect on NO x formation, as it has been shown that there are relevant differences in the NO x formation pathways under FC conditions (Perpignan et al, 2018b).…”

NOx Formation in MILD Combustion: Potential and Limitations of Existing Approaches in CFD

“…The formation of NO x was quite successfully modeled in laboratory flames (Bergmann et al, 1998;Barlow et al, 2000) and in a small-scale MILD combustor (Veríssimo et al, 2011). The joint CFD-CRN method was also employed to predict NO x emissions in a interturbine flameless combustor for gas turbines: the flamelet generate manifolds (FGM) method was used to model the combustion process in the CFD simulation, whereas a detailed mechanism was considered in the resolution of the network of PSRs (Perpignan et al, 2018b). Although the CRN approach can be used to evaluate the variation of NO x emissions under different operating conditions in a cost-effective way, the reliability of the CRN predictions is strongly dependent on the accuracy of the underlying CFD simulation.…”

Comparison of Conventional and Modified Burners in Performance with Different Fuels using a Linear and a Non-linear Eddy-viscosity Turbulence Model

“…CRN had shown the dominant pathway for NOx formation was the prompt NOx mechanism. In addition, they made some suggestions for improving the design by modifying the mixing ratios (Perpignan et al, 2018).…”