This work introduces a new method to improve the accuracy of the flamelet-generated manifold (FGM) method under conditions of flame-wall interactions (FWI). Special attention is given to the prediction of the pollutant CO. In existing FGM methods, in order to account for heat loss, usually flamelets with constant enthalpy are utilised. These constant enthalpy flamelets used to generate the manifold, do not include the effects of wall heat loss on the manifold composition, resulting in simulation inaccuracies in the near-wall region, where large enthalpy gradients are present. To address this issue, the idea to utilise 1D head on quenching (HOQ) flamelets for tabulated chemistry is adopted and applied here in the context of the FGM method. The HOQ qualitatively resembles the general phenomena of FWI. However, the rates of wall heat loss and the accompanied effects on the chemical species composition may quantitatively differ between various FWI configurations. In addition, the magnitude of heat transfer rate may vary in space and time in general configurations. Therefore, in this work, a method is introduced to generate a 3D manifold, based on multiple HOQ-like flamelets, that includes the variation of the rate of heat loss as an extra table dimension. This dimension is parametrised by a second reaction progress variable for which a transport equation is solved next to the equations for enthalpy and the first progress variable. The new developed method, referred to as Quenching Flamelet-generated Manifold (QFM), is described in this work. Further, the method is validated against detailed chemistry simulations of a two-dimensional premixed laminar side-wall quenching of a methane-air flame. A comparison is presented, analysing the performance obtained using the existing 2D FGM method, a 2D QFM that is based on a single HOQ flamelet which does not account for a varying rate of wall heat loss and a 3D QFM, which does. Finally, it is shown that the 3D QFM tabulated chemistry simulation yields a very good level of accuracy and that the accuracy for prediction of CO concentrations near the wall is improved tremendously.

Preferential diffusion is very important in simulations of hydrogen flames. Flame stretch and curvature induce strong preferential diffusion effects in laminar premixed hydrogen flames, causing strong local deviations from the unburnt mixture fraction in the reaction zone. In tabulated chemistry methods, this necessitates the use of a partially premixed model even if the inlet mixture is purely premixed. Furthermore, in realistic combustion problems heat losses often play a dominant role. In this paper we derive a preferential diffusion model for constant but non-unity species Lewis numbers using three controlling variables, namely mixture fraction, progress variable and enthalpy. The model has been implemented in the Flamelet Generated Manifold (FGM) approach and validated by comparing with detailed chemistry simulations. As a test case we investigate a 2D laminar premixed hydrogen flame stabilised on an isothermal slit burner. Additionally, the model was compared with the standard treatment of preferential diffusion in FGM to show the increase in accuracy of the new model presented in this paper. The new model shows a significant improvement compared to the previous model, which can be attributed to the inclusion of cross-diffusion. The importance of the additional diffusion terms and its variation in mixture fraction for initially purely premixed hydrogen flames is highlighted.

We propose a new approach to improve the accuracy of flamelet-generated manifolds (FGMs) method by extending the manifolds with additional chemically reactive degrees of freedom. Following the ideas of intrinsic low-dimensional manifold, the dimensionality of the FGM is increased by performing a local timescale analysis of the chemical source term. A few slow characteristic directions of the reaction kinetics are used to extend the FGM, while the remaining reaction groups, characterised by fast timescales , are assumed in steady state. The introduced method for FGM REactive Dimensionality extension is abbreviated as FGM-REDx. It is tested in onedimensional simulations reproducing an expansion of burnt gases in an aero-engine stator. This process is characterised by a rapid change of enthalpy and pressure, altering, among others, the chemistry of pollutants CO and NO. The primary focus was on the assessment of the FGM's capability to predict the pollutants emissions. The rates of physical/thermodynamic perturbations turned out to be severe enough for the chemical species composition to go off the flamelet. The FGM extended with one additional chemically reactive dimension has been generated and successfully applied to the test cases, yielding a high accuracy gain over the standard FGM.

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