Flamelet Generated Manifold Combustion Research Articles

Investigation of swirler configuration impacts on combustion dynamics and NOx emissions of NH3/air premixed flames with large eddy simulation method

Ammonia, as a renewable energy with broad future application prospects, can alleviate its deficiencies in combustion stability as well as NOx emission by swirl premixed combustion technology. To investigate the impacts of swirler configuration parameters on ammonia premixed combustion, vanes numbers, vanes angles, and inner/outer diameter ratios of the swirler are varied. The combustion characteristics and NOx emissions in the combustion chamber are analyzed using the ammonia combustion mechanism model proposed by Stagni, which is done by large eddy simulation and Flamelet generated manifold combustion model. The results indicate that a stronger inner recirculation and lower NO2/N2O emissions were obtained when the number of vanes is 10. Increasing the vanes angles has several benefits, including expanding the flame's main combustion region, enhancing the heat release rate and improving turbulence in the flow field. The highest combustion efficiency and the lowest NO emissions are achieved at a vanes angle of 35°. Additionally, a moderate inner/outer diameter ratio of 0.447 can ensure appropriate inner and outer circulation intensity and NOx emissions. Based on the investigation results, the references for swirler parameters design in premixed ammonia combustion are provided.

Effects of turbulence and flamelet combustion modelling on the CFD simulation of a dual inlet ramjet combustor

Abstract This manuscript presents Computational Fluid Dynamics simulation of a ramjet combustor using Reynolds Averaged Navier–Stokes approach for turbulence with flamelet combustion modelling. In the approach a one-dimensional premixed flame simulation is performed to cover a wide range of mixture fraction space. After a mesh study, effects of turbulence, Realizable k-ε and SST k-ω, and combustion modelling, Steady Laminar Flamelet and Flamelet Generated Manifold, are investigated in detail. The Flamelet Generated Manifold model that offers a reaction delay by employing an additional progress variable, shows there are no reactions taking place in the vicinity of jet inlets, hence the unrealistic temperature rise that is seen in the case of using Steady Laminar Flamelet is not observed. A study on the choice of progress variable based on the combustion products is carried out. The present study readily demonstrates good predictability of Flamelet Generated Manifold combustion modelling in such a dual inlet ramjet combustion chamber.

Verification of temperature and toxic species in methane compartment fire using flamelet generated manifold with radiation effect

This paper examined the effect of combustion model on compartment fire simulation. The results of the flamelet generated manifold (FGM) combustion model were compared with conventional combustion models in compartment fire simulation. Methane fuel was selected and the detailed kinetic mechanism was chosen for the FGM model. In addition, the radiation effect was investigated on the FGM combustion model. It was observed that it was necessary to apply the radiation effect in the FGM combustion model for the high heat release rate. For example, the temperature of FGM-base (in the absence of radiation effect) over-predicted near the ceiling of the room at heat release rate of 265 kW. However, if radiation effect was applied, the mean temperature reached 1250 K and the relative error was reduced to less than 10%. The important point is that the computational cost of the FGM was equal to other conventional combustion models in fire simulation. In addition, the conventional combustion models could model only one or two toxic species. However, the FGM was able to model all toxic species involved in the fire.

Numerical Simulations of Heat Loss Effect on Premixed Jet Flame Using Flamelet Generated Manifold Combustion Model

Numerical simulations are performed on a combustor setup which represents the recirculating behaviour of a combustor in the flameless combustion regime. Previous experimental and numerical studies showed that heat loss is prominent for this setup. Here, the amount of heat loss through the combustor walls is quantified and its effect analysed. For this a non-adiabatic Flamelet Generated Manifold (FGM) model is employed. This model uses tabulated chemistry in combination with governing equations for a small set of control variables to accurately describe a turbulent flame. In the current implementation, equations for enthalpy and the mean and variance of the reaction progress variable are solved. Turbulence-chemistry interactions are incorporated through a presumed-PDF approach. In contrast to earlier work, the model is applied in the commercial solver Ansys CFX, coupled to a low-mach, compressible, steady-state Reynolds-Averaged Navier-Stokes (RANS) turbulence model. Results from the simulations show that heat loss consumes over 30% of the combustor’s thermal power. Despite this large heat loss, its effect on the combustion chemistry is small. The inclusion of heat loss in the chemistry tabulation does improve the prediction of the velocity and temperature field in the primary reaction zone. However, the effect of including heat loss is limited in the prediction of species concentrations.

Determining the heating characteristics of non-spherical particles in combusting flows

In order to perform efficient numerical calculations of the heating characteristics of inert, non-spherical particles, an Euler – Lagrangian approach was used for this work. The continuous phase was the combusting flow field in a lab-scale furnace. The Steady Laminar Flamelet (SLF) and the Flamelet Generated Manifold (FGM) combustion model were used for simulations of the continuous phase and the corresponding results were evaluated. It was concluded that the FGM combustion model offers superior performance and moderate computational effort in combustion modelling of air and natural gas. The second phase consisted of discrete coal slag particles which were injected into the furnace. The heating characteristics of spherical and non-spherical particles were evaluated and a model for calculating the temperature of non-spherical particles was validated. The application of the FGM in combination with the Euler-Lagrange approach and specially developed multiphase model adaptions led to very precise results. The maximum deviation between experimentally and numerically determined mean temperatures of non-spherical particles was only 6 K at a temperature level of 680 K.

Investigation of Single-Jet Combustor Near Lean Blowout Conditions Using Flamelet-Generated Manifold Combustion Model and Detailed Chemistry

Numerical simulation results of a single-jet premixed combustion system at atmospheric pressure are compared against comprehensive particle image velocimetry (PIV) flow measurements and Raman scattering temperature measurements for natural gas and hydrogen fuels. The simulations were performed on hexahedral meshes with 1–5 × 106 elements. Reynolds-averaged Navier–Stokes (RANS) calculations were carried out with the k–ε realizable turbulence model. Combustion was modeled using the flamelet-generated manifold model (FGM) and detailed chemistry. Both the flame position and flame liftoff predicted by the FGM were in reasonable agreement with experiments for both fuels and showed little sensitivity to heat transfer or radiation modeling. The detailed chemistry calculation predicts the temperature gradients along the jet centerline accurately and compares very closely with the Raman scattering measurements. The much closer agreement of the jet axial velocity and temperature profiles with experimental values, coupled with the significantly protracted presence of intermediates in the detailed chemistry predictions, indicates that the impact of nonequilibrium intermediates on very lean natural gas flames is significant.