Heat loss prediction of a confined premixed jet flame using a conjugate heat transfer approach

The presented work addresses the investigation of the heat loss of a confined turbulent jet flame in a lab-scale combustor using a conjugate-heat transfer approach and large-eddy simulation. The analysis includes the assessment of the principal mechanisms of heat transfer in this combustion chamber: radiation, convection and conduction of heat over walls. A staggered approach is used to couple the reactive flow field to the heat conduction through the solid and both domains are solved using two implementations of the same code. Numerical results are compared against experimental data and an assessment of thermal boundary conditions to improve the prediction of the reactive flow field is given.The research leading to these results has received funding through the People Programme (Marie Curie Actions) of the European Union’s Seventh Framework Programme (FP7, 2007–2013) under the Grant agreement No. FP7-290042 for the project COPA-GT as well as the European Union’s Horizon 2020 Programme (2014–2020) and from Brazilian Ministry of Science, Technology and Innovation through Rede Nacional de Pesquisa (RNP) under the HPC4E Project, Grant agreement No. 689772. The authors thankfully acknowledge the computer resources, technical expertise and assistance provided by the Red Española de Supercomputación (RES). Finally, the authors would like to thank O. Lammel for the useful discussions and kindly providing the data for the comparison.Peer ReviewedPostprint (published version

Turbulent Combustion Modelling of a Confined Premixed Methane/Air Jet Flame Using Tabulated Chemistry

The present work addresses the coupling of a flamelet database that can accurately represent the flame structure in composition space with a low-Mach approximation of the Navier-Stokes equations. An advancement of the CFI combustion model, which is currently based on laminar premixed flamelets, is used for chemistry tabulation. This model can be applied to different combustion regimes from premixed to non-premixed combustion, although this work is concentrated on turbulent premixed flames for Reynolds-averaged Navier-Stokes (RANS) and large-eddy simulations (LES). A premixed confined jet flame, which has been investigated experimentally at the German Aerospace Center (DLR) is used for validation in adiabatic conditions showing satisfactory agreement

Characterization of low frequency combustion dynamics of hot blast stoves by means of a flame transfer function based on cfd forced response simulations: comparison of different hot blast stove designs

The combustion dynamics of thermo-acoustic systems like gas turbine combustors at elevated pressure and atmospheric industrial furnaces can be studied using a forced response approach. In this approach, the flame is excited by external perturbation of the upstream fuel or air mass flow. The flame transfer function can then be determined, which describes the response of the heat release rate in the combustor or furnace to the upstream velocity fluctuations. Subsequently, the flame transfer function can be used as an input for acoustic network models to further analyze the stability behavior of a given combustion system. Most of the applications of the flame transfer function analysis are for natural gas fired systems with dimensions such, that most of the relevant combustion dynamics is in the frequency range 100–500 Hz. The situation is different for hot blast stoves as used in the iron making process. Here the fuel is low calorific coal gas and the dimensions of the stove are huge, with heights of 30 m at a diameter of 5 m. This leads to a relevant frequency range for the combustion dynamics in interaction with acoustics of about 3–80 Hz. In order to cope with this combination of a large computational domain and extreme low frequent combustion dynamics in the response simulation, special attention was devoted to computational efficiency. In order to allow for a sufficient mesh resolution to capture the combustion characteristics while keeping the computational demands in a feasible range, the computational domain is to be drastically reduced by the use of symmetry assumptions. In a first step, the mesh dependency is studied and different combustion models are analyzed for a reference geometry on the basis of steady states results. The burning velocity model with adapted laminar flame speed description is subsequently chosen for the transient simulations. Transient numerical simulations are performed using a URANS turbulence model. The combustor is excited by a multi-harmonic perturbation of the fuel mass flow, to further reduce computational time. The flame transfer function is determined and compared for two different burner designs. The results show significant impact of combustor design on the acoustic behavior and combustion time scales. While the reference design acts like a low pass filter with a cut-off frequency of about 6 Hz, the modified design shows band-pass filter characteristics with a lower and higher cut-off frequency of 30 and 60 Hz, respectively.</jats:p

Heat loss prediction of a confined premixed jet flame using a conjugate heat transfer approach

The presented work addresses the investigation of the heat loss of a confined turbulent jet flame in a lab-scale combustor using a conjugate-heat transfer approach and large-eddy simulation. The analysis includes the assessment of the principal mechanisms of heat transfer in this combustion chamber: radiation, convection and conduction of heat over walls. A staggered approach is used to couple the reactive flow field to the heat conduction through the solid and both domains are solved using two implementations of the same code. Numerical results are compared against experimental data and an assessment of thermal boundary conditions to improve the prediction of the reactive flow field is given.The research leading to these results has received funding through the People Programme (Marie Curie Actions) of the European Union’s Seventh Framework Programme (FP7, 2007–2013) under the Grant agreement No. FP7-290042 for the project COPA-GT as well as the European Union’s Horizon 2020 Programme (2014–2020) and from Brazilian Ministry of Science, Technology and Innovation through Rede Nacional de Pesquisa (RNP) under the HPC4E Project, Grant agreement No. 689772. The authors thankfully acknowledge the computer resources, technical expertise and assistance provided by the Red Española de Supercomputación (RES). Finally, the authors would like to thank O. Lammel for the useful discussions and kindly providing the data for the comparison.Peer Reviewe

Demonstrating the self-healing behaviour of some selected ceramics under combustion chamber conditions

Closure of surface cracks by self-healing of conventional and MAX phase ceramics under realistic turbulent combustion chamber conditions is presented. Three ceramics namely; Al2O3, Ti2AlC and Cr2AlC are investigated. Healing was achieved in Al2O3 by even dispersion of TiC particles throughout the matrix as the MAX phases, Ti2AlC and Cr2AlC exhibit intrinsic self-healing. Fully dense samples (&gt;95%) were sintered by spark plasma sintering and damage was introduced by indentation, quenching and low perpendicular velocity impact methods. The samples were exposed to the oxidizing atmosphere in the post flame zone of a turbulent flame in a combustion chamber to heal at temperatures of approx. 1000 °C at low pO2 levels for 4 h. Full crack-gap closure was observed for cracks up to 20 mm in length and more than 10 μm in width. The reaction products (healing agents) were analysed by scanning electron microscope, x-ray microanalysis and XRD. A semi-quantification of the healing showed that cracks in Al2O3/TiC composite (width 1 μm and length 100 μm) were fully filled with TiO2. In Ti2AlC large cracks were fully filled with a mixture of TiO2 and Al2O3. And in the Cr2AlC, cracks of up to 1.0 μm in width and more than 100 μm in length were also completely filled with Al2O3.</p