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  • 1. Danon, B.
    et al.
    Swiderski, Artur
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Energy and Furnace Technology.
    de Jong, W.
    Yang, Weihong
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Energy and Furnace Technology.
    Roekaerts, D. J. E. M.
    EMISSION AND EFFICIENCY COMPARISON OF DIFFERENT FIRING MODES IN A FURNACE WITH FOUR HiTAC BURNERS2011In: Combustion Science and Technology, ISSN 0010-2202, E-ISSN 1563-521X, Vol. 183, no 7, p. 686-703Article in journal (Refereed)
    Abstract [en]

    Combustion in a furnace equipped with two HiTAC burner pairs, with a thermal power of 100kW(th) each, has been investigated experimentally and computationally. The objective of this study is (1) to observe differences in the performance of the furnace operating in two different firing modes, parallel and staggered, and (2) to explain these differences using detailed CFD simulations. Besides the permanent measurements of temperature, flow and pressure, in-furnace probe measurements of temperature, oxygen and emissions (NO and CO) have been performed. Experimental results show that the efficiency of the furnace was higher in parallel mode compared to staggered mode, 48% and 41% respectively. The values of CO emitted were equal for both firing modes. However, in parallel mode the NOx production was 39 ppm(v)@3%O-2, whereas in staggered mode 53 ppm(v)@3%O-2 NOx was produced. Considering both efficiency and emissions, parallel firing mode performs better than staggered mode. Next, CFD simulations of the furnace were performed in order to explain the observed differences. The simulations were validated with the in-furnace measurements. It was confirmed that the furnace firing in parallel mode achieved a higher efficiency. The radiative heat transfer was higher due to formation of a larger zone with gases with improved radiative properties. In addition, higher velocities along the cooling tubes, due to lower momentum destruction, led to higher convective heat transfer. Also, the lower production of NOx in parallel mode was reproduced by the simulations. This is due to the fact that in parallel mode the fuel jets are merging slower with the combustion air jet, leading to less intense combustion zones. Thus, lower peak temperatures and radical concentrations are achieved, and the NOx production via the thermal and N2O pathways was lower.

  • 2. Duwig, C.
    et al.
    Fuchs, Laszlo
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Mechanics of Industrial Processes.
    Large eddy simulation of a H-2/N-2 lifted flame in a vitiated co-flow2008In: Combustion Science and Technology, ISSN 0010-2202, E-ISSN 1563-521X, Vol. 180, no 3, p. 453-480Article in journal (Refereed)
    Abstract [en]

    A lifted turbulent H-2/N-2 flame in a vitiated co-flow is studied using Large Eddy Simulation together with a closure based on perfectly stirred reactors. A part of the closure, chemical look-up tables, are generated to close the filtered temperature equations and to compute local radical concentrations throughout the computational domain. The approach has been used to simulate a lifted turbulent flame. The results have been found to be insensitive to the combustion model employed and to the grid resolution. However, the results are very sensitive to the temperature of the co-flow stream and this result is well in line with previous findings. The numerical predictions were further compared to detailed experimental data obtained by Cabra et al. (2002). The agreement between the two sets of data is very good, indicating that the present approach predicts successfully the combustion process including the OH mass fractions. Finally, the LES data were used to study the flame dynamics and stabilization mechanisms.

  • 3. Duwig, C.
    et al.
    Fuchs, Laszlo
    Study of flame stabilization in a swirling combustor using a new flamelet formulation2005In: Combustion Science and Technology, ISSN 0010-2202, E-ISSN 1563-521X, Vol. 177, no 8, p. 1485-1510Article in journal (Refereed)
    Abstract [en]

    The dynamics in a swirl-stabilized flame is studied using large eddy simulation (LES). We account for the effect of turbulence on the flame through a model based on a filtered flamelet technique. The model provides a consistent and robust reaction-diffusion expression for simulating the correct propagation of premixed flames. The filtered flamelet formulation has been implemented into a high-order-accurate LES code and used to study the flame stabilization and the combustion dynamics in a gas-turbine combustion chamber. The effects of inlet boundary conditions, in terms of velocity and equivalence ratio radial profiles, have been studied. The flow is found to be very sensitive to small changes in terms of flame shapes and anchoring position. The sensitivity of the results to the subgrid-scale flame thickness has also been investigated. The influence on the flame position is not significant. However, a too-large subgridscale flame thickness leads to different flame dynamics.

  • 4. Duwig, C.
    et al.
    Stankovic, D.
    Fuchs, Laszlo
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Mechanics of Industrial Processes.
    Li, G.
    Gutmark, E.
    Experimental and numerical study of flameless combustion in a model gas turbine combustor2008In: Combustion Science and Technology, ISSN 0010-2202, E-ISSN 1563-521X, Vol. 180, no 2, p. 279-295Article in journal (Refereed)
    Abstract [en]

    Flameless combustion is an attractive solution to address existing problems of emissions and stability when operating gas turbine combustors. Theoretical, numerical and experimental approaches were used to study the flameless gas turbine combustor. The emissions and combustion stability were measured and the limits of the flameless regime are discussed. Using experimental techniques and Large Eddy Simulation (LES), detailed knowledge of the flow field and the oxidation dynamics was obtained. In particular the relation between the turbulent coherent structures dynamics and the flameless oxidation was highlighted. A model for flameless combustion simulations including detailed chemistry was derived. The theoretical analysis of the flameless combustion provides 2 non-dimensional numbers that define the range of the flameless mode. It was determined that the mixture that is ignited and burnt is composed of similar to 50% of fresh gases and similar to 50% vitiated gases.

  • 5. Duwig, Christophe
    et al.
    Fuchs, Laszlo
    Large eddy simulation of turbulent premixed combustion using a marker field2007In: Combustion Science and Technology, ISSN 0010-2202, E-ISSN 1563-521X, Vol. 179, no 10, p. 2135-2152Article in journal (Refereed)
    Abstract [en]

    A new laminar flamelet model is presented for Large Eddy Simulation ( LES) of premixed turbulent combustion. The model uses a marker field S+ to capture the flame. Compared to previous work on marker fields, a modification was introduced to simplify the boundary conditions. Although the scalar S+ is smooth in space, it allows describing steep flame fronts. The S+ equation captures the laminar or turbulent flame propagation via a reactive diffusive balance. The present LES model was used to simulate a turbulent premixed flame stabilized behind a sudden expansion. The LES predictions agree well with available experimental data in term of reproducing the time averaged velocity field as well as for capturing the flame dynamics and flame response to a perturbation.

  • 6. Hodzic, Erdzan
    et al.
    Alenius, Emma
    KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design.
    Duwig, Christophe
    Szasz, R. S.
    Fuchs, Laszlo
    KTH, School of Engineering Sciences (SCI), Mechanics.
    A Large Eddy Simulation Study of Bluff Body Flame Dynamics Approaching Blow-Off2017In: Combustion Science and Technology, ISSN 0010-2202, E-ISSN 1563-521X, Vol. 189, no 7, p. 1107-1137Article in journal (Refereed)
    Abstract [en]

    The mechanisms leading to blowoff were investigated numerically by analyzing bluff body stabilized flame at two conditions: a condition far from blowoff to a condition just prior to blowoff. Large eddy simulations have been used to capture the time dependent, three-dimensional evolution of the field. The results were first validated to available experimental data, showing very good agreement for the flow and overall good agreement for the flame. Changes in the large-scale structures are investigated by means of proper orthogonal decomposition and the wavelet method, elucidating the underlying dynamics of the complex flow-flame interaction of a flame approaching blowoff. Our results reveal that, when the flame approaches blowoff conditions, significant changes are found in the large-scale structures responsible for entrainment of species into the recirculation zone located downstream of the bluff body. Possible causes of this shift in large-scale structures are also discussed, which may be useful for extending the blowoff limits of bluff body stabilized burners.

  • 7.
    Hodzic, Erdzan
    et al.
    Queens Univ Belfast, Sch Mech & Aerosp Engn, Belfast, Antrim, North Ireland.;Lund Univ, Dept Energy Sci, Lund, Sweden..
    Jangi, Mehdi
    Univ Birmingham, Dept Mech Engn, Birmingham, W Midlands, England..
    Szasz, Robert-Zoltan
    Lund Univ, Dept Energy Sci, Lund, Sweden..
    Duwig, Christophe
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Geron, Marco
    Queens Univ Belfast, Sch Mech & Aerosp Engn, Belfast, Antrim, North Ireland..
    Early, Juliana
    Queens Univ Belfast, Sch Mech & Aerosp Engn, Belfast, Antrim, North Ireland..
    Fuchs, Laszlo
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Bai, Xue-Song
    Lund Univ, Dept Energy Sci, Lund, Sweden..
    Large Eddy Simulation of Bluff-Body Flame Approaching Blow-Off: A Sensitivity Study2019In: Combustion Science and Technology, ISSN 0010-2202, E-ISSN 1563-521X, Vol. 191, no 10, p. 1815-1842Article in journal (Refereed)
    Abstract [en]

    As almost all combustion processes of practical interest take place in the presence of turbulence, the development of the increasingly refined turbulence-chemistry interaction (TCI) models has led to highly sophisticated approaches. Nearly all of the studies comparing different models focus on stable premixed/non-premixed flame configurations. In this work, the focus is on well-documented, lean premixed bluff-body stabilized flames approaching blow-off and on the blow-off sequence itself. Large Eddy Simulations (LES) have been used to capture the time-dependent, three-dimensional flow-field using Transported Probability Density Function (TPDF), Partially Stirred Reactor Model (PaSR), and Implicit LES (ILES) models. Furthermore, the influence of finite-rate chemistry and different chemical mechanisms is evaluated to determine the limitation and capability of the different TCI approaches for modeling flames just prior to and during the transient blow-off process. While the average flow-fields do not reveal any significant differences between modeling approaches, detailed analysis of the flame reveals that there are differences in the predicted flame thickness and composition. The ability of the considered TCI models to predict local as well as full-flame extinction during the blow-off is investigated as well. It is demonstrated that such a blow-off sequence is not always governed by complex chemistry.

  • 8.
    Mörtberg, Magnus
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Blasiak, Wlodzimierz
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Gupta, A.K.
    Combustion of normal and low calorific fuels in high temperature and oxygen deficient environment2006In: Combustion Science and Technology, ISSN 0010-2202, E-ISSN 1563-521X, Vol. 178, no 7, p. 1345-1372Article in journal (Refereed)
    Abstract [en]

    Combustion characteristics of two different gaseous fuels (a low calorific value fuel and methane fuel) have been examined using high temperature and low oxygen concentration combustion air. The momentum flux ratio between the fuel jet and the combustion airflow was kept constant to provide similarity in mixing between the different experimental cases to understand the role of fuel jet property on combustion. Direct flame photography, 2-D Particle image velocimetry (PIV), Light Emission Spectroscopy and chemiluminescent NOX analyzer was used as the diagnostics. These diagnostics allowed information on global flame features, mean and rms components of axial and radial velocity, axial strain rates and vorticity, the spatial distribution of combustion intermediate species, such as, OH and CH, and overall NOX emission levels. The results indicate a slower mixing during high temperature air combustion with low calorific value fuel as compared to methane fuel. The results showed higher turbulence levels and higher axial strain rates for low calorific fuel jets as compared to methane fuel jet during the high temperature air combustion condition. This results in less intense (or mild) combustion conditions with the result of increased flame length and volume and lower NOX emissions. Even for the normal methane fuel high temperature and oxygen deficient combustion conditions provided lower NOX emission. Furthermore, the high temperatures obtained for methane combustion provided lower vorticity and axial strain rates than the low calorific value fuel due to the suppression of vortical structure formation from the stronger heat release. In the case of low calorific value fuel, higher fuel jet velocity into low-density high temperature air leads to longer jet length. This jet causes a local stagnation to the upstream cross-flow to create local higher value of turbulence levels immediately upstream of the jet. The spatial distribution of the flame generated radicals (OH and CH) revealed significant ignition delay of the LCV fuel jet and a far more uniform distribution of the intermediate species. The methane fuel jet showed a prolonged reaction zone and faster ignition at high temperature and oxygen deficient conditions when compared to normal temperature air combustion of methane.

  • 9. Schneider, Adrian
    et al.
    Mantzaras, John
    Eriksson, Sara
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Ignition and extinction in catalytic partial oxidation of methane-oxygen mixtures with large H2O and CO2 dilution2008In: Combustion Science and Technology, ISSN 0010-2202, E-ISSN 1563-521X, Vol. 180, no 1, p. 89-126Article in journal (Refereed)
    Abstract [en]

    The ignition and extinction in catalytic partial oxidation (CPO) of CH4/O-2 mixtures with large exhaust gas dilution (46.3% H2O and 23.1% CO2 vol.) has been investigated experimentally and numerically at 5 bar. Experiments were carried out in a short contact time Rh-coated honeycomb reactor and involved temperature measurements along the reactor and exhaust gas analysis. Numerical predictions were performed with a 2-D transient elliptic code that included detailed chemical reaction schemes and relevant heat transfer mechanisms in the solid. The employed heterogeneous reaction scheme reproduced the measured minimum inlet temperatures required for catalytic ignition (light-off), the elapsed times for the propagation of the reaction front, and the steady-state exhaust gas compositions at a fuel-to-air equivalence ratio of phi = 4.0. The chemical impact of the added H2O, although important already at the early light-off stages, was minimal on the ignition delay times because the latter were dominated by total oxidation and not by partial oxidation or reforming reactions. The key reaction controlling catalytic ignition was the surface oxidation of CO to CO2, which was the main exothermic heat release step in the induction zone. Measurements and predictions indicated that vigorous combustion could be sustained at inlet temperatures at least as low as 473K and 298K in CPO with and without exhaust gas dilution, respectively. The extended stability limits of CPO combustion were due to a shift from partial to total oxidation products, and hence to higher exothermicity, with decreasing inlet temperature. The key parameter controlling extinction was the CO(s) coverage, which led to catalyst poisoning. Finally, operation at non-optimal stoichiometries (phi = 2.5) was shown to be beneficial in CPO of power generation systems with large exhaust dilution, due to the moderating effect of dilution on the maximum reactor temperature.

  • 10. Szasz, R.
    et al.
    Subash, A. A.
    Lantz, A.
    Collin, R.
    Fuchs, Laszlo
    KTH, School of Engineering Sciences (SCI), Mechanics. Lund University, Sweden.
    Gutmark, E.
    Hysteretic Dynamics of Flashback in a Low-Swirl Stabilized Combustor2017In: Combustion Science and Technology, ISSN 0010-2202, E-ISSN 1563-521X, Vol. 189, no 2, p. 266-289Article in journal (Refereed)
    Abstract [en]

    The hysteretic behavior of flashback (FB) and flash forward (FF) in methane and natural gas flames, stabilized by a low swirl fuel injector, is investigated using high speed OH* chemiluminescence and particle image velocimetry. Due to the lack of vortex breakdown, the two mechanisms discussed are boundary layer and turbulence induced FB. Two hysteresis cycles were identified, one when FB is induced by increasing the equivalence ratio starting from lean conditions, and the other by decreasing the equivalence ratio starting from rich conditions. Impact of relevant parameters including Reynolds number (Re), equivalence ratio, fuel type, combustion chamber geometry, preheating, and mixing tube protrusions are investigated. As Re is increased, the equivalence ratio at which both rich and lean flashbacks occur approaches stoichiometric conditions. However, the range of the hysteresis cycle between FB and FF is independent on Re. The transition processes during FB and FF are quite variable and their duration is independent on Re. The mean duration of FB transition initiated from lean conditions is nearly twice longer than the rich branch and also longer than both the lean and rich FF. The geometry of the combustion chamber affected neither FB nor FF. However, preheating increased the equivalence ratio at which FB occurred but did not affect FF. Also, FB had significant effect on the mean flow field.

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