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The homogeneous ignition and volatile combustion of pulverized solid fuel in single-particle and particle group configurations were studied numerically in a laminar flat flame burner. Simulations with increasing particle streams were performed to investigate the influence of the interactions in particle groups on homogeneous ignition and combustion. An extensive set of simulations are conducted considering models with different levels of detail for both the gas-phase and solid fuel chemistry. The reference simulations employ the chemical percolation devolatilization model coupled with a detailed chemistry model for gas-phase reactions. The particle-fluid interactions were modeled with a fully coupled Eulerian-Lagrangian framework. Increased ignition delay times for higher particle streams were successfully validated against available experimental measurements. Furthermore, the transition from single-particle ignition to a conically shaped volatile flame with suppressed reactions near the flame base in particle group combustion was observed in both experiments and simulations. The subsequent detailed investigations revealed that the increased heat transfer to particles and, therefore, lower gas temperature for higher particle number densities together with the local oxygen depletion are the primary reasons for this transition. Based on the reference simulation, different simplified model combinations were assessed. The systematic model reduction investigation started with assessing the fixed volatile composition as a required assumption for flamelet models. Finally, the effects of gas-phase chemistry and different simple devolatilization models on ignition and combustion chemistry were studied. Overall, all model combinations provide reasonable predictions of volatile combustion with minor local deficits in the studied conditions.
Pooria Farmand; Hendrik Nicolai; Christoph Schumann; Antonio Attili; Lukas Berger; Tao Li; Christopher Geschwindner; Francesca di Mare; Christian Hasse; Benjamin Böhm; Johannes Janicka; Heinz Pitsch. Numerical investigation and assessment of flamelet-based models for the prediction of pulverized solid fuel homogeneous ignition and combustion. Combustion and Flame 2021, 111693 .
AMA StylePooria Farmand, Hendrik Nicolai, Christoph Schumann, Antonio Attili, Lukas Berger, Tao Li, Christopher Geschwindner, Francesca di Mare, Christian Hasse, Benjamin Böhm, Johannes Janicka, Heinz Pitsch. Numerical investigation and assessment of flamelet-based models for the prediction of pulverized solid fuel homogeneous ignition and combustion. Combustion and Flame. 2021; ():111693.
Chicago/Turabian StylePooria Farmand; Hendrik Nicolai; Christoph Schumann; Antonio Attili; Lukas Berger; Tao Li; Christopher Geschwindner; Francesca di Mare; Christian Hasse; Benjamin Böhm; Johannes Janicka; Heinz Pitsch. 2021. "Numerical investigation and assessment of flamelet-based models for the prediction of pulverized solid fuel homogeneous ignition and combustion." Combustion and Flame , no. : 111693.
Coal is the most abundant fossil fuel and is widely used as an energy source for combustion and gasification. Both experimental methods and computational tools are required for the development of new advanced, innovative clean coal technologies and systems. In particular, 3D computational fluid dynamics (CFD) simulations can provide detailed local and global information on the interaction of fluid dynamics, mixing, and heterogeneous and homogeneous chemical reactions even for complex systems such as combustors, gasifiers, or chemical reactors. The predictive capabilities of CFD simulations depend directly on appropriate models and their mutual interactions. The current state of modeling is reviewed in this paper and the need for further improvements of both individual models and their respective coupling is addressed. In addition, to evaluate and validate the models and their interactions, systems with increasing complexity and well-defined boundary and operating conditions are required that can provide suitable experimental data. A number of reference burners and combustors, developed especially at universities and research institutions, are also presented and recent simulation data for these systems is reviewed.
Christian Hasse; Paulo Debiagi; Xu Wen; Klaus Hildebrandt; Michele Vascellari; Tiziano Faravelli. Advanced modeling approaches for CFD simulations of coal combustion and gasification. Progress in Energy and Combustion Science 2021, 86, 100938 .
AMA StyleChristian Hasse, Paulo Debiagi, Xu Wen, Klaus Hildebrandt, Michele Vascellari, Tiziano Faravelli. Advanced modeling approaches for CFD simulations of coal combustion and gasification. Progress in Energy and Combustion Science. 2021; 86 ():100938.
Chicago/Turabian StyleChristian Hasse; Paulo Debiagi; Xu Wen; Klaus Hildebrandt; Michele Vascellari; Tiziano Faravelli. 2021. "Advanced modeling approaches for CFD simulations of coal combustion and gasification." Progress in Energy and Combustion Science 86, no. : 100938.
The here investigated Poly(oxymethylene) Dimethyl Ethers (OME3 and OME4) are pressurized and passed into a fused silica microcapillary, located in a heating block. By increasing the system pressure at constant temperature, the saturated vapor pressure is determined optically by detecting bubble or film formation, which indicates the transition from vapor to liquid phase. The therefrom obtained vapor pressure data are not yet available in the archival literature and are thus only compared to extrapolated and simulated data, both based on the same and only available low temperature data set of Richard H. Boyd. The experimental method was validated by measuring the vapor pressure curves up to the critical points of ethanol and 1-octanol. The obtained experimental results are in good agreement with literature data, showing low average absolute deviations of 2.1% (ethanol) and 4.1% (1-octanol). The heats of vaporization of the Poly(oxymethylene) Dimethyl Ethers are derived by the Clapeyron equation. Therein the saturated molar volumes were obtained by the Peng Robinson EOS (for the vapor phase) and the correlation of Rackett, Spencer and Danner (for the liquid phase).
Michael H. H. Fechter; Philip Haspel; Christian Hasse; Andreas S. Braeuer. Vapor pressures and latent heats of vaporization of Poly(oxymethylene) Dimethyl Ethers (OME3 and OME4) up to the vicinity of the critical temperature. Fuel 2021, 303, 121274 .
AMA StyleMichael H. H. Fechter, Philip Haspel, Christian Hasse, Andreas S. Braeuer. Vapor pressures and latent heats of vaporization of Poly(oxymethylene) Dimethyl Ethers (OME3 and OME4) up to the vicinity of the critical temperature. Fuel. 2021; 303 ():121274.
Chicago/Turabian StyleMichael H. H. Fechter; Philip Haspel; Christian Hasse; Andreas S. Braeuer. 2021. "Vapor pressures and latent heats of vaporization of Poly(oxymethylene) Dimethyl Ethers (OME3 and OME4) up to the vicinity of the critical temperature." Fuel 303, no. : 121274.
Side-wall quenching (SWQ) is one of the generic configurations for flame-wall interaction and has been widely investigated through simulations using detailed and reduced chemical kinetics. In all previous related studies using manifold-based reduced kinetic models, the reduced model equations are solved in thermokinetic coordinates. This study, by contrast, will for the first time conduct SWQ simulations based on reduced model equations in generalised coordinates. The implementation has been validated by comparison to both simulation results using detailed kinetics and experimental data. Comparing the results of computations solving reduced model equations in generalised coordinates to those in thermokinetic coordinates, it is found that there are only slight differences when the manifold is perfectly invariant, while large discrepancies appear if the manifold is not exactly invariant. Under the latter condition, only reduced model equations in generalised coordinates yield correct results. Within the combined framework of reduced model equations in generalised coordinates and the so-called reaction–diffusion manifold for tabulation, the sensitivity with respect to the gradient estimation is investigated to find out what degree of simplification is reasonable for SWQ simulations.
Yujuan Luo; Christina Strassacker; Christian Hasse; Ulrich Maas. Simulation of side-wall quenching of laminar premixed flames with manifold-based reduced kinetic models implemented in generalised coordinates. Combustion Theory and Modelling 2021, 25, 669 -694.
AMA StyleYujuan Luo, Christina Strassacker, Christian Hasse, Ulrich Maas. Simulation of side-wall quenching of laminar premixed flames with manifold-based reduced kinetic models implemented in generalised coordinates. Combustion Theory and Modelling. 2021; 25 (4):669-694.
Chicago/Turabian StyleYujuan Luo; Christina Strassacker; Christian Hasse; Ulrich Maas. 2021. "Simulation of side-wall quenching of laminar premixed flames with manifold-based reduced kinetic models implemented in generalised coordinates." Combustion Theory and Modelling 25, no. 4: 669-694.
A sweptback angle can directly regulate a leading-edge vortex on various aerodynamic devices as well as on the wings of biological flyers, but the effect of a sweptback angle has not yet been sufficiently investigated. Here, we thoroughly investigated the effect of the sweptback angle on aerodynamic characteristics of low-aspect-ratio flat plates at a Reynolds number of 2.85 × 104. Direct force/moment measurements and surface oil-flow visualizations were conducted in the wind-tunnel B at the Technical University of Munich. It was found that while the maximum lift at an aspect ratio of 2.03 remains unchanged, two other aspect ratios of 3.13 and 4.50 show a gradual increment in the maximum lift with an increasing sweptback angle. The largest leading-edge vortex contribution was found at the aspect ratio of 3.13, resulting in a superior lift production at a sufficient sweptback angle. This is similar to that of a revolving/flapping wing, where an aspect ratio around three shows a superior lift production. In the oil-flow patterns, it was observed that while the leading-edge vortices at aspect ratios of 2.03 and 3.13 fully covered the surfaces, the vortex at an aspect ratio of 4.50 only covered up the surface approximately three times the chord, similar to that of a revolving/flapping wing. Based on the pattern at the aspect ratio of 4.50, a critical length of the leading-edge vortex of a sweptback plate was measured as ~3.1 times the chord.
Jong-Seob Han; Christian Breitsamter. Leading-Edge Vortex Characteristics of Low-Aspect-Ratio Sweptback Plates at Low Reynolds Number. Applied Sciences 2021, 11, 2450 .
AMA StyleJong-Seob Han, Christian Breitsamter. Leading-Edge Vortex Characteristics of Low-Aspect-Ratio Sweptback Plates at Low Reynolds Number. Applied Sciences. 2021; 11 (6):2450.
Chicago/Turabian StyleJong-Seob Han; Christian Breitsamter. 2021. "Leading-Edge Vortex Characteristics of Low-Aspect-Ratio Sweptback Plates at Low Reynolds Number." Applied Sciences 11, no. 6: 2450.
The present work is part of the Clean Sky 2 project Full-Fairing Rotor Head Aerodynamic Design Optimization (FURADO), which deals with the aerodynamic design optimization of a full-fairing rotor head for the Rapid And Cost-Effective Rotorcraft (RACER) compound helicopter. The rotor head is a major drag source and previous investigations have revealed that the application of rotor head fairings can be an effective drag reduction measure. As part of the full-fairing concept, a new blade-sleeve fairing was aerodynamically optimized for cruise flight. Within this publication, the newly developed blade-sleeve fairing is put to test on an isolated, five-bladed rotor head and compared to an already existing reference blade-sleeve fairing, which was developed at Airbus Helicopters. Numerical flow simulations are performed with ANSYS Fluent 2019 R2 considering a rotating rotor head with cyclic pitch movement. The aerodynamic forces of the isolated rotor head are analyzed to determine the performance benefit of the newly developed blade-sleeve fairing. A drag reduction of 4.7% and a lift increase of 20% are obtained in comparison to the Airbus Helicopters reference configuration. Furthermore, selected surface and flow field quantities are presented to give an overview on the occurring flow phenomena.
Patrick Pölzlbauer; Andreas Kümmel; Damien Desvigne; Christian Breitsamter. Numerical Investigation of an Optimized Rotor Head Fairing for the RACER Compound Helicopter in Cruise Flight. Aerospace 2021, 8, 66 .
AMA StylePatrick Pölzlbauer, Andreas Kümmel, Damien Desvigne, Christian Breitsamter. Numerical Investigation of an Optimized Rotor Head Fairing for the RACER Compound Helicopter in Cruise Flight. Aerospace. 2021; 8 (3):66.
Chicago/Turabian StylePatrick Pölzlbauer; Andreas Kümmel; Damien Desvigne; Christian Breitsamter. 2021. "Numerical Investigation of an Optimized Rotor Head Fairing for the RACER Compound Helicopter in Cruise Flight." Aerospace 8, no. 3: 66.
In the present work, a systematic experimental and numerical study of sulfur release from coal in varying atmospheres at low heating rates (LHR) is presented. To this aim, two bituminous coals were investigated, Colombian hard coal (K1) with typical sulfur content, and American high-sulfur coal (U2), with elevated sulfur content. Mass loss and release of target volatile species - H2S, COS, SO2 - were tracked using a TG-MS. The samples were heated at 10 Kmin−1 under different atmospheres: argon, CO2, synthetic air (21 vol% O2/79 vol% Ar) and oxy-fuel (21 vol% O2/79 vol% CO2). The role of the different atmospheres in the sulfur release was elucidated as well as the fate of the volatile species in the gas-phase. The advantage of investigating the release at LHR is that heat and mass transfer effects can be neglected, as the experimental conditions allow the process to remain in the kinetic regime. The successive increase in atmosphere complexity allowed to individuate the chemical paths leading to the formation of SOX and its precursors in each of the conversion steps: devolatilization, char conversion as well as the coupling to gas-phase reactions. The experiments were further analyzed with a kinetic model for the solid-phase of coal conversion, coupled with a detailed gas-phase kinetic mechanism. The solid-phase kinetic model was modified accounting for the particularities of the fuels, for the effects of oxy-fuel atmosphere. A small number of kinetic parameters was adjusted for improved predictions of the release rate and the yields of sulfur species.
P. Debiagi; C. Yildiz; J. Ströhle; B. Epple; T. Faravelli; C. Hasse. Systematic evaluation and kinetic modeling of low heating rate sulfur release in various atmospheres. Fuel 2020, 289, 119739 .
AMA StyleP. Debiagi, C. Yildiz, J. Ströhle, B. Epple, T. Faravelli, C. Hasse. Systematic evaluation and kinetic modeling of low heating rate sulfur release in various atmospheres. Fuel. 2020; 289 ():119739.
Chicago/Turabian StyleP. Debiagi; C. Yildiz; J. Ströhle; B. Epple; T. Faravelli; C. Hasse. 2020. "Systematic evaluation and kinetic modeling of low heating rate sulfur release in various atmospheres." Fuel 289, no. : 119739.
The catalytic effects of mineral compounds on the conversion of a biomass-derived char in air- and oxyfuel-related atmospheres were investigated by thermogravimetric analysis at atmospheric pressure. The applied char originated from the hydrothermal carbonization (HTC) of cellulose followed by pyrolysis at 1073 K and subsequent mixing with 20 wt% of minerals by grinding to achieve tight contact. The reactivities of the mineral-loaded HTC chars were evaluated based on isothermal experiments in O2-, CO2-, and H2O-containing atmospheres as a function of their composition applying a magnetic suspension balance. The reactivity sequence K2CO3 > Na2CO3 ≫ Fe2O3 > CaO > MgO ≥ mineral-free was derived consistently for char oxidation in O2/inert as well as for char gasification in diluted H2O and CO2 mixtures. In addition to this qualitative assessment, the kinetic experiments were first modelled based on a simple global nth-order power-law rate expression. Then, the more complex Carbon Burnout Kinetics (CBK/G) model and the PoliMi model were applied. All three modeling approaches enabled a systematic quantification of the catalytic effects and led to a comparable lowering in the apparent activation energy. In combination with the kinetic parameters determined for the mineral-free char, the lowered apparent activation energies specific for the applied mineral and atmosphere facilitate the implementation of catalytic effects on the conversion of biomass-derived char into combustion models.
Christin Pflieger; Katrin Lotz; Nikoline Hilse; Cornelius M. Berger; Martin Schiemann; Paulo Debiagi; Christian Hasse; Viktor Scherer; Martin Muhler. Catalytic influence of mineral compounds on the reactivity of cellulose-derived char in O2-, CO2-, and H2O-containing atmospheres. Fuel 2020, 287, 119584 .
AMA StyleChristin Pflieger, Katrin Lotz, Nikoline Hilse, Cornelius M. Berger, Martin Schiemann, Paulo Debiagi, Christian Hasse, Viktor Scherer, Martin Muhler. Catalytic influence of mineral compounds on the reactivity of cellulose-derived char in O2-, CO2-, and H2O-containing atmospheres. Fuel. 2020; 287 ():119584.
Chicago/Turabian StyleChristin Pflieger; Katrin Lotz; Nikoline Hilse; Cornelius M. Berger; Martin Schiemann; Paulo Debiagi; Christian Hasse; Viktor Scherer; Martin Muhler. 2020. "Catalytic influence of mineral compounds on the reactivity of cellulose-derived char in O2-, CO2-, and H2O-containing atmospheres." Fuel 287, no. : 119584.
In the present work, a reduced-order modeling (ROM) framework based on a recurrent neuro-fuzzy model (NFM) that is serial connected with a multilayer perceptron (MLP) neural network is applied for the computation of transonic aileron buzz. The training data set for the specified ROM is obtained by performing forced-motion unsteady Reynolds-averaged Navier Stokes (URANS) simulations. Further, a Monte Carlo-based training procedure is applied in order to estimate statistical errors. In order to demonstrate the method’s fidelity, a two-dimensional aeroelastic model based on the NACA651213 airfoil is investigated at different flow conditions, while the aileron deflection and the hinge moment are considered in particular. The aileron is integrated in the wing section without a gap and is modeled as rigid. The dynamic equations of the rigid aileron rotation are coupled with the URANS-based flow model. For ROM training purposes, the aileron is excited via a forced motion and the respective aerodynamic and aeroelastic response is computed using a computational fluid dynamics (CFD) solver. A comparison with the high-fidelity reference CFD solutions shows that the essential characteristics of the nonlinear buzz phenomenon are captured by the selected ROM method.
Rebecca Zahn; Christian Breitsamter. Neuro-Fuzzy Network-Based Reduced-Order Modeling of Transonic Aileron Buzz. Aerospace 2020, 7, 162 .
AMA StyleRebecca Zahn, Christian Breitsamter. Neuro-Fuzzy Network-Based Reduced-Order Modeling of Transonic Aileron Buzz. Aerospace. 2020; 7 (11):162.
Chicago/Turabian StyleRebecca Zahn; Christian Breitsamter. 2020. "Neuro-Fuzzy Network-Based Reduced-Order Modeling of Transonic Aileron Buzz." Aerospace 7, no. 11: 162.
In the present study, we report the first large eddy simulation (LES) study of the Cambridge CCB2 coal flames, one of the target flames in the Workshop on Measurement and Simulation of Coal and Biomass Conversion, with an extended flamelet progress variable (FPV) model. The extended FPV model is based on two mixture fractions considering the volatiles and char off-gases. The normalized total enthalpy is used for the interphase heat transfer modelling. Turbulence-chemistry interaction is treated with an assumed probability density function approach. The results show that the present LES can generally capture the flow field and particle distribution, while there are considerable deviations in the OH prediction due to the boundary treatment of using a mixture of volatiles and carrier gas to replace the methane-containing mixtures in the primary and pilot flow. It indicates that for such gas-assisted coal flames, the pilot fuel stream needs to be rigorously considered in the flamelet tabulation that could be resolved by extending the two-mixture-fraction model into a three-mixture-fraction model. The instantaneous Lagrangian particles histories show that the increasing of coal load has a negligible effect on devolatilization, but delays the char conversion.
Jiangkuan Xing; Kun Luo; Yiran Chen; Oliver T. Stein; Andreas Kronenburg; Kai Hong Luo; Christian Hasse; Jianren Fan. Large eddy simulation of Cambridge bluff-body coal (CCB2) flames with a flamelet progress variable model. Proceedings of the Combustion Institute 2020, 38, 5347 -5354.
AMA StyleJiangkuan Xing, Kun Luo, Yiran Chen, Oliver T. Stein, Andreas Kronenburg, Kai Hong Luo, Christian Hasse, Jianren Fan. Large eddy simulation of Cambridge bluff-body coal (CCB2) flames with a flamelet progress variable model. Proceedings of the Combustion Institute. 2020; 38 (4):5347-5354.
Chicago/Turabian StyleJiangkuan Xing; Kun Luo; Yiran Chen; Oliver T. Stein; Andreas Kronenburg; Kai Hong Luo; Christian Hasse; Jianren Fan. 2020. "Large eddy simulation of Cambridge bluff-body coal (CCB2) flames with a flamelet progress variable model." Proceedings of the Combustion Institute 38, no. 4: 5347-5354.
In this work, effects of air and oxy-fuel atmospheres on flamelet modeling of NOx and SOx formation in two-dimensional laminar counterflow pulverized coal flames are investigated. The release and combustion of volatile-N, char-N and volatile-S are incorporated in the flamelet model, and a newly developed reaction mechanism for oxy-fuel combustion (129 species and 911 elementary reactions) is employed to describe the chemistry. Two different methods for prediction of pollutant species are evaluated using the flamelet model, in which the pollutant mass fractions are obtained by either extracting the flamelet library directly (“M1”) or solving the corresponding transport equations with the reaction source terms being taken from the flamelet library (“M2”). To evaluate the performance of proposed flamelet models, the flamelet predictions are compared to the reference results of the detailed chemistry solutions, in which the transport equations for the species mass fractions and total enthalpy are directly solved. At first, the atmosphere effects on the NOx and SOx formation are analyzed based on the detailed chemistry solutions, then the effects of atmosphere on flamelet modeling of pollutant formation are evaluated. The results show that M1 overall performs better than M2 at predicting the NOx and SOx species in both air and oxy-fuel atmospheres. The major pollutant species of NO and SO2 are over-predicted by M2 in certain regions for both atmospheres, and the reason for the incorrect prediction is explored by attributing to the interpolation error of the reaction source terms in the middle branch of the S-Shaped curve.
Xu Wen; Hendrik Nicolai; Oliver T. Stein; Johannes Janicka; Andreas Kronenburg; Christian Hasse. Effects of air and oxy-fuel atmospheres on flamelet modeling of pollutant formation in laminar counterflow solid fuel flames. Fuel 2020, 285, 119079 .
AMA StyleXu Wen, Hendrik Nicolai, Oliver T. Stein, Johannes Janicka, Andreas Kronenburg, Christian Hasse. Effects of air and oxy-fuel atmospheres on flamelet modeling of pollutant formation in laminar counterflow solid fuel flames. Fuel. 2020; 285 ():119079.
Chicago/Turabian StyleXu Wen; Hendrik Nicolai; Oliver T. Stein; Johannes Janicka; Andreas Kronenburg; Christian Hasse. 2020. "Effects of air and oxy-fuel atmospheres on flamelet modeling of pollutant formation in laminar counterflow solid fuel flames." Fuel 285, no. : 119079.
Transported probability density function (PDF) methods are widely used to model turbulent flames characterized by strong turbulence-chemistry interactions. Numerical methods directly resolving the PDF are commonly used, such as the Lagrangian particle or the stochastic fields (SF) approach. However, especially for premixed combustion configurations, characterized by high reaction rates and thin reaction zones, a fine PDF resolution is required, both in physical and in composition space, leading to high numerical costs. An alternative approach to solve a PDF is the method of moments, which has shown to be numerically efficient in a wide range of applications. In this work, two Quadrature-based Moment closures are evaluated in the context of turbulent premixed combustion. The Quadrature-based Moment Methods (QMOM) and the recently developed Extended QMOM (EQMOM) are used in combination with a tabulated chemistry approach to approximate the composition PDF. Both closures are first applied to an established benchmark case for PDF methods, a plug-flow reactor with imperfect mixing, and compared to reference results obtained from Lagrangian particle and SF approaches. Second, a set of turbulent premixed methane-air flames are simulated, varying the Karlovitz number and the turbulent length scale. The turbulent flame speeds obtained are compared with SF reference solutions. Further, spatial resolution requirements for simulating these premixed flames using QMOM are investigated and compared with the requirements of SF. The results demonstrate that both QMOM and EQMOM approaches are well suited to reproduce the turbulent flame properties. Additionally, it is shown that moment methods require lower spatial resolution compared to SF method.
Martin Pollack; Federica Ferraro; Johannes Janicka; Christian Hasse. Evaluation of Quadrature-based Moment Methods in turbulent premixed combustion. Proceedings of the Combustion Institute 2020, 38, 2877 -2884.
AMA StyleMartin Pollack, Federica Ferraro, Johannes Janicka, Christian Hasse. Evaluation of Quadrature-based Moment Methods in turbulent premixed combustion. Proceedings of the Combustion Institute. 2020; 38 (2):2877-2884.
Chicago/Turabian StyleMartin Pollack; Federica Ferraro; Johannes Janicka; Christian Hasse. 2020. "Evaluation of Quadrature-based Moment Methods in turbulent premixed combustion." Proceedings of the Combustion Institute 38, no. 2: 2877-2884.
Many modeling strategies for combustion rely on laminar flamelet concepts to determine structure and properties of multi-dimensional and turbulent flames. Using flamelet tabulation strategies, the user anticipates certain aspects of the combustion process prior to the simulation and selects a flamelet model which mimics local flame conditions in the more complex configuration. Flame stretch, which can be decomposed into contributions from strain and curvature, is one of the conditions influencing a flame’s properties, structure, and stability. The objective of this work is to study premixed flame structures in the strain-curvature space using a recently published composition space model (CSM) and three physical space models for canonical flame configurations (stagnation flame, spherical expanding flame and inwardly propagating flame). Flames with effective Lewis numbers both smaller and larger than unity are considered. For canonical laminar flames, the stretch components are inherently determined through boundary conditions and their specific flame configuration. Therefore, canonical flames can only represent a certain sub-set of stretch effects experienced by multi-dimensional and turbulent flames. On the contrary, the CSM allows arbitrary combinations of strain and curvature to be prescribed for premixed flames exceeding the conditions attainable with the canonical flame setups. Thereby, also influences of negative strain effects and large curvatures can be studied. A parameter variation with the CSM shows that flame structures still significantly change outside the region of the canonical flame configurations. Furthermore, limits in the strain-curvature space are discussed. The present paper highlights advantages of composition space modeling which is achieved by detaching the representation of the flame structure from a specific canonical flame configuration in physical space.
H. Böttler; A. Scholtissek; X. Chen; Z. Chen; C. Hasse. Premixed flames for arbitrary combinations of strain and curvature. Proceedings of the Combustion Institute 2020, 38, 2031 -2039.
AMA StyleH. Böttler, A. Scholtissek, X. Chen, Z. Chen, C. Hasse. Premixed flames for arbitrary combinations of strain and curvature. Proceedings of the Combustion Institute. 2020; 38 (2):2031-2039.
Chicago/Turabian StyleH. Böttler; A. Scholtissek; X. Chen; Z. Chen; C. Hasse. 2020. "Premixed flames for arbitrary combinations of strain and curvature." Proceedings of the Combustion Institute 38, no. 2: 2031-2039.
A large-eddy simulation of a swirl-stabilized multi-stream laboratory-scale pulverized coal burner designed specifically for oxy-fuel investigation is conducted using a three-mixture-fraction flamelet model, in which both NOx and SOx emissions are considered. The simulation results are compared to those in an air atmosphere and the available experimental data. The flame structures and pollutant formation mechanisms are analyzed in detail. The results show that the oxy-coal flame is narrower in the radial direction compared to the air-coal flame. Further, the particle clustering phenomenon can be observed in the oxy-fuel atmosphere. The distributions of the thermo-chemical quantities in different conditions are significantly different. For pollutant formation, the results show that NO is mainly formed around the quarl zone in an oxy-fuel atmosphere, while a large amount of NO is formed in the far downstream region in an air atmosphere. Although the instantaneous distributions of SOx are qualitatively similar in different conditions, they are quantitatively different due to the different oxygen partial pressure in the air and oxy-fuel atmospheres.
Xu Wen; Hendrik Nicolai; Henrik Schneider; Liming Cai; Johannes Janicka; Heinz Pitsch; Christian Hasse. Flamelet LES of a swirl-stabilized multi-stream pulverized coal burner in air and oxy-fuel atmospheres with pollutant formation. Proceedings of the Combustion Institute 2020, 38, 4141 -4149.
AMA StyleXu Wen, Hendrik Nicolai, Henrik Schneider, Liming Cai, Johannes Janicka, Heinz Pitsch, Christian Hasse. Flamelet LES of a swirl-stabilized multi-stream pulverized coal burner in air and oxy-fuel atmospheres with pollutant formation. Proceedings of the Combustion Institute. 2020; 38 (3):4141-4149.
Chicago/Turabian StyleXu Wen; Hendrik Nicolai; Henrik Schneider; Liming Cai; Johannes Janicka; Heinz Pitsch; Christian Hasse. 2020. "Flamelet LES of a swirl-stabilized multi-stream pulverized coal burner in air and oxy-fuel atmospheres with pollutant formation." Proceedings of the Combustion Institute 38, no. 3: 4141-4149.
A carrier-phase direct numerical simulation (CP-DNS) of pulverized coal combustion in a mixing layer is performed, considering three NOx formation mechanisms (fuel-NOx, thermal-NOx and prompt-NOx). Detailed analyses, including reaction path analysis, chemical timescale analysis, and a priori and budget analyses are conducted to investigate the NOx production mechanisms and the performance of the flamelet model. Considering the high computational cost of CP-DNS, this work focuses on the early phase governed by devolatilization, where char reactions are less important. The reaction path analyses show that the principal thermal-NO reaction contributes to the net consumption of NO in fuel-bound nitrogen pulverized coal flames, which is essentially different from fuel-nitrogen-free flames. The chemical timescale analyses show that the production rates of NOx species are faster than those of major species, which confirms the suitability of the flamelet tables. The a priori analyses show that the gas temperature and major/intermediate species can be predicted well by the flamelet model, while the NOx species show significant discrepancies in certain regions. Finally, the budget analyses explain why the flamelet model performs differently for major/intermediate and NOx species.
Xu Wen; Ali Shamooni; Oliver T. Stein; Liming Cai; Andreas Kronenburg; Heinz Pitsch; Andreas M. Kempf; Christian Hasse. Detailed analysis of early-stage NO formation in turbulent pulverized coal combustion with fuel-bound nitrogen. Proceedings of the Combustion Institute 2020, 38, 4111 -4119.
AMA StyleXu Wen, Ali Shamooni, Oliver T. Stein, Liming Cai, Andreas Kronenburg, Heinz Pitsch, Andreas M. Kempf, Christian Hasse. Detailed analysis of early-stage NO formation in turbulent pulverized coal combustion with fuel-bound nitrogen. Proceedings of the Combustion Institute. 2020; 38 (3):4111-4119.
Chicago/Turabian StyleXu Wen; Ali Shamooni; Oliver T. Stein; Liming Cai; Andreas Kronenburg; Heinz Pitsch; Andreas M. Kempf; Christian Hasse. 2020. "Detailed analysis of early-stage NO formation in turbulent pulverized coal combustion with fuel-bound nitrogen." Proceedings of the Combustion Institute 38, no. 3: 4111-4119.
In this work, the flame structures of the recent Darmstadt turbulent premixed/stratified flame series with 20% volume fraction H2 addition (Schneider et al., PCI, 2019) are analyzed using flamelet tabulated manifolds. Three different methane/hydrogen flames (MHFs) with increasing complexity are studied. The effects of differential diffusion, stretch and stratification on the applicability of the flamelet model are investigated in detail. Specifically, to investigate the differential diffusion effects, three different modeling approaches are considered, in which the diffusion fluxes are calculated using the multi-component (MC), mixture-averaged (MA) and unity Lewis number (Le1) approaches. To investigate stretch effects, a strained premixed flamelet (SPF) model is proposed, in which the flame’s internal response to stretch is characterized with an additional tabulation coordinate. A double-conditioning analysis is conducted for different flame series. The dataset is conditioned on both the local equivalence ratio and local stratification to analyze the coupling effects of stratification and differential diffusion on the flame structure. Overall, the flamelet predictions are consistent with the experimental findings for all flames.
Xu Wen; Sandra Hartl; Andreas Dreizler; Johannes Janicka; Christian Hasse. Flame structure analysis of turbulent premixed/stratified flames with H2 addition considering differential diffusion and stretch effects. Proceedings of the Combustion Institute 2020, 38, 2993 -3001.
AMA StyleXu Wen, Sandra Hartl, Andreas Dreizler, Johannes Janicka, Christian Hasse. Flame structure analysis of turbulent premixed/stratified flames with H2 addition considering differential diffusion and stretch effects. Proceedings of the Combustion Institute. 2020; 38 (2):2993-3001.
Chicago/Turabian StyleXu Wen; Sandra Hartl; Andreas Dreizler; Johannes Janicka; Christian Hasse. 2020. "Flame structure analysis of turbulent premixed/stratified flames with H2 addition considering differential diffusion and stretch effects." Proceedings of the Combustion Institute 38, no. 2: 2993-3001.
The numerical investigation of quenching distances in laminar flows is mainly concerned with two setups: head-on quenching (HOQ) and side-wall quenching (SWQ). While most of the numerical work has been conducted for HOQ with good agreement between simulation and experiment, far less analysis has been done for SWQ. Most of the SWQ simulations used simplified diffusion models or reduced chemistry and achieved reasonable agreement with experiments. However, it has been found that quenching distances for the SWQ setup differ from experimental results if detailed diffusion models and chemical reaction mechanisms are employed. Side-wall quenching is investigated numerically in this work with steady-state 2D and 3D simulations of an experimental flame setup. The simulations fully resolve the flame and employ detailed reaction mechanisms as well as molecular diffusion models. The goal is to provide data for the sensitivity of numerical quenching distances to different parameters. Quenching distances are determined based on different markers: chemiluminescent species, temperature and OH iso-surface. The quenching distances and heat fluxes at the cold wall from simulations and measurements agree well qualitatively. However, quenching distances from the simulations are lower than those from the experiments by a constant factor, which is the same for both methane and propane flames and also for a wide range of equivalence ratios and different markers. A systematic study of different influencing factors is performed: Changing the reaction mechanism in the simulation has little impact on the quenching distance, which has been tested with over 20 different reaction mechanisms. Detailed diffusion models like the mixture-averaged diffusion model and multi-component diffusion model with and without Soret effect yield the same quenching distances. By assuming a unity Lewis number, however, quenching distances increase significantly and have better agreement with measurements. This was validated by two different numerical codes (OpenFOAM and FASTEST) and also by 1D head-on quenching simulations (HOQ). Superimposing a fluctuation on the inlet velocity in the simulation also increases the quenching distance on average compared to the reference steady-state case. The inlet velocity profile, temperature boundary condition of the rod and radiation have a negligible effect. Finally, three dimensional simulations are necessary in order to obtain the correct velocity field in the SWQ computations. This however has only a negligible effect on quenching distances.
Thorsten Zirwes; Thomas Häber; Feichi Zhang; Hidemasa Kosaka; Andreas Dreizler; Matthias Steinhausen; Christian Hasse; Alessandro Stagni; Dimosthenis Trimis; Rainer Suntz; Henning Bockhorn. Numerical Study of Quenching Distances for Side-Wall Quenching Using Detailed Diffusion and Chemistry. Flow, Turbulence and Combustion 2020, 106, 649 -679.
AMA StyleThorsten Zirwes, Thomas Häber, Feichi Zhang, Hidemasa Kosaka, Andreas Dreizler, Matthias Steinhausen, Christian Hasse, Alessandro Stagni, Dimosthenis Trimis, Rainer Suntz, Henning Bockhorn. Numerical Study of Quenching Distances for Side-Wall Quenching Using Detailed Diffusion and Chemistry. Flow, Turbulence and Combustion. 2020; 106 (2):649-679.
Chicago/Turabian StyleThorsten Zirwes; Thomas Häber; Feichi Zhang; Hidemasa Kosaka; Andreas Dreizler; Matthias Steinhausen; Christian Hasse; Alessandro Stagni; Dimosthenis Trimis; Rainer Suntz; Henning Bockhorn. 2020. "Numerical Study of Quenching Distances for Side-Wall Quenching Using Detailed Diffusion and Chemistry." Flow, Turbulence and Combustion 106, no. 2: 649-679.
Gradient free regime identification (GFRI) is applied to 1D Raman/Rayleigh/LIF measurements of temperature and major species from the intermediate velocity case of the Sydney piloted inhomogeneous jet flame series to better understand the structure of reaction zones and the downstream evolution of multi-regime characteristics. The GFRI approach allows local reaction zones to be detected and characterized as premixed, dominantly premixed, multi-regime, dominantly non-premixed, or non-premixed flame structures, based on flame markers (mixture fraction, chemical mode, and heat release rate) derived from the experimental data. The statistics of chemical mode zero-crossings, which mark premixed reaction zones, and the relative populations of flame structures are shown to be sensitive to the state of mixing in the near field of the flame and to the level of local extinction farther downstream. Multi-regime structures, where premixed and non-premixed reaction zones occur in close proximity and both contribute to overall heat release, account for nearly half the total population at streamwise locations within the first several jet diameters. There is a rapid transition within the near field whereby the relative population of non-premixed and dominantly non-premixed structures grows from 0.05 to nearly 0.5, and the population of premixed and dominantly premixed structures decreases correspondingly as fluid entering the reaction zone becomes progressively fuel-rich. Local extinction and re-ignition bring a resurgence in premixed-type structures, many of which occur at fuel-lean conditions. There are also modest populations of multi-regime structures, having chemical mode zero-crossings at lean conditions, which would not exist in a fully burning jet flame.
R.S. Barlow; S. Hartl; C. Hasse; H.C. Cutcher; A.R. Masri. Characterization of multi-regime reaction zones in a piloted inhomogeneous jet flame with local extinction. Proceedings of the Combustion Institute 2020, 38, 2571 -2579.
AMA StyleR.S. Barlow, S. Hartl, C. Hasse, H.C. Cutcher, A.R. Masri. Characterization of multi-regime reaction zones in a piloted inhomogeneous jet flame with local extinction. Proceedings of the Combustion Institute. 2020; 38 (2):2571-2579.
Chicago/Turabian StyleR.S. Barlow; S. Hartl; C. Hasse; H.C. Cutcher; A.R. Masri. 2020. "Characterization of multi-regime reaction zones in a piloted inhomogeneous jet flame with local extinction." Proceedings of the Combustion Institute 38, no. 2: 2571-2579.
In this work, the first flamelet analysis is conducted of a highly resolved DNS of a multi-injection flame with both auto-ignition and ignition induced by flame-flame interaction. A novel method is proposed to identify the different combustion modes of ignition processes using generalized flamelet equations. The state-of-the-art DNS database generated by Rieth et al. (US National Combustion Meeting, 2019) for a multi-injection flame in a Diesel engine environment is investigated. Three-dimensional flamelets are extracted from the DNS at different time instants with a focus on auto-ignition and interaction-ignition processes. The influences of mixture field interactions and the scalar dissipation rate on the ignition process are investigated by varying the species composition boundary conditions of the transient flamelet equations. Budget analyses of the generalized flamelet equations show that the transport along the mixture fraction iso-surface is insignificant during the auto-ignition process, but becomes important when interaction-ignition occurs, which is further confirmed through a flamelet regime classification method.
Xu Wen; Martin Rieth; Wang Han; Jacqueline H. Chen; Christian Hasse. Investigation of the ignition processes of a multi-injection flame in a Diesel engine environment using the flamelet model. Proceedings of the Combustion Institute 2020, 38, 5605 -5613.
AMA StyleXu Wen, Martin Rieth, Wang Han, Jacqueline H. Chen, Christian Hasse. Investigation of the ignition processes of a multi-injection flame in a Diesel engine environment using the flamelet model. Proceedings of the Combustion Institute. 2020; 38 (4):5605-5613.
Chicago/Turabian StyleXu Wen; Martin Rieth; Wang Han; Jacqueline H. Chen; Christian Hasse. 2020. "Investigation of the ignition processes of a multi-injection flame in a Diesel engine environment using the flamelet model." Proceedings of the Combustion Institute 38, no. 4: 5605-5613.
Coal combustion releases elevated amounts of pollutants to the atmosphere including SOX. During the pyrolysis step, sulfur present in the coal is released to the gas phase as many different chemical species such as H2S, COS, SO2, CS2, thiols and larger tars, also called SOX precursors, as they form SOX during combustion. Understanding the sulfur release process is crucial to the development of reliable kinetic models, which support the design of improved reactors for cleaner coal conversion processes. Sulfur release from two bituminous coals, Colombian hard coal (K1) and American high sulfur coal (U2), were studied in the present work. Low heating rate (LHR) experiments were performed in a thermogravimetric analyzer coupled with mass spectrometry (TG-MS), allowing to track the mass loss and the evolution of many volatile species (CO, CO2, CH4, SO2, H2S, COS, HCl and H2O). High heating rate (HHR) experiments were performed in an entrained flow reactor (drop-tube reactor – DTR), coupled with MS and nondispersive infrared sensor (NDIR). HHR experiments were complemented with CFD simulation of the multidimentional reacting flow field. A kinetic model of coal pyrolysis is employed to reproduce the experiments allowing a comprehensive assessment of the process. The suitability of this model is confirmed for LHR. The combination of HHR experiments with CFD simulations and kinetic modeling revealed the complexity of sulfur chemistry in coal combustion and allowed to better understand of the individual phenomena resulting in the formation of the different SOX precursors. LHR and HHR operating conditions lead to different distribution of sulfur species released, highly-dependent on the gas-phase temperature and residence time. Higher retention of total sulfur in char is observed at LHR (63%) when compared to HHR (37–44%), at 1273 K. These data support the development of reliable models with improved predictability.
Paulo Debiagi; Coskun Yildiz; Marcel Richter; Jochen Ströhle; Bernd Epple; Tiziano Faravelli; Christian Hasse. Experimental and modeling assessment of sulfur release from coal under low and high heating rates. Proceedings of the Combustion Institute 2020, 38, 4053 -4061.
AMA StylePaulo Debiagi, Coskun Yildiz, Marcel Richter, Jochen Ströhle, Bernd Epple, Tiziano Faravelli, Christian Hasse. Experimental and modeling assessment of sulfur release from coal under low and high heating rates. Proceedings of the Combustion Institute. 2020; 38 (3):4053-4061.
Chicago/Turabian StylePaulo Debiagi; Coskun Yildiz; Marcel Richter; Jochen Ströhle; Bernd Epple; Tiziano Faravelli; Christian Hasse. 2020. "Experimental and modeling assessment of sulfur release from coal under low and high heating rates." Proceedings of the Combustion Institute 38, no. 3: 4053-4061.