@article{Lulic.2023,

title = {On polyhedral structures of lean methane/hydrogen Bunsen flames: Combined experimental and numerical analysis},

author = {Haris Lulic and Adrian Breicher and Arne Scholtissek and Pasquale Eduardo Lapenna and Andreas Dreizler and Francesco Creta and Christian Hasse and Dirk Geyer and Federica Ferraro},

url = {https://www.sciencedirect.com/science/article/pii/S1540748922003091},

doi = {10.1016/j.proci.2022.07.251},

year  = {2023},

date = {2023-01-01},

journal = {Proceedings of the Combustion Institute},

volume = {39},

number = {2},

pages = {1977–1986},

abstract = {In premixed flame propagation of lean hydrogen or hydrogen-enriched blends, both hydrodynamic and thermo-diffusive instabilities are governing the flame front shape and affect its propagation velocity. As a result, different types of cellular patterns can occur along the flame front in a laminar scenario. In this context, an interesting phenomenon is the formation of polyhedral flames which can be observed in a Bunsen burner. It is the objective of this work to systematically characterize the polyhedral structures of premixed methane/hydrogen Bunsen flames in a combined experimental and numerical study. A series of lean flames with hydrogen content varying between 20 and 85% at two equivalence ratios is investigated. The experiments encompass chemiluminescence imaging together with Planar Laser-induced Fluorescence (PLIF) measurements of the OH radical. Characteristic cell sizes are quantified from the experiments and related to the characteristic length scales obtained from a linear stability analysis. In the experiments, it is observed that the cell sizes at the base of the polyhedral Bunsen flames decrease almost linearly with hydrogen addition and only a weak dependence on the equivalence ratio is noted. These trends are well reflected in the numerical results and the length scale comparison further shows that the wavelength with the maximum growth rate predicted by the linear stability analysis is comparable to the cell size obtained from the experiment. The correlation between the experimental findings and the linear stability analysis is discussed from multiple perspectives considering the governing time and length scales, furthermore drawing relations to previous studies on cellular flames.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Luo.2023,

title = {A novel flamelet manifold parametrization approach for lean CH4–H2-air flames},

author = {Yujuan Luo and Federica Ferraro and Adrian Breicher and Hannes Böttler and Andreas Dreizler and Dirk Geyer and Christian Hasse and Arne Scholtissek},

url = {https://www.sciencedirect.com/science/article/pii/S0360319922044706},

doi = {10.1016/j.ijhydene.2022.09.233},

year  = {2023},

date = {2023-01-01},

journal = {International Journal of Hydrogen Energy},

abstract = {Hydrogen is a carbon-free energy carrier that can substantially support the decarbonization of the power generation and transportation sector in the near future. Blending H2 into natural gas represents a feasible option to continue using the current infrastructure, allowing a smooth transition to pure H2 combustion technologies. In the present study, a flamelet model is proposed to describe lean CH4–H2-air laminar Bunsen flames with inert gas as a coflow, simultaneously taking into account multiple complex physical phenomena such as differential diffusion, heat losses at the burner wall and mixing between the main flow and coflow. In most previous works based on manifold-based reduction methods, transport equations are solved for the progress variable, mixture fraction and enthalpy. In contrast, transport equations for several species and enthalpy are solved in the present study and species diffusivities are evaluated with a mixture-averaged diffusion model. The control variables of the manifold are then reconstructed with those transported variables. In order to consider the mixing between the main flow and the inert coflow, two different approaches based on a three-dimensional and a four-dimensional manifold, respectively, are formulated and assessed. Utilizing a ``linear mixing'' assumption, the three-dimensional manifold is parameterized by a progress variable, an approximate Bilger mixture fraction and enthalpy. The four-dimensional manifold relaxes this assumption and additionally includes the inert gas mass fraction as the fourth control variable. The accuracy of the two approaches is evaluated by comparison with detailed chemistry results and experimental measurements. Overall, results obtained with both approaches show good agreement with the reference data, both qualitatively and quantitatively, indicating that all the effects mentioned above are well captured. Slightly better agreement is achieved with the four-dimensional manifold, which shows superiority in the mixing layer between the main flow and the inert coflow.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Richter.2023,

title = {Extinction strain rates of premixed ammonia/hydrogen/nitrogen-air counterflow flames},

author = {M. Richter and R. Schultheis and J. R. Dawson and A. Gruber and R. S. Barlow and A. Dreizler and D. Geyer},

url = {https://www.sciencedirect.com/science/article/pii/S1540748922003790},

doi = {10.1016/j.proci.2022.09.011},

year  = {2023},

date = {2023-01-01},

journal = {Proceedings of the Combustion Institute},

volume = {39},

number = {2},

pages = {2027–2035},

abstract = {Chemical energy vectors will play a crucial role in the transition of the global energy system, due to their essential advantages in storing energy in form of gaseous, liquid, or solid fuels. Ammonia (NH3) has been identified as a highly promising candidate, as it is carbon-free, can be stored at moderate pressures, and already has a developed distribution infrastructure. As a fuel NH3 has poor combustion properties that can be improved by the addition of hydrogen, which can be obtained energy-efficiently by partially cracking ammonia into hydrogen (H2) and nitrogen (N2) prior to the combustion process. The resulting NH3/H2/N2 blend leads to significantly improved flame stability and resilience to strain-induced blow-out, despite similar laminar flame properties compared to equivalent methane/air flames. This study reports the first measurements of extinction strain rates, measured using the premixed twin-flame configuration in a laminar opposed jet burner, for two NH3/H2/N2 blends over a range of equivalence ratios. Local strain rates are measured using particle tracking velocimetry (PTV) and are related to the inflow conditions, such that the local strain rate at the extinction point can be approximated. The results are compared with 1D-simulations using three recent kinetic mechanisms for ammonia oxidation. By relating the extinction strain rates to laminar flame properties of the unstretched flame, a comparison of the extinction behaviour of CH4 and NH3/H2/N2 blends can be made. For lean mixtures, NH3/H2/N2-air flames show a significant higher extinction resistance in comparison to CH4/air. In addition, a strong non-linear dependence between the resistance to extinction and equivalence ratio for NH3/H2/N2 blends is observed.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Trabold.2022,

title = {Fast shutter line-imaging system for dual-dispersion Raman spectroscopy in ethanol and OME flames},

author = {Johannes Trabold and David Butz and Silvan Schneider and Kevin Dieter and Robert Barlow and Andreas Dreizler and Dirk Geyer},

url = {https://www.sciencedirect.com/science/article/pii/S0010218021006076},

doi = {10.1016/j.combustflame.2021.111864},

year  = {2022},

date = {2022-01-01},

journal = {Combustion and Flame},

volume = {243},

pages = {111864},

abstract = {Chemical energy carriers synthesized from renewable energy sources such as ethanol or oxymethylene ethers (OME) will become increasingly important for CO2<math><msub is=textquotedbltruetextquotedbl><mrow is=textquotedbltruetextquotedbl></mrow><mn is=textquotedbltruetextquotedbl>2</mn></msub></math>-neutral thermochemical energy conversion processes. Therefore, it is important to make these processes efficient and clean. This needs more predictive numerical simulation tools and an improved understanding of the combustion process. For this purpose, spatially resolved measurements of local thermochemical states in reaction zones are required, for which combined Raman- and Rayleigh spectroscopy is suitable. Since a large number of intermediate hydrocarbons occur in the reaction zones of ethanol and OME flames, Raman spectroscopy must be evolved for quantitative measurement of these species over a wide temperature range. Against this background, this study pursues the goal of creating the instrumental and apparatus-related pre-requisites. The setup of a new dual-dispersion spectrometer and its main specifications are presented. The usability of the spectrometer is demonstrated on the example of premixed and partially-premixed ethanol/air and OME-3/air flames. For this purpose, a new counterflow burner is presented, which enables laminar, single-phase combustion processes of pre-vaporized fuels.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Butz.2022,

title = {Turbulent multi-regime methane-air flames analysed by Raman/Rayleigh spectroscopy and conditional velocity field measurements},

author = {D. Butz and A. Breicher and R. S. Barlow and D. Geyer and A. Dreizler},

doi = {10.1016/j.combustflame.2021.111941},

year  = {2022},

date = {2022-01-01},

journal = {Combustion and Flame},

number = {09},

pages = {111941},

abstract = {Combustion and Flame, Corrected proof, 111941. doi:10.1016/j.combustflame.2021.111941},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Dieter.2022,

title = {Development of a Raman spectrometer for the characterization of gaseous hydrocarbons at high temperatures},

author = {K. Dieter and K. Koschnick and J. Lill and G. Magnotti and A. Weinmann and A. Dreizler and D. Geyer},

doi = {10.1016/j.jqsrt.2021.107978},

year  = {2022},

date = {2022-01-01},

journal = {Journal of Quantitative Spectroscopy and Radiative Transfer},

volume = {277},

pages = {107978},

abstract = {Journal of Quantitative Spectroscopy and Radiative Transfer, 277 (2022) 107978. doi:10.1016/j.jqsrt.2021.107978},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Paudel.2022,

title = {Experimental and numerical study of Zuppinger water wheel model},

author = {Shakun Paudel and Martin Weber and Dirk Geyer and Nicole Saenger},

doi = {10.1680/jwama.20.00056},

issn = {1741-7589},

year  = {2022},

date = {2022-01-01},

journal = {Proceedings of the Institution of Civil Engineers - Water Management},

volume = {175},

number = {4},

pages = {206–216},

abstract = {Proceedings of the Institution of Civil Engineers - Water Management 2022.175:206-216},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Trabold.2021,

title = {Fuel Effects in Turbulent Premixed Pre-vaporised Alcohol/Air Jet Flames},

author = {J. Trabold and S. Hartl and S. Walther and A. Johchi and A. Dreizler and D. Geyer},

doi = {10.1007/s10494-020-00166-6},

year  = {2021},

date = {2021-01-01},

journal = {Flow, Turbulence and Combustion},

volume = {106},

number = {2},

pages = {547–573},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Dunn.2021,

title = {Spontaneous Raman–LIF–CO–OH measurements of species concentration in turbulent spray flames},

author = {M. J. Dunn and A. R. W. Macfarlane and R. S. Barlow and D. Geyer and K. Dieter and A. R. Masri},

doi = {10.1016/j.proci.2020.07.037},

year  = {2021},

date = {2021-01-01},

journal = {Proceedings of the Combustion Institute},

volume = {38},

number = {1},

pages = {1779–1786},

abstract = {Proceedings of the Combustion Institute, Corrected proof. doi:10.1016/j.proci.2020.07.037},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Popp.2021,

title = {Assessing multi-regime combustion in a novel burner configuration with large eddy simulations using tabulated chemistry},

author = {Sebastian Popp and Sandra Hartl and David Butz and Dirk Geyer and Andreas Dreizler and Luc Vervisch and Christian Hasse},

doi = {10.1016/j.proci.2020.06.098},

year  = {2021},

date = {2021-01-01},

journal = {Proceedings of the Combustion Institute},

volume = {38},

number = {2},

pages = {2551–2558},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Butz.2019b,

title = {Local flame structure analysis in turbulent CH4/air flames with multi-regime characteristics},

author = {David Butz and Sandra Hartl and Sebastian Popp and Steffen Walther and Robert S. Barlow and Christian Hasse and Andreas Dreizler and Dirk Geyer},

year  = {2019},

date = {2019-01-01},

journal = {Combustion and Flame},

volume = {210},

pages = {426–438},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Butz.2019,

title = {Local flame structure analysis in turbulent CH4/air flames with multi-regime characteristics},

author = {David Butz and Sandra Hartl and Sebastian Popp and Steffen Walther and Robert S. Barlow and Christian Hasse and Andreas Dreizler and Dirk Geyer},

url = {https://www.sciencedirect.com/science/article/pii/S0010218019303967},

doi = {10.1016/j.combustflame.2019.08.032},

year  = {2019},

date = {2019-01-01},

journal = {Combustion and Flame},

volume = {210},

pages = {426–438},

abstract = {In practical applications, partial premixing of fuel and oxidizer, as well as recirculation of combustion products, result in complex combustion scenarios where multi-regime effects arise and a numerical representation of local reaction zones by purely premixed or purely non-premixed flame structures may not hold. Here, a novel burner system is introduced to investigate the fundamental characteristics of multi-regime combustion and to provide a basis for validating numerical models. This multi-regime burner (MRB) is specifically designed to produce flames with multi-regime characteristics while maintaining well-defined boundary conditions. Thermochemical data from Raman/Rayleigh/CO-LIF scattering experiments are provided for two selected operating conditions. The experimental investigation focuses on the overall flame structure by examining radial profiles of temperature and mixture fraction, as well as scatter plots of temperature, CH4, and CO versus mixture fraction. In order to assess the relative importance of different flame regimes, the gradient-free regime identification (GFRI) approach is extended to allow for an automated classification of local reaction zone structures. Classification criteria are defined, based on the ratio of local heat release rate peaks associated with premixed and non-premixed reaction zones located in close spatial proximity, and an automated process is implemented to classify 1D Raman/Rayleigh sample lines as premixed, dominantly premixed, multi-regime, dominantly non-premixed, or non-premixed flame zones. The importance of different flame zones, indicated by their population fractions, are found to evolve with downstream distance and show distinct differences between the two selected flames. Further, a prior analysis is used to test the applicability of 1D flame structure assumptions for the underlying combustion regime.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Hartl.2019,

title = {Assessing the relative importance of flame regimes in Raman/Rayleigh line measurements of turbulent lifted flames},

author = {S. Hartl and R. Winkle and D. Geyer and A. Dreizler and G. Magnotti and C. Hasse and R. S. Barlow},

doi = {10.1016/j.proci.2018.06.067},

year  = {2019},

date = {2019-01-01},

journal = {Proceedings of the Combustion Institute},

volume = {37},

number = {2},

pages = {2297–2305},

abstract = {Proceedings of the Combustion Institute, 37 (2018) 2297-2305. doi:10.1016/j.proci.2018.06.067},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Hartl.2019b,

title = {Assessing an experimental approach for chemical explosive mode and heat release rate using DNS data},

author = {Sandra Hartl and Dirk Geyer and Christian Hasse and Xinyu Zhao and Haiou Wang and Robert S. Barlow},

doi = {10.1016/j.combustflame.2019.07.038},

year  = {2019},

date = {2019-01-01},

journal = {Combustion and Flame},

volume = {209},

pages = {214–224},

abstract = {Combustion and Flame, 209 (2019) 214-224. doi:10.1016/j.combustflame.2019.07.038},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Schneider.2019,

title = {Structure of a stratified CH4 flame with H2 addition},

author = {Silvan Schneider and Dirk Geyer and Gaetano Magnotti and Matthew J. Dunn and Robert S. Barlow and Andreas Dreizler},

doi = {10.1016/j.proci.2018.06.205},

year  = {2019},

date = {2019-01-01},

journal = {Proceedings of the Combustion Institute},

volume = {37},

number = {2},

pages = {2307–2315},

abstract = {Proceedings of the Combustion Institute, 37 (2018) 2307-2315. doi:10.1016/j.proci.2018.06.205},

keywords = {},

pubstate = {published},

tppubtype = {article}

}