Helmut Kronemayer
Heidelberg University
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Publication
Featured researches published by Helmut Kronemayer.
Applied Optics | 2005
Tonghun Lee; Wolfgang G. Bessler; Helmut Kronemayer; Christof Schulz; Jay B. Jeffries
An accurate temperature measurement technique for steady, high-pressure flames is investigated using excitation wavelength-scanned laser-induced fluorescence (LIF) within the nitric oxide (NO) A-X(0, 0) band, and demonstration experiments are performed in premixed methane/air flames at pressures between 1 and 60 bars with a fuel/air ratio of 0.9. Excitation spectra are simulated with a computational spectral simulation program (LIFSim) and fit to the experimental data to extract gas temperature. The LIF scan range was chosen to provide sensitivity over a wide temperature range and to minimize LIF interference from oxygen. The fitting method is robust against elastic scattering and broadband LIF interference from other species, and yields absolute, calibration-free temperature measurements. Because of loss of structure in the excitation spectra at high pressures, background signal intensities were determined using a NO addition method that simultaneously yields nascent NO concentrations in the postflame gases. In addition, fluorescence emission spectra were also analyzed to quantify the contribution of background signal and to investigate interference in the detection band-width. The NO-LIF temperatures are in good agreement with intrusive single-color pyrometry. The proposed thermometry method could provide a useful tool for studing high-pressure flame chemistry as well as provide a standard to evaluate and validate fast-imaging thermometry techniques for practical diagnostics of high-pressure combustion systems.
Combustion Science and Technology | 2008
H.-W. Ge; I. Düwel; Helmut Kronemayer; Robert W. Dibble; Eva Gutheil; Christof Schulz; J. Wolfrum
A turbulent ethanol spray flame is characterized through quantitative experiments using laser-based imaging techniques. The experimental data set is used to validate a numerical code for the simulation of spray combustion. The spray burner has been constructed to facilitate the computational treatment of the experiment; in particular the spray flame is stabilized without a bluff body or a pilot flame. The experiments include spatially resolved measurements of droplet sizes (Mie/LIF-dropsizing and PDA), droplet velocity (PDA), liquid-phase temperature (two-color LIF temperature imaging with Rhodamine B) and gas-phase temperature (multi-line NO-LIF temperature imaging). The measurements close to the nozzle exit are used to determine the initial conditions for numerical simulations. A novel probability density function (PDF) method is applied to calculate the development of the spray flame. A joint mixture fraction and enthalpy PDF is formulated. Its transport equation is modeled and solved using a Monte-Carlo method. A detailed ethanol/air combustion mechanism consisting of 38 species and 337 elementary reactions is implemented through the spray flamelet model enabling the prediction of pollutant emission in spray flames. Good agreement with the experimental data is found for the gas temperature. The numerical predictions for the liquid-phase temperature are in reasonable agreement with the experimental data. The flame structure with two reaction zones is compared with other spray flames, and it is analyzed with the help of the experimental and numerical results. The formation mechanism of such a structure is revealed.
Tenth International Symposium on Solid Oxide Fuel Cells, (Nara New Public Hall, Japan, 2007) | 2007
Marcel Vogler; Daniel Barzan; Helmut Kronemayer; Christof Schulz; Michio Horiuchi; Shigeaki Suganuma; Yasue Tokutake; Jürgen Warnatz; Wolfgang G. Bessler
We present a combined experimental and modeling study of a direct-flame type solid oxide fuel cell (DFFC). The operation principle of this system is based on the combination of a flame with an SOFC in a simple, no-chamber setup. Experiments were performed using 13-mm-diameter planar SOFCs with Ni-based anode, samaria-doped ceria electrolyte and cobaltite cathode. At the anode, a 7-mm-diameter flat-flame burner provided methane/air rich premixed flames. The cell performance reaches power densities of up to 200 mW/cm2. A detailed analysis of the electrical efficiency is carried out. Observed system efficiencies are below 0.5%. Equilibrium calculations of the flame exhaust gas were performed. From the simulations, both H2 and CO were identified as species that are available as fuel for the SOFC.
Applied Optics | 2007
Helmut Kronemayer; Kemal Omerbegovic; Christof Schulz
Two-dimensional gas-phase temperature fields were quantitatively measured in an evaporating ethanol spray with multiline excitation thermometry based on laser-induced fluorescence of nitric oxide (NO-LIF). This technique yields absolute temperature fields without calibration and simultaneously detects the spray position. The accuracy of the presented temperature measurements is +/-1 K. Systematic errors of the scanned multiline thermometry approach due to time averaging in turbulent systems were investigated and found to be negligible. The pulsed spray was generated by a gasoline direct-injection nozzle with swirl injecting ethanol into air in a flow cell at room temperature and atmospheric pressure. The gas temperature inside the spray cloud was found to decrease by 10 K at approximately 5-10 ms after injection. Different injection pressures influence the evaporation behavior.
Journal of Physics: Conference Series | 2006
Takayuki Fuyuto; Helmut Kronemayer; B Lewerich; W. Koban; Kazuhiro Akihama; Christof Schulz
Two novel techniques based on Laser-Induced Fluorescence (LIF) were applied to measure gas-phase temperature distributions in boundary layers close to wall surfaces. Single- line toluene-LIF thermometry was used to image temperature in a nitrogen gas flow above a heated wall. The nitrogen gas flow was doped with evaporated toluene. When excited at 266 nm, the toluene LIF-signal shows an exponential dependence on temperature. This behavior was used to calculate absolute temperatures from LIF images after calibration at known conditions. The second technique, multi-line NO-LIF thermometry was applied to image temperature in the quenching boundary layer close to a metal wall located on a flat flame burner. A small amount of nitric oxide was mixed into the air/methane mixture. NO molecules were excited in the A-X (0,0)-band at 225 nm. NO-LIF excitation spectra were acquired by tuning the excimer laser wavelength and recording the NO LIF-signal with an ICCD camera. Absolute temperatures were calculated for every pixel by fitting simulated excitation spectra to the experimental data. Temperature distributions close to the wall surface were measured at two different flow-rate conditions. A high nominal spatial resolution of 0.016 mm/pixel in direction perpendicular to the wall was reached. Wall surface temperatures were recorded simultaneously by embedded thermocouples and compared with gas-phase temperature near the wall surface.
Journal of Power Sources | 2007
Helmut Kronemayer; Daniel Barzan; Michio Horiuchi; Shigeaki Suganuma; Yasue Tokutake; Christof Schulz; Wolfgang G. Bessler
Proceedings of the Combustion Institute | 2007
I. Düwel; Hai-Wen Ge; Helmut Kronemayer; Robert W. Dibble; Eva Gutheil; Christof Schulz; J. Wolfrum
Experiments in Fluids | 2010
Takayuki Fuyuto; Helmut Kronemayer; Burkhard Lewerich; Jan Brübach; Taketoshi Fujikawa; Kazuhiro Akihama; Thomas Dreier; Christof Schulz
Journal of Power Sources | 2009
Michio Horiuchi; Fumimasa Katagiri; Jun Yoshiike; Shigeaki Suganuma; Yasue Tokutake; Helmut Kronemayer; Wolfgang G. Bessler
Applied Physics B | 2009
C. Hecht; Helmut Kronemayer; Thomas Dreier; Hartmut Wiggers; Christof Schulz