Laser-induced fluorescence study of OH in flat flames of 1–10 bar compared with resonance CARS experiments

Kohse-Höinghaus K, Meier U, Attal-Trétout B. Laser-induced fluorescence study of OH in flat flames of 1–10 bar compared with resonance CARS experiments. Applied Optics. 1990;29(10):1560-1569.Laser-induced fluorescence (LIF) measurements of OH were performed in flat stoichiometric CH4/air flames burning at 1, 3, 5, 7, and 9.6 bar, which had previously been investigated using OH resonance CARS. In the LIF study, line shape information and temperatures were extracted from excitation spectra; in addition, OH profiles as a function of height above the burner surface and an estimate of the OH concentration for the different flames were obtained. The perspectives and feasibility of quantitative fluorescence measurements in high pressure flames are discussed, particularly in comparison with the application of resonance CARS

Two-photon excited LIF determination of H-atom concentrations near a heated filament in a low pressure H2 environment

Meier U, Kohse-Höinghaus K, Schäfer L, Klages C-P. Two-photon excited LIF determination of H-atom concentrations near a heated filament in a low pressure H2 environment. Applied Optics. 1990;29(33):4993-4999.With respect to the investigation of low pressure filament-assisted chemical vapor deposition processes for diamond formation, absolute concentrations of atomic hydrogen were determined by two-photon laserinduced fluorescence in the vicinity of a heated filament in an environment containing H2 or mixtures of H2 and CH4. Radial H concentration profiles were obtained for different pressures and filament temperatures, diameters, and materials. The influence of the addition of various amounts of methane on the H atom concentrations was examined

Flame experiments at the Advanced Light Source: New insights into soot formation processes

Hansen N, Skeen SA, Michelsen HA, Wilson KR, Kohse-Höinghaus K. Flame experiments at the Advanced Light Source: New insights into soot formation processes. JOURNAL OF VISUALIZED EXPERIMENTS. 2014;87(87):E51369

Microwave spectroscopic detection of flame-sampled combustion intermediates

Hansen N, Wullenkord J, Obenchain DA, Graf I, Kohse-Höinghaus K, Grabow J-U. Microwave spectroscopic detection of flame-sampled combustion intermediates. RSC Advances. 2017;7(60):37867-37872

Homogeneous conversion of NOx_{x} and NH3_{3} with CH4_{4}, CO, and C2_{2}H4_{4} at the diluted conditions of exhaust-gases of lean operated natural gas engines

Understanding gas‐phase reactions in model gas mixtures approximating pre‐turbine heavy‐duty natural gas engine exhaust compositions containing NO, NH$_{3}$, NO$_{2}$, CH$_{4}$, CO, and C$_{2}$H$_{4}$ is extremely relevant for aftertreatment procedure and catalyst design and is thus addressed in this work. In a plug‐flow reactor at atmospheric pressure, five different model gas mixtures were investigated in the temperature range of 700‐1 200 K, using species analysis with electron ionization molecular‐beam mass spectrometry. The mixtures were designed to reveal influences of individual components by adding NO$_{2}$, CH$_{4}$, CO, and C$_{2}$H$_{4}$ sequentially to a highly argon‐diluted NO/NH$_{3}$ base mixture. Effects of all components on the reactivity for NO$_{x}$ conversion were investigated both experimentally as well as by comparison with three selected kinetic models. Main results show a significantly increased reactivity upon NO$_{2}$ and hydrocarbon addition with lowered NO conversion temperatures by up to 200 K. Methane was seen to be of dominant influence in the carbon‐containing mixtures regarding interactions between the carbon and nitrogen chemistry as well as formaldehyde formation. The three tested mechanisms were capable to overall represent the reaction behavior satisfactorily. On this basis, it can be stated that significant gas‐phase reactivity was observed among typical constituents of pre‐turbine natural gas engine exhaust at moderate temperature

Laser-induced fluorescence determination of temperatures in low pressure flames

Rensberger KJ, Jeffries JB, Copeland RA, Kohse-Höinghaus K, Wise ML, Crosley DR. Laser-induced fluorescence determination of temperatures in low pressure flames. Applied Optics. 1989;28(17):3556-3566.Spatially resolved temperatures in a variety of low pressure flames of hydrogen and hydrocarbons burning with oxygen and nitrous oxide are determined from OH, NH, CH, and CN laser-induced fluorescence rotational excitation spectra. Systematic errors arising from spectral bias, time delay, and temporal sampling gate of the fluorescence detector are considered. In addition, we evaluate the errors arising from the influences of the optical depth and the rotational level dependence of the fluorescence quantum yield for each radical. These systematic errors cannot be determined through goodness-of-fit criteria and they are much larger than the statistical precision of the measurement. The severity of these problems is different for each radical; careful attention to the experimental design details for each species is necessary to obtain accurate LIF temperature measurements

Exploring the interaction kinetics of butene isomers and NOx_{x} at low temperatures and diluted conditions

The oxidation of 1-butene and i-butene with and without addition of 1000 ppm NO was experimentally and numerically studied primarily at fuel-rich (ϕ = 2.0) conditions under high dilution (96% Ar) in a flow reactor operated at atmospheric pressure in the low temperature range of approximately 600-1200 K. Numerous intermediate species were detected and quantified using synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS). An elementary-step reaction mechanism consisting of 3996 reactions among 682 species, based on literature and this work, was established to describe the reactions and interaction kinetics of the butene isomers with oxygen and nitrogenous components. Model predictions were compared with the experimental results to gain insight into the low- and high-temperature fuel consumption without and with NO addition and thus the respective interaction chemistry. This investigation firstly contributes a consistent set of temperature-dependent concentration profiles for these two butene isomers under conditions relevant for engine exhaust gases. Secondly, the observed oxidation kinetics is significantly altered with the addition of NO. Specifically, NO promotes fuel consumption and introduces for i-butene a low-temperature behavior featuring a negative temperature coefficient (NTC) region. The present model shows reasonable agreement with the experimental results for major products and intermediate species, and it is capable to explain the promoting effect of NO that is initiated by its contribution to the radical pool. Further, it can describe the observed NTC region for the i-butene/NO mixture as a result of the competition of chain propagation and chain terminating reactions that were identified by reaction flow and sensitivity analyses

H2-laser photochemical study of the temperature dependent quenching of O2(b 1[Sigma]g+)

Kohse-Höinghaus K, Stuhl F. H2-laser photochemical study of the temperature dependent quenching of O2(b 1[Sigma]g+). The Journal of Chemical Physics. 1980;72(6):3720-3726