Steven Wagner's research while affiliated with Technische Universität Darmstadt and other places

Publications (61)

Article
Turbulent mixing processes and species transport govern many important properties like stability and pollutant formation of reactive systems. We propose spectrally resolved absorption tomography as a viable tool to quantitatively assess species transport by imaging tracer pulses at high time resolution. Measurements on a gas-assisted solid-fuel com...
Conference Paper
Stronger regulation requirements for industrial application based thermo-chemical energy conversion processes demand for new measurement approaches to characterize the composition of the exhaust gas emission. We present a robust multi-channel, multi species measurements system for the quantification of exhaust gas species direct at the tail pipe en...
Chapter
The tomographic imaging of chemical species distributions has undergone rapid development in the last 20 years, driven by the combination of key scientific and technological challenges, the emergence of new optoelectronic hardware, and fundamental progress in inverse problems. We describe here the state of the art in Chemical Species Tomography usi...
Article
Full-text available
Oxy-fuel combustion is a promising strategy to minimize the environmental impact of combustion-based energy conversion. Simple and flexible tools are required to facilitate the successful integration of such strategies at the industrial level. This study couples measured residence time distribution with chemical reactor network analysis in a close-...
Article
Full-text available
In this work, wavelengths were determined for the robust and simultaneous measurement of film thickness, urea concentration and fluid temperature. Film parameters such as film thickness, film temperature and the composition of the film are typically dynamically and interdependently changing. To gain knowledge of these quantities, a measurement meth...
Article
Full-text available
In this work, an experimental investigation of AdBlue film formation in a generic selective catalytic reduction (SCR) exhaust gas test bench is presented. AdBlue is injected into a generic SCR test bench resulting in liquid film formation on the lower wall of the channel. The thickness of this liquid film is measured using a film thickness sensor b...
Article
Oxy-fuel combustion promises efficient and inexpensive carbon dioxide sequestration and is therefore subject to active experimental research. However, the transfer of mature, non-intrusive diagnostic methods for temperature measurement like Coherent Anti-Stokes Raman Spectroscopy (CARS) from air-fed to oxy-fuel systems is challenging due to the def...
Conference Paper
The fulfillment of quality and regulation requirements for thermo-chemical industrial processes rely on new measurement technologies based on laser-optical methods. Here we present a robust multi-channel, multi species measurements system for the quantification of exhaust gas species direct at the tail pipe end of a driving car. The application of...
Article
We present a tomographic spectrometer for the measurement of gas phase species parameter distributions within the cross section of a generic exhaust gas test rig built for the investigation of the physico-chemical processes during exhaust gas aftertreatment with selective catalytic reduction (SCR). A urea-water solution (UWS) is injected into the h...
Article
Full-text available
Image based diagnostics are interpreted in the context of spatial resolution. The same is true for tomographic image reconstruction. Current empirically driven approaches to quantify spatial resolution in chemical species tomography rely on a deterministic formulation based on point-spread functions which neglect the statistical prior information,...
Article
In this work, a generic exhaust gas test bench is introduced on which reproducible experiments can be performed to gain a deeper understanding of processes during exhaust gas aftertreatment of internal combustion engines. We present the design and initial flow characterization as well as tomographic measurement results of gaseous water distribution...
Preprint
Image based diagnostics are interpreted in the context of spatial resolution. The same is true for tomographic image reconstruction. Current empirically driven approaches to quantify spatial resolution rely on a deterministic formulation based on point-spread functions which neglect the statistical prior information, that is integral to rank-defici...
Article
Full-text available
High-resolution absorption spectroscopy is a promising method for non-invasive process monitoring, but the computational effort required to evaluate the data can be prohibitive in high-speed, real-time applications. This study presents a fast method to estimate absorbance spectra from transmitted intensity signals. We employ Bayesian statistics to...
Article
Hyperspectral absorption tomography (HAT) reconstructs the distribution of key gas parameters, including composition, pressure, and temperature, from multi-beam absorbance data with numerous spectral resolution elements. There is a nonlinear relationship between the parameters of interest and the spectral absorption coefficient, which must be incor...
Article
The residence time distribution (RTD) of fluid elements in combustion chambers is a key feature of the flow field, and its knowledge is therefore important for the design and improvement of combustion systems. The hostile yet sensitive environment of burners, in particular with high particle loads of solid-fuel firing, impede direct access to this...
Conference Paper
An absorption based laser sensor for film thickness measurement of DEF in an exhaust gas test bench is presented. A wavelength pre-selection ensures that film-thicknesses could be measured without cross sensitivity to temperature or concentration.
Conference Paper
A multispecies in situ TDLAS-system for simultaneous detection of NO, CO, CO2, H2O and NH3 was applied at an engine test rig for exhaust gas measurements and results were compared to commercially available reference systems.
Article
For the analysis of spectroscopic data, model fitting approaches are commonly applied. The spectrum model applied in these fitting processes significantly influences the performance of the spectroscopic evaluation, which can be critical in real-time process diagnostics and control. In this work a spectrum model is introduced that uses a polynomial...
Article
The level of understanding of coal combustion compared to the requirements of predictive engineering is still insufficient due to the complexity of the processes and breadth of scales involved. In particular, in modern oxy-coal firing, where the fuel is burned in an oxygen/carbon-dioxide atmosphere to reduce the emission of greenhouse gases and pol...
Article
Full-text available
A set of algorithms is presented that facilitates the evaluation of super continuum laser absorption spectroscopy (SCLAS) measurements with respect to temperature, pressure and species concentration without the need for simultaneous background intensity measurements. For this purpose a non-linear model fitting approach is employed. A detailed discu...
Article
We present a multi-species mole fraction and temperature sensor for in situ exhaust gas diagnostic of internal combustion (IC) engines. The sensor is based on Tunable Diode Laser Absorption Spectroscopy (TDLAS) and incorporates four optical channels - two miniature White cells and two double-traversal cells - with base lengths of 6 cm. It has been...
Article
Full-text available
For an improved understanding of the in-cylinder processes in internal combustion (IC) engines, advanced diagnostics are needed to measure the thermodynamic state of the in-cylinder fluid. This is essential to validate numerical simulations which aim at predicting the in-cylinder processes during motored engine operation. Here, knowledge of the in-...
Article
In this work, an absorption based laser sensor for the investigation of dynamically changing liquid film thicknesses is developed and validated. For the wavelength selection of the single-ended, fibre-coupled, diode-laser sensor, near-infrared spectra of liquid water are measured at various thicknesses and temperatures. To reduce the influence of t...
Article
Full-text available
A set of high-resolution absorption spectrometers based on TDLAS was used to determine the impact of combustion-relevant gases on the pressure shift and broadening of H2O, CO2, C2H2 and CH4 absorption lines in the near-infrared spectral region. In particular, self- and foreign-broadening coefficients induced by CO2, N2, O2, air, C2H2 and CH4 were m...
Article
Full-text available
We present an experimental study on the effects of an oxy-fuel atmosphere with 30 %Vol. O2/70 %Vol. CO2 content on a laminar, non-premixed methane flame based on measured spatial profiles of gas temperature as well as H2O, CH4, OH and CO concentrations, with the aim of providing thermochemical validation data for numerical simulations in the oxy-fu...
Conference Paper
A mobile exhaust gas measuring TDLAS-system was tested on public roads. It is capable of in-situ detection of CO2 and H2O, using multi-pass cells at the tailpipe end, while electronic is located inside the car.
Conference Paper
An absorption based laser sensor for the investigation of liquid film thicknesses of DEF is presented. A wavelength pre-selection ensures that film thicknesses could be measured without cross sensitivity to temperature or concentration.
Conference Paper
More stringent exhaust emissions regulation of IC engines requires more detailed investigation of the aftertreatment and conversion processes of the exhaust flow. Here, we present three independent laser absorption spectrometers for the measurement of mole fractions and temperature during EGR, SCR aftertreatment and at the tail pipe end.
Conference Paper
A technique to measure residence time distributions in chemical reactors without the need of modelling by using pulse-injections of HCl with TDLAS-detection is presented and demonstrated under non-reacting and reacting conditions in an oxy-coal/oxy-gas combustor.
Article
Full-text available
For improving the design of combustors, the knowledge of residence-time distributions (RTD) is important as they influence exhaust gas compositions. Measuring RTDs in combustors is challenging, due to high temperatures, chemical reactions, the presence of particles or corrosive species as well as high turbulence levels. This paper presents a techni...
Article
A multichannel tunable diode laser absorption spectrometer is used to measure absolute ammonia concentrations and their distributions in exhaust gas applications with intense CO2 and H2O background. Designed for in situ diagnostics in SCR after treatment systems with temperatures up to 800 K, the system employs a fiber coupled near-infrared distrib...
Article
We present the design, setup, and characterization of a new lens-free fibre-coupled miniature White cell for extractive gas analysis using direct tunable diode laserabsorption spectroscopy (dTDLAS). The construction of this cell is based on a modified White cell design and allows for an easy variation of the absorption length in the range from 29 c...
Article
In this work, a novel broadband fitting approach for quantitative in-flame measurements using supercontinuum broadband laser absorption spectroscopy (SCLAS) is presented. The application and verification of this approach in an atmospheric, laminar, non-premixed CH4/air flame (Wolfhard–Parker burner, WHP) is discussed. The developed fitting scheme a...
Conference Paper
A probe-based, fiber-coupled TDLAS sensor, operating at 1.4 μm for the measurement of gas turbine inlet temperatures using two line thermometry is developed and validated in a pressurized generic single-sector combustor.
Conference Paper
In-situ concentration measurements of nitric oxide in the microwave-plasma-heated turbulent air-co-flow (800-1300 K) of an auto-ignition test rig have been performed, employing tunable diode laser absorption spectroscopy at a wavelength of 5.2 μm.
Conference Paper
In modernen Kraftfahrzeugen ist die SCR-Technologie, d.h. die Selektive Katalytische Reduktion von Stickoxiden zu Wasser und Stickstoff mit dem Reaktionspartner Ammoniak, ein häufig verwendetes Abgasnachbehandlungssystem, das hohe Umsetzungsraten bei gleichzeitig effizienten Motorbetriebspunkten ermöglicht. In der Auslegungsphase solcher Systeme ko...
Article
Long-distance fiber links require precise knowledge of fiber dispersion characteristics. Similar dispersion characteristics are necessary for supercontinuum broadband laser absorption spectroscopy (SCLAS) to allow proper data evaluation and species concentration determination, as well as numerous other applications. In this work, a time-of-flight a...
Article
We report on the development and application of a broadband absorption spectrometer utilizing a pulsed supercontinuum laser light source and dispersion compensating fiber with a single-pass absorption path to obtain absolute methane mole fractions in a laminar nonpremixed CH4/air flame supported on a Wolfhard–Parker burner. The basic principle of s...
Article
A new developed tunable diode laser spectrometer for the measurement of ammonia (NH3) mole fractions in exhaust gas matrices with strong CO2 and H2O background at temperatures up to 800 K is presented. In-situ diagnostics in harsh exhaust environments during SCR after treatment are enabled by the use of ammonia transitions in the v2+v3 near-infrare...
Article
Simultaneous detection of two analytes, carbon dioxide (CO2), and water vapor (H2O), has been realized using tunable diode laser absorption spectroscopy (TDLAS) with a single distributed feedback diode laser at 2.7 μ. The dynamic range of the spectrometer is extended from the low parts per million to the percentage range using two gas cells, a sing...
Conference Paper
A time-multiplexed isotope-selective open-path TDLAS spectrometer was developed for the AIDA cloud chamber as part of the ISOCLOUD project and achieves detection limits of 4ppb for H216O and 170ppt for H218O.
Conference Paper
Durch steigende Temperaturen in Gebieten mit Permafrostböden werden zunehmend klimarelevante Gase emittiert. Zur Untersuchung einer möglichen Rückkopplung der Gasemission aus den auftauenden Böden sind H2O-Konzentrationsmessungen in der Boden-Luft-Grenzschicht von Interesse. Hierbei ist die Strukturierung der Bodenoberfläche zu berücksichtigen und...
Article
Themenkreis 13 UP 13.1-13.3 Methoden - Fernerkundung, Messverfahren und Datenauswertung, Fachvortrag UP 13.2 , Jena 25.Februar-1. März 2013
Article
Full-text available
Abstract We developed a new, spatially traversing, direct tunable diode laser absorption spectrometer (TDLAS) for quantitative, calibration-free, and spatially resolved in situ measurements of CO profiles in atmospheric, laminar, non-premixed CH4 /air model flames stabilized at a Tsuji coun-ter-flow burner. The spectrometer employed a carefully cha...
Article
Full-text available
Acetylene (C2H2), as an important precursor for chemiluminescence species, is a key to understand, simulate and model the chemiluminescence and the related reaction paths. Hence we developed a high resolution spectrometer based on direct Tunable Diode Laser Absorption Spectroscopy (TDLAS) allowing the first quantitative, calibration-free and spatia...
Conference Paper
We report absolute OH concentrations as well as temperatures derived from two-line thermometry of water vapor using direct Tunable Diode Laser Absorption Spectroscopy (direct-TDLAS) in a methane/air non-premixed slot burner flame. We modified a NIST design Wolfhard-Parker slot burner to minimize the edge flames at the ends of the slot. The modified...
Conference Paper
The TDLAS based hygrometer was used for measurements of absolute water vapor concentrations in motored IC engines with time resolutions from 500µs up to 100µs. Measured concentrations indicate a detection limit of 0.06 vol%.
Article
Die Abgasrückführung (AGR) spielt bei der Entwicklung neuer schadstoffarmer Motoren eine wichtige Rolle. Zur Bestimmung der optimalen AGR-Rate ist eine genaue Kenntnis, der im Brennraum, ablaufenden Prozesse nötig. Die TDLAS (Tunable Diode Laser Absorption Spectroscopy) eignet sich hervorragend zur Untersuchung von Gaskonzentrationen in Prozessen,...
Article
Water vapor is the most important greenhouse gas in the Earth's atmosphere and a key component for several physical and chemical processes. Therefore it is a key parameter to be measured during most research campaigns. The Hygrometer for Atmospheric Investigations (HAI) is especially designed for operations on the research aircraft HALO (High Altit...
Article
EGU General Assembly 2010, held 2-7 May, 2010 in Vienna, Austria, p.12351 Ice clouds in the tropical tropopause layer (TTL, ~12-18 km, ~180-200 K) play a key role in dehydrating air entering the stratosphere. However, in-situ measurements show that air within these clouds is unexpectedly supersaturated(1); normally the growth of ice crystals rapid...
Article
Full-text available
Ice clouds in the tropical tropopause layer play a key role in dehydrating air as it enters the stratosphere1, 2. However, in situ measurements show that water vapour within these clouds is unexpectedly supersaturated3, 4, 5; normally the growth of ice crystals rapidly quenches supersaturation3. The high in-cloud humidity may be related to the low...
Article
We report the first quantitative and calibration-free in situ C2H2 measurement in a flame environment using direct Tunable Diode Laser Absorption Spectroscopy(TDLAS). Utilizing a fiber-coupled Distributed Feedback diode laser near 1535 nm we measured spatially resolved, absolute C2H2 concentration profiles in a laminar non-premixed CH4/air flame su...
Article
A new, compact, spatially scanning, open-path 2.7 microm tunable diode laser absorption spectrometer with short absorption path lengths below 10 cm was developed to analyze the spatiotemporal dynamics of one-dimensional (1D) spatial water vapor gradients. This spectrometer, which is based on a room-temperature distributed feedback diode laser, is c...
Article
A new sampling-free and calibration-free multi-channel hygrometer using near infrared (NIR) tunable diode laser absorption spectroscopy (TDLAS) at 1.37 μm was developed and used to determine absolute transpiration rates of single plant leafs. Four 8×6× 4 cm3, fiber-coupled absorption cells are used to simultaneously measure absolute water vapor con...
Conference Paper
A new 2.7µm laser spectrometer was designed and characterized with regard to static/dynamic tuning properties and used for first spatially resolved measurements on heterogeneous distributed H2O vapor concentration fields.
Article
Full-text available
At measurements of the atmospheric methane background with in an open path herriott cell, we achieved an optical resolution of 2.3 • 10-5ODe(3σ), respectively 9 ppb CH4(3σ) resolution of concentration.
Conference Paper
Full-text available
Water concentrations were determined using tunable diode laser absorption and optical density measurements. These measurements were made in a cup burner apparatus to aid in the determination of fire suppression effectiveness of water mist.
Article
Der empfindliche Nachweis von Kohlenmonoxid ist von groß er Bedeutung für den Brandschutz oder die Optimierung technischer Feuerungsprozesse. Neu verfügbare, raumtemperaturtaugliche Distributed-Feedback-Diodenlaser (DFB-DL) im Bereich des CO-2$nu$-Bandes bei 2.3$mu$m in Kombination mit absorptionsspektroskopischen Messverfahren bieten viel versprec...

Citations

... Discretizing the flow field into pixels often produces a matrix having more unknowns than equations, in which case the solution relies strongly on prior information [154,155]. Other examples include Kudo et al. [156] (source estimation in a participating medium using TSVD): Linhua et al. [157] (inverse radiation temperature field in three-dimensional furnaces); Liu et al. [50] (reconstruction of flame distribution in coal-fired furnaces); Lou et al. [49] (measurement of temperature and radiative properties in oil-fired furnace); Miguel et al. [158] (inverse parameter correlation to compute radiation from flames); Ren and Modest [159] (temperature profile inversion through Tikhonov regularization); Ren et al. [160][161][162] and Li et al. [163] (ANN and machine learning methods applied to retrieval of temperature and concentration distributions from infrared emission measurements); and Wei et al. [164] (ANN inversion for 3D laser absorption imaging of methane in reacting flows). ...
... In particular, the situation when droplets and film liquid differ lacks a detailed description in the literature but is of high relevance for many technical applications. For instance in catalytic exhaust gas after-treatment systems, where a spray of urea-water solution impinges onto a wall film, which has, due to evaporation and temperature gradient, different fluid properties than the impinging spray droplets [4]. A further example is the situation in an internal combustion engine, where fuel droplets may impinge on the piston and cylinder walls, which are wetted by oil. ...
... To resolve the concentrations along the LOS, laser absorption tomography (LAT) can then be applied, which reconstructs the three-dimensional (3D) distribution of the analyte concentration from several 2D projections at different angles using inversion algorithms. 4 This technique has been applied to imaging of water vapor (H 2 O) and temperature at the exhaust of a jet engine, 5 in coal-fired combustors, 6,7 and for hydrocarbon imaging in the cylinders of an internal combustion engine. 8 Given the large bandwidth of available photodetectors, the advantage of the grid-type implementation of LAT is speed. ...
... This requirement is particularly important in BOS and LAS due to the nonlinear relationship between the QoI and measured signal(s). One solution is to perform instantaneous or time-resolved tomography using simultaneous measurements from multiple cameras or laser beams to reconstruct the QoI in an interrogation plane or volume, as has been done in BOS (Ihrke et al 2007, Atcheson et al 2008, Nicolas et al 2017, Amjad et al 2020, chemiluminescence imaging (Floyd and Kempf 2011, Worth and Dawson 2012, Mohri et al 2017, and LAS (Wright et al 2010, Lengden et al 2020, van der Kley et al 2021. This approach requires considerable optical access, which is not always possible and increases the cost and complexity of an experiment. ...
... The posterior covariance is . 7 The rank of Tik is − 1 so pr in Eq. (54) must be approximated in terms of the pseudoinverse of T Tik Tik [86,163]. However, since post is of interest, not pr per se, there is generally no need to perform this calculation. ...
... The interaction between the flow and the spray was particularly intense in the case of air-assisted injector application. The flow rig was aimed at optical spray measurements and the similar results were also presented by Schmidt et al. [16]. The rig enabled relevant tests for a diesel engine in crossflow conditions with a mass flow rate up to 1000 m 3 /h and a temperature of 800 K. ...
... Lubnow implemented near-infrared imaging using four wavelengths with a filter wheel, increasing the image acquisition time. Schmidt et al. investigated the dynamic changing of fluid thickness by using an absorptionbased laser sensor and the near-infrared spectra of liquid water for film thickness up to 440 µm [55]. Film thickness measurements in evaporation and flow processes of the refrigerant R1233zd by absorption spectroscopy in the near-infrared area were studied by Kong et al. [56]. ...
... Bayesian statistics was recently employed to directly estimate the absorbance spectrum from the transmitted intensity data 43 . While this approach shows promising results, it was only validated using a limited set of water vapor simulated spectra. ...
... The result is a system of equations with one equation per beam and one variable per basis function (pixel or node). Reconstruction consists in inverting these equations for a set of absorbance data using either a sequential-linear [29] or unified-nonlinear [30] approach. ...
... In this work, the mathematical model is solved by transforming it into the Laplace domain [44], and the routine implemented in MATLAB ® /Simulink ® (Natick, MA, USA) [45]. Based on these principles, the CRN shown in this work was designed following a stepwise approach starting from elementary arrangements [32,46,47]. Complexities were gradually added for implementing more features of the flow field. ...