Christof Schulz

University of Duisburg-Essen | uni-due · Institut for Combustion and Gas Dynamics

Despite considerable efforts to develop electrolyzers for energy conversion, progress has been hindered during the implementation stage by different catalyst development requirements in academic and industrial research. Herein, a coherent workflow for the efficient transition of electrocatalysts from basic research to application readiness for the...

Spray-flame synthesis uses low-cost precursors dissolved in organic solvents to produce functional metaloxide nanoparticles. In the spray flame, the precursor-laden droplets show frequent and intense thermally-induced disruption, so-called puffing and micro-explosion. This process is often correlated with high uniformity of particle sizes. Whether...

In sodium-ion batteries (SIBs), TiO2 or sodium titanates are discussed as cost-effective anode material. The use of ultrafine TiO2 particles overcomes the effect of intrinsically low electronic and ionic conductivity that otherwise limits the electrochemical performance and thus its Na-ion storage capacity. Especially, TiO2 nanoparticles integrated...

Akademische Forschung und industrielle Anwendung – wie die Zusammenarbeit zwischen Industrie und Akademia zu optimieren ist, zeigt ein Blick aus der technischen Elektrochemie auf deren Anwendung in der Industrie. Wichtig ist dabei eine klare Kommunikation auf beiden Seiten.

Syngas is a desirable fuel for combustion in the Allam-Fetvedt cycle which involves combustion under supercritical-CO2 (sCO2) conditions. While some work has been conducted in collecting ignition delay times at the extreme pressures required by these systems, significant model deficiencies remain. Additionally, considerable barriers in terms of non...

Syngas is a desirable fuel for combustion in the Allam-Fetvedtcycle which involves combustion under supercritical-CO2(sCO2) conditions. While some work has been conducted in collecting ignition delay times at the extreme pressures required by these systems, significant model deficiencies remain. Additionally, considerable barriers in terms of non-i...

The reaction between Fe atoms and O2 in a mixture of iron-pentacarbonyl (IPC, 2 ppm) and oxygen (100 ppm), diluted in argon, has been studied in a shock tube behind reflected shock waves over the temperature and pressure ranges of 1050–3400 K and 0.7–2.0 bar. Time-resolved measurements of Fe and FeO have been performed simultaneously using a combin...

Premixed flat flames provide an ideal platform for investigation of soot formation by optical diagnostics. The local conditions can, however, be strongly affected by species diffusion and heat transfer perpendicular to the flow direction. This work investigates the influence of the burner geometry and shielding of the target flame by a nitrogen cof...

Facility-dependent non-ideal effects were investigated in two different shock-tube laboratories at Texas A&M University and University of Duisburg-Essen, concentrating on the influence of shock-tube heating (T1) on non-ideal pressure rise (dp*/dt). The experiments conducted in nitrogen varied in shock strength with Mach number ranging from 1.68 to...

We demonstrate high-repetition-rate imaging of the liquid-film thickness in the 50–1000 µm range resulting from impinging water droplets on a glass surface. The pixel-by-pixel ratio of line-of-sight absorption at two time-multiplexed near-infrared wavelengths at 1440 and 1353 nm was detected with a high-frame-rate InGaAs focal-plane array camera. F...

Premixed flat flames provide an ideal platform for investigation of soot formation by optical diagnostics. The local conditions can, however, be strongly affected by species diffusion and heat transfer perpendicular to the flow direction. This work investigates the influence of the burner geometry and shielding of the target flame by a nitrogen cof...

The combustor and turbine inlet pressures of modern aviation and power-generation gas turbine engines can vary between 30 and 50 bar. Innovative diagnostic methods are needed to understand the complex thermo-physical processes taking place under these conditions. Non-intrusive, spatially, and temporally resolved optical and laser diagnostic methods...

The product properties of mixed oxide nanoparticles generated via spray-flame synthesis depend on an intricate interplay of solvent and precursor chemistries in the processed solution. The effect of two different sets of metal precursors, acetates and nitrates, dissolved in a mixture of ethanol (35 Vol.%) and 2-ethylhexanoic acid (2-EHA, 65 Vol.%)...

A novel Eulerian particle model tailored for the application in computational fluid dynamics (CFD) is presented. The model is based on a bivariate moment method and features a full coupling with the gas-phase by kinetic formulations for inception, and activated and non-activated surface reactions. A new formulation for the particle composition acco...

In many high-temperature gas-phase nanoparticle synthesis processes, freshly nucleated particles are liquid and solidify during growth and cooling. This study presents an approach to determine the location of the liquid-to-solid phase transition and the volume fraction and number density of particles of both phases within a gas phase reactor. Spect...

The influence of methanol and butanol on soot formation during the pyrolysis of a toluene primary reference fuel mixture with a research octane number (RON) of 91 (TPRF91) was investigated by conducting shock-tube experiments. The TPRF91 mixture contained 17 mol % n-heptane, 29 mol % iso-octane, and 54 mol % toluene. To assess the contribution of i...

We report on our recent progress in advancing intracavity absorption spectroscopy into the mid-infrared spectral range by using novel Cr ²⁺ - and Fe ²⁺ -doped chalcogenide-crystal lasers. Broadband and highly sensitive measurements of various species will be presented.

Gas-phase microwave plasma-assisted synthesis of freestanding graphene is a promising route to produce high-quality graphene flakes. However, a comprehensive understanding of the gas-phase kinetics that is required to advance production rates and yields is still lacking. Here, we use line-of-sight Fourier-transform infrared (FTIR) absorption spectr...

La 1– x Sr x CoO 3 ( x = 0, 0.1, 0.2) and LaCo 0.8 Fe 0.2 O 3 perovskite nanoparticles were synthesized by spray-flame synthesis, and their electrocatalytic water oxidation activity was evaluated in the prepared state. Highly crystalline, rhombohedrally distorted cubic structures of the cobaltite perovskites were confirmed by STEM and XRD analyses....

We demonstrate the first application of a Cr:CdSe laser for highly-sensitive multicomponent intracavity absorption spectroscopy around λ = 3.1–3.4 µm. A detection scheme based on an integrated recording of multiple (∼70) individual Cr:CdSe laser pulses after a single pump-pulse excitation is reported. The sensitivity of our system corresponds to an...

In flame synthesis of nanoparticles, the temperature history experienced by the nascent particle aerosol defines the morphology, composition, and crystallinity of the resulting nanomaterial. Commonly, flame-synthesis processes are modeled with an isothermal approximation assuming that the particle temperature replicates that of the surrounding gas...

One of the key parameters for spray-flame synthesis of nanoparticles with defined properties is the temporal flame stability. Flame pulsation and consequently flame stability strongly depend on spray characteristics (e.g., droplet sizes and velocities), which are directly influenced by the nozzle geometry. This influence is analyzed in this work. F...

A novel particle model is presented to simulate the synthesis of silicon nanoparticles from monosilane in a laboratory sized microwave plasma reactor. The simulations contribute essentially to the understanding of the particle formation process and the spatial and size distribution of particles observed in the experiment. The model approach feature...

Metal leaching in perovskite-based catalysts during peroxymonosulfate activation processes can severely restrict their application in wastewater treatment. Therefore, enhancing the stability of perovskite nanostructures is crucial to improve catalytic performance and broaden applications but has been rarely achieved so far. We developed a scalable...

The influence of ozone on the ignition delay times and product formation of methane and natural gas was determined in a high-pressure shock tube at fuel-rich conditions (ϕ = 2 and 10), ozone concentrations of 550 ppm, temperatures between 850 and 1700 K and pressures of about 30 bar. The addition of ozone causes a strong reduction of the ignition d...

In the SpraySyn burner (Schneider et al., 2019) a solution of metal salts in a combustible liquid is atomized in a two-fluid nozzle with molecular oxygen as dispersion gas to generate oxide nanoparticles via combustion synthesis. The flame is anchored by a methane (CH4)/oxygen (O2) premixed flat flame stabilized on a porous plate surrounding the sp...

In spray-flame synthesis of nanoparticles, a precise understanding of the reaction processes is necessary to find optimal process parameters for the formation of the desired products. Coupling the chemistries of flame, solvent, and gas-phase species initially formed from the particle precursor in combination with the complex flow geometry of the sp...

The high potential of oxymethylene ethers (OMEs) and related compounds as fuels and fuel-additives motivated a multitude of experimental and theoretical investigations on, e.g., dimethoxy methane (DMM), the smallest member of the OME family. The present work adds to this research by providing combined experimental and theoretical rate coefficients...

Single-pulse shock-tube experiments were used to study the thermal decomposition of selected oxygenated hydrocarbons: Ethyl propanoate (C2H5OC(O)C2H5; EP), propyl propanoate (C3H7OC(O)C2H5; PP), isopropyl acetate ((CH3)2HCOC(O)CH3; IPA), and methyl isopropyl carbonate ((CH3)2HCOC(O)OCH3; MIC) The consumption of reactants and the formation of stable...

The influence of various oxygenated co-reactants on soot formation was addressed by studying the pyrolysis of gas mixtures using ethylene as a base fuel in the absence of molecular oxygen. Alcohols (methanol, ethanol, and n-butanol) and ethers (diethyl ether, dimethoxymethane, furan, and tetrahydrofuran) were selected as oxygenated co-reactants. Th...

The synthesis of iron oxide nanoparticles from iron nitrate in the SpraySyn spray flame reactor was investigated by experiment and simulation. The focus was on the spray and flame structure, the particle growth by nucleation and coagulation, and the unresolved effects and their impact on the dispersed phase. The reacting flow was modeled in large e...

Tomographic imaging using multi-simultaneous measurements (TIMes) of spontaneous light emission was performed on various operating conditions of the SpraySyn burner to analyse the flame morphology and its potential impact on spray flame pyrolysis. Concurrent instantaneous and time-averaged three-dimensional measurements of CH* chemiluminescence (fl...

Laser-induced incandescence (LII) is a widely used combustion diagnostic for in situ measurements of soot primary particle sizes and volume fractions in flames, exhaust gases, and the atmosphere. Increasingly, however, it is applied to characterize engineered nanomaterials, driven by the increasing industrial relevance of these materials and the fu...

A fiber-coupled, compact, remotely operated laser absorption instrument is developed for CO, CO2, and H2O measurements in reactive flows at the elevated temperatures and pressures expected in gas turbine combustor test rigs with target pressures from 1–25 bar and temperatures of up to 2000 K. The optical engineering for solutions of the significant...

The influence of the addition of oxygenated hydrocarbons (methanol, ethanol, and n-butanol) and ethers (diethyl ether, dimethoxymethane, furan, and tetrahydrofuran) on soot formation from benzene pyrolysis was studied. The pyrolysis process was investigated behind reflected shock waves at pressures around 1.4 bar and in the temperature range of 167...

In phase-selective laser-induced breakdown spectroscopy (PS-LIBS), gas-borne nanoparticles are irradiated with laser pulses (∼2.4 GW/cm2) resulting in breakdown of the nanoparticle phase but not the surrounding gas phase. In this work, the effect of excitation laser-pulse duration and energy on the intensity and duration of TiO2-nanoparticle PS-LIB...

Nanoparticulate CoxFe3-xO4 (0 ≤ x ≤ 3) catalysts were prepared by spray-flame synthesis and applied in liquid phase cyclohexene oxidation with O2 as oxidant. The catalysts were characterized in detail...

We present a method to simultaneously measure the film thickness and individual concentrations of two urea derivates (urea ${{\rm CH}_4}{{\rm N}_2}{\rm O}$ C H 4 N 2 O and dimethylurea ${{\rm C}_3}{{\rm H}_8}{{\rm N}_2}{\rm O}$ C 3 H 8 N 2 O ) mixed in an aqueous solution at constant temperature using near-infrared (NIR) absorption at multiple spec...

In this study, the temperature and volume fraction distributions of liquid silicon nanoparticles in the aerosol flow in gas-phase synthesis were retrieved using tomographic reconstruction of emission and extinction spectra in the 230–700 nm range. Measurements were done in an optically accessible microwave-plasma flow reactor fed with a SiH4/H2/Ar...

The liquid‐phase oxidation of cyclohexene was studied over a series of Sr‐substituted La1−xSrxCoO3 catalysts of perovskite structure under mild reaction conditions with O2 as oxidant in an autoclave. The substitution of Sr into the perovskite structure led to the formation of catalytically active oxygen species. In‐situ ATR IR measurements provided...

La1−xSrxCoO3 (x=0, 0.1, 0.2, 0.3, 0.4) nanoparticles were prepared by spray‐flame synthesis and applied in the liquid‐phase oxidation of cyclohexene with molecular O2 as oxidant under mild conditions. The catalysts were systematically characterized by state‐of‐the‐art techniques. With increasing Sr content, the concentration of surface oxygen vacan...

Two-dimensional thermographic particle image velocimetry (T-PIV) is presented for the in situ measurement in optically accessible internal combustion (IC) engines. Temperature and velocity measurements are combined using thermographic phosphor particles as tracers for PIV. For three commercially available phosphors (BAM:Eu ²⁺ , ZnO, and ZnO:Zn), te...

We systematically studied the role of oxygen in gas-phase synthesis of graphene in atmospheric hydrocarbon-fed microwave plasmas. Oxygen is introduced through the use of alcohols, and mixtures of ethylene and water. These reactants were contrasted with oxygen-free hydrocarbon reactants, including ethylene and toluene. Solid materials were collected...

Si-C-H-O-containing radicals are important intermediates during the combustion and pyrolysis of precursors applied for the gas-phase synthesis of silica nanoparticles. Despite the industrial importance of silica nanoparticles, a comprehensive thermodynamics database of organosilane species is still missing. This work presents thermochemical data of...

Shock-tube experiments were conducted to determine rate-coefficient data of the H-atom abstraction reactions H + HMDSO (hexamethyldisiloxane) → H2 + HMDSO−H and H + TMDSO (tetramethyldisiloxane) → H2 + TMDSO−H. The experiments comprised a temperature range of 1109–1240 K and pressures between 1.2 and 1.5 bar. In all experiments, C2H5I was used as a...

Predictions made by climate researchers are highly worrisome and demand rapid action to avoid the threat of climate catastrophe. Global energy systems must be transformed as quickly as possible by minimising or avoiding net greenhouse gas emissions. There is broad agreement on this goal, demonstrated by international treaties such as the Sustainabl...

The distinct optical properties of solid and liquid silicon nanoparticles are exploited to determine the distribution of gas-borne solid and liquid particles in situ using line-of-sight attenuation measurements carried out across a microwave plasma reactor operated at 100 mbar. The ratio between liquid and solid particles detected downstream of the...

Comprehensive characterization of crumpled graphene materials is required to understand their morphologically dependent properties. This study connects the optical properties of crumpled few-layer graphene (FLG) aerosols and colloidal suspensions with particle morphology. The mass absorption cross-section (MAC) of crumpled FLG was measured in the a...

In this work, we introduce a new particle mass spectrometer (AP-PMS) that is able to detect particle-size distributions at ambient pressure using a three-stage pumping design. This device is demonstrated for direct sampling from the particle formation in spray-flame synthesis of iron oxide nanoparticles. Aerosol sampling is performed by a probe wit...

The fluorescence spectra of dye solutions change their spectral signature with temperature. This effect is frequently used for temperature imaging in liquids and sprays based on two-color laser-induced fluorescence (2cLIF) measurements by simultaneously detecting the fluorescence intensity in two separate wavelength channels resulting in a temperat...

Soot formation at lean-threshold conditions referred to as “near-threshold sooting conditions” (i.e., with stoichiometry, ϕ, around 1.90 for ethene as a fuel) are studied in laminar premixed ethylene/air flames at pressure from 1 to 10 bar. Laser extinction is used to measure the soot volume fraction. Time-resolved laser-induced incandescence (TiRe...

The survivability of two thermographic phosphors, YAG:Pr ³⁺ and SMP:Sn ²⁺ ((Sr,Mg) 3 (PO 4 ) 2 :Sn ²⁺ ), in a combustion environment is studied in the post-flame regime of a premixed propane/air flame. While the laser-induced luminescence of YAG:Pr ³⁺ can be exploited for in situ temperature measurements in the exhaust gas above the flame, there is...

We demonstrate an intracavity absorption spectroscopy system based on a broadband single-crystal pulsed Fe:ZnSe laser. The laser operates at room-temperature and is continuously tunable in the spectral range of 3.76–5.29 µm. The long-wavelength emission up to 5.29 µm is a record achievement for Fe:ZnSe lasers, to the best of our knowledge. The deve...

Fluorescence spectra and lifetimes of anisole and toluene vapor in nitrogen have been measured at conditions below ambient (257–293 K and 100–2000 mbar) upon excitation with 266-nm laser light to expand the applicable range of anisole and toluene laser-induced fluorescence (LIF) for conditions below room temperature that occur in expanding flows an...