This review discusses the role of laser diagnostics in combustion science and technology. In its first part, it may guide understanding of advanced diagnostic methods, and is particularly helpful for ...non-specialized experimentalists. Various challenges for future developments and applications of optical combustion diagnostics are highlighted. In the second part of this review, flame-wall interactions are selected for a more in-depth discussion. Flame-wall interactions are scientifically interesting and are of great importance to any enclosed practical combustion process. Following a description of current understanding, the focus is on using optical diagnostics to probe thermal, fluidic, and chemical properties of head-on and sidewall quenching. The review ends with a discussion of issues and implications for future experimental research and specific diagnostic needs.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Improved understanding of in-cylinder flows requires knowledge from well-resolved experimental velocimetry measurements and flow simulation modeling. Engine simulations using large eddy simulations ...(LES) are making large progress and the need for well documented velocimetry measurements for model validation is high. This work presents velocimetry measurements from PIV, high-speed PIV, stereoscopic PIV, and tomographic PIV to extensively describe the in-cylinder flow field in a motored optical engine operating at 800 RPM. These measurements also establish a comprehensive database designed for LES model development and validation. Details of the engine, engine accessory components, and well-controlled boundary conditions and engine operation are presented. The first two statistical moments of the flow field are computed and show excellent agreement among the PIV database. Analysis of statistical moments based on limited sample size is presented and is important for modeling validation purposes. High-speed PIV resolved the instantaneous flow field throughout entire engine cycles (i.e. 719 consecutive crank-angles), while tomographic PIV images are further used to investigate the 3D flow field and identify regions of strong vortical structures identified by the Q-criterion. Principle velocity gradient components are computed and emphasize the need to resolve similar spatial scales between experimental and modeling efforts for suitable model validation.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Electric motors with high-power densities are required for the implementation of electromobility. To achieve this, direct liquid cooling methods are increasingly being considered, in which oil is ...injected into the motor compartment. This results in a two-phase flow that can be used for efficient cooling. However, the oil, which can also penetrate the air gap between the rotor and stator, can also lead to additional losses due to increased friction. Since little is known about the two-phase flow in such systems, especially in the air gap, it is investigated by means of simple optical visualizations and high-speed laser-induced fluorescence imaging as well as torque measurements. The measurements are carried out in the air gap of an optically accessible generic model of a directly cooled electric motor. Speed variations were performed from 100 to 2000 rpm, and three different two-phase flow regimes were observed. At low speeds (Flow Regime 1), the air gap is filled locally with oil in radial direction, in the medium speed range (Flow Regime 2) with foam, while at high speeds (Flow Regime 3) separated films were observed on the rotor and stator. The torque difference between the two-phase and single-phase operation, which quantifies the mechanical losses due to the injected oil, increased continuously due to the oil in the air gap until it reached a maximum in Flow Regime 2 due to foam formation. In Flow Regime 3, the torque difference was negative. This was attributed to the fact that the grooves in the stator were filled with oil, thus reducing the turbulence generation of the air flow.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
This work presents first-of-its-kind high-speed planar laser-induced fluorescence measurements of the hydroxyl radical in the boundary layer of single coal particles. Experiments were performed in a ...laminar flow reactor providing an oxygen-enriched exhaust gas environment at elevated temperatures. Single coal particles in a sieve fraction of 90–125 µm and a significant amount of volatiles (36 wt%) were injected along the burner’s centerline. Coherent anti-Stokes Raman spectroscopy measurements were taken to characterize the gas-phase temperature. Time-resolved imaging of the OH distribution at 10 kHz allowed identifying reaction and post-flame zones and gave access to the temporal evolution of burning coal particles. During volatile combustion, a symmetric diffusion flame was observed around the particle starting from a distance of ~150 µm from the particle surface. For subsequent char combustion, this distance decreased and the highest OH signals appeared close to the particle surface.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Precise evaluation of flame surface area plays a pivotal role in the fundamental understanding and accurate modelling of turbulent premixed flames. This necessity is reflected in the requirement for ...the instantaneous flame area evaluation of the turbulent burning velocity (by making use of Damköhler’s first hypothesis). Moreover, the information regarding flame area is required in the context of flame surface density based modelling, and for determining the wrinkling factor or estimating the efficiency function. Usually flame surface areas in experiments and Direct Numerical Simulation (DNS) analyses are evaluated differently and the present analysis aims at comparing these approaches by making use of a detailed chemistry DNS database of turbulent, statistically planar flames. It has been found that the flame surface area evaluation is sensitive to the choice of scalar quantity and the isosurface level, and this holds particularly true for two-dimensional evaluations. The conditions, which provide a satisfactory agreement between experimental and numerical approaches in the flame area evaluation, have been identified by a detailed comparative analysis of the usual postprocessing techniques.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
•Particle group combustion of pulverized coal was investigated by optical and sampling methods.•Temperature statistics were investigated for sooty volatile flames and char temperatures.•Particles in ...group combustion show a lower temperature in comparison to single particles.•Burnout progress was analyzed with a solid sample probe for single particles and particles in groups.•Dataset adds significant information and correlated statistics on the observed phenomena.
The transition from single to group particle combustion is experimentally investigated in a laminar flow reactor. Optical techniques including two-colour pyrometry and a sampling probe provide data on surface temperature and composition of high-volatile bituminous coal particles during ignition, volatile combustion, and char burnout. Adjustable particle number densities (PND) permit studying the transition from single to group particle combustion. An optical imaging pyrometer provides simultaneously acquired data on the soot particles during the volatile combustion and the particle temperature, particle size and position in the 3D particle streak. These parameters are investigated as a function of the PND, which is used to differentiate between single and group particle combustion. Additionally, particle sampling provides particle composition data, which together with the particle temperatures extends a previously published data set from the same reactor. The results show a direct relation between the particle temperature during char burnout and the PND. As particles in group combustion absorb a significant amount of thermal energy from the surrounding atmosphere and reduce the oxygen content in the group, the measurements prove a lower temperature for particles that burn in group compared to single particle. Furthermore, sampling at several residence times indicates a notable difference in the burnout process between single particle (SP) and group particle (GP) combustion. While the effect of different atmospheres impacts the results of SP combustion, GP combustion is significantly less affected. The results of the current study are jointly discussed with previously acquired data of the same burner for a thorough interpretation.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The regulation of temporo-spatial compartmentalization of protein synthesis is of crucial importance for a variety of physiologic cellular functions. Here, we demonstrate that the cell ...membrane-anchored disintegrin metalloproteinase ADAM15, upregulated in a variety of aggressively growing tumor cells, in the hyperproliferative synovial membrane of inflamed joints as well as in osteoarthritic chondrocytes, transiently binds to poly(A) binding protein 1 (PABP) in cells undergoing adhesion. The cytoplasmic domain of ADAM15 was shown to selectively interact with the proline-rich linker of PABP. Immunostainings of adhesion-triggered cells demonstrate an ADAM15-dependent recruitment of PABP to cell membrane foci coinciding with ongoing mRNA translation as visualized by the detection of puromycin-terminated polypeptides. Moreover, the increase in cell membrane-associated neosynthesis of puromycylated proteins upon induction of cell adhesion was proven linked to ADAM15 expression in HeLa and ADAM15-transfected chondrocytic cells. Thus, down regulation of ADAM15 by siRNA and/or the use of a cell line transfected with a mutant ADAM15-construct lacking the cytoplasmic tail resulted in a considerable reduction in the amount of cell membrane-associated puromycylated proteins formed during induced cell adhesion. These results provide first direct evidence for a regulatory role of ADAM15 on mRNA translation at the cell membrane that transiently emerges in response to triggering cell adhesion and might have potential implications under pathologic conditions of matrix remodeling associated with ADAM15 upregulation.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
•Novel velocimetry methodologies studying complex spray-induced turbulent flows.•Fuel injection produces a spray-induced jet imparting turbulence onto ambient flow.•Spray-induced turbulence occurs as ...strong shear layers and 3D vortical structures.•Turbulent flow dissipates with radial distance from spray-induced jet.•3D vortical structures are not characterized by a single strain rate component.
Fuel sprays produce high-velocity, jet-like flows that impart turbulence onto the ambient flow field. This spray-induced turbulence augments rapid fuel-air mixing, which has a primary role in controlling pollutant formation and cyclic variability in direct-injection engines. This paper presents tomographic particle image velocimetry (TPIV) measurements to analyze the 3D spray-induced turbulence during the intake stroke of a direct-injection spark-ignition (DISI) engine. The spray produces a strong spray-induced jet (SIJ) in the far field, which travels through the cylinder and imparts turbulence onto the surrounding flow. Planar high-speed PIV measurements at 4.8 kHz are combined with TPIV at 3.3 Hz to evaluate spray particle distributions and validate TPIV measurements in the particle laden flow. A comprehensive uncertainty analysis is performed to assess the uncertainty associated with individual vorticity and strain rate components.
TPIV analyses quantify the spatial domain of the turbulence in relation to the SIJ and describe how turbulent flow features such as turbulent kinetic energy (TKE), strain rate (S) and vorticity (Ω) evolve into the surrounding flow field. Access to the full S and Ω tensors facilitate the evaluation of turbulence for individual spray events. TPIV images reveal the presence of strong shear layers (visualized by high S magnitudes) and pockets of elevated vorticity along the immediate boundary of the SIJ. S and Ω values are extracted from spatial domains extending in 1 mm increments from the SIJ. Turbulence levels are greatest within the 0–1 mm region from the SIJ boarder and dissipate with radial distance. Individual strain rate and vorticity components are analyzed in detail to describe the relationship between local strain rates and 3D vortical structures produced within strong shear layers of the SIJ. Analyses are intended to understand the flow features responsible for rapid fuel-air mixing and provide valuable data for the development of numerical models.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The measurement of flame surface evolution in both space and time is necessary for the advancement of knowledge concerning the physical processes contributing to lifted jet flame stabilisation. ...Previous studies either reproduce the flame front accurately in three-dimensional space or in time. In this study a measurement system capable of both is presented. Based on the Mie-scattering of oil droplets added to the jet flow, the system reconstructs the volumetric surface at the base of a lifted jet flame from a series of two-dimensional slices. The slices are created using a pulsed high-speed laser and a polygonal laser scanner unit which serves to sweep the laser beam through the measurement volume. A single high-speed camera is used for recording the subsequent measurement slices. The achieved temporal and spatial resolution as well as the accuracy and precision of the sheet placement are discussed in respect to the flames' scales. The first results of the reconstruction of the lifted jet flame at its stabilisation point show the potential of such measurements to avoid the ambiguities in interpreting conventional 2D-data.
Measurements of instantaneous volumetric flow fields are required for an improved understanding of turbulent flames. In non-reacting flows, tomographic particle image velocimetry (TPIV) is an ...established method for three-dimensional (3D) flow measurements. In flames, the reconstruction of the particles location becomes challenging due to a locally varying index of refraction causing beam-steering. This work presents TPIV measurements within a turbulent lifted non-premixed methane jet flame. Solid seeding particles were used to provide the 3D flow field in the vicinity of the flame base, including unburned and burned regions. Four cameras were arranged in a horizontal plane around the jet flame. Following an iterative volumetric self-calibration procedure, the remaining disparity caused by the flame was less than 0.2 pixels. Comparisons with conventional two-component PIV in terms of mean and rms values provided additional confidence in the TPIV measurements.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
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