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"Kaiser, Sebastian"
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Optical Diagnostics for Knock in Compression-Ignition Engines via High-Speed Imaging
Knocking combustion is associated with extremely high in-cylinder pressure rise rates, strong pressure oscillations, destructive engine vibration, as well as audible noise. It not only exists in spark-ignition (SI) engines but also in compression-ignition (CI) engines, for both conventional Diesel and more premixed modes of combustion. Recent work showed that during Diesel knock the flame’s motion synchronizes with the in-cylinder pressure ringing. To improve the optical method and investigate knock in CI engines further, we imaged the flame luminosity with n-dodecane as a Diesel surrogate in an optically accessible engine during knock at very high frame rates (60 kHz). First, the knocking time interval was determined based on the temporal variation of the mean image intensity. Within this time interval, the instantaneous flow fields were calculated by “optical flow” based on cross-correlation. From these velocity-vector time series, the oscillation frequencies were obtained and compared to those from pressure-trace analysis and theoretical calculation. The images show a “sloshing” motion of the flame, with nearly the same frequency content as that of pressure ringing. Cavity modes, as predicted by theoretical analysis, can clearly be identified. As opposed to pressure-trace analysis, the optical diagnostic is spatially resolved and shows less cycle-to-cycle variation. Combustion in our CI engine experiments occurred by both sequential auto-ignition and reaction-front propagation. Knock originated from auto-ignition of end gas, resembling knock in SI engines. In one very severe cycle, a shock wave was seen, while the velocity of the gas was found to be always subsonic. From the vector field, the spatial origin of the knock could be estimated. The knock intensity evaluated from optical metrics correlated reasonably well with that from conventional methods based on pressure-trace analysis.
Journal Article
The structural and functional characterization of human RecQ4 reveals insights into its helicase mechanism
RecQ4 is a member of the RecQ helicase family, an evolutionarily conserved class of enzymes, dedicated to preserving genomic integrity by operating in telomere maintenance, DNA repair and replication. While reduced RecQ4 activity is associated with cancer predisposition and premature aging, RecQ4 upregulation is related to carcinogenesis and metastasis. Within the RecQ family, RecQ4 assumes an exceptional position, lacking several characteristic RecQ domains. Here we present the crystal structure of human RecQ4, encompassing the conserved ATPase core and a novel C-terminal domain that lacks resemblance to the RQC domain observed in other RecQ helicases. The new domain features a zinc-binding site and two distinct types of winged-helix domains, which are not involved in canonical DNA binding or helicase activity. Based on our structural and functional analysis, we propose that RecQ4 exerts a helicase mechanism, which may be more closely related to bacterial RecQ helicases than to its human family members.
RecQ helicases are important for maintaining genomic integrity. Here, the authors present functional data and the crystal structure of human RecQ4, which exerts a helicase mechanism that may be more closely related to bacterial RecQ helicases than to its human family members.
Journal Article
Laser-induced emission from iron oxide nanoparticles in spray-flame synthesis: in situ high-speed microscopy
NRC publication: Yes
Journal Article
A dispensable SepIVA orthologue in Streptomyces venezuelae is associated with polar growth and not cell division
Background
SepIVA has been reported to be an essential septation factor in
Mycolicibacterium smegmatis
and
Mycobacterium tuberculosis
. It is a coiled-coil protein with similarity to DivIVA, a protein necessary for polar growth in members of the phylum Actinomycetota. Orthologues of SepIVA are broadly distributed among actinomycetes, including in
Streptomyces
spp.
Results
To clarify the role of SepIVA and its potential involvement in cell division in streptomycetes, we generated
sepIVA
deletion mutants in
Streptomyces venezuelae
and found that
sepIVA
is dispensable for growth, cell division and sporulation. Further, mNeonGreen-SepIVA fusion protein did not localize at division septa, and we found no evidence of involvement of SepIVA in cell division. Instead, mNeonGreen-SepIVA was accumulated at the tips of growing vegetative hyphae in ways reminiscent of the apical localization of polarisome components like DivIVA. Bacterial two-hybrid system analyses revealed an interaction between SepIVA and DivIVA. The results indicate that SepIVA is associated with polar growth. However, no phenotypic effects of
sepIVA
deletion could be detected, and no evidence was observed of redundancy with the other DivIVA-like coiled-coil proteins Scy and FilP that are also associated with apical growth in streptomycetes.
Conclusions
We conclude that
S. venezuelae
SepIVA, in contrast to the situation in mycobacteria, is dispensable for growth and viability. The results suggest that it is associated with polar growth rather than septum formation.
Journal Article
In-situ Investigation of the Onset of Cavitation Damage from Single Bubbles on Technical Alloys
Cavitation erosion is typically studied with ultrasonic sonotrodes. Only a few attempts have been made to study cavitation erosion of technical alloys on the level of repeated single bubbles. Such single cavitation bubbles can be induced by a focused laser pulse with high spatio-temporal repeatability. In this work, the surface damage caused by series of laser-induced single bubbles in water is observed with a light microscope in-situ between two successive bubbles. Polished samples from pure aluminum, an austenitic steel (316L, X2CrNiMo18-15-3), and a nickel aluminum bronze (CuAl10Ni5Fe5) were subjected to series of bubbles that typically had a maximum diameter of
d
= 2.5 mm and a non-dimensional stand-off distance
γ
= 1.4. Via in-situ microscopy, the appearance of individual pits can be assigned to a specific, single bubble collapse event without removing the sample. Consistent with literature, for the chosen parameters the damaged region after many bubbles is circular, with individual pits that are deeper for aluminum than for the bronze and the steel. Additionally, our findings suggest that even high-strength materials can be damaged by the impact of just one single bubble, while not every single bubble causes a pit on the soft aluminum. From series of images after each bubble, the rate of pit accumulation was determined to be 2.6 pits/bubble for aluminum and around 0.3–0.5 pits/bubble for the two technical alloys.
Journal Article
Optical Investigation of Mixture Formation in a Hydrogen-Fueled Heavy-Duty Engine with Direct-Injection
Mixture formation in a hydrogen-fueled heavy-duty engine with direct injection and a nearly-quiescent top-hat combustion chamber was investigated using laser-induced fluorescence imaging, with 1,4-difluorobenzene serving as a fluorescent tracer seeded into hydrogen. The engine was motored at 1200 rpm, 1.0 bar intake pressure, and 335 K intake temperature. An outward opening medium-pressure hollow-cone injector was operated at two different injection pressures and five different injection timings from early injection during the intake stroke to late injection towards the end of compression stroke. Fuel fumigation upstream of the intake provided a well-mixed reference case for image calibration. This paper presents the evolution of in-cylinder equivalence ratio distribution evaluated during the injection event itself for the cylinder-axis plane and during the compression stroke at different positions of the light sheet within the swirl plane. During the injection event, the originally annular jet collapses onto the jet axis within 1°CA after jet emergence and within 10 mm downstream of the nozzle. Multiple shock cells are visible – their size decreases with decreasing pressure ratio. The results of the equivalence ratio distribution show high cyclic variability of mixing for all injection timings during the compression stroke, but only minor variability with early injection during the intake stroke. The ensemble-mean fuel distribution shows that fuel-rich zones shift from the intake side to the exhaust side of the combustion chamber as the injection is advanced. Probability density functions of global equivalence ratio and equivalence ratio at potential spark locations suggest that retarded fuel injection might significantly increase NO emissions and the cyclic variability of early flame kernel development.
Journal Article
Frictional and Particle Emission Behavior of Different Brake Disk Concepts Correlated with Optical Pin Surface Characterization
Brake wear emissions can be reduced by altering the surface of brake disks. A parametric study using a gray cast iron and a laser-cladded brake disk was performed in a pin-on-disk experiment with integrated optical pin surface characterization and particle emission measurement. Significant differences in the friction, wear and emission behavior are present. The high wear-resistance of the laser-cladded disk led to a reduction of 70% of the particle number emission relative to the gray cast iron disk, but the coefficient of friction was unstable. The surface of the pin used with the gray cast iron showed an initial large debris extension and protruding patches that were removed at high braking energies, exposing white patches and creating holes. These observations correspond to known processes from the plateau theory. The surface of the pin used with the laser-cladded disk showed a topography dominated by holes with almost no protruding patches. The braking condition did not influence the pin surface, implying that the disk and not solely the pin surface might be governing the friction process, and therefore challenging the applicability of the plateau theory to laser-cladded disks. To further study this aspect, a segmentation method was developed for the pin surface images and topographical data to extract and quantify different features on the pin, such as debris, patches, holes and the tribolayer. The correlation of the surface coverage ratios of the feature classes with the braking conditions (speed and applied pressure), the coefficient of friction and the emissions confirmed the differences between the gray cast iron and laser-cladded brake disk.
Journal Article
Genome Sequence Analysis of Native Xenorhabdus Strains Isolated from Entomopathogenic Nematodes in Argentina
Entomopathogenic nematodes from the genus Steinernema (Nematoda: Steinernematidae) are capable of causing the rapid killing of insect hosts, facilitated by their association with symbiotic Gram-negative bacteria in the genus Xenorhabdus (Enterobacterales: Morganellaceae), positioning them as interesting candidate tools for the control of insect pests. In spite of this, only a limited number of species from this bacterial genus have been identified from their nematode hosts and their insecticidal properties documented. This study aimed to perform the genome sequence analysis of fourteen Xenorhabdus strains that were isolated from Steinernema nematodes in Argentina. All of the strains were found to be able of killing 7th instar larvae of Galleria mellonella (L.) (Lepidoptera: Pyralidae). Their sequenced genomes harbour 110 putative insecticidal proteins including Tc, Txp, Mcf, Pra/Prb and App homologs, plus other virulence factors such as putative nematocidal proteins, chitinases and secondary metabolite gene clusters for the synthesis of different bioactive compounds. Maximum-likelihood phylogenetic analysis plus average nucleotide identity calculations strongly suggested that three strains should be considered novel species. The species name for strains PSL and Reich (same species according to % ANI) is proposed as Xenorhabdus littoralis sp. nov., whereas strain 12 is proposed as Xenorhabdus santafensis sp. nov. In this work, we present a dual insight into the biocidal potential and diversity of the Xenorhabdus genus, demonstrated by different numbers of putative insecticidal genes and biosynthetic gene clusters, along with a fresh exploration of the species within this genus.
Journal Article
Investigation of an IC Engine Intake Flow Based on Highly Resolved LES and PIV
To reduce emissions and fuel consumption, the current generation of gasoline engines uses technologies such as direct injection, downsizing and supercharging. All of them require a strong vortical in-cylinder charge motion, usually described as “tumble”, to improve fuel-air mixing and enhance flame propagation. The tumble development strongly depends on the flow field during the intake stroke. This flow field is dominated by the intake jet, which has to be captured well in the simulation. This work investigates the intake jet on a steady-state flow bench, especially in the vicinity of the intake valve. At first, the general flow dynamics of the intake jet for three different valve lifts and three different mass flows were investigated experimentally. For the smallest valve lift (3 mm), flow-field measurements using Particle Image Velocimetry (PIV) show that the orientation of the intake jet significantly depends on the air flow rate, attaching to the pent roof for low flow rates. This phenomenon is less pronounced for higher valve lifts. An intermediate valve lift and flow rate were chosen for further investigations by scale-resolving simulations. Three different meshes (coarse, medium and fine) and two turbulence models (Sigma and Detached Eddy Simulation-Shear Stress Transport (DES-SST)) are applied to consider their effect on the numerical results. An ad-hoc post-processing methodology based on the ensemble-averaged velocity field is presented capturing the jet centerline’s mean velocity and velocity fluctuations as well as its orientation, curvature and penetration depth. The simulation results are compared to each other as well as to measurements by PIV.
Journal Article