Search Results (19)

The aim of the current study was to examine the unique relations between introversion and indices of well-being while accounting for aspects of solitude (i.e., time spent alone, shyness, affinity for solitude, and negative thinking while alone). Participants were n = 1036 adolescents (15–19 years of age, M = 16.19 years, SD = 0.58; 67% girls) who completed a series of self-report measures assessing introversion, time spent alone, negative thinking while alone, motivations for solitude (shyness, affinity for solitude), and indices of well-being (i.e., loneliness, positive/negative affect, general well-being). Overall, results from correlational analyses indicated that introversion was associated with poorer functioning across all indices of well-being. However, when controlling for aspects of solitude, results from hierarchical regression analyses indicated a complex set of associations that varied across indices of well-being. Introversion remained associated significantly and negatively with well-being and positive affect, was no longer related significantly to loneliness, and became related significantly and negatively to negative affect. Findings are discussed in terms of how personality characteristics and aspects of solitude can impact the well-being of adolescents. Full article

The homogenized lattice Boltzmann method (HLBM) has emerged as a flexible computational framework for studying particulate flows, providing a monolithic approach to modeling pure fluid flows and flows through porous media, including moving solid and porous particles, within a unified framework. This paper presents a thorough review of HLBM, elucidating its underlying principles and highlighting its diverse applications to particle-laden flows in various fields as reported in literature. These include studies leading to new fundamental knowledge on the settling of single arbitrarily shaped particles as well as application-oriented research on wall-flow filters, hindered settling, and evaluation of the damage potential during particle transport. Among the strengths of HLBM are its monolithic approach, which allows seamless simulation of different fluid-solid interactions, and its ability to handle arbitrary particle shapes, including irregular and concave geometries, while resolving surface interactions to capture local forces. In addition, its parallel scheme based on the lattice Boltzmann method (LBM) results in high computational efficiency, making it suitable for large-scale simulations, even though LBM requires small time steps. Important future development needs are identified, including the addition of a lubrication force correction model, performance enhancements, such as support for hybrid parallelization and GPU, and the extension of compatible contact models to accommodate concave shapes. These advances promise expanded capabilities for HLBM and broader applicability for solving complex real-world problems. Full article

Curved free shear layers emerge in many engineering problems involving complex flow geometries, such as the flow over a backward-facing step, flows with wall injection in a boundary layer, the flow inside side-dump combustors, or wakes generated by vertical axis wind turbines, among others. Previous studies involving centrifugal instabilities have mainly focused on wall-flows where Taylor instabilities between two rotating concentric cylinders or Görtler vortices in boundary layers are generated. Curved free shear layer flows, however, have not received sufficient attention, especially in the nonlinear regime. The present work investigates the development of centrifugal instabilities in a curved free shear layer flow in the nonlinear compressible regime. The compressible Navier–Stokes equations are reduced to the nonlinear boundary region equations (BREs) in a high Reynolds number asymptotic framework, wherein the streamwise wavelength of the disturbances is assumed to be much larger than the spanwise and wall-normal counterparts. We study the effect of the freestream Mach number $M_{\infty }$, the shear layer thickness $\delta$, the amplitude of the incoming disturbance A, and the relative velocity difference across the shear layer $\Delta V$ on the development of these centrifugal instabilities. Our parametric study shows that, among other things, the kinetic energy of the curved shear layer flow increases with increasing $\Delta V$ and A decreases with increasing $delta$. It was also found that increasing the disturbance amplitude of the incoming disturbance leads to significant growth in the mushroom-like structure’s amplitude and renders the secondary instability structures more prominent, indicating increased mixing for all Mach numbers under consideration. Full article

Plants in the genus Erysimum produce both glucosinolates and cardenolides as a defense mechanism against herbivory. Two natural isolates of Erysimum cheiranthoides (wormseed wallflower) differed in their glucosinolate content, cardenolide content, and their resistance to Myzus persicae (green peach aphid), a broad generalist herbivore. Both classes of defensive metabolites were produced constitutively and were not further induced by aphid feeding. To investigate the relative importance of glucosinolates and cardenolides in E. cheiranthoides defense, we generated an improved genome assembly, genetic map, and segregating F2 population. The genotypic and phenotypic analysis of the F2 plants identified quantitative trait loci, which affected glucosinolates and cardenolides, but not the aphid resistance. The abundance of most glucosinolates and cardenolides was positively correlated in the F2 population, indicating that similar processes regulate their biosynthesis and accumulation. Aphid reproduction was positively correlated with glucosinolate content. Although the overall cardenolide content had little effect on aphid growth and survival, there was a negative correlation between aphid reproduction and helveticoside abundance. However, this variation in defensive metabolites could not explain the differences in aphid growth on the two parental lines, suggesting that processes other than the abundance of glucosinolates and cardenolides have a predominant effect on aphid resistance in E. cheiranthoides. Full article

Wall-flow filters are applied in the exhaust treatment of internal combustion engines for the removal of particulate matter (PM). Over time, the pressure drop inside those filters increases due to the continuously introduced solid material, which forms PM deposition layers on the filter substrate. This leads to the necessity of regenerating the filter. During such a regeneration process, fragments of the PM layers can potentially rearrange inside single filter channels. This may lead to the formation of specific deposition patterns, which affect a filter’s pressure drop, its loading capacity and the separation efficiency. The dynamic formation process can still not consistently be attributed to specific influence factors, and appropriate calculation models that enable a quantification of respective factors do not exist. In the present work, the dynamic rearrangement process during the regeneration of a wall-flow filter channel is investigated. As a direct sequel to the investigation of a static deposition layer in a previous work, the present one additionally investigates the dynamic behaviour following the detachment of individual layer fragments as well as the formation of channel plugs. The goal of this work is the extension of the resolved particle methodology used in the previous work via a discrete method to treat particle–particle and particle–wall interactions in order to evaluate the influence of the deposition layer topology, PM properties and operating conditions on dynamic rearrangement events. It can be shown that a simple mean density methodology represents a reproducible way of determining a channel plug’s extent and its average density, which agrees well with values reported in literature. The sensitivities of relevant influence factors are revealed and their impact on the rearrangement process is quantified. This work contributes to the formulation of predictions on the formation of specific deposition patterns, which impact engine performance, fuel consumption and service life of wall-flow filters. Full article

The genus Ceutorhynchus Germar (Coleoptera: Curculionidae) is composed of canola pests, natural enemies of Brassicaceae, and other species associated with non-crop and non-weed plants. This study aimed to establish trophic associations of Ceutorhynchus with their host plants and with their parasitoids in the agricultural landscape, in order to assess the actual beneficial or noxious ecological roles of the insects. Trophic associations were established by identifying Ceutorhynchus species and their parasitoids emerging from collected Brassicaceae plants in areas adjacent to canola fields and other crops in 2019 and 2020. Five Ceutorhynchus species were collected and identified as hosts of parasitoids in the families Pteromalidae and Eulophidae. Two functional groups were characterized: natural enemies of weeds and agricultural pests. The exotic wormseed wallflower, Erysimum cheiranthoides was identified as a new host plant of the invasive canola pest Ceutorhynchus obstrictus (Marsham), and the native tower rockcress, Arabis glabra, as a new host plant of the native Ceutorhynchus neglectus Blatchley. Association between the exotic Ceutorhynchus typhae (Herbst) and a parasitoid of the genus Elachertodomyia is reported for the first time. Finally, Ceutorhynchus neglectus and C. typhae hosted the exotic parasitoid Trichomalus perfectus, an important natural enemy of C. obstrictus. Full article

Rearrangement events in wall-flow filters lead to the formation of specific deposition patterns, which affect a filter’s pressure drop, its loading capacity and the separation efficiency. A universal and consistent formulation of probable causes and influence factors does not exist and appropriate calculation models that enable a quantification of respective influence factors are missing. In this work, a previously developed lattice Boltzmann method, which has been used with inflow velocities of up to $2 {\mathrm{m} \mathrm{s}}^{-1}$, is applied to elevated velocities of up to $60 {\mathrm{m} \mathrm{s}}^{-1}$. The particle-free flow, a single layer fragment and a deposition layer during break-up are investigated as three different scenarios. One goal of this work is a comprehensive quantification of the stability and accuracy of both particle-free and particle-including flows, considering static, impermeable deposition-layer fragments. A second goal is the determination of the hydrodynamic surface forces and the deduction of the local detachment likelihood of individual layer fragments. Satisfactory stability and accuracy can be shown for fluid velocity, fluid pressure and the hydrodynamic forces. When considering layer fragments, the parameter domain turns out to be limited to inflow velocities of $28 {\mathrm{m} \mathrm{s}}^{-1}$. It is shown that fragment detachment rather occurs consecutively and regions of no possible detachment are identified. The work contributes to an understanding of rearrangement events and respective deposition pattern predictions and enables potential optimizations in engine performance, fuel consumption and the service life of wall-flow filters. Full article

The skin friction of a hypersonic vehicle surface can account for up to 50% of the total resistance, directly affecting the vehicle’s effective range and load. A wind tunnel experiment is an important and effective method to optimize the aerodynamic shape of aircraft, and Micro-Electromechanical System (MEMS) skin friction sensors are considered the promising sensors in hypersonic wind tunnel experiments, owing to their miniature size, high sensitivity, and stability. However, the sensitive structure including structural appearance, a gap with the package shell, and flatness of the sensor will change the measured flow field and cause the accurate measurement of friction resistance. Aiming at the influence of sensor-sensitive structure on wall-flow characteristics and friction measurement accuracy, the two-dimensional and three-dimensional numerical models of the sensor in the hypersonic flow field based on Computational Fluid Dynamics (CFD) are presented respectively in this work. The model of the sensor is verified by using the Blathius solution of two-dimensional laminar flow on a flat plate. The results show that the sensor model is in good agreement with the Blathius solution, and the error is less than 0.4%. Then, the influence rules of the sensitive structure of the sensor on friction measurement accuracy under turbulent flow and laminar flow conditions are systematically analyzed using 3D numerical models of the sensor, respectively. Finally, the sensor-sensitive unit structure’s design criterion is obtained to improve skin friction’s measurement accuracy. Full article

Wall-flow filters are a standard component in exhaust gas aftertreatment and have become indispensable in vehicles. Ash and soot particles generated during engine combustion are deposited in diesel or gasoline particulate filters. During regeneration, the soot particles are oxidized. The remaining ash particles can form different deposition patterns: a homogenous layer or plug-end filling. It has not yet been clarified whether the plug-end filling is first formed by rearrangements of agglomerates before and during the regeneration of the reactive particles. In this study, experiments are carried out with a single channel of a wall-flow filter. For the investigations, a layer of inert and reactive particles is formed. The rearrangement of agglomerates is achieved by flowing through the model filter channel and observed with a high-speed camera. The particulate structures detach at the channel inlet, are transported along the channel and deposited at the plug. The velocity of the detached agglomerates depends on their size, shape, track and the gas velocity in the channel. If the agglomerate is near the walls of the model filter channel, the gas velocity deviates from the gas velocity in the core flow. The higher the gas velocity, the higher the agglomerate velocity achieved and the larger the detached agglomerates. Full article

Soot-catalyst contact represents the main critical issue for an effective regeneration of catalytic (i.e., catalyst-coated) diesel particulate filters (DPFs). Most of the literature reviews on this topic have mainly been focused on studies dealing with powdered soot-catalyst mixtures. Although the results obtained on powders surely provide significant indications, especially in terms of intrinsic activity of materials towards soot oxidation, they cannot be directly extended to DPFs due to completely different soot-catalyst contact conditions generated during filtration and subsequent regeneration. In this work, attention is devoted to catalytic DPFs and, more specifically, studies on both catalyst dispersion and soot distribution inside the filter are critically reviewed from the perspective of soot-catalyst contact optimization. The main conclusion drawn from the literature analysis is that, in order to fully exploit the potential of catalytic DPFs in soot abatement, both a widespread and homogeneous presence of catalyst in the macro-pores of the filter walls and a suitably low soot load are needed. Under optimal soot-catalyst contact conditions, the consequent decrease in the temperature required for soot oxidation to values within the temperature range of diesel exhausts suggests the passage to a continuous functioning mode for catalytic filters with simultaneous filtration and regeneration, thus overcoming the drawbacks of periodic regeneration performed in current applications. Full article

The forthcoming implementation of the China VI emission regulations, which are currently the most stringent around the world targeted at light-duty gasoline engine vehicles, will not only further restrict the emissions of gaseous pollutants, but also put forward, for the first time, the requirements of particulate number (PN) emissions with a limit set at 6 × 10¹¹#/km. To achieve the stringent emission targets, the ceramic wall-flow gasoline particulate filter (GPF) will be effective to achieve the reduction of the particulate number tailpipe emissions in a way similar to the widely applied diesel particulate filter (DPF) in diesel engines. This paper investigated the effect of a coated gasoline particulate filter (GPF) on the PN emission and engine performance. The effects of two factors, including the washcoat powder material bulk density and type of coating, were studied with regard to three primary performances of GPF, including high three-way catalytic performance, low pressure drop, and high PN filtration efficiency, according to the original equipment manufacturer (OEM) requirements. The outcomes show that the use of high bulk density materials resulted in a low washcoat volume and hence a decrease of flow resistance and backpressure, in addition to high PN filtration efficiency. The type of coating had notable influence on the backpressure and PN filtration efficiency. The coating length and coating amount both had notable influence on the backpressure and PN filtration efficiency. Full article

To meet the increasingly strict emission limits imposed by regulations, internal combustion engines for transport applications require the urgent development of novel emission abatement systems. The introduction of biodiesel or other biofuels in the engine operation is considered to reduce greenhouse gas emissions. However, these alternative fuels can affect the performance of the post-combustion systems due to the variability they introduce in the exhaust particle distribution and their particular physical properties. Bioceramic materials made from vegetal waste are characterized by having an orthotropic hierarchical microstructure, which can be tailored in some way to optimize the filtration mechanisms as a function of the particle distribution of the combustion gases. Consequently, they can be good candidates to cope with the variability that new biofuel blends introduce in the engine operation. The objective of this work is to predict the filtration performance of a wall-flow particulate filter (DPF) made of biomorphic silicon carbide (bioSiC) with a systematic procedure that allows to eventually fit different fuel inputs. For this purpose; a well-validated DPF model available as commercial software has been chosen and adapted to the specific microstructural features of bioSiC. Fitting the specific filtration and permeability parameters of this biomaterial into the model; the filtration efficiency and pressure drop of the filter are predicted with sufficient accuracy during the loading test. The results obtained through this study show the potential of this novel DPF substrate; the material/microstructural design of which can be adapted through the selection of an optimum precursor. Full article

Diesel particulate filter is one of the most effective after-treatment techniques to reduce Particulate Matters (PM) emissions from a diesel engine, but the blocking Diesel Particulate Filter (DPF) will seriously affect the engine performance, so it is necessary to study the fault diagnosis of blocking DPF. In this paper, a simulation model of an R425DOHC diesel engine with wall-flow ceramic DPF was established, and then the model was verified with experimental data. On this basis, the fault diagnosis of the blocking DPF was studied by using spectral analysis on instantaneous exhaust pressure. The results showed that both the pre-DPF mean exhaust pressure and the characteristic frequency amplitude of instantaneous exhaust pressure can be used as characteristic parameters of monitoring the blockage fault of DPF, but it is difficult to monitor DPF blockage directly by instantaneous exhaust pressure. In terms of sensitivity, the characteristic frequency amplitude of instantaneous exhaust pressure is more suitable as a characteristic parameter to monitor DPF blockage than mean exhaust pressure. This work can lay an important theoretical foundation for the on-board diagnosis of DPF. Full article

Late fuel post-injections are the most usual strategy to reach high exhaust temperature for the active regeneration of diesel particulate filters. However, it is important to optimise these strategies in order to mitigate their negative effect on the engine fuel consumption. This work aims at understanding the influence of the post-injection parameters, such as its start of injection and its fuel quantity, on the duration of the regeneration event and the fuel consumption along it. For this purpose, a set of computational models are employed to figure out in a holistic way the involved phenomena in the interaction between the engine and the exhaust gas aftertreatment system. Firstly, an engine model is implemented to evaluate the effect of the late fuel post-injection pattern on the gas properties at the exhaust aftertreatment system inlet in different steady-state operating conditions. These are selected to provide representative boundary conditions of the exhaust gas flow concerning dwell time, exhaust temperature and ${\mathrm{O}}_2$ concentration. In this way, the results are later applied to the analysis of the diesel oxidation catalyst and wall-flow particulate filter responses. The dependence of the diesel particulate filter (DPF) inlet temperature is discussed based on the efficiency of each post-injection strategy to increase the exhaust gas temperature. Next, the influence on the dynamics of the regeneration of the post-injection parameters through the change in gas temperature and ${\mathrm{O}}_2$ concentration is finally studied distinguishing the pre-heating, maximum reactivity and late soot oxidation stages as well as the required fuel consumption to complete the regeneration process. Full article

We examine the time-dependent three-dimensional gas-particle flow in an intact wall-flow filter consisting of channels alternatively plugged at each end and a partially damaged filter in which the rear plugs are removed. Our focus is placed on highlighting the differences in the flow pattern and the deposition process between the two geometries. The Navier–Stokes equations are solved for the fluid flow coupled with a Brinkman/Forchheimmer model in order to simulate the flow in the porous walls and plugs. Discrete particle simulation is utilized to determine the nanoparticle trajectories. Using this scheme, we are able to characterize the main features of the flow fields developing in the intact and damaged filters with respect to the Reynolds number and identify those affecting the transport and deposition of particles that have three representative response times. We present fluid velocity iso-contours, which describe the flow regimes inside the channels, as well as in regions upstream and downstream of them. We provide evidence of local recirculating bubbles at the entrance of the channels and after their exit, whereas back-flow occurs in front of the rear plugs of the intact channels. We show that the flow leaves the channels as strong jets that may break up for certain flow parameters, leading to turbulence with features that depend on the presence of the rear plugs. The removal of the rear plugs affects the flow distribution, which, in turn influences the flow rates along the channels and through the walls. We describe the particle trajectories and the topology of deposited particles and show that particles follow closely the streamlines, which may cross the surface of permeable walls for both flow configurations. The distribution of deposited particles resembles the spatial variation of the through-wall flow rate, exhibiting two peak values at both ends of the intact filter channel, and one local maximum near the entrance of the damaged filter channel that is diminished at the exit. We also investigate in detail the particle deposition on the frontal face and indicate that particle accumulation at the edges of the entrance is favored for particles with low response times in flows with high fluid mass rates for both intact and damaged filters. Finally, we examine the filtration efficiency for the defective channels without rear plugs and show that fewer particles are captured as the Reynolds number is increased. A smaller reduction of the filtration efficiency is also predicted with increasing particle size. Full article