Jet Formations Research Articles

Impact of Passive Pre-Chamber Nozzle Diameter on Jet Formation Patterns and Dilution Tolerance in a Constant-Volume Optical Engine

<div>Pre-chamber jet ignition technologies have been garnering significant interest in the internal combustion engine field, given their potential to deliver shorter burn durations, increased combustion stability, and improved dilution tolerance. However, a clear understanding of the relationship between pre-chamber geometry, operating condition, jet formation, and engine performance in light-duty gasoline injection engines remains under-explored. Moreover, research specifically focusing on high dilution levels and passive pre-chambers with optical accessibility is notably scarce. This study serves to bridge these knowledge gaps by examining the influence of passive pre-chamber nozzle diameter and dilution level on jet formation and engine performance. Utilizing a modified constant-volume gasoline direct injection engine with an optically accessible piston, we tested three passive pre-chambers with nozzle diameters of 1.2, 1.4, and 1.6 mm, while nitrogen dilution varied from 0 to 20%. With the help of high-speed imaging, we captured pre-chamber jet formations and subsequent flame propagation within the main chamber. Our novel findings reveal that asymmetric temporal and spatial jet formation patterns arising from pre-chambers significantly impact engine performance. The larger-nozzle-diameter pre-chambers exhibited the least variation in jet formation due to their improved scavenging and main mixture filling processes, but had the slowest jet velocity and lowest jet penetration depth. At no dilution condition, the 1.2 mm-PC demonstrated superior performance attributed to higher pressure build-up in the pre-chamber, resulting in accelerated jet velocity and increased jet penetration depth. However, at high dilution condition, the 1.6 mm-PC performed better, highlighting the importance of scavenging and symmetry jet formation. This study emphasizes the importance of carefully selecting the pre-chamber nozzle diameter, based on the engine’s operating conditions, to achieve an optimal and balanced configuration that can improve both jet formation and jet characteristics, as well as scavenging.</div>

Impact of bulk viscosity on flow morphology of shock-accelerated cylindrical light bubble in diatomic and polyatomic gases

Shock-accelerated bubbles have long been an intriguing topic for understanding the fundamental physics of turbulence generation and mixing caused by the Richtmyer–Meshkov instability. In this study, the impact of bulk viscosity on the flow morphology of a shock-accelerated cylindrical light bubble in diatomic and polyatomic gases is investigated numerically. An explicit mixed-type modal discontinuous Galerkin scheme with uniform meshes is employed to solve a two-dimensional system of unsteady physical conservation laws derived rigorously from the Boltzmann–Curtiss kinetic equations. We also derive a new complete viscous compressible vorticity transport equation including the bulk viscosity. The numerical results show that, during the interaction between a planar shock wave and a cylindrical light bubble, the bulk viscosity associated with the viscous excess normal stress in diatomic and polyatomic gases plays an important role. The diatomic and polyatomic gases cause significant changes in flow morphology, resulting in complex wave patterns, vorticity generation, vortex formation, and bubble deformation. In contrast to monatomic gases, diatomic and polyatomic gases produce larger rolled-up vortex chains, various inward jet formations, and large mixing zones with strong, large-scale expansion. The effects of diatomic and polyatomic gases are explored in detail through phenomena such as the vorticity generation, degree of nonequilibrium, enstrophy, and dissipation rate. Furthermore, the evolution of the shock trajectories and interface features is investigated. Finally, the effects of bulk viscosity on the flow physics of shock-accelerated cylindrical light bubble are comprehensively analyzed.

Morphological peculiarities of flowers, pollen grains and fruits of Valeriana tuberosa (Valerianaceae)

The results of the study of flowers, pollen grains and fruits of Valeriana tuberosa (sect. Tuberosae, Valerianaceae) are presented. Materials of the National Herbarium of the M.G. Kholodny Institute of Botany, National Academy of Sciences of Ukraine (KW) were studied. The morphological structures of flowers, pollen grains and fruits were examined using both light microscopy and scanning electron microscopy; detailed descriptions of the elements of the flower, pollen grains and fruits were made and their specific features were established. The morphological features of the inflorescence, bracteoles, and the elements of the hermaphrodite flowers have been clarified. The pollen grains of V. tuberosa are 3-colpate, suboblate to subprolate (P/E = 0.85–1.33), medium- or large-sized. Their outline in equatorial view is elliptic, rarely circular, in polar view slightly trilobate or trilobate. Exine sculpture is echinate-microechinate with verrucae. The known and new carpological features are specified. In particular, papillate growth of periclinal walls of exocarp with stroke-shaped, jet and warty cuticular formations of the surface were noted the first time; details of exocarp stomatal system were revealed; features of trichomes and their cuticular structure on fruit wall are described. The obtained data are important additional characters for identification of the species and for the issues of taxonomy and phylogeny.

An experimental study of cavity and Worthington jet formations caused by a falling sphere into an oil film on water

In this paper, air cavity and Worthington jet formations due to the entrance of a hydrophilic steel sphere into three different target liquids are studied. The liquids are water, silicone oil and silicone oil film on water. A high-speed camera is used to observe cavity and jet formations, and the resulting data is used to measure important parameters such as jet height, deep-seal time and deep-seal depth of the cavity. It was observed that no cavity forms after a hydrophilic sphere enters water. However, when a very thin layer of silicone oil is put on the water surface, a large air cavity and Worthington jet were observed. The results observed did not strongly vary with oil film thickness for the range studied in this work, and that as long as there is a layer of oil on water that wets the sphere surface before its entrance, an air cavity and jet will form. Additionally, an energy analysis is done for better understanding how kinetic energy of the sphere is transferred to the fluid. In the case of an oil film on water, the sphere lost its kinetic energy much more than when the target liquid was silicone oil or water. As a result, the fluid gained a significant amount of energy to form an air cavity which did not happen without oil film, and a Worthington jet of greater maximum height than the other two cases. Kinetic, surface and potential energies of the Worthington jet as it forms and reaches its peak are studied as well.

Nonlinear Spatial Localized Strain Waves

A possible way of study of single waves in solids is discussed. The soliton is one of these waves without shape and parameters varying. Soliton deformation parameters are connected with the elastic moduli of the third order that allows defining values of these moduli by means of the measured solitondeformation parameters in various type waveguides made of the same material. The conditions under which a soliton can exist in a rod are analytically determined. For simultaneous excitation of loading in several wave guides two new energetic photosensitive structures (the mixtures are given) initiated by means of short light impulses of noncoherent light sources are proposed. Conditions of excitation of the waves on the basis of multipoint optical initiation loading impulses are described. As a technique for registration the shadowgraph visualization is proposed. It is discussed, how the problem connected to the use of energetic initiation structures consisting in the power background illumination can be solved. The shadow scheme with the use of a tiny dot explosive light source (Tbr ~41 kK) allows to carry out modelling experiments on research of slabbing actions, jet formations, fluffings, hydrodynamic instability during shock-wave loading of investigated samples, which makes it attractive for determination of parameters in equations-of-state for investigated materials, creation of numerical models and their validation. Some examples showing basic possibility of application of the declared techniques are included.

Jet Formation and Penetration Study of Double-Layer Shaped Charge

ABSTRACTA theoretical analysis on detonation wave propagation in a double-layer shaped charge (DLSC) is performed. Numerical simulations using the AUTODYN software are carried out to compare the distinctions between jet formations in DLSC and ordinary shaped charge (OSC), in particular, the OSC made using a higher detonation velocity explosive, which is treated as the outer layer charge in the DLSC. The results show that the improved detonation velocity ratio and radial charge percentage of outer-to-inner layer charge are conducive to the formation of a convergent detonation wave, which contributes to enhancement of jet tip velocity in DLSC. The thickness and mass percentages of liner flowing into jet in DLSC closely follow the exponential distribution along the radial direction, but the percentages in DLSC and the mass of effective jet, which have significant influence on the penetration depth, are lower than those in OSC with the outer layer charge. This implies that the total charge energy is the major factor controlling the effective jet formation, which is confirmed by the verification tests using flash X-ray system and following penetration tests. The numerical simulation and test results compare well, while penetration test results indicate that the performance of DLSC is not better than that of OSC with the outer layer charge, due to the differences in jet formation.

Numerical Simulation of Steel Target Penetration by Shaped Charge Distended Jet with a High-Polymer Liner

This study investigates the characteristics of shaped charge jet formed with a high-polymer (PTFE) liner, as well as its penetration capabilities, by theoretical, experimental, and numerical methods. This work presents a viscoplastic model and equation of compressible fluid to describe the jet cohesive condition. It also shows that the high-polymer jet is inevitably distended. Two types of liner materials were studied: a high-polymer PTFE liner and a pure copper one. The corresponding numerical simulations of the two jet formations are presented. The pulse X-ray photographic technology was employed to observe the distended jet of the PTFE liner and the particulate jet of the copper one. The simulation and jet radiography results show that the two types of jet behavior with particulate and radial dispersion are ductile and related to the liner material. The distended jet formation result from the liner material was crushed at the high-pressure region because a sudden pressure jump induces the radial velocity rise, which results in lateral expansion. As compared with a typical copper penetration performance, the polymer distended jet had a larger aperture and lower penetration depth. Due to polymer liner lower density, this jet will have limited penetration as compared to that of a copper liner. The simulated results strongly agree with the experimental ones. The polymer material can be modified to obtain much better performance, which will greatly enhance the penetration capacity of polymer jets.

Some Possibilities of Hypercumulative Regime of Jet Formations

Basic physical problems of jet formation process on the basis of Lavrentiev-Birkhoff classical scheme are analyzed. It is shown that in process of realization of hypercumulation conditions for jet formation without complete stagnation point involving formation of the inner zone of constant pressure (dead zone), the flow mass is always greater than slug mass, that is unachievable in the known models. Smoothing effect of this zone on the development of different types disturbances, particularly, smoothing Rayleigh-Taylor instability for thin liner may be expected and shown in simulations.

AB0827-HPR Alexithymia phenomenon in systemic sclerosis patients

ObjectivesOur aim was to study the phenomenon of alexithymia – a special mental quality of psychosomatic personality in systemic sclerosis patients.MethodsWe observed 54 patients suffering from systemic sclerosis (SS) using...

The 11 March 2011 East Japan Earthquake and Tsunami: Tsunami Effects on Coastal Infrastructure and Buildings

The 11 March 2011 East Japan Earthquake and Tsunami caused unprecedented damage to well-engineered buildings and coastal structures. This report presents some notable field observations of structural damage based on our surveys conducted along the Sanriku coast in April and June 2011. Engineered reinforced concrete buildings failed by rotation due to the high-velocity and deep tsunami inundation: entrapped air in the buildings and soil liquefaction by ground shaking could have contributed to the failure. The spatial distribution pattern of destroyed and survived buildings indicates that the strength of tsunami was affected significantly by the locations of well-engineered sturdy buildings: weaker buildings in the shadow zone tended to survive while jet and wake formations behind the sturdy buildings enhanced the tsunami forces. We also found that buildings with breakaway walls or breakaway windows/doors remained standing even if the surrounding buildings were washed away or destroyed. Several failure patterns of coastal structures (seawalls) were observed. Flow-induced suction pressure near the seawall crown could have caused the failure of concrete panels that covered the infill. Remarkable destruction of upright solid-concrete type seawalls was closely related with the tsunami induced scour and soil instability. The rapid decrease in inundation depth during the return-flow phase caused soil fluidization down to a substantial depth. This mechanism explains severely undermined roads and foundations observed in the area of low flow velocities.

Simulation Study on Characteristics of the Vortex Structure in Human Mouth-throat Model in Cyclic Respiratory Pattern

The research on vortex structure and vortex evolution in human upper respiratory tract can deepen understanding of the characteristics of the airflow in human upper respiratory tract and plays a very important role in analyzing the diffusion, transition and deposition patterns of aerosol in human upper respiratory tract. Large eddy simulation was used to simulate the vortex structure and vortex movement in human mouth-throat model in cyclic respiratory pattern, and the vortex structure and vortex evolution in mouth-throat model was discussed. The results show that jet formations in pharynx and laryngeal lead to two vorticity growth regions at cyclic inhalation flow, flat vortex appeared in the throat, a curved vortex like the trachea wall appeared in the anterior wall of trachea, and nearly symmetric reverse vortex pairs appeared in the trachea; a vortex like “3” appeared in the posterior wall of the throat, two curved vortexes like eyebrow appeared in the posterior wall of the pharynx.

Direct numerical simulation of collective bubble behavior

The present paper studied the nonlinear collective bubble behavior using direct numerical simulation (DNS) coupled with front tracking method. The bubbles inside cloud are deformable according to surrounding environment. The effects of viscosity and bubble-bubble interaction have been considered in the simulations. Response of bubble cloud with large void fraction (1%–25%) to continuous pressure wave with finite amplitudes has been simulated. A collective bubble behavior and associated pressure oscillation have been revealed from the simulations. Strong shape oscillations including jet formations of bubbles have also been observed when a strong pressure wave is passing through the bubble cloud.

Effect of waterjet formation on surface preparation and profiling of aluminum alloy

Three types of waterjet formations were used in this study to evaluate their effects on surface characteristics of a 6061-T6 aluminum alloy. The jet formations were made by using fan jet, fuzzy jet, and round jet nozzles. Surfaces preparation resulting from these types of jet impingements were evaluated using surface profilometry, scanning electron and optical microscopy. Surface characteristics in terms of surface texture on treated specimens in relation to process conditions were analyzed and discussed. It was found that the fan jet produces more homogenous surfaces than the round jet when the surfaces are compared under the same process conditions. However, at lower jet pressure and velocity conditions, the use of the fuzzy jet is found to produce surfaces similar to those of the fan jet.

Morphological Study of Cavity and Worthington Jet Formations for Newtonian and Non-Newtonian Liquids

In this article a morphological study of the cavity formation and the liquid column formation of the Worthington jet with lapse of time for the Newtonian liquids of water and glycerine wt 70% solution and for non-Newtonian liquids of acrylic copolymer solution of ACA-wt1%, ACA-wt2%, and ACA-wt3% by a droplet falling to the free surface of the target liquid in the cylindrical container from a height of H = 100, 200, 300, 400, and 500 mm is described. The calculated results by the energy equation for the maximum cavity radius Rmax/d and for the morphological size D · h/d2 of the Worthington jet are in agreement with the experimental results. In order to take photographs of the cavity formation and the Worthington jet formation with lapse of time, a CCD camera was used. The falling droplet and the target liquid are the same material. Here d is the mean diameter of the droplet and D and h are the mean diameter and maximum height of the liquid column of the Worthington jet.

Possible Periodic Components in the Flickering of CH Cyg and MWC 560

CH Cyg and MWC 560 are very peculiar symbiotic binaries consisting of an M giant and a white dwarf companion. The systems have many features in common. In particular, both show occasional eruptions with sub-Eddington luminosity, followed by the appearance of high-velocity jets. Recently, Mikołajewski, Mikołajewska & Tomov (1995) have proposed a model of activity for these systems with a rapidly rotating magnetic white dwarf accreting from the M giant’s wind. Two states of activity are possible: propeller and accretor. Although, both stars spend most time in the propeller state, occasional propeller-accretor (and vice versa) transitions may give rise to bipolar outflows and rapid jet formations. Mikołajewski et al. (1995) also proposed to distinguish a new subclass of interacting binaries – propeller stars – with CH Cyg and MWC 560 being the prototypes.