Orifice Axis Research Articles

Optical study on the single and multiple regions of flame propagation and combustion characteristics of methane/air mixture ignited by pilot diesel

The combustion characteristics of lean methane/air mixtures ignited by single and multiple diesel sprays were investigated using an optical RCEM test bench. The experimental approach included flame natural luminescence photography, pressure data acquisition, and heat release analysis. The results revealed that the relationships of ignition delay and orifice diameter varied under single diesel and dual fuel combustion mode. Under dual fuel mode, increasing the orifice diameter of the single-orifice nozzle resulted in a reduction in ignition delay, an acceleration in flame propagation, and an increase in the heat release rate. Increasing the number of orifices multiplied the flame regions, expanded the flame propagation pathways, and enhanced the promoting effect between the flames, resulting in faster flame propagation and increased heat release. The orifice axis angle significantly affected the ignition position and flame propagation direction. An appropriate axis angle would shorten the flame propagation distance, optimize the flame propagation direction and mitigate the impediment effect between flames.

Effect of key structure parameters of passive pre-chamber on in-cylinder combustion processes and emissions within a gasoline engine

Due to increasingly strict global emission regulations and energy conservation policies, gasoline engines are facing significant challenges. Achieving high efficiency and ultra-low emissions in gasoline engines has become a critical technical challenge that requires attention. Pre-chamber (PC) Turbulent Jet Ignition (TJI) is a highly promising technology for improving thermal efficiency and reducing emissions in gasoline engines. This study employs a three-dimensional flow simulation analysis combined with a detailed chemical reaction mechanism. The investigation is based on eight distinct passive PC structural configurations. The effects of various structural parameters, including the orifice number (ON), orifice axis angle (OAA), orifice diameter (OD), and volume ratio (VR), on the in-cylinder combustion process and emission characteristics are investigated, in which the formation of the fire nucleus and the propagation of the flame are intensively involved. The investigation is conducted under equivalence ratio working condition. Among these, the ITE of the best configuration is relatively 5.46% higher than the baseline engine. The combustion duration decreased by 55.95% to 7.4 °CA compared to the baseline engine, while particulate soot emissions also decreased by 51.22%.

Impingement Cooling by Multiple Asymmetric Orifice Jets

Abstract This study presents impingement cooling from a flat plate by multiple asymmetric jets. Such jets are discharged through blunt-edge inline orifice holes with a thickness-to-diameter ratio of t/Dj = 0.5 and a jet-to-jet spacing of T/Dj = 4.0, at the Reynolds number of 20,000. First, fluidic features are established both in free exit and with impingement, at varying short target spacing (e.g., H/Dj ≤ 4.0). Second, thermal characteristics of the jet impingement are elucidated. Results demonstrate that, due to a skewed incidence of the coolant stream upstream of concave orifice holes, the resulting multiple orifice jets are asymmetric and skewed relative to the orifice axis. These results mimic multiple fluidically inclined jets. However, asymmetric entrainment that takes place causes faster mixing with the surrounding fluid at rest as well as faster decay of momentum. This shows more effective cooling from a flat plate for the relatively short H/Dj range than conventional symmetric orifice and nozzle jets.

Near-Wall Velocimetry in the Impingement-Zones of a Microdroplet and a Round Jet Stream

Abstract Near-wall fluid velocimetry in the impingement zone of a microdroplet stream on a flat surface is reported utilizing microparticle tracking velocimetry (μPTV). The results are then compared with the near-wall fluid velocimetry in the impingement region of a steady microjet stream. The presence of tracer particles in the fluid results in a small random movement of the droplets away from the orifice axis, causing a change in the location of the droplet impingement center. A new method to find the center of impingement is described, and an algorithm is developed to obtain the radial velocities in the impingement zone at three out-of-plane heights of 2, 7, and 10 ± 2 μm from the wall. Single-frame double-exposed images of low loading fluorescent tracer particles are used for the experiments. As the impingement frequency of the droplet stream is much higher than the image-capturing rate of the camera, each double-exposed image corresponds to a random instance within the impingement period of the droplets. The presented results show the occurrence of a higher normalized root-mean-square along with positive skewness of the measured radial velocity values for the droplet stream. These indicate higher velocity fluctuations or fluid mixing characteristics induced by the droplet-crown propagation for the droplet stream when compared to that of a jet stream. The near-wall velocity measurements support previously reported observations of the enhanced convection heat transfer characteristics for a droplet stream case.

Acoustic and Flow Aspects of Novel Synthetic Jet Actuator

The acoustic and flow aspects of the novel synthetic jet actuator (SJA) with fins inside the cavity were experimentally investigated for three types of enclosure design and two models of loudspeaker. The aim of the study is to find the parameter which connects the flow and acoustic properties of the SJA and allows us to choose the optimal solution in those regards. The hot wire anemometry was used for the velocity measurements and the sound pressure level was measured with a sound level meter. The model of the loudspeaker turned out to have a significantly stronger impact on the flow parameters and noise level than the shape of the fins in the cavity. The parameter that showed a dependence on the shape of the fins was the actuator’s efficiency. A ratio of the root-mean-square velocity at the orifice axis to the sound pressure level (U0.c/SPL) was used to connect the acoustic and flow properties of the tested actuators. This parameter was subsequently applied to determine the best configuration among the tested actuators.

Experimental Investigation of the Self-Ignition and Jet Flame of Hydrogen Jets Released under Different Conditions

Hydrogen is a promising clean energy source and an important chemical raw material. To use hydrogen energy more safely, a high-pressure hydrogen-release platform for hydrogen self-ignition and for generating hydrogen jet flames under different experimental conditions was investigated in this study. The associated experimental analysis was based on the theory of high-pressure hydrogen tube diffusion. We found that the higher the initial release pressure, the greater the intensity of the leading shock. When the initial release pressure was high and the leading shock intensity was strong, hydrogen was more likely to ignite spontaneously inside the tube. The higher the initial release pressure, the faster the average propagation speed of the shock in the same pipe length. The time during which a stable leading shock was formed inside the tube may be related to the initial release pressure. It was found that flame combustion intensified after the passage of air through a Mach disk, and a stable flame was formed more easily at the jet boundary layer away from the orifice axis. The maximum speed of the flame tip and the flame decay speed were very high. Moreover, the flame length and the diameter of the ball flame first increased and then decreased.

A zero-net-mass-flux actuator for unmanned underwater vehicles

A set of water tunnel experiments were conducted to establish the viability of a zero-net-mass-flux actuator as a maneuvering mechanism for unmanned underwater vehicles. The actuator, which consisted of a solenoid driving a piston in a cylindrical cavity, was enclosed in a streamlined model vehicle. The forces and moments on the model vehicle were measured by a six-axis load cell connected to the model through a sting. The actuator whose orifice axis was oriented perpendicular to the freestream was located near the aft end of the model. The time averaged thrust was measured for actuator frequencies up to 24 Hz and freestream velocities up to 8 m/s. In absence of freestream flow, scaling arguments indicate that the average thrust increases linearly with the actuator frequency, expelled mass and a characteristic expulsion velocity. The linear frequency dependence was verified experimentally up to a limit imposed by the solenoid response time. Thrust decreased linearly with increasing freestream velocity for values up to the characteristic velocity of actuator. An expression was developed for the time averaged thrust as a function of the actuator design, operating parameters, and freestream velocity.

Optimization of the shape and size of seed plate orifice for accurate single seed planting of the crops

The shape and size of seed plate orifice were decided on the basis of the dimensions of the different seeds. For all the seeds, the shape of the seed plate orifice showed its effect upon the planting accuracy. For cotton, groundnut and sesame seeds, best results were found with elliptical shaped orifice, with longer and shorter axis (5, 4.50), (3, 2.50) and (1.50, 1) mm, respectively. Whereas, for okra seed, the optimum seed plate orifice shape was circular with 3 mm diameter. For positive release of the sesame seed, air velocity of 3 m/s through chamber open to atmosphere showed best results.

On the behaviour of impinging zero-net-mass-flux jets

This paper reports on an experimental study of the influence of the Strouhal number (0.011, 0.022 and 0.044) and orifice-to-plate distances (2, 4 and 6 orifice diameters) on the flow field of an impinging zero-net-mass-flux jet at a Reynolds number equal to 35 000. These jets are generated by a reciprocating piston that oscillates in a cavity behind a circular orifice. Instantaneous two-dimensional in-plane velocity fields are measured in a plane containing the orifice axis using multigrid/multipass cross-correlation digital particle image velocimetry. These measurements have been used to investigate the mean flow quantities and turbulent statistics of the impinging zero-net-mass-flux jets. In addition, the vortex ring behaviour is analysed via its trajectory and azimuthal vorticity as well as the saddle point excursion, the flow rate and entrainment. The behaviour of all these quantities depends on the Strouhal number and the orifice-to-plate distance because the former governs the presence and the relative importance of the vortex ring and the trailing jet on the flow field and the latter delimits the downstream evolution of these structures.

Development and application of an automatic measurement method for nozzle orifice diameter and length

Diesel sprays are important to engine combustion and emission formation processes, however, their behaviors are difficult to predict as they are very sensitive to the internal geometries of the nozzle. Based on synchrotron radiation X-ray tomography, a novel method is presented for measuring automatically the orifice diameter and length of fuel nozzles. According to this method, a clear definition of orifice inlet and outlet is given, and the diameters along the orifice from inlet to outlet as well as the orifice length can be measured. Measurements of a single-hole nozzle and an eight-hole nozzle have been performed accordingly. The results show that this method can automatically measure the orifice diameters from outlet to inlet along the whole orifice axis with relatively high precision, regardless of whether it is a single-hole or a multi-hole nozzle. The profile of the diameters obtained shows the differences between the nominal dimensions and the actual ones, which gives a more precise feedback for nozzle manufacture, and provides a new basis for precisely studying the impacts of internal geometries on spray behavior.

New method for measuring diesel nozzle orif ice inlet structures based on synchrotron X-ray tomography

Spray behavior is regarded as one of the main factors influencing engine performances, fuel consumption and emissions for diesel engines. Under high injection pressure, diesel spray behaviors are extremely sensitive to the nozzle internal geometries, especially the geometric structures of orifice entrance. Based on the synchrotron radiation X-ray tomography technique, the 3D digital models of nozzle tips can be constructed. A new automatic method is presented to reveal the inlet structures according to these nozzle orifice models. The planes passing through the orifice axis are determined and used to cut the models, and then the corresponding cutting images are applied to measure the inlet chamfer radii around the orifice axis automatically. The orifices of a single-hole nozzle and an eight-hole nozzle are measured according to this method. The results show that this method can automatically measure the orifice inlet chamfer radii around the orifice axis with high precision. The obtained inlet chamfer radius shows the whole profile of the orifice entrance, which is a precise feedback for nozzle designing and manufacturing, and it also provides precise geometrical boundary conditions for the study of spray behaviors.

Salvage Endoscopic Correction of High-Grade Vesicoureteral Reflux After Unsuccessful Cross-Trigonal Ureteral Reimplantation

Introduction: Persistent vesicoureteral reflux (VUR) after reimplantation of ureters requiring reoperation has been reported in up to 7.5% of cases. This video demonstrated a successful endoscopic salvage option for correction of persistent, high-grade VUR after a bilateral cross-trigonal ureteral reimplantation. Methods: A 19-month-old female with a double collecting system and a ureterocele underwent a Cohen cross-trigonal ureteral common sheath reimplantation. A year later, she presented with persisting right-sided grade 5 VUR. We corrected her reflux with salvage endoscopic injection of dextranomer/hyaluronic Acid (Dx/HA). Results: The major challenge in this case was the ureteral orifice axis post-Cohen cross-trigonal ureteral reimplantation, which was nearly perpendicular to the axis of the urethra-cystoscope axis. We used a 4F whistle-tip catheter, which was inserted into the right ureter. The rigidity of this catheter allowed us to torque the ureter to reduce the angulation and allowed the cystoscope to be inserted into the dilated refluxing ureter. Four injections of Dx/HA were performed in the intramural part of the ureter and one at the ureteral orifice location. A final injection was placed below the ureteral tunnel just proximal to the orifice. A voiding cystourethrogram three months postimplantation confirmed the resolution of the reflux. Conclusion: This video demonstrated a successful endoscopic salvage option for correction of persistent, high-grade VUR after a bilateral cross-trigonal ureteral reimplantation. We recommend using a ureteric catheter to align the reimplanted ureter with the urethra-cystoscope axis, followed by insertion of the cystoscope into the ureter for the first intramural injection of Dx/HA. No competing financial interests exist. Runtime of video: 7 mins 54 secs

Lateral Orifice of Prussak's Space Assessed With a High-Resolution Cone Beam 3-Dimensional Computed Tomography

To describe how to obtain high-resolution computed tomography (CT) images of the en face view of the lateral orifice of Prussak's space (Ps orifice) and tympanic ring and to investigate the shape and size of these structures in normal ears and in those with chronic otitis media and attic cholesteatoma. University-affiliated referral center. Using the Accuitomo image reconstruction algorithm, the slope of the eardrum was turned to vertical on both coronal and axial images. A sagittal slice view at the eardrum gave the en face view of the eardrum. The width and height of the Ps orifice and vertical axis of the tympanic ring were measured with an automatic measuring device. In the normal Ps orifice, the height is less than 1.30 mm, and the width is less than 2.63 mm. The height and width in the Ps orifice with attic cholesteatoma were significantly larger than those in normal ears and in ears with COM (p < 0.01). In the ears with COM, the width and height on average seemed larger than normal, but no significant difference was verified. The vertical axis of the tympanic ring was unaffected by the diseases. CT imaging of the en face view of the Ps orifice obtained by the present method is useful as an objective measure to assess bone destruction at the Ps orifice, a scutum defect, in ears with COM and attic cholesteatoma.

The evolution of round zero-net-mass-flux jets

This paper reports on an experimental investigation to determine the structure and mean flow quantities of round zero-net-mass-flux (ZNMF) jets. These jets are generated by a piston oscillating in a cavity behind a circular orifice. Several different flow patterns were observed with dye flow visualization and a parameter map of these was generated. Cross-correlation digital particle image velocimetry was used to measure instantaneous two-dimensional in-plane velocity fields in a plane containing the orifice axis. These velocity fields are used to investigate the existence of a self-preserving velocity profile in the far field of the ZNMF jet. The mean flow quantities and turbulent statistics of the ZNMF jets were compared with measurements for ‘equivalent’ continuous jets in the same apparatus. Phase-averaged velocity measurements were obtained in the near field of the ZNMF jets and were used to determine the radial entrainment. The out-of-plane vorticity fields were also investigated to gain an understanding of the mechanisms responsible for the difference in spreading rate of ZNMF jets compared to conventional continuous jets. A conceptual model of the ZNMF jet structure in the near field for Strouhal numbers much less than one is proposed that explains the observed behaviour of these ZNMF jets.

Human head model as an aerosol sampler: Calculation of aspiration efficiencies for coarse particles using an idealized human head model facing the wind

Theoretical quantification of the entry of coarse particles to the human mouth or nose under different inhalation rates and ambient wind velocities is an important topic in understanding inhalability, in extrapolating empirical results and designing inhalable aerosol samplers. Using an idealized human head model facing the wind and potential flow approximation for the velocity fields, coarse particle aspiration efficiencies were calculated for a set of inhalation and external fluid motion parameters. The inhalation parameters are orifice size, the frequency and the tidal volume of breathing which depend upon the level of exertion assumed as well as interpersonal variabilities. The external fluid motion parameters are introduced by the fluid motion external to the head and the orientation of the orifice axis with respect to the flow axis. The total velocity field was modeled by superimposing the velocity field generated by breathing onto the external velocity field generated by an ambient wind. In this three-dimensional velocity field around the idealized human head figure, the particle equations of motion for coarse particles result in a set of coupled ordinary differential equations. The numerical solution of this set can be used to obtain particle trajectories and particle aspiration efficiency. The aspiration efficiency calculation for 25–200 μm particle aerodynamic equivalent diameters, for tidal volumes of 750, 1450, 2250 cm 3 and for 0.5–9 m/s ambient wind speed conform to the main trends observed in the experimental studies. Thus they may be used to extrapolate the experimental findings. Most importantly, the calculations did not suggest an evidence of zero aspiration efficiency (cutoff) for aerodynamic equivalent diameters up to 200 μm for the range of inhalation and external fluid motion parameters examined.

The three-dimensional hydrodynamic interaction of a finite sphere with a circular orifice at low Reynolds number

This paper proposes a combined multipole-series representation and integral-equation method for solving the low-Reynolds-number hydrodynamic interaction of a finite sphere at the entrance of a circular orifice. This method combines the flexibility of the intergral-equation method in treating complicated geometries and the accuracy and computational efficiency of the multipole-series-representation technique. For the axisymmetric case, the hydrodynamic force has been solved for the difficult case where the sphere intersects the plane of the orifice opening, which could not be treated by previous methods. For the three-dimensional case, the first numerical solutions have been obtained for the spatial variation of the twelve force and torque correction factors describing the translation or rotation of the sphere in a quiescent fluid at a pore entrance or the Sampson flow past a fixed sphere. Restricted by excessive computation time, accurate three-dimensional solutions are presented only for a sphere which is one-half the orifice diameter. However, based on an analysis of the behaviour of the force and torque correction factors for this case, approximate interpolation formulas utilizing the results on or near the orifice axis and in the far field are proposed for other diameter ratios, thus greatly extending the usefulness of the present solution.

Pulse shapes from particles traversing Coulter orifice fields

A jet 'directer' is described which permits particles to be directed along selected trajectories through a Coulter orifice. The resulting current waveshapes are seen to be characteristics of the paths taken by the particles. No evidence of the effect of the motion of charged particles on the waveshapes was detected which supports the theoretical prediction of the small magnitude of this effect. The waveshapes from known paths, when examined in the light of measured or calculated electric fields in these orifices, support a direct relationship between the resistive component of the instantaneous current amplitude and the magnitude of the local electric field at the position of the particle. In short Coulter orifices a region of uniform axial electric field is found midway between the orifice axis and the edge. Neither the axis nor the edge has regions of axial uniformity. Only spheres sized while traversing the region of uniform field will produce a true size distribution in these short orifices.

Electrical Sizing of Particles in Suspensions: III. Rigid Spheroids and Red Blood Cells

The processes involved during the passage of a suspended particle through a small cylindrical orifice across which exists an electric field are investigated experimentally for an approximate prolate spheroid in the form of two tangent, rigid spheres (ragweed pollen particles) and for fresh, human red blood cells. Oscillograms of current pulses produced by both types of particles are presented and discussed in terms of particle shape and orientation and the effects of the hydrodynamic field. It is concluded that all the particles enter the orifice with their major axes aligned parallel to the orifice axis (electric field), but that during their passage some are rotated by the hydrodynamic field. Cells with their equatorial plane perpendicular to a radius of the orifice change their orientation with respect to the electric field as they are rotated, the others do not; only in the former case is there any deformation. It is shown that the bimodal or skewed size distributions can be explained on this basis, and that size (shape factor x volume) is actually a normally distributed variable (P > 95%). The average size of samples from 10 healthy adults was found to be 102.7 mu(3) with a coefficient of variation of 1.8%. For a volume of 87 mu(3), this corresponds to a shape factor of 1.18, an axial ratio (assuming a perfect oblate spheroid) of 0.26, and an equivalent major axis of 8.6 mu. The effect of high electric fields on red cell size distributions is mentioned.

Electrical Sizing of Particles in Suspensions: I. Theory

The processes involved during the passage of a suspended particle through a small cylindrical orifice across which exists an electric field are considered in detail. Expressions are derived for the resulting change in current in terms of the ratios of particle to orifice volume and particle to suspending fluid resistivity, and particle shape. Graphs are presented of the electric field and of the fluid velocity as functions of position within the orifice, and of the shape factor of spheroids as a function of their axial ratio and orientation in the electric field. The effects of the electric and hydrodynamic fields on the orientation of nonspherical particles and on the deformation of nonrigid spheres is treated, and the migration of particles towards the orifice axis is discussed. Oscillograms of current pulses produced by rigid, nonconducting spheres in various orifices are shown and compared with the theoretical predictions.

Influence of the eccentric nozzle orifice position on the spray pattern and droplet size

The influence of the orifice displacement in a swirl spraying nozzle has been theoretically calculated and experimentally investigated. It is shown that a very small displacement of the orifice axis off centre of the fluid vortex leads to considerable deformation of the droplet cone and an explicit increase of droplet size.