scholarly journals Combined visualisation of cavitation and vortical structures in a real-size optical diesel injector

2020 ◽  
Vol 62 (1) ◽  
Author(s):  
I. K. Karathanassis ◽  
J. Hwang ◽  
P. Koukouvinis ◽  
L. Pickett ◽  
M. Gavaises
Keyword(s):  
High Speed ◽  
Cone Angle ◽  
Frame Rate ◽  
Flow Visualisation ◽  
Fuel Injector ◽  
Two Phase ◽  
Vortical Structures ◽  
Flow Motion ◽  
Real Size ◽  
Set Up

Abstract A high-speed flow visualisation set-up comprising of combined diffuse backlight illumination (DBI) and schlieren imaging has been developed to illustrate the highly transient, two-phase flow arising in a real-size optical fuel injector. The different illumination nature of the two techniques, diffuse and parallel light respectively, allows for the capturing of refractive-index gradients due to the presence of both interfaces and density gradients within the orifice. Hence, the onset of cavitation and secondary-flow motion within the sac and injector hole can be concurrently visualised. Experiments were conducted utilising a diesel injector fitted with a single-hole transparent tip (ECN spray D) at injection pressures of 700–900 bar and ambient pressures in the range of 1–20 bar. High-speed DBI images obtained at 100,000 fps revealed that the orifice, due to its tapered layout, is mildly cavitating with relatively constant cavity sheets arising mainly in regions of manufacturing imperfections. Nevertheless, schlieren images obtained at the same frame rate demonstrated that a multitude of vortices with short lifetimes arise at different scales in the sac and nozzle regions during the entire duration of the injection cycle but the vortices do not necessarily result in phase change. The magnitude and exact location of coherent vortical structures have a measurable influence on the dynamics of the spray emerging downstream the injector outlet, leading to distinct differences in the variation of its cone angle depending on the injection and ambient pressures examined. Graphic abstract

scholarly journals Experimental Investigation of the Performance and Spray Characteristics of a Supersonic Two-Phase Flow Ejector with Different Structures

Energies ◽  
2020 ◽  
Vol 13 (5) ◽  
pp. 1166 ◽  
Author(s):  
Shizhen Li ◽  
Wei Li ◽  
Yanjun Liu ◽  
Chen Ji ◽  
Jingzhi Zhang
Keyword(s):  
High Speed ◽  
Two Phase Flow ◽  
Fire Suppression ◽  
Cone Angle ◽  
Water Mist ◽  
Pulsation Period ◽  
Phase Flow ◽  
Two Phase ◽  
Half Cone ◽  
Half Cone Angle

A two-phase flow ejector is an important part of a water mist fire suppression system, and these devices have become a popular research topic in recent years. This paper proposes a supersonic ejector that aims to improve the efficiency of water mist fire suppression systems. The effects of ejector geometric parameters on the entrainment ratio (ER) were explored. The effects of primary flow pressure (PP) on the mixing process and flow phenomena were studied by a high-speed camera. The experimental results show that the ER first increases and then decreases with increasing PP. ER increases with increasing ejector area ratio (AR). The PP corresponding to the maximum ER of ejectors with a different nozzle exit position (NXP) is 3.6 bar. The ejector with an NXP of +1 and AR of 6 demonstrate the best performance, and the ER of this ejector reaches 36.29. The spray half-cone angle of the ejector increases with increasing ER, reaching a maximum value of 7.07°. The unstable atomization half-cone angle is mainly due to a two-phase flow pulsating phenomenon. The pulsation period is 10 ms. In the present study, a general rule that provides a reference for ejector design and selection was obtained through experiments.

scholarly journals Vortex flow and cavitation in diesel injector nozzles

2008 ◽  
Vol 610 ◽  
pp. 195-215 ◽  
Author(s):  
A. ANDRIOTIS ◽  
M. GAVAISES ◽  
C. ARCOUMANIS
Keyword(s):  
High Speed ◽  
Fuel Injection ◽  
Dimensional Space ◽  
Three Dimensional ◽  
Flow Distribution ◽  
Fuel Injector ◽  
Flowing Liquid ◽  
Injection Quantity ◽  
Dimensional Reconstruction ◽  
Real Size

Flow visualization as well as three-dimensional cavitating flow simulations have been employed for characterizing the formation of cavitation inside transparent replicas of fuel injector valves used in low-speed two-stroke diesel engines. The designs tested have incorporated five-hole nozzles with cylindrical as well as tapered holes operating at different fixed needle lift positions. High-speed images have revealed the formation of an unsteady vapour structure upstream of the injection holes inside the nozzle volume, which is referred to as ‘string-cavitation’. Computation of the flow distribution and combination with three-dimensional reconstruction of the location of the strings inside the nozzle volume has revealed that strings are found at the core of recirculation zones; they originate either from pre-existing cavitation sites forming at sharp corners inside the nozzle where the pressure falls below the vapour pressure of the flowing liquid, or even from suction of outside air downstream of the hole exit. Processing of the acquired images has allowed estimation of the mean location and probability of appearance of the cavitating strings in the three-dimensional space as a function of needle lift, cavitation and Reynolds number. The frequency of appearance of the strings has been correlated with the Strouhal number of the vortices developing inside the sac volume; the latter has been found to be a function of needle lift and hole shape. The presence of strings has significantly affected the flow conditions at the nozzle exit, influencing the injected spray. The cavitation structures formed inside the injection holes are significantly altered by the presence of cavitation strings and are jointly responsible for up to 10% variation in the instantaneous fuel injection quantity. Extrapolation using model predictions for real-size injectors operating at realistic injection pressures indicates that cavitation strings are expected to appear within the time scales of typical injection events, implying significant hole-to-hole and cycle-to-cycle variations during the corresponding spray development.

Designing the Spindle Parameters of Vortex Spinning by Modeling the Fiber/Air Two-Phase Flow

2014 ◽  
Vol 136 (3) ◽  
Author(s):  
Zeguang Pei
Keyword(s):  
High Speed ◽  
Two Phase Flow ◽  
Cone Angle ◽  
Phase Flow ◽  
Two Phase ◽  
Novel Technology ◽  
Yarn Properties ◽  
Vortex Yarn ◽  
Negative Effect ◽  
Yarn Tenacity

Vortex spinning is a novel technology which produces short-staple yarns by utilizing high-speed swirling airflow. The structure of the spindle plays an important role in vortex spinning in terms of its effect on the resulting yarn properties. In this paper, a two-dimensional fluid-structure interaction (FSI) model for the fiber/air two-phase flow is presented to design the two spindle parameters—the spindle cone angle and spindle diameter by evaluating their effects on the fiber dynamics in the flow field inside the twisting system and the resulting yarn tenacity. The coupling between the fiber and airflow is solved and the motional characteristics of the fiber are obtained. It is found that the fiber moves downstream in a varying wavy shape and its spreaded trailing portion is then in a helical motion to form the yarn. The results also show that the increase of the spindle cone angle has a negative effect on the tenacity of the produced vortex yarn. The increased spindle diameter gives rise to the decreased vortex yarn tenacity. The numerical results can provide an explanation for the experimental results reported by previous studies.

scholarly journals Capillarity Effect on Two-Phase Flow Resistance in Microchannels

2007 ◽  
Author(s):  
Prakash Rapolu ◽  
Sang Young Son
Keyword(s):  
Pressure Drop ◽  
High Speed ◽  
Energy Surface ◽  
Two Phase Flow ◽  
Surface Wettability ◽  
Phase Flow ◽  
Two Phase ◽  
Flow Pressure ◽  
Set Up ◽  
Phase Water

An experimental set-up is developed to investigate the effects of surface energy/surface wettability on characteristics of two-phase flow in microchannels. Two-phase (water and air) slug flow is established in entrance effect free microchannel test sections of various surface wettabilities. Pressure drop measurements and flow pattern detection by high speed visualization are employed to characterize the flow. Pressure drop of flow in hydrophilic channels is lesser than that of flow in hydrophobic channels. Significant change in contact line in advancing and receding interface section with surface wettability is observed.

scholarly journals Evaluation of a vertical downward water film thickness using visualization and image recognition techniques

2020 ◽  
Vol 21 (1) ◽  
pp. 1-13
Author(s):  
Edgar Fernando Larrainzar Solís ◽  
José Javier Moctezuma Reyes ◽  
Florencio Sánchez Silva ◽  
Ignacio Carvajal Mariscal ◽  
Lino García Demedices
Keyword(s):  
Film Thickness ◽  
Liquid Film ◽  
High Speed ◽  
Water Film ◽  
Surface Characteristic ◽  
Turbulent Regime ◽  
Falling Film ◽  
Two Phase ◽  
Set Up ◽  
Average Film Thickness

The present work is focused on the experimental study of a vertical downward annular flow to determine the thickness and stability of a falling film water flow. For this purpose, it was designed and implemented an experimental set up to generate the annular two-phase flow pattern, provided with an injection head with a special geometry to induce a liquid film inside a cylinder. Due to the small dimensions, the film was visualized using a pulsated laser to illuminate the region and the pictures were taken with a high-speed camera. This technique allowed the determination of the falling film thickness by means of an algorithm to recognize image contours. In some of the studied cases, a concurrent air flow was injected in the center of the cylinder in order to evaluate its influence on the interfacial hydrodynamics of the liquid film. Average film thickness were obtained for different Reynolds numbers in different axial observation points, and it was observed that the liquid film annular area and the shape of the header to inject the water, are important factors for the surface characteristic and thickness of the film, and its stability as well. The experimental results show that the standard deviation increases in proportion to the average film thickness, especially in the turbulent regime.

Two-Phase Heat Transfer and Flow Regimes in Pin Fin-Enhanced Microgaps—Effect of Pin Spacing

2020 ◽  
Vol 143 (2) ◽  
Author(s):  
Pouya Asrar ◽  
S. Mostafa Ghiaasiaan ◽  
Yogendra K. Joshi
Keyword(s):  
Heat Transfer ◽  
High Speed ◽  
Flow Boiling ◽  
Frame Rate ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Pin Fin ◽  
Speed Flow ◽  
Wide Range ◽  
Two Phase Heat Transfer

Abstract An experimental investigation of the flow boiling of dielectric refrigerant R245fa is conducted in microgaps with enhancement features. A silicon microgap of height 200 μm populated with pin fin arrays of diameter 150 μm with spacing 200 μm in both horizontal and vertical directions is examined. For five different test conditions and in a wide range of mass flux from 781 to 5210 kg/m2s, and inlet temperatures in the range of 13–18 °C, average single-phase and two-phase heat transfer coefficients, pressure drop, and exit vapor quality are reported. Three major flow patterns are observed in the pin finned area using high-speed flow visualization at frame rate of 2229 fps: foggy, bubbly, and slug flow. Based on the experimental data, a flow regime map is constructed.

Experimental Analysis of Altitude Relight Under Realistic Conditions Using Laser and High-Speed Video Techniques

2010 ◽  
Author(s):  
T. Mosbach ◽  
R. Sadanandan ◽  
W. Meier ◽  
R. Eggels
Keyword(s):  
Mass Flow ◽  
High Speed ◽  
Frame Rate ◽  
Research Centre ◽  
Oh Radicals ◽  
Fuel Injector ◽  
Flow Rates ◽  
Flame Kernel ◽  
High Speed Video ◽  
Mass Flow Rates

The altitude relight performance of a lean fuel injector and combustor was investigated at the altitude relight test rig at the Rolls-Royce Strategic Research Centre (SRC) in Derby. The studies were performed for different mass flow rates of air and kerosene, a combustor temperature and pressure of 278 K and 0.5 bar, respectively. Good optical access to the combustion chamber enabled the application of optical and laser measuring techniques. High-speed video imaging in the UV and visible wavelength range at a frame rate of 3.5 kHz was used to visualize the temporal development of the flame kernel. The observed differences between the UV and visible flame emissions demonstrate the different origins of the luminosity, i.e. OH* chemiluminescence and soot radiation. Further, laser-induced fluorescence of kerosene and OH radicals was applied at a frame rate of 5 Hz to visualize the fuel distribution and regions of hot and reacting mixtures. For two exemplary flames with different mass flow rates and fuel-to-air ratios, the steady burning flames after successful ignition are characterized in this paper by the distributions of kerosene, OH*, OH and soot luminosity. An example of the flame kernel development for a successful ignition is given by an image sequence from a high-speed video recording of the chemiluminescence. The importance of the upstream movement of the flame kernel as a condition preceding successful flame stabilization is identified.

The Effects of Ester Structure on Transient Fuel Spray Characteristics Including Novel Image Analysis to Quantify Air Entrainment

2015 ◽  
Author(s):  
Luis G. Gutierrez ◽  
Mohammad Fatouraie ◽  
Steve B. Xiao ◽  
Margaret S. Wooldridge ◽  
Dong Han ◽  
...  
Keyword(s):  
Diesel Fuel ◽  
High Speed ◽  
Penetration Rate ◽  
Cone Angle ◽  
Air Entrainment ◽  
Fuel Injector ◽  
Spray Characteristics ◽  
Spray Cone ◽  
Penetration Distance ◽  
Injection Process

Achieving efficient and clean combustion of biodiesel as a renewable source of energy requires a fundamental understanding of the effects of the different thermophysical properties on the fuel injection process at conditions relevant to diesel engines. In this study, the spray characteristics of two fatty acid esters, methyl oleate and ethyl oleate, are compared to a baseline diesel fuel using high-speed imaging of the sprays in a constant volume chamber. A single hole fuel injector with a nozzle diameter of 280 μm was used with a single injection event with a duration of 1.0 ms. The spray development was investigated for fuel-rail pressures of 40, 60, 80 and 100 MPa and the chamber gas densities of 1.15 kg/m3, 5.75 kg/m3 and 11.5 kg/m3. High-speed shadowgraph imaging of the non-vaporizing sprays was performed at 15,000 frames per second. Image processing algorithms were developed to quantify the spray penetration distance, penetration rate and cone angle as a function of time for the injection process. Penetration distance and penetration rate results were similar for the esters and diesel fuel for the range of experimental conditions studied. However, diesel had a larger spray cone angle compared to both esters. Additionally a novel metric for air entrainment was developed based on the macro-scale features of the spray. The integrated mixing volume metric showed no difference in air entrainment between the fuels, which is in good agreement with the behavior expected based on spray theory.

Research on the Measurement Method of the Sub-Pixel Image Motion Based on Optical Correlator

2011 ◽  
Vol 271-273 ◽  
pp. 7-12
Author(s):  
Chao Fan ◽  
Tie Jun Yang ◽  
Hong Liang Fu ◽  
Yi Tao Liang
Keyword(s):  
Measurement Error ◽  
High Speed ◽  
Measurement Method ◽  
Frame Rate ◽  
Image Motion ◽  
High Speed Camera ◽  
Joint Transform Correlator ◽  
Experiment Platform ◽  
Pixel Image ◽  
Set Up

To measure the sub-pixel image motion of the sequence images which are captured by the high-speed camera at the high frame rate with poor SNR, the joint transform correlator (JTC) is used. The relative image motion of the two adjacent images can be measured by inputting these images into the correlator. The principle of this method is described, and the effect of the defocussing of the CCD in the JTC on the accuracy is analyzed. To research the measurement performance of the JTC concretely, the experiment platform is set up. By using different images with different image motion, the results showed that, the JTC can measure the sub-pixel image motion entirely even for the images with SNR=1, and the measurement error submits to the normal distribution, which implies zero mean and the RMS is no more than 0.12 pixel under the conspicuous level is equal to 0.05.

Two-Phase Short Circuit in the Power Grid Powered by a Transformer with a Y/Δ-11 Winding Connection

2020 ◽  
pp. 25-30
Author(s):  
Aleksandr S. Serebryakov ◽  
Vladimir L. Osokin ◽  
Sergey A. Kapustkin
Keyword(s):  
High Speed ◽  
Short Circuit ◽  
Relay Protection ◽  
Electric Circuit ◽  
Operational Reliability ◽  
Research Purpose ◽  
Industrial Complex ◽  
Two Phase ◽  
Short Circuit Currents ◽  
Secondary Winding

The article describes main provisions and relations for calculating short-circuit currents and phase currents in a three-phase traction transformer with a star-triangle-11 connection of windings, which feeds two single-phase loads in AC traction networks with a nominal voltage of 25 kilovolts. These transformers provide power to the enterprises of the agro-industrial complex located along the railway line. (Research purpose) The research purpose is in substantiating theoretical equations for digital intelligent relay protection in two-phase short circuits. (Materials and methods) It was found that since the sum of instantaneous currents in each phase is zero, each phase of the transformer works independently. We found that this significantly simplifies the task of analyzing processes with a two-phase short circuit. In this case, the problem of calculating short-circuit currents in the traction network can be simplified by reducing it to the calculation of an ordinary electric circuit with three unknown currents. (Results and discussion) The article describes equations for calculating short-circuit resistances for one phase of the transformer when connecting the secondary winding as a star or a triangle. The currents in the phases of the transformer winding at short circuit for the star-triangle-11 and star-star-with-ground schemes are compared. It was found that when calculating short-circuit currents, there is no need to convert the secondary winding of the traction transformer from a triangle to a star. (Conclusions) It was found that the results of the research can be used in the transition of relay protection systems from electromagnetic relays to modern high-speed digital devices, which will increase the operational reliability of power supply systems for traction and non-traction power consumers.

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