X-ray Phase Contrast Imaging Technique Research Articles

Morphology and dynamics of the liquid jet in high-speed gas-assisted atomization retrieved through synchrotron-based high-speed X-ray imaging

The breakup of a liquid jet by a surrounding high-speed gas jet with different liquid Reynolds numbers and gas Weber numbers was studied using high speed phase-contrast X-ray imaging technique. Focusing on the liquid core, the portion of liquid that is connected to the nozzle, four distinct morphologies were observed and can be associated with changes in the large-scale configurations of the two-phase flow are reported in a phase diagram. Gas-to-liquid kinetic energy balance arguments capture several transitions between the liquid core regimes. The temporal evolution of the center of mass of the liquid core is extracted to quantify its motion, whose statistics can be utilized as a signature to distinguish different regimes. At low to moderate gas Weber numbers, the dynamics are strongly influenced by flapping, while long-time dynamics develop at high Weber numbers, that give way to quasi-periodic motions when swirl is impeded to the gas jet.

Inline edge illumination X-ray phase contrast imaging through mask misalignment.

X-ray imaging is becoming more commonplace for inline industrial inspection, where a sample placed on a conveyor belt is translated through a scanning setup. However, the conventional X-ray attenuation contrast is often insufficient to characterize soft materials such as polymers and carbon reinforced components. Edge illumination (EI) is an X-ray phase contrast imaging technique that provides complementary differential phase and dark field contrasts, next to attenuation contrast. Combining multiple of these contrasts has been shown to improve industrial defect detection tasks. Unfortunately, conventional EI imaging is incompatible with an inline setup, as it requires moving part of the setup during acquisitions, while for inline scanning objects translate through a fixed inspection setup. Current solutions require either limiting the number of retrieved contrasts, or acquiring dedicated hardware. In this work, we demonstrate a method of inline EI imaging that does not limit the number of retrieved contrasts and does not require any new hardware. The method is validated through both simulation and experiment, demonstrating high flexibility and possible noise reduction, while successfully retrieving all three EI contrasts.

Effect of nozzle geometry features on the nozzle internal flow and cavitation characteristics based on X-ray dynamic imaging

The nozzle geometry has a significant impact on the nozzle internal flow, which affects the fuel spray atomization and combustion of internal combustion engine. In this study, the internal geometry and flow characteristics of the nozzle was studied visually by using X-ray phase contrast imaging technique. The results indicate that the angle between the orifice wall and sac significantly influences the formation and development of cavitation in the orifice. A numerical model including the nozzle internal flow and the spray near-field characteristics was established to provide a more detailed description of how the inlet included angle affects the orifice's internal flow. It has been found that the hydraulic flip width increases with the decrease of the inlet included angle. The symmetry of cavitation distribution is greater when the inlet included angles on the left and right sides of the orifice are equal. When the inlet included angles on the left and right sides of the orifice are different, as the right inlet included angle increases, the cavitation strength near the orifice right-side wall decreases, and the hydraulic flip width to decrease, which causes leading to an increase in the effective flow area of the orifice.

Near-field plume-to-plume interaction of multi-hole GDI injector under elevated ambient density conditions

Spray collapse can occur in the multi-hole injector under elevated ambient density conditions due to the plume-to-plume interaction. Numerous studies have investigated spray collapse in high ambient density conditions, but limited literature is available regarding the near-field plume-to-plume interaction triggering the spray collapse due to the optical density of the spray in the near field. In this study, an X-ray phase-contrast imaging (XPCI) technique that can visualize the spray structure and dynamics in the near field is applied to resolve the optical difficulties. With this method, the plume-to-plume interaction of a multi-hole gasoline direct injection injector is analyzed by measuring the transverse spray droplet size and axial velocity distributions under various ambient densities and injection pressures. The results showed that in the high ambient density condition with the low injection pressure, the spray droplet size started to increase, and the axial velocity remained stagnant from around 3 mm axial location as a result of plume-to-plume interaction and following spray collapse. The region of large droplets appeared asymmetric based on the hole arrangement. As the injection pressure increased in the high ambient density condition, the plume-to-plume interaction was suppressed in the near field and the spray collapse appeared farther downstream. Through the results, the spray collapse phenomenon and associated mechanism in the near field were discussed considering the droplet collision/coalescence and pressure structure in the spray.

On the equivalence of the X-ray scattering retrieval with beam tracking and analyser-based imaging using a synchrotron source

X-ray phase contrast imaging (XPCI) methods give access to contrast mechanisms that are based on the refractive properties of matter on top of the absorption coefficient in conventional x-ray imaging. Ultra small angle x-ray scattering (USAXS) is a phase contrast mechanism that arises due to multiple refraction events caused by physical features of a scale below the physical resolution of the used imaging system. USAXS contrast can therefore give insight into subresolution structural information, which is an ongoing research topic in the vast field of different XPCI techniques. In this study, we quantitatively compare the USAXS signal retrieved by the beam tracking XPCI technique with the gold standard of the analyzer based imaging XPCI technique using a synchrotron x-ray source. We find that, provided certain conditions are met, the two methods measure the same quantity.

Grating designs for cone beam edge illumination X-ray phase contrast imaging: a simulation study.

Edge illumination is an emerging X-ray phase contrast imaging technique providing attenuation, phase and dark field contrast. Despite the successful transition from synchrotron to lab sources, the cone beam geometry of lab systems limits the effectiveness of using conventional planar gratings. The non-parallel incidence of X-rays introduces shadowing effects, worsening with increasing cone angle. To overcome this limitation, several alternative grating designs can be considered. In this paper, the effectiveness of three alternative designs is compared to conventional gratings using numerical simulations. Improvements in flux and contrast are discussed, taking into account practical considerations concerning the implementation of the designs.

Correlating armature and needle dynamics with voltage waveforms of solenoid-actuated GDI injector

The injector voltage hump that appears near the needle closing has been used for the real-time monitoring and feedback control of fuel injection duration in modern engines. This voltage hump has been thought to result from the abrupt change in electromagnetic induction by the stoppage of needle motion but detailed electromagnetic processes and associated armature and needle dynamics during the needle closing have not been thoroughly investigated in a wide range of injection conditions, which knowledge is crucial for the delicate control of fuel injection based on the voltage hump. The current study analyzes the transient armature and needle dynamics of a solenoid-actuated gasoline direct injection injector using an X-ray phase-contrast imaging technique. Then, the results are correlated with voltage waveforms during the needle closing transient under various injection pressures, injection pulse durations, and dwell times of split injections. The time derivatives of voltage waveforms showed lower and upper peaks in order in the regime of the voltage hump. Inconsistent with conventional understandings, the lower peak timing of the voltage derivative did not match with the timing of needle closing (end of injection) but rather matched with the abrupt descent timing of the armature and needle. The inflection timing and upper peak timing of the voltage derivative matched with the timings of actual needle closing and armature closing respectively. The amplitude of the voltage hump was near linearly dependent on the needle closing speed. The needle closing speed decreased upon the decrease of injection pulse duration and injection pressure which made it difficult to detect the voltage humps in ballistic injection regimes and low injection pressures. In split injection conditions, the voltage hump of the first injection was not detectable if the dwell time was shorter than the needle closing delay, the time from the current cut-off to the actual needle closing.

Spray dynamics of synthetic dimethyl carbonate and its blends with gasoline

Synthetic dimethyl carbonate (DMC) is a promising alternative or oxygenated additive fuel to reduce not only CO2 but also particle number (PN) emissions from gasoline direct injection (GDI) engines. Despite many investigations on the engine performance of DMC-gasoline blends in the literature, limited reports can be found focusing on their spray characteristics. However, a comprehensive understanding of spray characteristics is crucial to interpret the results of GDI engine tests. Therefore, this study was to examine the near-nozzle spray dynamics of the DMC-gasoline blends by using the X-ray phase contrast imaging technique. First, the fuel properties of the synthetic DMC and regular gasoline blends were quantified. Then, the near-nozzle spray dynamics were examined in both non-evaporating and evaporating conditions, and discussions were made accordingly to link the near-nozzle spray dynamics with fuel properties. It is found that increasing DMC content could enlarge the spray spreading angle and reduce the near-nozzle spray velocity by up to +22 % and –18 %, respectively. The near-nozzle-exit spray velocity depends sharply on the fuel density as the DMC content varies in the blends. However, this dependency gradually becomes insignificant as the spray propagating distance increases. Pure DMC has the largest Sauter mean diameter (SMD) and least droplet number than other blends, but they tend to be consistent as the ambient gas temperature increases. The existing empirical correlation is still feasible to predict the SMD of the DMC-gasoline blends, but certain tuning of the constants is necessary. Within the experimental conditions in this study, the DMC-gasoline blends should undergo the same spray breakup regime, i.e., the atomization regime.

Unified Modulation Pattern Analysis (UMPA) algorithm for 1D sensitive X-ray phase contrast imaging techniques

X-ray phase contrast imaging (XPCI) techniques are sensitive to refraction (differential-phase) and small-angle X-ray scattering (dark-field) signals, not measurable with conventional absorption imaging techniques. Among XPCI techniques, edge illumination (EI), grating interferometry (GI), and speckle-based imaging (SBI) make use of wavefront markers, such as absorbing masks with periodical apertures or random diffusers, to encode refraction and dark-field signals induced by the sample. The Unified Modulated Pattern Analysis (UMPA) provides an algorithmic solution to extract the transmission, refraction, and dark-field images from EI, GI, and SBI datasets where the wavefront marker is directly resolved by the employed detection system. In its original implementation, UMPA has been designed for XPCI techniques sensitive to refractions along two axes. This work presents a modified version of the algorithm to extend its applicability to all the existing XPCI techniques that use wavefront markers with sensitivity to refraction limited along one direction (UMPA-1D). The algorithm, written in C++ and Cython and parallelized with OpenMP, enables fast reconstruction times that are particularly convenient for large tomographic datasets. The validity of the UMPA-1D has been demonstrated using both simulated images and real acquisitions with an EI setup in beam-tracking mode.

Transient Nozzle-Exit Velocity Profile in Diesel Spray and Its Influencing Parameters

Article Transient Nozzle-Exit Velocity Profile in Diesel Spray and Its Influencing Parameters Ya Gao 1, Weidi Huang 2,*, Raditya Hendra Pratama 2, and Jin Wang 1 1 Advanced Photon Source, Argonne National Laboratory, 9700 S Cass Ave, Lemont, IL 60439, United States 2 Research Institute for Energy Conservation, National Institute of Advanced Industrial Science and Technology, Ibaraki 305-8564, Japan * Correspondence: wd.huang@aist.go.jp Received: 24 September 2022 Accepted: 10 November 2022 Published: 25 December 2022 Abstract: The primary breakup in the diesel spray relies closely on the initial dynamics at the nozzle exit. However, solid experimental results are still missing due to the great difficulties in measuring the near-nozzle spray dynamics. This study proposed an investigation focusing on the transient nozzle-exit spray dynamics by taking advantage of the X-ray phase contrast imaging technique. The in-nozzle needle motion, spray morphology, and dynamics at a commercial diesel nozzle exit were obtained. Experimental results were then examined, linking with the needle motion to understand the transient spray dynamics. The effect of the initial conditions (i.e., the injection pressure and ambient density) on the resulting trends were also considered. It is found that the nozzle-exit spray morphology and velocity profile highly relate to the in-nozzle needle lift. Once the needle sufficiently opens, the spray reaches steady status, and the nozzle-exit velocity becomes almost constant. The spray width slightly increases with the increasing ambient gas density or the decreasing injection pressure. Injection pressure significantly affects the spray velocity amplitude, whereas the ambient gas density alters the spray-velocity profiles mainly in the periphery of the spray. Finally, an analytic analysis was conducted to further examine the transient spray axial velocity with the changing radial locations. It is found the nozzle-exit spray velocity can be predicted in the Gaussian-type formula. This feature likely relates to in-nozzle flow characteristics.

Hole number effect on internal and discharged flow characteristics of diesel injector during transient operation

Selecting the proper number of nozzle holes is a critical matter to achieving optimal combustion in diesel engines. In recent years, short transient injections with ultra-high injection pressure have been adopted in diesel engines to achieve cleaner combustion but the effect of hole number on this transient diesel injection has not been thoroughly investigated. The current study performs an experimental observation of discharged flows from diesel injectors during transient operation using the X-ray phase-contrast imaging technique for six multi-hole injectors (three-, five-, six-, eight-, nine- and ten-hole). The observation results showed that discharged flows varied without any distinctive trends among the injectors. The largest spray dispersion angle and fastest velocity deceleration were observed in the 3-hole injector which showed an almost 3 times larger dispersion angle and 10% faster deceleration than the 10-hole injector. To understand possible factors governing such flow characteristics, three-dimensional internal flow simulations were conducted for the injectors. Unlike the results trend of discharged flows, the pressure and vorticity magnitude in the nozzle sac showed a linear change by altering the hole number. However, the hole-to-hole interaction of vortex flows varied in a complex way depending on the nozzle hole number. The nozzles with small and odd hole numbers, in general, showed a stronger hole-to-hole vortex interaction that can be the primary factor governing the discharged flow characteristics during the transient operation.

Element differentiation with a Hartmann- based X-ray phase imaging system

ABSTRACT Significant efforts are currently ongoing in X-ray imaging to provide multimodal imaging systems, targeting better sensitivity and specificity for both biomedical or non-destructive testing applications. Knowing the elemental composition of specific structures, such as breast microcalcifications in mammography, would help to differentiate malign and benign tumours. Standard X-ray Phase Contrast Imaging techniques provide only qualitative information on elements with similar absorption properties. However, their chemical composition can be determined from the measurement of the phase as it is directly related to the optical index of elemental materials. We will show new experimental results obtained with an X-ray phase imaging system based on a Hartmann mask. Early data treatment succeeded in retrieving both the real and imaginary parts of the refractive index. The system demonstrates the capability to discriminate materials based on elemental composition.

Correlation between needle behavior and fuel flow rate for gasoline direct injection injector using X-ray phase contrast imaging technique

To meet strong emission regulations such as Euro-7, which is expected to be implemented in 2025. The multiple-injection strategy is one of well-known solutions to reduce exhaust gas and improve combustion performance on GDI engine. In order to realize multiple-injection strategy, it is necessary to secure excellent flow rate repeatability within short period. Therefore, the purpose of this study was to analyze the flow rate repeatability of GDI injector under various multiple injection conditions and to correlate with needle behavior of GDI injector and flow rate repeatability. To analyze flow rate repeatability, the injection rate data was obtained by the Bosch method and the individual flow rates of 110 shots were analyzed under several experimental conditions. The movements of the ball and armature inside the injector were visualized using the X-ray phase contrast imaging (XPCI) technique, and the individual behaviors of the ball and the armature were quantitatively analyzed by image post-processing analysis. In this study were used two test GDI injectors with same structure. Whereas Flow rate results were different on shorter dwell time conditions. This study revealed that a specific injector had unstable injection rate and worse Shot to Shot (STS) deviation under dwell time 0.7 ms. In addition, armature bouncing appeared in a specific GDI injector. This armature bouncing affects unstable flow rate characteristics because when armature lift up again, the position of armature was different at every time.

Element differentiation with a Hartmann based X-ray phase imaging system

Significant efforts are currently ongoing in X-ray imaging to provide multimodal imaging systems, targeting better sensitivity and specificity for both biomedical or non-destructive testing (NDT) applications. For example, in mammography, knowing the elemental composition of breast microcalcifications would help to differentiate malign and benign tumours. Standard X-ray Phase Contrast Imaging (XPCI) techniques provide only qualitative information of elements with similar absorption. However, their chemical composition can be determined from the measurement of the phase as it is directly related to the optical index of elemental materials. We will show new experimental results obtained with a novel X-ray phase imaging system based on a Hartmann mask. The system demonstrates capacity to discriminate and quantify the elemental composition. Early data treatment succeeded to retrieve both the real and imaginary parts of the index of refraction.

End-of-injection fuel dribbling dynamics of multi-hole GDI injector

The fuel dribbling at the end-of-injection (EOI) transient is believed to be harmful to the emission performance. However, quantitative characterization and detailed explanation of the fuel dribbling process for GDI injectors are rarely reported, and the mechanism is not thoroughly understood. This study conducted a comprehensive investigation on the fuel dribbling process at the EOI transient for a multi-hole sac-type GDI injector using the high-speed X-ray phase-contrast imaging (XPCI) technique. Simultaneous visualization of needle bouncing, in-nozzle flow, and fuel dribbling directly illustrated that the fuel dribbling process was strongly correlated with needle bouncing. Further quantitative analysis of dribble volume and needle bouncing showed that the fuel dribbling process could be divided into the pre-needle-bouncing stage and the needle-bouncing stage. Distinct mechanisms of the two stages were explained through the dribbling source and the driving force. For the pre-needle-bouncing stage, the dribbling source was the residual fuel in the sac, and the driving force was the pressure difference between the sac and the ambient. For the needle-bouncing stage, the dribbling source was the fuel fed to the sac from upstream, and the driving force was the needle bouncing. Possible control strategies of fuel dribbling were also discussed according to the dribbling mechanisms of the two stages. A high injection pressure tended to increase the dribble amount but to reduce the dribble size and dribbling duration, which was believed to be overall favorable to restrain the adverse effect of fuel dribbling.

Correlation between Needle Behavior and Fuel Flow Rate for Gasoline Direct Injection Injector Using X-Ray Phase Contrast Imaging Technique

Correlation between Needle Behavior and Fuel Flow Rate for Gasoline Direct Injection Injector Using X-Ray Phase Contrast Imaging Technique

In situ x-ray observation of keyhole dynamics for laser beam welding of stainless steel with 16 kW disk laser

Focused laser is one of the highest power density sources available to industries such as automotive industry, heavy industry, and nuclear power plant industry because thermal influence is narrow and it is excellent in local workability. However, laser welding causes defects of cracks and pores. In particular, the formation of keyholes, which are factors for forming these welding defects, and the mechanism of spatter generation have not been sufficiently investigated. In this study, an x-ray phase contrast imaging technique was employed to investigate the keyhole welding with laser in order to clarify the spatter generation mechanism and keyhole formation mechanism in vacuum. Furthermore, the amount of spatter generated by vacuum laser welding was quantitatively analyzed, and the factors that suppress the spatter under vacuum were clarified. As a result, it was found that the penetration depth was dependent on the keyhole aperture.

Single-shot grating-based phase-contrast imaging of a micrometer sample at a laser-driven x-ray backlighter source

A single-shot x-ray phase-contrast imaging technique with short exposure time allows to capture sharp images of fast dynamic processes despite low absorption contrast. We demonstrate the capabilities of a robust single-shot grating-based phase-contrast imaging setup at the Petawatt High-Energy Laser for Heavy Ion EXperiments (PHELIX) at the GSI Helmholtzzentrum für Schwerionenforschung GmbH. A static test sample was imaged at 47-fold magnification using a laser-driven high-energy x-ray backlighter source. The retrieved transmission and phase-contrast images yield reproducible results. The reconstructed differential phase-images are quantitatively explained. In addition to the phase-images, propagation signatures are found in the data and used for result verification. The obtained results demonstrate the capabilities of the grating setup which can be used to image microscopic dynamic processes in high-energy density plasma experiments at PHELIX or similar high-power laser facilities.

Nozzle Tip Wetting in GDI Injector at Flash-boiling Conditions

The flash-boiling spray has become a timely topic of seeking the high mixture quality and clean combustion of the gasoline-direction-injection (GDI) engines. The flash-boiling spray, which has the enlarged individual spray cone angles and enhanced plume-plume interactions, are likely to favor the fuel-film formation, otherwise known as the nozzle tip wetting. Recently, the nozzle tip wetting has caused widespread concern because it is considered to be an essential source of particle emissions in GDI engines. In this study, an experimental investigation was proposed to clarify the possible influence of flash-boiling spray on nozzle tip wetting by taking advantage of the X-ray phase-contrast imaging (XPCI) technique. Due to the high brilliance, high energy, and low emittance of X-ray, the fuel flow inside the metal nozzle and spray characteristics at the nozzle exit was observed simultaneously, and results were discussed quantitatively to understand the underlying mechanism. It is found that the post-injected fuel caused by the needle bouncing is one primary source that results in tip wetting at non-flash-boiling conditions. Rising fuel temperature at non-flash-boiling conditions would not significantly affect spray dynamics and tip wetting. At flash-boiling conditions, tip wetting rises quickly during fuel injection, and a maximum appears under transitional flash-boiling conditions. This phenomenon can be understood by the enhanced droplet collision against the nozzle wall and boosted droplet evaporation under flash-boiling.

Potential for Shock-Wave Generation at Diesel Engine Conditions and Its Influence on Spray Characteristics

Increasing the fuel injection pressure is currently the most effective way to achieve a better fuel–air mixing quality in modern engines. Systems capable of delivering fuels at a pressure of over 250 MPa have been widely adopted in diesel engines. At such high injection pressures, the shock-wave generation during fuel injection has been noticed. Investigations can be found widely discussing on how the shock-wave generation during fuel injection would affect the spray dynamics. However, the argument remains whether the shock wave can occur at diesel engine conditions since the diesel engine is operated at very high ambient temperature and density. Even if it could occur, how significantly the spray-induced shock wave affects the spray characteristics is rarely known. To address these concerns, this study was proposed. First, experiments were conducted to obtain the detailed spray dynamics from the nozzle exit to spray downstream field by taking advantage of the X-ray phase-contrast imaging (XPCI) and schlieren imaging techniques. It is found that supersonic and subsonic ligaments coexist in one spray. Increasing the injection pressure or reducing the ambient density would extend the supersonic part in the spray. Multiple shock waves occur subsequently from the nozzle exit, where the spray has the highest local velocity. Shock-wave generation during fuel injection could enhance spray penetration, whereas this effect depends on the length of the supersonic part in the spray. Finally, a diagram was proposed to predict the potential for the shock-wave generation and discuss the possible effect on spray characteristics at diesel engine conditions.