Injection Pattern Research Articles

Design and testing of a Multi-Fuel industrial burner suitable for syn-gases, flare gas and pure hydrogen

The complete design and validation procedure of a novel Multi-Fuel heavy-duty burner is illustrated, starting from the conception and CFD analysis, up to an extensive experimental campaign assessing the actual performance of an industrial scale prototype.The need for an innovative burner to be employed in utility boilers comes from the context of energy transition with still increasing steam demand for process/industrial applications. The capability to burn a wide range of fuels, going from natural gas to flare-gases, syn-gases and fuels with even lower heating values, up to pure hydrogen, with high efficiency and low emissions is mandatory: it is shown and explained how all the above tasks are pursued starting from the early stage of conceptual design, leading to the development of a 2.5 MW prototype; then the burner operation is studied more in depth by CFD analysis, with particular attention to the implementation of MILD combustion regime: internal recirculation along with mixing, namely fuel dilution in flue gases leads to distributed volumetric reaction with oxygen, involving low peak temperatures with high conversion efficiency. Furthermore, numerical analysis helps to investigate the effectiveness of a central stabilizing flame, the coupling between furnace and burner in view of the tests, and also helps to evaluate different injection patterns for the fuel jets.As a final step, a 1.5 MW prototype is tested in a refractory lined furnace: the performance is assessed with natural gas, either pure or diluted with nitrogen to mimic a low heating value syn-gas, and with increasing percentage of hydrogen up to 95% as thermal input. Different levels of input to the central stabilizing flame are tested, and excellent flame stability of burner operation is proven. NOx emissions decrease for lower heating value fuels, increase for hydrogen/natural gas mixtures up to 35% H2, and remain almost constant above this threshold. Though, keeping a very low excess of air and almost no carbon monoxide in the exit flue gases, the absolute NOx levels compare very well with state of the art Ultra-Low-NOx industrial burners developed for standard fossil fuels. The presented data set can be relevant both for industrial designers, as a reference for heavy-duty burners operating with a wide range of fuels, up to pure hydrogen, and for academic researchers investigating on combustion, even in MILD regime.

Data-driven production optimization using particle swarm algorithm based on the ensemble-learning proxy model

Production optimization is of significance for carbonate reservoirs, directly affecting the sustainability and profitability of reservoir development. Traditional physics-based numerical simulations suffer from insufficient calculation accuracy and excessive time consumption when performing production optimization. We establish an ensemble proxy-model-assisted optimization framework combining the Bayesian random forest (BRF) with the particle swarm optimization algorithm (PSO). The BRF method is implemented to construct a proxy model of the injection–production system that can accurately predict the dynamic parameters of producers based on injection data and production measures. With the help of proxy model, PSO is applied to search the optimal injection pattern integrating Pareto front analysis. After experimental testing, the proxy model not only boasts higher prediction accuracy compared to deep learning, but it also requires 8 times less time for training. In addition, the injection mode adjusted by the PSO algorithm can effectively reduce the gas–oil ratio and increase the oil production by more than 10% for carbonate reservoirs. The proposed proxy-model-assisted optimization protocol brings new perspectives on the multi-objective optimization problems in the petroleum industry, which can provide more options for the project decision-makers to balance the oil production and the gas–oil ratio considering physical and operational constraints.

Conversion to AbobotulinumtoxinA Increases Waning Time and Efficacy for Cervical Dystonia.

Symptom re-emergence before re-injection negatively impacts cervical dystonia (CD) patients receiving botulinum toxin type A (BoNT-A) therapy. Longer waning time is associated with abobotulinumtoxinA (abo-BoNT-A) as compared to onabotulinumtoxinA (ona-BoNT-A)/incobotulinumtoxinA (inco-BoNT-A) formulations. To compare waning time and treatment outcomes when chronically injected CD patients experiencing early waning despite being optimized on BoNT-A (ona-BoNT-A/inco-BoNT-A) were converted to abo-BoNT-A. Thirty-three chronically injected CD participants with a waning time of ≤8 weeks were converted to abo-BoNT-A (1:2.5 dose ratio) for three injections every 12-weeks. The second and third injection patterns were kinematically optimized. Participants were converted back to their original BoNT-A for the fourth injection (1:2.5) using the same third abo-BoNT-A pattern. Participant-perceived waning times were collected post-injections. Clinical scales (Toronto Western Spasmodic Torticollis Rating Scale (TWSTRS)) and kinematic measures were collected 12-weeks post-injection and at three peak effect time-points. Compared to baseline, waning time (12-22 days) significantly increased following all abo-BoNT-A treatments (P < 0.005) but was not significantly different at the fourth injection (original BoNT-A reconversion). TWSTRS sub-scores significantly reduced following all abo-BoNT-A treatments (P < 0.0001) and at peak effect following the third injection compared to original BoNT-A. Dysphagia and muscle weakness were reported and comparable to safety of original BoNT-A formulations. Optimized patients experiencing waning had significant improvement in the peak benefit as well as the duration of effect when converted to abo-BoNT-A. This effect was toxin dependent as reconversion to the original BoNT-A using the kinematically optimized pattern failed to produce an improvement in waning.

Liquid film and heat transfer characteristics during superheated wall cooling via pulsed injection of a liquid jet

Pulse firing is one of the major operation modes of bipropellant thrusters for the attitude control of small-scale spacecrafts. In the pulse-firing mode, the operational range of the thruster depends on the deterioration of liquid film cooling performance. Because cooling performance is determined by the balance of heat removed by the liquid film and transferred to the manifold, the behavior and heat transfer characteristics of liquid films under the intermittent injection of liquid jets must be understood to enable a wider range of operational patterns. We conducted cooling tests on a superheated metal plate via the pulsed injection of a liquid jet for better understanding of the pulsed cooling process. Different injection patterns, including continuous injection, with the same injection quantity were examined on two types of metal plates (aluminum alloy and copper), because the thermal properties of metal plates affect both the heat transfer characteristics of the liquid film and temperature rise of the plate during the inter-pulse duration. The cooling process was evaluated based on the evolution of the liquid film on the metal plate and rear-side temperature of the metal plate. The evolution and temperature were simultaneously visualized using a high-speed camera and infrared camera, respectively. To link the liquid film state to the heat transfer process, the temperature and heat flux on the cooled surface were estimated by solving the inverse problem of three-dimensional transient heat conduction. The results indicate that the wetting front position corresponds to the position of the maximum temperature gradient. Additionally, the residual liquid film is consumed through the evaporation and the droplet dispersion related to the nucleate boiling. The effects of thermal inertia and diffusivity of the metal plate highlight the differences in the amount of heat removed by the liquid film. The heat removed by the liquid film during pulsed cooling exhibited a peak and was higher than that removed by continuous injection on the aluminum alloy plate. Less heat was removed under low-duty-cycle conditions, and the amount of heat removed by the liquid film was lower than that removed by continuous injection on the copper plate.

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Clostridium histolyticum (CCH-aesthetic formulation [CCH-aaes]) is a recently approved, targeted enzymatic treatment for cellulite in the buttock. Cellulite also develops in thighs, and the treatment areas require different injection techniques and product dilutions. This Phase 4 study aims to assess the effectiveness of multiple concentrations of CCH-aaes for the concomitant treatment of mild to moderate cellulite in the buttock and thighs of adult females. Cellulite severity was assessed using the Investigator Global Aesthetic Improvement Scale (I-GAIS) on days 1, 22, 43, and 90, and the Body-Q appraisal of cellulite and the Clinician Reported-Photonumeric Cellulite Severity Scale (CR-PCSS) on days 1 and 90. Treatments were performed on buttock and thigh dimples on days 1, 22, and 43 with reference to a provided calculation matrix, which is based upon the reconstitution, dilution, and injection patterns and volumes identified as optimal for these distinct areas by early research endeavors. The matrix permits customization to the desired number and location of cellulite dimples to be treated. Among the 5 subjects treated, 3 experienced improvement of cellulite severity in both treatment areas as measured by all 3 scales, and 2 participants showed improvement or no change in CR-PCSS and Body-Q Appraisal of Cellulite and worsening I-GAIS scores for one or both treatment areas. This study suggest that use of CCH-aaes in the concurrent treatment of the thigh and buttocks is predictable and efficacy and safety are similar for both areas.

The efficacy of femoral augmentation for hip fracture prevention using ceramic-based cements: A preliminary experimentally-driven finite element investigation.

Femoral fractures due to sideways falls continue to be a major cause of concern for the elderly. Existing approaches for the prevention of these injuries have limited efficacy. Prophylactic femoral augmentation systems, particularly those involving the injection of ceramic-based bone cements, are gaining more attention as a potential alternative preventative approach. We evaluated the mechanical effectiveness of three variations of a bone cement injection pattern (basic ellipsoid, hollow ellipsoid, small ellipsoid) utilizing finite element simulations of sideways fall impacts. The basic augmentation pattern was tested with both high- and low-strength ceramic-based cements. The cement patterns were added to the finite element models (FEMs) of five cadaveric femurs, which were then subject to simulated sideways falls at seven impact velocities ranging from 1.0m/s to 4.0m/s. Peak impact forces and peak acetabular forces were examined, and failure was evaluated using a strain-based criterion. We found that the basic HA ellipsoid provided the highest increases in both the force at the acetabulum of the impacted femur ("acetabular force", 55.0% ± 22.0%) and at the force plate ("impact force", 37.4% ± 15.8%). Changing the cement to a weaker material, brushite, resulted in reduced strengthening of the femur (45.2% ± 19.4% acetabular and 30.4% ± 13.0% impact). Using a hollow version of the ellipsoid appeared to have no effect on the fracture outcome and only a minor effect on the other metrics (54.1% ± 22.3% acetabular force increase and 35.3% ± 16.0% impact force increase). However, when the outer two layers of the ellipsoid were removed (small ellipsoid), the force increases that were achieved were only 9.8% ± 5.5% acetabular force and 8.2% ± 4.1% impact force. These results demonstrate the importance of supporting the femoral neck cortex to prevent femoral fractures in a sideways fall, and provide plausible options for prophylactic femoral augmentation. As this is a preliminary study, the surgical technique, the possible effects of trabecular bone damage during the augmentation process, and the effect on the blood supply to the femoral head must be assessed further.

Investigating the effects of split injection with different injection patterns on diesel spray mixing

In recent studies, it has been established that improvements in the injection rate results in improved mixing, combustion efficiency, and reduced pollutant emissions. Varying injection rates have been observed to find out the optimization injection rate. In this study, split injection with different injection rates was used as the flexible injection to investigate the diesel spray mixing efficiency. Large eddy simulation (LES) was used to investigate the complex diesel mixing processes of unsteady turbulence. The split injection was combined with different fuel injection rates to approximate the ramping-down rate shape. The simulation results of flexible injection rates showed the formation of a highly unstable aerosol vapor structure with the turbulence structure that produces the vortex in the spray area. The powerful injection rates provide a very strong spray turbulence structure and vortex formation. The backflow and vortex are evident when the dwell time of injection is setup. The flexible injection rates have a huge influence on the mixing efficiency of the fuel spray. Basic mixing efficiency predictions revealed that the dwell time of the split injection and inverse injection pressure affect the turbulence structure. Another prediction is that the initial pressure of the injection rate has a significant impact on evaporation and mixing efficiency, even using the same fuel quantity and same condition. The double-rectangular split injection has a slight effect on the spray radial extension, and the spray area grows rapidly while the equivalence ratio is low. The double-drop split injection with a high pressure difference has a great influence on the spray radial extension and spray length. Additionally, the higher injection pressure results in lower equivalence ratios and more efficient mixing.

Comparative study on gas-particle transport characteristics subjected to the central and annular coaxial jets

The gas-particle transport characteristics subjected to the central and annular coaxial jets were investigated using particle image velocimetry (PIV) and optical fiber probe technologies. The powder transport behaviors, the distributions of particle velocity, concentration, fluxes, and turbulence properties, as well as the spatial variations of vortex structures and vorticity, were measured with various jet velocities. The results showed that the injection patterns significantly influence the transport characteristics of the gas-particle two-phase coaxial jets. Compared with the annular coaxial jets, the powder jet subjected to the central coaxial jets exhibits better momentum transfer and particle dispersion characteristics, leading to the acceleration and fluctuation in the axial and radial velocities of particles. Correspondingly, the vortex structures formed in the shear layer of the annular coaxial jets do not undergo pairing, coalescing, and breaking up into small-scale eddies as rapidly as the central coaxial jets, which significantly decreases the entrainment and turbulence intensity. The combing interactions of the recirculating entrainment and the wall effect result in the particle accumulation near the wall ( r / R = 0.83– 1). Although the uneven distribution of particles was observed in both coaxial jets, the radial profiles of particle concentration are more uniform in the central coaxial jets than in the annular coaxial jets. • The injection patterns showed a significant effect on powder transport behaviors. • The turbulence properties and the evolution of coherent structures were captured. • The central coaxial jet exhibited better momentum transfer and particle dispersion. • The near-wall accumulation of particles increases with gas jet velocity.

Numerical Simulation of Low Salinity Water and Alkaline Surfactant-Polymer Flooding with Optimal Injection Pattern

Combined Low Salinity Water (LSW) and Alkaline-Surfactant-Polymer (ASP) flooding is a new enhanced oil recovery method that aids oil recovery from reservoirs following the traditional recovery methods. Experimental studies on combined LSW and ASP flooding show additional oil recovery potential. This paper used numerical simulation to investigate different flooding patterns with LSW and ASP combined. A homogenous reservoir was saturated with oil and water to obtain the required modelled factors. Oil reservoir simulations of 11 flooding patterns were created and run using ECLIPSE 100. These patterns were used in the field's development for five years. The results showed the normal 7-spot pattern to provide the best recovery, while the direct line drive provided the worst. The high salinity, low salinity, and combined LSW and ASP flooding recorded oil recoveries of 30%, 55%, and 93%, respectively. An economic analysis was also done to analyse the project’s economic viability which proved to be economical with a profit margin of 40.7%. Furthermore, it was discovered that normal flood patterns outperformed their inverted counterparts. It was thus concluded that the normal 7-spot pattern provides the highest profits from a purely technical standpoint.

The Injection Practice Patterns of Retina Specialists in Managing Exudative Age-Related Macular Degeneration: A Retrospective Study.

To compare the PRN anti-VEGF injection patterns of four retina specialists with respect to the visual and anatomic outcomes in the management of wet age-related macular degeneration (AMD). Medical records of patients who received bevacizumab, ranibizumab, and aflibercept anti-VEGF injections (years 2010-2020) by four retina specialists were reviewed for frequency, injection intervals, best corrected visual acuity (BCVA), and central macular thickness, center involved (CMT) for statistical analysis. Outcomes measured were change in logMAR BCVA and CMT from the first to last injection visit. Out of 137 AMD patients, 172 eyes were injected by four retina specialists in PRN fashion. Although all four specialists started the injection at similar baseline BCVA and CMT (p > 0.1), significant differences in mean injection number (9.0, p = 0.0001), injection intervals (5.06 weeks, p = 0.001), and total length of treatments (53.3 weeks, p = 0.0001) were observed. The mean change in logMAR BCVA between the first and last injection was -0.05, -0.22, 0.07, and 0.06 for the four specialists, respectively (p = 0.031), and the mean change in CMT was -53.3, -41.4, -72.7, and -21.9 µm (p = 0.41), respectively. Despite similar baseline criteria for injections by the retina specialists, different anti-VEGF injection regimens were practiced resulting in variations in BCVA and CMT outcomes. This suggests a need in establishing a universally adoptable injection regimen with possible integration of the confounding factors to reduce burden on both patients and retina specialists.

EIT for tactile sensing:considerations regarding the injection-measurement pattern

Bipolar current injection and voltage measurement (I–M) patterns are frequently used in electrical impedance tomography (EIT) for tactile sensing. In this work, the total set of 36 unique combinations for 16-electrode systems is investigated using simulations. Performance is evaluated on a circular sensor as a function of hyperparameter and target position with respect to critical performance measures for tactile sensing; these include not only peak amplitude and resolution, but also susceptibility to noise and, importantly, the uniformity of performance over the sensor area. The determination of which pattern to employ can therefore be based on the needs of the particular application. The relative performance of the I–M patterns is determined at small hyperparameters by electrode placement symmetry, but at large hyperparameters by sensitivity at the center of the sensor. Patterns with high spatial symmetry should be avoided; these include electrode pairs on opposite sides of the sensor. Patterns with electrodes in adjacent positions, which have been the norm for tactile sensing, should also not generally be used. If performance on all metrics across a wide range of hyperparameters is needed, then placing both the injection and measurement electrodes 3 spaces apart (the 3–3 pattern) can be a good strategy for the Gauss-Newton 1-step algorithm with the Laplacian prior. The use of 13 electrodes instead of 16 is also examined. The absence of symmetry provides greater flexibility in the choice of I–M pattern, and the loss in performance may be small; furthermore, the reduction in data collection time may be advantageous. Beyond avoiding the worst I–M patterns, the most important measure to take is decreasing noise on the signal to permit the use of a smaller hyperparameter; this is of greater importance than selecting from among the remaining I–M patterns.

The Role of Turbine Operating Conditions on Combustor–Turbine Interaction—Part II: Loading Effects

Abstract Aero-engine combustors burn a lean and premixed blend releasing vorticity and temperature perturbations. Interacting with the first turbine stage, these disturbances impact the cascade aerodynamics, add criticality to the blade cooling, and are sources of noise. The first of these issues is addressed in this paper, focusing on off-design turbine conditions, as experienced by aero-engines in their duty. This paper, Part II of a two-fold contribution, analyses the effect of the stage loading obtained by changing the rpm (three different values) at the same expansion ratio of 1.4, representative of subsonic flow conditions. Engine-representative disturbances are generated by a combustor simulator able to produce a swirling entropy wave. Two injection positions and four injection patterns are considered. Experimental measurements are carried out through the stage, measuring the injected disturbance and the aerothermal flow field downstream of the stator and the rotor. Results show that the swirl profile mostly impacts the stage aerodynamics. The different work extraction and the interaction with secondary flow structures change the entropy wave transport, diffusion, and decay through the rotor. Furthermore, the increased angle of the incidence caused by the injected disturbance can make the blade stall under the most loaded operating condition.

Impact of Glabellar Injection Technique With DaxibotulinumtoxinA for Injection on Brow Position.

Precise injection technique is vital for avoiding suboptimal eyebrow position when treating glabellar lines with botulinum toxin type A. The aim of this study was to evaluate the impact of glabellar injection technique on eyebrow position in patients treated with DaxibotulinumtoxinA for Injection (DAXI). This retrospective post hoc analysis involved 60 adults who received a single treatment with DAXI 40 U to the glabella and had standardized facial photography. Median vertical and horizontal displacement of the brows (at rest) at baseline and 2 weeks after glabellar injection were measured. Brow position outcomes were evaluated by an oculoplastic surgeon and expert anatomist. Investigators were interviewed to ascertain individual injection techniques. Precise injection location and depth, and median resting brow position following treatment varied between investigators. Positive brow outcomes were achieved with deep DAXI injections into the medial corrugator, superficial lateral corrugator injections placed between the midpupil and lateral limbus, and deep midline procerus injections. Glabellar injection technique that more precisely targeted the corrugator muscles resulted in longer glabellar line treatment duration compared to a less targeted technique. Medial corrugator injections above the medial brow; lateral corrugator injections administered deeply or more medially, toward the medial third of the brow; and procerus injections superior to the inferomedial brow tended to be associated with suboptimal outcomes that were more apparent during dynamic expression. Aesthetically pleasing brow outcomes and greater duration of efficacy can be achieved with an injection pattern that precisely treats the anatomic location of the corrugator supercilii and procerus muscles, avoiding the frontalis.

Performance Evaluation of CO2 Soaking and Flooding Processes in Tight Oil Reservoirs

CO2 injection has been proven to be an effective method to improve oil recovery of tight oil reservoirs. CO2 soaking and flooding are common processes used to constitute some CO2 injection patterns. To investigate the difference of oil recovery performance and asphaltene precipitation distribution between CO2 soaking and CO2 flooding processes, CO2 soaking and flooding tests under immiscible and miscible conditions were carried out with tight core samples. Then the NMR technique was utilized to analyze the microscopic remaining oil distribution and the asphaltene precipitation distribution after each test. The results indicated that the oil recovery in the small pores less than 0.6 μm was more influenced by the injection pressure, while the oil recovery in the large pores larger than 0.6 μm was more influenced by injection patterns. On the other hand, the asphaltene precipitation degree in different pores is usually relevant to oil recovery. In the large pores, the asphaltene precipitation degree of the soaking process was much lower than that of CO2 flooding by 8.02 and 19.76% under immiscible and miscible conditions, respectively. In the small pores, the asphaltene precipitation degree of the soaking process was higher than that of CO2 flooding by about 4%. Moreover, as injection pressure increased, the asphaltene precipitation caused by the soaking process was much less than that caused by CO2 flooding. The results of the study can provide some theoretical support to determine a better CO2 injection strategy for tight oil reservoirs with different characteristics.

Investigation on the Injection Pattern of Intermittent Natural Gas Flooding in Ultra-Low Permeability Reservoirs

Natural gas is a viable oil displacement agent in ultra-low-permeability reservoirs due to its good fluidity. It can also cause gas channeling during continuous injection, which limits its oilfield application. In order to relieve gas channeling during natural gas flooding, the injection mode should be changed. The use of intermittent natural gas injection (IGI) after the continuous natural gas injection in an ultra-low-permeability reservoir is proposed, and optimization of the injection parameters is discussed. The results show that IGI can be divided into three stages, the gas injection stage, the well shutting stage and the oil production stage. With the increase in injection time, the oil recovery enhances obviously as a result of IGI because the gas fingering can be controlled at the well shutting stage, and the gas/liquid ratio grows slowly because the gas breakthrough can be reduced at the oil production stage. The oil recovery improves with the increase in cycle time of IGI, while the increase rate reduces evidently after the cycle time reaches 360 min. The oil recovery increment is low if the cycle index exceeds 3 in the ultra-low-permeability reservoir. Thus, the optimal cycle time for each round and the appropriate cycle index of IGI are 360 min and three rounds.

Capillary and viscous forces during CO2 flooding in tight reservoirs

In this study, the multiphase multicomponent Shan-Chen lattice Boltzmann method is employed to analyze the impact of capillary force on oil-CO2-water fluid flow and enhanced oil recovery. Various sizes of the single throat are designed to simulate the interaction between displacing and displaced phases as well as their mechanical equilibrium. Several sensitivities are taken into account, such as wettability, miscibility, interfacial tension, and pore aperture. Based on the objective reservoir conditions, supercritical CO2 as an injection fluid is adopted to study the influence of different displacement patterns on the mechanical equilibrium in both homogenous and heterogeneous porous media, in which enhanced oil recovery is also quantitatively estimated. The results show that the water-alternating-gas injection pattern reduces the moving speed of the leading edge by increasing the swept area of the residual oil, and inhibits the breakthrough effect of the gas, making it the optimal displacement method in terms of the degree of oil production. Compared with the results of different displacement patterns, the enhanced oil recovery of water-alternatinggas injection is the highest, followed by supercritical CO2 flooding after water flooding, and lastly, continuous supercritical CO2 flooding. C ited as: Zhang, C., Zhang, Q., Wang, W., Xie, Q., Su, Y., Zafar, A. Capillary and viscous forces during CO2 flooding in tight reservoirs. Capillarity, 2022, 5(6): 105-114. https://doi.org/10.46690/capi.2022.06.01

Trends and distinct profiles of persons who inject drugs in the United States, 2015–2019

Drug injection represents a major health problem in the US, with severe health consequences including the transmission of blood-borne infections. An examination of the most recent trends in drug injection is warranted by the fast-evolving drug epidemic and recent policy changes such as the federal funding ban on needle exchange programs. This research examines current drug injection trends, patterns, and socioeconomic and behavioral profiles of people who inject drugs (PWID). Data were derived from the 2002 to 2019 National Survey on Drug Use and Health (NSDUH). After examining the annual prevalence of drug injection since 2002, a latent class analysis was conducted to identify drug injection and other substance misuse patterns among PWID using the latest (2015–2019) NSDUH datasets. Associations between class membership and behavioral health comorbidities and treatment receipt were also assessed. The drug injection prevalence among US adults aged 18–64 increased from 0.21% in 2002/2004 to 0.36% in 2017/2019. Three distinctive groups were identified: the heroin injection group (45.2%), the methamphetamine injection group (28.0%), and the multi-drug injection group (26.8%). The methamphetamine injection group reported greater risks of experiencing serious psychological distress, suicidality, and limited substance use treatment. Special attention is needed for those who primarily injected methamphetamine. Programs to promote harm reduction and increase access to addiction treatment need to be expanded in at-risk communities while accounting for their distinct socioeconomic and drug use/misuse profiles.

On the mechanisms of the multiplicity and bifurcation of detonation waves in 3D rotating detonation engines

The mechanisms of the multiplicity and bifurcation of detonation waves in 3D rotating detonation engines (RDEs) with cavity combustor and array-holes injection are numerically investigated. Array-holes injection is adopted to mimic the discontinuous distribution of reactants in real RDE experiments. Four kinds of injection patterns with different inlet-area ratios and four RDE models C1 - C4 of different cavity depths are employed. The result shows that as the inlet-area ratio increases the detonation waves number decreases generally. A more underlying mechanism of the multiplicity is assumed that the multiplicity of detonation waves is closely related to the inhomogeneous distribution of the detonable reactants, and the decrease of homogeneity of the detonable reactants (HDR) level causes the increase of wave number. The relative frequency's variance of the detonable mixture, as a metric of the HDR level, is calculated and the results show that the wave count decreases as the variance of the relative frequency decreases, which testifies to the rationality of our hypothesis. Model C2 shows a mode-locked state and exhibits a likelihood that the detonation mode may be more stable in these RDEs of specific configuration. Additionally, the process of bifurcation in cavity RDEs is tortuous, which is because the frequent disordered collision and quenching in the cavity delay the stable detonation waves' formation. And the mechanism of the periodic bifurcation in annular RDEs is related to the periodic distribution of the detonable reactant, which is verified by comparing the HDR level at different instants. The mode stability and propulsive performance are also mentioned and the cavity RDEs show a promising prospect in some cases.

Admissible Region of Renewable Generation Ensuring Power Flow Solvability in Distribution Networks

The uncertainty of renewable generation makes the operating status of distribution systems more volatile, as fully controllable resource at the distribution level is rare. A dispatchable region refers to the set that consists of all admissible patterns of nodal renewable power injections under which the power flow is solvable without violating security bound constraints. This article studies the dispatchable region in distribution networks under alternating current power flow model. A rank minimization problem is proposed to test power flow solvability under a fixed nodal power injection pattern, providing basic operation to construct the exact dispatchable region. A sequential low-order semidefinite programming procedure is developed to solve the problem. Furthermore, based on a global outer approximation of the second-order conic relaxation of the distflow model, a linear programming-based polyhedral projection algorithm is developed to calculate an outer approximation of the dispatchable region. The projection algorithm is also applied to the traditional linearized distflow model. Combining the feasibility test procedure, it is shown that the intersection of the respective dispatchable regions obtained from two linearized power flow models produces a fairly accurate approximation for the true dispatchable region under the exact nonlinear distflow model. The proposed method is an extension of existing studies on security assessment for distribution systems under uncertainty.

A selective water control and gas augmentation method based on APR gel

Water production will seriously affect the economics of gas well in the development of oil field. However, the conventional water shutoff agent is easy to block the gas flow channel at the same time of plugging the water. In this paper, a temperature and salt resistant polymer gel system composed of acrylamide/acryloyl morpholine/vinylpyrrolidone terpolymer (APR) and polyethyleneimine/modified alumina nanoparticle cross-linker was developed. At the same time, a selective water control and gas augmentation method based on APR gel was established. The effect of gel composition on its performance was mainly studied, and the water & gas shutoff performance in harsh environment was also researched by sandpack flow experiment. The gelation time could be controlled within 2–14 h by adjusting the concentration of the polymer, cross-linker, and deoxidant. In addition, the dehydration rate of the gel was only 2.6% after 180 days heat aging at 107 °C and 230,000 mg/L mineralization. The scanning electron microscope (SEM) showed that the uniform distribution of the network structure resulted in the gel with excellent stability in harsh environments. Sand filling experiments indicated that the plugging rate of gel for sand filling models with different permeability was all above 90% in harsh environment (107 ℃, 230000 mg/L salinity). Besides, laboratory experiments have illustrated that the injection pattern of the gel has a significant influence on its water & gas shutoff performance. Injecting 0.5PV gel solution first, then injecting 6PV N2, the shutoff performance of gel for water was nine times as good as that of gas. The research provides technical guidance for the water shutoff of high-temperature and high-salt gas reservoirs.